# Upgrading My 1990 Miata Miata



## ClassicCarLover (1 mo ago)

How much power are you wanting out of the forklift motor? I can't imagine it will do anything to the Miata driveshaft. If you are concerned about it, you could get a beefier one made, which you might need to do anyways unless you place the motor where the trans output shaft was. And there's probably no room for that in a Miata.


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## ClassicCarLover (1 mo ago)

It sounds like some guys are breaking the mounting ears off of the diff itself. Here's a good forum post  about some solutions


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## remy_martian (Feb 4, 2019)

If you do what @Duncan does, it'll turn a Miata driveshaft into a pretzel.


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## Forrest (7 mo ago)

I figure this - the stock miata engine is rated for 100 ft lbs of torque. The transmission can do a 3:1 in first gear - so max _rated_ torque on drive shaft is 300 ft lbs. I am not worried about the drive shaft itself. I am worried about the reactionary force that is usually handled by the C beam (Learned this part is called the PPF, or power plant frame). If I remove the C beam when I take out the transmission then the torque would go through the mounting ears as mentioned.

As per that thread - user "gavin_eakins" found that:


> [The PPF] Makes the whole drivetrain one piece, effectively.
> 
> However, diff's ears are rubber as are the engine mounts, so driveline can still move relative to MX5 chassis.


At this point I am leaning toward extending the PPF based on the thread and continue to allow the motor to rotate slightly with respect to the diff. Looks like the engine that broke their diff made about 200 ft lbs, so in first gear call it maybe 600 ft lbs that the diff had to resist? Who knows. Also in my experience momentary torques due to bumps and whatnots on drivetrains can be 10x what the regular torque is.


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## 1967 Ranchero (1 mo ago)

Honestly what I would do (but only because I can fabricate) is swap in a solid rear axle. Junkyard Ford 8.8's are cheap, and easy to narrow if you get two passenger-side axles. There are a lot of benefits to it, and the Fabrication Series has an excellent set of videos on how to do it, and the link explains some of the benefits. It's way overkill for a forklift motor, but you'll never have to worry about it again. I wouldn't bother with an IRS, because half shafts are going to be the next limiting factor if not the ring/pinion itself on the Miata diff


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## 1967 Ranchero (1 mo ago)

With that being said, an IRS 8.8 would also likely be enough for what you need to do, and probably easier to swap in. I'm a drag racer, so I say solid axle swap everything haha. But a solid axle would be a lot more work, and I don't know if there is much gain to it in your application compared to an IRS. Either way, I would say lose the Miata stuff...


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## brian_ (Feb 7, 2017)

The PowerPlant Frame does not take reaction to propeller shaft torque. It is a beam under bending stress in the vertical plane, not a torque tube. It is a C-channel, and that would be a terrible choice to handle torque. 

Torque reaction to motor torque on the shaft is through the final drive (differential) housing mounts (that's why there are two and they are widely spaced), then the rear subframe, then the body structure, then the front subframe, then the engine mounts, engine block, and transmission housing. After conversion everything at the back is the same; the motor mounts need to transfer torque to the body structure, and this still has nothing to do with the PPF.

In the stock Miata the PPF ties the final drive housing and transmission housing into one structure which then only needs mounts at each end (on the engine and final drive) - there's no transmission mount because none is needed. 

If the same method is used on the conversion, the PPF is retained, the motor just needs two mounts (to take output torque reaction), and there's no change at the back.
If the PPF is eliminated, the motor needs mounts front and back (and at the output end it needs mounts left and right), and the final drive needs an added front mount to the subframe (this is commonly done in Miata engine swaps that change the transmission to one that doesn't have provisions for attaching the PPF).

There is a torque reaction function of the PPF: reaction to axle torque. The PPF is a long arm that, like a pry bar or wrench, keeps the final drive from twisting nose-up in reaction to drive torque. That's why if the PPF is eliminated the final drive needs a front mount... and there's a lot of force on that mount.


It would also be possible to replace the PPF with an actual tube which would both perform the current function of the PPF and take the motor torque reaction; this has been done in several production vehicle car designs (the best known are some Alfas, the Porsche 924/944/968 and 928, and C5/C6/C7 Corvettes), but it would not be a trivial project. Old Miatas handle the torque of even radical engine swaps, so this is not necessary.


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## remy_martian (Feb 4, 2019)

Going to a live axle from an IRS (or the other way around) pretty much doubles the scope of the conversion on a road car.

With a drag car, you can always cheat and build to the underlying tubing space frame.


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## brian_ (Feb 7, 2017)

Going from a decent IRS (which any Miata has) to a live beam axle is a step backward for any car. It might amusing to suggest this in a group of Miata owners to see if anyone faints or vomits, but there's always the risk of violence...


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## 1967 Ranchero (1 mo ago)

Depends on goals. I would much rather a well set up solid axle than IRS in a drag car. This isn't what this build is though. But there is a place for live axles lol


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## remy_martian (Feb 4, 2019)

I'm thinking a good place for them is hay wagons 😛

Ranchero's close enough to being a hay wagon (lopped off station wagon), yet you are not going solid axle there, are you? 🤨

The beauty of an EV's torque curve is in the twisties as a road car. 10 seconds and put it away? Half assed road handling in trade for 10 seconds every month?


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## 1967 Ranchero (1 mo ago)

If I can make it work I will. Probably not in the Ranchero we were discussing on the other thread because it doesn't need it, but if I ever make a dedicated racecar then I would like to keep it solid axle


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## remy_martian (Feb 4, 2019)

Dinosaur tech.

Look at Cletus McFarland - he's raced a pair of C5's ("leroy" and "ruby") into the 8's, iirc.


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## 1967 Ranchero (1 mo ago)

Yup, but now he went solid axle in Leroy


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## remy_martian (Feb 4, 2019)

Correct - but you were talking 10 second car.


