# Trimming the Fat.



## bipole (Sep 8, 2009)

Can motors be lightened up a bit?

I'm mainly referring to series wound DC motors since that is what I'll be using. I know the all the copper is there for a reason, how about all the steel? I'm guessing the steel housing size is selected by the manufacturer from some commercially available pipe size and wall thickness that will accommodate the internals and end bolt threads. If I wanted to trim some off the outside are there any negative consequences to performance?

I've been working very hard and spending a bit of money to trim a pound here and there, so if I can trim more than a few pounds off the motor I'll probably do it.


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## Amberwolf (May 29, 2009)

Some questions to ponder before you do that:

How are you lifting and mounting the motor? 

If you're lifting it by the boltholes in the casing, well, those boltholes can lift it because they're spreading that load around the structure of the cylinder plus endcaps.... 

If your mounts for the motor include supporting along the housing, then remember the housing has to support it's own weight and that of the motor, and spreads it's load around that cylinder.

Material removed from it can reduce it's stiffness.

Also, at least in permanent magnet motors, the cylinder is used as a flux ring to help the magnetic fields of the "field" portion work