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## 1967 Ranchero (1 mo ago)

1967 Ranchero said:


> Probably not in the Ranchero we were discussing on the other thread *because it doesn't need it*, but if I ever make a dedicated racecar then I would like to keep it solid axle


This is if I build a dedicated racecar. I agree, you don't need a solid axle for a while. I do think that there are advantages to it, and it's hard to beat a 4 link setup for the simplicity/tunability/cost. Can we just say there are advantages to both and leave it at that? Lol


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## Duncan (Dec 8, 2008)

Hi
I had similar issues
The diff - a Subaru diff - reacts out the Wheel Torque - so about 4 times the motor torque
With the Subaru diff the front of the diff is a long way forwards which drops the loads

I have the rear of the diff mounted as usual with rubber mounts to the subframe
The front of the diff mounts to four of those rubber mounts usually used for exhausts - two upwards and two downwards
The idea was to always load the rubber mounts in compression

The motor is mounted to the chassis with six of those rubber mounts
Four at the bottom - loaded downwards 
Two above them loaded upwards

The front motor mounting bolts onto the front of the motor and downwards onto the chassis rails

The rear mount has the bottom piece with two bottom mounts - and a top piece with two upward facing mounts

The mounts are about a foot apart - so with say 300lbft of torque the mounts on one side are pushed down by 150 lbs and the other side are lifted up by 150 lbs

This has worked rather well while I have been abusing it for the last 9 years 

With your car I would be looking at that "C" beam as part of the motor mounting assembly


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## Electric Land Cruiser (Dec 30, 2020)

@Forrest You will want to tie the PPF into the motor somehow. The issue is going to be that your motor is much shorter than the original engine + transmission so where the PPF connects to the trans is a good 16-20 inches or so from where the motor mounts are. The motor mounts are also in the front subframe so they can't really be moved backwards. The rest of the car is just thin sheetmetal so you can't really mount it without a lot of fabrication and building new subframes etc.

You could extend the PPF and mount the motor in the engine bay, but then you also need to extend the driveshaft to make up the difference, and the whole trans tunnel is wasted space.

This is the issue with front engined Miata conversions, the chassis does not accommodate it very well and you end up with a lot of wasted space.


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## Forrest (7 mo ago)

Thank you everyone - I am going to leave the rear axle and differential as they are. Too much work to do otherwise. I understand alternatives have their place and appreciate being taught about them and what I currently have.

Thank you Duncan for sharing the pictures of your parts. Really helpful to see what I'll need to build.

The plan as it stands (this week is finals week for me, so I'll start work next Sunday when I get home)

Somehow extend the driveshaft (Current plan is to cut it in half and then weld a tube with an inner diameter that equals the diameter of the driveshaft onto both ends)
Create a PPF extender so I can mount it to something hard up front (the PPF is necessary for the reactionary wheel torque force that would otherwise send the front of the diff upwards). If the wheels have 300 ft lbs * 4.3 diff ratio so 1200 ft lb of torque, that point where I connect my extender to the PPF needs to be able to handle hundreds of pounds.



Electric Land Cruiser said:


> You could extend the PPF and mount the motor in the engine bay, but then you also need to extend the driveshaft to make up the difference, and the whole trans tunnel is wasted space.


Looks like this is the current plan. Yeah, the space where the transmission used to be will be a waste of space.


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## 1967 Ranchero (1 mo ago)

Nice!
One thing I'll add, extending a driveshaft is not that simple. It needs to be dead straight, with almost no runout (typically 2 thousandths of an inch is borderline acceptable) and balanced near perfectly (QA1 uses the STICKER to finalize the balancing on their shafts). It will vibrate like crazy and eat all the bearings in the driveline if it's not done properly. I get the sentiment of doing it yourself, but you have to be set up well to do it.


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## Forrest (7 mo ago)

Oh, ok. Scratch that then. How should I aquire / make a driveshaft that is within a few inches of what I need (TBD what I need)?

I could buy one... that seems expensive (>$200) am I wrong?


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## remy_martian (Feb 4, 2019)

If there's a 4 door RWD Mazda that uses the same transmission...


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## 1967 Ranchero (1 mo ago)

You can try and research driveshaft lengths of cars you would find in a junkyard, and try and buy one that way. Maybe a one-piece aluminum shaft out of a chevy express or truck? But a junkyard would be my first choice, then get adapter u-joints to put your Miata flange on. Or you can go to your local driveshaft shop and get them to make you one/cut a junkyard one down. I'm not sure if they would add to your current shaft, but I'm sure they could shorten one for you.


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## brian_ (Feb 7, 2017)

Forrest said:


> Somehow extend the driveshaft (Current plan is to cut it in half and then weld a tube with an inner diameter that equals the diameter of the driveshaft onto both ends)


It probably makes more sense to just have a new driveshaft built (using new joints or re-using the same joints) of the required length, rather than hacking together some splices. This is a routine service by driveline shops.

There are no other rear-wheel-drive Mazdas in production. Back when this Miata was built there were still Mazda pickups, but they didn't use the same transmission. Perhaps there is a Mazda (or Ford) model using the same transmission and thus compatible driveshaft, but the chance of finding either a shaft with the same rear end as well or one of just the right length seems very slim, let alone both.

Later Miatas were mechanically related to the RX-8, which is RWD and longer than a Miata but much rarer... and might not even use a driveshaft which is compatible with the related NC Miata, let alone an NA or NB Miata.


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## Electric Land Cruiser (Dec 30, 2020)

You could try to build a cradle to hold the motor and attach the PPF that extends forward to the motor mount locations and tie it into a battery box all in the same structure.


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## Forrest (7 mo ago)

brian_ said:


> Perhaps there is a Mazda (or Ford) model using the same transmission and thus compatible driveshaft


Why would I need a driveshaft that is compatible with my transmission? I only need it to bolt onto the differential - the side that used to go into the transmission would now be bolted to the motor somehow, something I'll figure out later.


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## Duncan (Dec 8, 2008)

Re- the space where the transmission used to be

That is where your motor goes

YES its a wee bit fatter - you will have to modify the transmission tunnel 

Remember you will NOT be needing the clutch pedal - so you can steal quite a lot of space in the drivers side footwell


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## 1967 Ranchero (1 mo ago)

If you are putting the motor in the trans tunnel anyways, I would try hard to put it in a spot where you can still use your stock driveshaft. Kill 2 birds with one stone and save money on a driveshaft. It might be worth the effort.🤷‍♂️


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## Forrest (7 mo ago)

Duncan said:


> Remember you will NOT be needing the clutch pedal - so you can steal quite a lot of space in the drivers side footwell


I wish - my car is made for driving on the right, so this would cut into the gas pedal region.



1967 Ranchero said:


> I would try hard to put it in a spot where you can still use your stock driveshaft.


I will try - first step is to finalize the motor selection - then I can mock it up in card board and see what I would need to cut to get it to fit.

The shifter is above where the driveshaft goes into the transmission. The area by my feet (around firewall level) is probably big enough, but the area by the shifter gets small - because that's where folks' knees are.

I found a drawing of the miata - I agree if I could put it here I would, but it seems unlikely.


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## remy_martian (Feb 4, 2019)

Crazy, but you could flip the rear diff over and put the motor in the back...


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## brian_ (Feb 7, 2017)

Forrest said:


> ...
> The shifter is above where the driveshaft goes into the transmission. The area by my feet (around firewall level) is probably big enough, but the area by the shifter gets small - because that's where folks' knees are.
> 
> I found a drawing of the miata - I agree if I could put it here I would, but it seems unlikely.
> ...


That's typical. To place a motor in the transmission tunnel and use the stock shaft, the motor would typically need an output end extension housing, equivalent to the tail housing on a typical transmission.


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## brian_ (Feb 7, 2017)

Forrest said:


> Why would I need a driveshaft that is compatible with my transmission? I only need it to bolt onto the differential - the side that used to go into the transmission would now be bolted to the motor somehow, something I'll figure out later.


True... the transmission no longer matters; sorry for the confusion (too many projects being discussed, some with the stock transmission and some not). You do need to work out what forward end you need before having the shaft fabricated. And another Mazda with the same rear coupling and desired length is still unlikely.


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## brian_ (Feb 7, 2017)

There are many rear-engine vehicles and some rear-motor EVs, even as conversions of front-engine vehicles. The Solectria E-10, which was a commercially produced conversion of the Chevrolet S-10, used a motor mounted behind the rear axle. 

To do this, the final drive (diff in housing or axle) is typically not flipped over, but rather rotated on the vertical axis, so that the lubrication still works properly. The subframe mounts for the final drive would then be in the wrong places, but it is possible (specifically in the NA and NB Miata) that the whole subframe could be turned around, due to the geometry of the rear suspension and the pattern of mounting points on top of the subframe... although of course the trunk floor would need to be cut out. The motor should be mounted to an extension of the subframe to take the axle torque reaction.


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## Duncan (Dec 8, 2008)

Hi Forrest
I know you guys drive on the wrong side of the road - but the comment about the clutch still rings true - you only need enough space for two pedals not three which frees up a lot of space

My motor - which is a chunky one - is 11 inches diameter - so you only need 11 (and a half) inches for your new tunnel - that space is needed where your feet and knees are - by the time that you get back to the seat you only need room for the propshaft

The other thing that you can do is to shift the motor a few inches over to the passengers side - your driveshaft and diff will be fine

My car is effectively a lot narrower than a Miata - its the same width but driving bit is only as wide as the INSIDE of the tyres - not the OUTSIDE like the Miata and that still gives me "enough" space (just)

Just thinking - the bit about using the existing propshaft - not going to work - so should not be a factor in placing the motor

I chose to separate the "engine bay" from the middle bit - so that dictated the position of the motor


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## Forrest (7 mo ago)

Ok, the motor will go where the transmission used to be - aka no rework of the driveshaft needed (besides the adapter to the new motor)

How do I support a motor when its hanging where the transmission used to hang? Just off of the old PPF and then a mount in the front?


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## Forrest (7 mo ago)

Duncan said:


> Just thinking - the bit about using the existing propshaft - not going to work - so should not be a factor in placing the motor


Why do you think the existing driveshaft won't work?


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## Duncan (Dec 8, 2008)

Forrest said:


> Ok, the motor will go where the transmission used to be - aka no rework of the driveshaft needed (besides the adapter to the new motor)
> 
> How do I support a motor when its hanging where the transmission used to hang? Just off of the old PPF and then a mount in the front?


You will need to build a frame for the motor - which will have to attach to the car
Petrol engines need very soft engine mounts to stop the bang bang bang from being transmitted
Electric motor should be rubber mounted but much much stiffer
Think about the loads - torque loads - and the weight/inertia of the motor when the car is hitting bumps
Design your frame - and ensure that the bits of the car it bolts to are strong enough


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## Duncan (Dec 8, 2008)

Forrest said:


> Why do you think the existing driveshaft won't work?


The propshaft is three bits
The bit that bolts onto the diff - we need that
The middle bit - just a tube
The bit that adapts onto the motor - this is the bit that means we will almost certainly NOT be able to use the existing prop

Remember also that the propshaft has two UJs - and that a sliding bit is also needed - as the diff moves (even a small amount) the horizontal distance between the UJs changes

Your best bet is to find a motor with a brake and to get your local engineering company to make you up new prop with a UJ each end 
My Subaru had a two piece prop shaft - so I had enough "bits" to take to Grace Engineering to make my new propshaft


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## Forrest (7 mo ago)

Duncan said:


> The propshaft is three bits
> The bit that bolts onto the diff - we need that
> The middle bit - just a tube
> The bit that adapts onto the motor - this is the bit that means we will almost certainly NOT be able to use the existing prop
> ...


Got it, that's what I was thinking. My propshaft has a universal joint on each end... but I do not know how it previously handled the extension and retraction.

Current plan is to find a motor with a brake as you say and get something made that will go onto the propshaft and mount to the motor brake. Then make an motor frame that will attach to the PPF and the engine mount in the front.


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## MattsAwesomeStuff (Aug 10, 2017)

Duncan said:


> My car is effectively a lot narrower than a Miata


Not something you hear often.


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## brian_ (Feb 7, 2017)

Forrest said:


> Ok, the motor will go where the transmission used to be - aka no rework of the driveshaft needed (besides the adapter to the new motor)
> 
> How do I support a motor when its hanging where the transmission used to hang? Just off of the old PPF and then a mount in the front?


It depends on the motor. I doubt that many electric motor cases are intended to be stressed elements of a structure. To carry the load forward without using the motor case would mean a truss-like frame on each side of the motor, from the motor mounting plate or housing (where the PPF would also attach to the original engine mounts or something at another suitable point on the front subframe.


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## brian_ (Feb 7, 2017)

Duncan said:


> Remember also that the propshaft has two UJs - and that a sliding bit is also needed - as the diff moves (even a small amount) the horizontal distance between the UJs changes





Forrest said:


> My propshaft has a universal joint on each end... but I do not know how it previously handled the extension and retraction.


The Miata shaft (at least this early one) uses a slip yoke on the front, which is a very traditional system. That means that the transmission side yoke of the front U-joint isn't attached to flange or to a plain shaft; instead, the part that connects to the transmission is a tube with splines inside that is free to slide in and out on the externally splined output shaft of the transmission. The TransWarp motors from NetGain (old brushed DC series motors) have an output shaft which is splined to work with this sort of system, and optionally even has a tail shaft housing of a Chevy Turbo 400 transmission around the shaft; you can take the same approach, but you need to use some sort of adapter to attach that male splined shaft (with splines to match whatever you use for a slip yoke) to the motor's output shaft.

Other ways to accommodate plunge (axial length change of the shaft) are

use a joint at one end of the shaft which can plunge, such as the tripod joints commonly used at the inboard end of axle shafts in independent-suspension vehicles
include a sliding section within the shaft, so it is front and rear parts with splines (even ball splines) between them


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## Duncan (Dec 8, 2008)

Forrest said:


> Got it, that's what I was thinking. My propshaft has a universal joint on each end... but I do not know how it previously handled the extension and retraction.
> 
> Current plan is to find a motor with a brake as you say and get something made that will go onto the propshaft and mount to the motor brake. Then make an motor frame that will attach to the PPF and the engine mount in the front.


My brake bit is on splines - so I allow the splines to slide a wee bit in and out to take out the extension/retraction bit
It physically can't extend enough to fall off


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## Duncan (Dec 8, 2008)

brian_ said:


> It depends on the motor. I doubt that many electric motor cases are intended to be stressed elements of a structure. To carry the load forward without using the motor case would mean a truss-like frame on each side of the motor, from the motor mounting plate or housing (where the PPF would also attach to the original engine mounts or something at another suitable point on the front subframe.


If you are using an old DC forklift motor the motor "barrel" is thick steel - very very substantial - I would not worry at all about using that as a stressed element of a structure


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## MattsAwesomeStuff (Aug 10, 2017)

Duncan said:


> If you are using an old DC forklift motor the motor "barrel" is thick steel - very very substantial - I would not worry at all about using that as a stressed element of a structure


Likewise. It'll easily be the strongest part of the car. It's probably thicker than the entire cross section of the Miata put together... frame, rockers, floor pan, roof... all of it.

Some amount of motor wall thickness is necessary to contain the magnetic field, with a side effect of being strong. But, often with forklifts, where you'd just loading up a thousand pounds of steel weights on the ass end anyway, motors were hardly ever shy about throwing extra weight around. "Last forever when you smash into things over and over" was more important.


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## piotrsko (Dec 9, 2007)

MattsAwesomeStuff said:


> Likewise. It'll easily be the strongest part of the car. It's probably thicker than the entire cross section of the Miata put together... frame, rockers, floor pan, roof... all of it.
> 
> Some amount of motor wall thickness is necessary to contain the magnetic field, with a side effect of being strong. But, often with forklifts, where you'd just loading up a thousand pounds of steel weights on the ass end anyway, motors were hardly ever shy about throwing extra weight around. "Last forever when you smash into things over and over" was more important.


Not driven many forklifts in actual warehouses then? The weight is only a plus for keeping the rubber side down when schlepping pallets of steel plate. Frame and structure is beefy, the appearance tin on the outside is just a wee bit heavier than a car, well, because.

Otoh, think a miata has a bit more steel than my 13" motor @250 lbs.


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## brian_ (Feb 7, 2017)

Usually when discussing motor mounting in this forum the general opinion is that the motor needs to be supported at both ends, even though it only has mounting provisions at the output, because it can't hold itself up; however, in this case the general opinion is that any random motor case is probably a good component of a structural beam.  I think that's bizarre.


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## MattsAwesomeStuff (Aug 10, 2017)

piotrsko said:


> The weight is only a plus for keeping the rubber side down when schlepping pallets of steel plate.


Been around plenty of forklifts. The Hyster my motor came from had a slab of steel 6" deep , probably 4 feet tall and 3 feet wide at the back. It's not for strength. It's for weight. Can't pick things up on the front all cantilevered like that and not tip over otherwise.



brian_ said:


> Usually when discussing motor mounting in this forum the general opinion is that the motor needs to be supported at both ends, even though it only has mounting provisions at the output, because it can't hold itself up; however, in this case the general opinion is that any random motor case is probably a good component of a structural beam.  I think that's bizarre.


Heh, guilty.

But, I don't think the logic is inconsistent, it makes sense in context of each of those claims.

One is a claim about the motor's weight and its effect on the way it's mounted to the car frame unsupported. The other is a claim about the motor's strength in terms of the structure of its housing.

You don't want the motor only supported on one end, not because the motor can't handle it, but because whatever you're bolting the motor to can't handle it. It's a 250lb weight levering on the face of the transmission, or something. In a forklift, the frame that the motor is mounted to is a 700lb gearbox with 3/4" thick walls, or the sides of the forklift frame with 3/8-1/2" thick steel, bolstered immediately on 3 sides. The forklift frame, motor mounts, or gearbox mounts aren't going to buckle. On a light sportscar with 1/16" sheet metal rails, or perhaps 1/8" frame at best, having a 250lb weight with 18" of leverage bobbing around is going to destroy it. I

The motor itself isn't a concern. Its housing isn't going to twist or bend. You could replace any piece of the car structure with the housing of the motor, and it would be a significant strength upgrade. Like, 400% increase minimum.


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## SCOTT 79 TR7 (Aug 29, 2020)

Forrest said:


> This will be the thread about my attempt at upgrading my working (albeit slow and loud) Mazda Miata conversion. Everyone's feedback and comments are welcome. I can take it.
> 
> First - about the car at present - the body is in great condition for being 30 years old. The top is new, all the lights and accessories work. It has a custom battery I made (mostly because I wanted to learn about the process) which is 21s (77V) and 136 AH. (10kWh). For V1 I used two 72V motors connected with the loudest chain on the planet. I have a Soliton 1 controller (340 V, 1000 amps) waiting to go in. I invite you to check out details on my website, here.
> 
> ...


Did your 72v (DC?) motors chain drive power into the transmission? Keeping the trans is common and lets you pick a gear (including reverse) if you think something is going to snap, just limit yourself to the Miata rates of acceleration. Most forklifts are low voltage, have a low rpm red line, and giant torque from 0 to 3000 rpm so you can run 4th gear all the time. Why remove the transmission? You can't care about weight if you are going with a big DC forklift motor. Keep your design under control, once you get it on the road you will see 100 changes that are needed and you didn't think of beforehand.


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## remy_martian (Feb 4, 2019)

Why remove the transmission?

Because it's in 4th all the time because of the low RPM high torque motor, so it's dead weight.


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## Duncan (Dec 8, 2008)

remy_martian said:


> Why remove the transmission?
> 
> Because it's in 4th all the time because of the low RPM high torque motor, so it's dead weight.


AND connecting the motor to the trans is a non trivial problem with the need for a support for the input shaft


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## MattsAwesomeStuff (Aug 10, 2017)

Having a mechanical reverse is handy.

Not having to modify a driveshaft if that troubles you more than making a coupler and a mounting plate, might be a reason.

If you're going to exceed your motor's rating for a long period of time, a tow up a long hill for example, maybe you would wish you had a transmission. So that you can choose to go slower and load the motor less. If you don't have a transmission, you can slow down, but, it's not going to help the amp load on your motor. You need to spin the motor faster, with lower load, to ease up on it.

Is a miata going to tow?

Is the motor going to be power limited?

Are you going to have enough battery to climb uphill long enough to overheat the motor anyway?

If not, probably doesn't matter.

Back in the day with more underpowered motors (or batteries, or controllers), it was a bit more of a concern


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## remy_martian (Feb 4, 2019)

Back in the day, you were using forklift motors - the concerns have not changed.


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## piotrsko (Dec 9, 2007)

Back in the day you needed a pickup bed full of FLA & helper springs to drive any distance on the freeway.


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## Forrest (7 mo ago)

MattsAwesomeStuff said:


> Is a miata going to tow?
> 
> Is the motor going to be power limited?


The miata will never tow, and hill climbing isn't in the cars future either. The motor is severely limited by the battery at the moment, hoping to increase that soon. The dream is 150 kW throughput.

Current thoughts:

Option A: Extend driveshaft and PPF
Pros: Motor can sit in the front, won't require mutilating the car / cutting away at transmission tunnel.
Cons: Requires significant work at a machine shop to make the new driveshaft. PPF just needs to be strong, like hundreds of pounds strong where I would start extending it.

Option B: Motor goes in transmission tunnel
Pros: Can use the original driveshaft tube, PPF with less modifications, front is empty.
Cons: Must create really strong "stretcher" thing to support the motor by connect the PPF and the front motor mounts. Would require cutting the transmission tunnel based on the size of the motor I get.

For A and B the driveshaft would go onto the motor with a spline to allow small changes in the distance between the diff housing and motor.

Option C: Transmission stays
Pros: Already have something going onto the transmission input that I could bolt my motor too easily. Would not have to adjust PPF or driveshaft.
Cons: *Limited to low torque - like 150 ft-lbs at max. *The original miata engine did 110 ft-lbs at max into the transmission. The internet says my transmissions lifetime is quite finite at 250 ft-lbs. 2000 rpm * 150 ft-lbs is 42.6 kW.

Breaking my transmission with a high torque low RPM motor is the biggest concern with leaving it in, otherwise I would.


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## Forrest (7 mo ago)

SCOTT 79 TR7 said:


> Did your 72v (DC?) motors chain drive power into the transmission?


Yep. The sprocket is on a keyed shaft that connects to part of an old clutch that has the right spline to power the transmission.


SCOTT 79 TR7 said:


> so you can run 4th gear all the time. Why remove the transmission?


This would be the reason - I wouldn't ever change gear and would just leave it in 4th. Although given how much easier this path is sounding... it might stay in and I would just go easy on the transmission as you say.


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## brian_ (Feb 7, 2017)

Forrest said:


> Option C: Transmission stays
> ...
> Cons: *Limited to low torque - like 150 ft-lbs at max. *The original miata engine did 110 ft-lbs at max into the transmission. The internet says my transmissions lifetime is quite finite at 250 ft-lbs. 2000 rpm * 150 ft-lbs is 42.6 kW.


Why would you limit the motor speed to only 2,000 RPM? 4,000 RPM @ 150 lb-ft is 85 kW, etc.


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## brian_ (Feb 7, 2017)

Forrest said:


> This would be the reason - I wouldn't ever change gear and would just leave it in 4th.


Many people apparently do keep the transmission and never shift it, but this is a sports car... keeping the entire mass and bulk of the transmission while not shifting it and so getting no value from it seems contrary to the nature of the car. If you just want a small convertible with two seats and low performance, I suggest an old Suzuki Swift / Geo Metro convertible for an easier conversion and lots of battery space where the back seat was.


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## Duncan (Dec 8, 2008)

Motor power

A forklift motor will be rated for an hour - and at relatively low rpm
My motor is 10 kW - 48 volts - about 200 amps - about 1400 rpm
If you spin it at 4200 rpm you will need a lot more volts - and you will have more cooling air flow so you will actually be able to increase the current!
But if you just leave the current alone at 3 times the rpm you will get 3 times the power

With the extra cooling running twice the current seems reasonable - so double the power again

Now we are up to 60 kW - a reasonable amount of power for a Miata

The base levels that most people use (and that I started with) are 144v and 500 amps - that gave me sprightly performance - and did not stress the motor

You CAN go further if you want


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## remy_martian (Feb 4, 2019)

Obviously need to put temperature sensor(s) in the motor for a road car so you can go turtle on power when that lame-ass motor air-cooling system fails to keep up with your aggressive driving. 

Most of the motor cooling is heat soak in the iron...get it hot and you'll be sitting at the side of the road for 45 minutes until it cools down again. For most driving, you'll only need about 15-20kW continuous power.


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## Duncan (Dec 8, 2008)

remy_martian said:


> Obviously need to put temperature sensor(s) in the motor for a road car so you can go turtle on power when that lame-ass motor air-cooling system fails to keep up with your aggressive driving.
> 
> Most of the motor cooling is heat soak in the iron...get it hot and you'll be sitting at the side of the road for 45 minutes until it cools down again. For most driving, you'll only need about 15-20kW continuous power.


A motor that is continuously rated (1 hour) at 10 kW at 1400 rpm will definitely be OK at 30 kW at 4200 rpm as that will require the same current
- and the extra cooling flow from the higher rpm means it MAY be OK at a continuous 60 kW


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## remy_martian (Feb 4, 2019)

No argument on 30kW. 

Seems you missed this part, though:



Forrest said:


> The motor is severely limited by the battery at the moment, hoping to increase that soon. The dream is *150 kW throughput*.


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## Duncan (Dec 8, 2008)

remy_martian said:


> No argument on 30kW.
> 
> Seems you missed this part, though:


Not really - I'm hitting well over double that! - but unless you are towing a caravan up a hill (not a sportscar thing) you can't sustain 150 kW - you hit the speed limit and have to lift off
With a voltage limited system the current drops
When I had 130 volts the current dropped as the speed rose until at 100 kph I was foot flat to the floor and not accelerating at all - I calculated that I was getting 26 kW


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## Forrest (7 mo ago)

To be clear on my goals - 150 kW will be once I have a 144 volt pack - I figure I can do 1000 motor amps for a few seconds @ 144 volts... That will be a complete success.

For now a lot less amps at 72 volts is gonna do. If I push 700 amps through and get 50 kW this round thats a win.

After consideration I think I am going to keep the transmission in - the scope of the other options aren't worth the only drawback (less input torque).


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## piotrsko (Dec 9, 2007)

Probability you wont hit 1000 motor amps on 144 volts unless you have a couple ton worth of batteries in parallel and large diameter windings, 0000 connect wires. Even with the motor rotor locked stop. Best I ever got was +600 amps @ 192 measured for a couple seconds. Why? Because even lithium can only discharge so fast.


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## MattsAwesomeStuff (Aug 10, 2017)

Duncan said:


> you can't sustain 150 kW - you hit the speed limit and have to lift off


Hell, you can't sustain 150kW because your batteries will be empty before the motor gets hot enough.

How much battery are you fitting into a Miata? 30kwh?

At 150kW you'll be empty in 12 minutes. That's your S2 rating, you'll never make it to S3.


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## brian_ (Feb 7, 2017)

MattsAwesomeStuff said:


> At 150kW you'll be empty in 12 minutes. That's your S2 rating, you'll never make it to S3.


"S2" and "S3" are not durations.

An arbitrarily selected explanation:
4 Types of Motor Duty Cycles Every Engineer Should Know


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## Duncan (Dec 8, 2008)

piotrsko said:


> Probability you wont hit 1000 motor amps on 144 volts unless you have a couple ton worth of batteries in parallel and large diameter windings, 0000 connect wires. Even with the motor rotor locked stop. Best I ever got was +600 amps @ 192 measured for a couple seconds. Why? Because even lithium can only discharge so fast.


No
Not how it works
You will start with 1000 amps motor and about 100 amps battery
Then as revs rise the battery current will have to rise while the motor current remains the same
Until you hit the 100% controller - then as the revs continue to rise the motor and battery current will drop

With my Chevy Volt batteries I can hit 1200 amps from the battery - with about a 20% sag - for a couple of seconds


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## Forrest (7 mo ago)

MattsAwesomeStuff said:


> Hell, you can't sustain 150kW because your batteries will be empty before the motor gets hot enough.
> 
> How much battery are you fitting into a Miata? 30kwh?
> 
> At 150kW you'll be empty in 12 minutes. That's your S2 rating, you'll never make it to S3.


That's my 6 second once a day rating (ok, maybe 5 times a day). So really just the instantaneous rating of motor, controller, batteries.

The 144 volt pack will probably be 136 AH at 40s (148V) which is 20kWh.



Duncan said:


> No
> Not how it works
> You will start with 1000 amps motor and about 100 amps battery
> Then as revs rise the battery current will have to rise while the motor current remains the same
> ...


This was my understanding of how it works - at 0 speed the motor pretty much takes infinite amps - there's no (?) back emf so the only needed voltage is to overcome resistive losses - I figure for thick wire this could mean 10-20 volts to push 1000 A through it.


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## Duncan (Dec 8, 2008)

Forrest said:


> That's my 6 second once a day rating (ok, maybe 5 times a day). So really just the instantaneous rating of motor, controller, batteries.
> 
> The 144 volt pack will probably be 136 AH at 40s (148V) which is 20kWh.
> 
> ...


Only if you don't have a controller 
The controller will change its mark-space ratio until the motor current matches the "demand" from the throttle


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## MattsAwesomeStuff (Aug 10, 2017)

brian_ said:


> "S2" and "S3" are not durations.


S2 is, unless otherwise specified. It's 10 minutes. It's "fully cooled down to ambient" between cycles.

And by S3 I meant S1. Brainfart.


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## piotrsko (Dec 9, 2007)

Duncan said:


> No
> Not how it works
> 
> With my Chevy Volt batteries I can hit 1200 amps from the battery - with about a 20% sag - for a couple of seconds


Like I said: you cant hit 1000 motor amps on 144 volts. 20% sag means not 144 volts but 115 ish. I also though we agreed a year or so back that maybe you weren't getting that much because you hadn't blown your 400 amp pack fuse yet.


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## brian_ (Feb 7, 2017)

MattsAwesomeStuff said:


> S2 is, unless otherwise specified. It's 10 minutes. It's "fully cooled down to ambient" between cycles.


No, S2 is a pattern of use (on for a specified period, then off long enough to cool to ambient). The fact that the time needs to be specified confirms that "S2" is a pattern, not a period. All of the same applies to S3 (except that it is a repeating pattern). The time periods for an S2 specification and an S3 specification could be the same, because "S2" and "S3" are not durations.


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## Duncan (Dec 8, 2008)

piotrsko said:


> Like I said: you cant hit 1000 motor amps on 144 volts. 20% sag means not 144 volts but 115 ish. I also though we agreed a year or so back that maybe you weren't getting that much because you hadn't blown your 400 amp pack fuse yet.


Voltage and current are different - at zero revs its probably only about 10 volt to get the 1200 amps
We see that with my "sag" graph - there is zero sag at the start when I hit the power but as the revs rise the battery current rises and it starts to sag

I'm hitting the 1200 amps - but for a few seconds - the 400 amp fuse would take longer than a few seconds to blow - not sure how much longer

I will clarify that - my motor sees 1200 amps right from the start
The battery (and the fuse) see a steadily increasing current that ramps up to 1200 amps then fall off again 
Roughly roughly the motor current ramps up to 1200 amps over about 5 seconds then drops off again - I suspect its down below 500 amps after the 11.6 seconds 
(I do a 12.2 second 1/4 mile - but the drivers reflexes are not that good and 11.6 seconds is the time from breaking the first beam)
So the battery (and fuse) are only above the 400 amps for about 6 seconds


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## MattsAwesomeStuff (Aug 10, 2017)

brian_ said:


> All of the same applies to S3 (except that it is a repeating pattern). The time periods for an S2 specification and an S3 specification could be the same, because "S2" and "S3" are not durations.





https://electrical-engineering-portal.com/10-duty-types-three-phase-asynchronous-motors



"If no otherwise specified, the duration of a duty cycle shall be 10 minutes"


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## brian_ (Feb 7, 2017)

MattsAwesomeStuff said:


> https://electrical-engineering-portal.com/10-duty-types-three-phase-asynchronous-motors
> 
> 
> 
> "If no otherwise specified, the duration of a duty cycle shall be 10 minutes"


That text is in the description for *periodic duty* (type S3 to S8), not S2 (short-term duty).

Different duty types do not indicate different durations.

But that page is a good reference.


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## Forrest (7 mo ago)

Hello All - update on my project:

The old motors and transmission and PPF are all out. I built a cardboard mockup of the current motor proposal and it actually fits quite nicely in the spot where the transmission used to be.

Current plan:

Build "sled" that connects from PPF to front engine mounts and is strong enough to transmit reactionary motor torque as well as support motor.
Create adapter that will go from motor (1.125" keyed shaft) to driveshaft (female spline shaft)

Previously, I decided to keep the transmission. (New) reasons for getting rid of it

The motor actually fits where the transmission went without cutting into the car, or extending the driveshaft.
I would have to make a motor->male spline thing to connect the motor to the transmission - just as easy to make a motor to female spline on driveshaft connector.

I also used my phone to create a pretty good 3d model of the inside of the car - turns out you can use the iphone face id stuff to generically make 3d models. I brought it into my CAD software and simplified the mesh and got rid of other bits. (The original file was 300MB ). It might be helpful, might not.









Here's the front of the car - empty and dusty and with many remnants of the last design.









And here is the transmission and PPF out








Next steps are waiting for the motor to arrive (est delivery 1/3, we shall see) and taking off the driveshaft so I can have it on the bench. Then designing the sled, in cad maybe?


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## Forrest (7 mo ago)

Ok - question for everyone: How do I connect my 1.125 in keyed shaft from my motor to the propshaft?

My proposal: I have the manual transmission output shaft on order - I am thinking that I will weld the spline stub to some sort of an adapter that would bolt to a taper lock flange that would be on the motor.

Something of this nature: (Use your imagination on the taper lock flange)









Expanded: (Again, use your imagination on the taper lock flange regarding the bolt holes and the taper lock mechanism)










I think this would be strong (assume the weld is of decent quality) and wouldn't require complex machining. (Just turning the inside of the spline flange to be exactly the diameter of that shaft)

Another idea that was to have a sectioned tube that would have two inner diameters - one section the size of the spline shaft, and one with the inner diameter the same as the motor shaft. This would have to be machined... then the tube would get welded onto the spline stub, but then I didn't have any good ideas about connecting the section of tube to the motor. Something doesn't feel right about just putting a few bolts through both the tube and the motor shaft...

Thoughts on either idea?


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## 428RC (12 mo ago)

maybe look at an older mercedes driveline. they have a flange similar to your first joint that would bolt up, then use a mercedes driveshaft with a integral spline. there are coupes which may give you a good driveshaft length, they also have very nice couplers to remove vibrations. look at a CE or SL. if you have pick and pulls go there with a tape measure and you may find something correct length.


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## Forrest (7 mo ago)

Updates

Yesterday the motor arrived - Warp 9. Yeah, costs more than a forklift motor (but not much more, I got it shipped for 1k). However, how much is it worth to have it work? It spins, plus there are technical drawings and performance data. So far looking good.

The motor came with some handy parts - a taper lock (Quick Detachable Variant) on the drive end with the accompanying hub to squeeze the tapers. Saved me 50 dollars. It also came with an RPM sensor on the non drive end as well as a mounting plate - don't think I'll need it but it sure made it easier to move around.










I bought the manual transmission output shaft a few days ago - it comes tomorrow. The idea is to cut off the relevant spline bit of the output shaft and weld it into the taper lock. Then I can taper lock the male spline that will go into the driveshaft onto the motor.

This is the "Sled". It will be mounted in front to the motor mounts and at the rear to a beam that will get welded to the bottom of the car.









I screwed a piece of wood that is in the spot where the welded cross beam will be. I laid the 1.5" sled rails down as well as the PPF - it will be lopped off at the appropriate length and bolted to the sled, similarly how it used to be attached to the transmission.










Hopefully I can be ready to start welding next week.


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## Duncan (Dec 8, 2008)

The Warp 9 - is a forklift motor!
Which is good - means that you can overload it


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## remy_martian (Feb 4, 2019)

You're running outa time - doesn't school start next week? 👨‍🎓


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## remy_martian (Feb 4, 2019)

Come on, Duncan - he spent all of this coming semester's school lunch money on that motor 😂


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## Duncan (Dec 8, 2008)

Forrest said:


> Updates
> 
> Yesterday the motor arrived - Warp 9. Yeah, costs more than a forklift motor (but not much more, I got it shipped for 1k). However, how much is it worth to have it work? It spins, plus there are technical drawings and performance data. So far looking good.
> 
> ...


I like your "sled" - I would recommend some rubber in the mountings either motor to sled or (easier) sled to chassis


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## MattsAwesomeStuff (Aug 10, 2017)

Forrest said:


> Yeah, costs more than a forklift motor (but not much more, I got it shipped for 1k). However, how much is it worth to have it work? It spins, plus there are technical drawings and performance data.


 - Forklift motor is as cheap as free. At most it's 20% the price of what you paid.
- The forklift motor you would've found almost certainly would have worked just fine and you could've tested it with a spare battery. It's not a grandfather clock that fell down the stairs, it's a motor with a 1/4" thick shell and 1" thick end caps. So, zero added value there.
- A forklift motor would also spin. This is what motors do. No modifications were necessary to accomplish this.
- Technical drawings aren't worth anything really, and, every forklift motor I've ever looked at I was able to find technical drawings of just fine, either by google or just by asking for them. You have successfully avoided having to measure, or to use google.
- Performance data on the Warp9s are generally marketing wankery. Not worth anything. And, whatever they're worth, you'd get the same out of any random motor the same size yanked out of a forklift... because it's the same thing. What performance data are you needing? Take motor. Use motor. Done.

...

So, what you've done is pay $1000 for a motor worth $200. The $800 difference is in not having to look around for one. Which is just fine, but I would've figured you were more of a type to need to save money than to be buying shortcuts to a little bit of effort. Else... why are you doing a DC build if you've got money to waste for convenience?



> Hopefully I can be ready to start welding next week.


Congrats on moving forward on your project. It's an exciting step.


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## remy_martian (Feb 4, 2019)

He paid $1000 for a motor that sells for $4000 now.

He can always his his money back for it, so that means it's costing him $10 a year in lost bank account interest 😂

The car's also worth more than one with "found it in a scrap pile", because...motor salvage value again.

Kid's clearly got some scholarship money he's spending, so it's either spend it on a decent motor or on hookers and blow.

And you just know the hookers would just go out and buy themselves a Hyper9 to EV convert Big Daddy's Caddy.


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## Duncan (Dec 8, 2008)

remy_martian said:


> He paid $1000 for a motor that sells for $4000 now.
> 
> He can always his his money back for it, so that means it's costing him $10 a year in lost bank account interest 😂
> 
> ...


I agree with remy - $1000 is not a bargain - but its a lot better than $4000 and the old DC motors are getting scarce mow


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## Forrest (7 mo ago)

remy_martian said:


> You're running outa time - doesn't school start next week? 👨‍🎓


UMD has a pretty long break - School starts 25th; I'll go back the 24th. So I'll aim to have it all assembled for the first time by the 18th - two weeks, and then 5 days for breaking and fixing.



Duncan said:


> the old DC motors are getting scarce mow


This is exactly what I found... I figure in 2010 it wasn't worth buying a new DC forklift, but it was worth repairing one. Now we are getting to the point where the DC forklifts are dying and they aren't worth keeping around to repair other DC forklifts - I heard from several shops that they remove and sell motors for their cores.

Another thing - I searched in Baltimore - maybe in such a commercial hub it is easier to transport a motor core and melt it back down to use the copper again. Maybe in the middle of nowhere there are still loads of DC forklifts just sitting around. But I tried and I couldn't find one.


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## Forrest (7 mo ago)

Sled is assembled - bolt holes are in the right spot and everything fits together. Tomorrow is hopefully welding day for both the cross beam on the car and the sled (towing the car with the tractor to the neighbors who has a lift and a welder).










The todo list:
- Weld Sled (Tomorrow)
- Weld Cross Beam (Tomorrow)
- Bend metal plate that will connect engine mounts to sled in the front (Asking around... maybe by tuesday?)
- Cut and weld section of transmission driveshaft into old motor adapter. (Asking around... maybe by tuesday?)
- Mount and wire controller (As soon as the sled is in for good... Sunday?)

My optimistic and totally not achievable goal is wheels spinning by the end of next week.


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## Duncan (Dec 8, 2008)

Where is the rubber?


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## Forrest (7 mo ago)

Duncan said:


> Where is the rubber?


Good question. Rubber mounts that would allow the sled to move with the diff were originally part of the plan, but I spoke to someone with a lot of experience with gas miatas. He said that rubber mounts are on stock cars to make the car feel softer and more beginner friendly. He also said that one of the first things people do to upgrade their cars is to remove those mounts if they are ok with vibration. He said the mounts primarily absorb noisy frequencies and not to protect the car.

I am aware though that rubber mounts help reduce instantaneous spikes of force that could otherwise break my stuff. If I change my mind I can add them up front between the engine mounts and the sled as well as in back between the cross beam and the sled.


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## Duncan (Dec 8, 2008)

Forrest said:


> Good question. Rubber mounts that would allow the sled to move with the diff were originally part of the plan, but I spoke to someone with a lot of experience with gas miatas. He said that rubber mounts are on stock cars to make the car feel softer and more beginner friendly. He also said that one of the first things people do to upgrade their cars is to remove those mounts if they are ok with vibration. He said the mounts primarily absorb noisy frequencies and not to protect the car.
> 
> I am aware though that rubber mounts help reduce instantaneous spikes of force that could otherwise break my stuff. If I change my mind I can add them up front between the engine mounts and the sled as well as in back between the cross beam and the sled.


He is talking bollocks
The soft engine mounts are to stop the low frequency vibration from the pulses of an idling engine
The much stiffer mountings I am talking about are to stop the much higher frequency of vibrations from your motor and from the road

Stiffer mountings are a good idea - but bugger all to do with "more beginner friendly" - solid mountings are a bad bad idea


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## remy_martian (Feb 4, 2019)

Duncan's Silver Hammer

Not only a mangled title from a Beatles song about a deranged [DC forklift motor] maniac, but hammers are how you test structural response and tune vibration out...

You'll find a LOT of vibration coming from a motor unless you are _really_ good at sinewave synth at 30kW - with brushed you are a victim of pwm, though. The hockey pucks are a good idea, imo.


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## Forrest (7 mo ago)

Ok, I'll add them. I think I'll use something like this - I could easily add them to the front and pretty easily add them between the sled and the cross beam in the back.

In other news ... it's welded!








The cross beam on the bottom of the car is done as well. My neighbor welder said it was hard to weld the 1/4" beam to the paper thin miata frame... but then at the end he did a few aggressive pull ups on it... he probably weighs 250 lbs. I also added a 4*2*.25 plate just below the carpet by the seats that bolts the cross beam to the floor of the car.

The todo list:

Weld Sled
Weld Cross Beam
Add plate to strengthen the cross beam
Bend metal plate that will connect engine mounts to sled in the front (Asking around... maybe by tuesday?)
Cut and weld section of transmission driveshaft into old motor adapter. (Asking around... maybe by tuesday?)


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## 428RC (12 mo ago)

with no or stiff rubber isolators you can expect a your bolted on assembly to experience higher g force. so 250# hanging on it is no test. I would look at 3X minimum and as high as 5X with the suspensions. At the least I would add a spreader plate opposite your sheetmetal mounts so it doesn't rip out. I think if you can use the hard mounts for the old trans and motor that would be the best start.


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## Duncan (Dec 8, 2008)

I use rubber mounts like those - BUT mine are always in compression - in compression they are great - in tension or sheer not so good

Remember they need to take the torque loads - and more importantly the acceleration loads as the car goes over bumps - also side loads but they are probably less


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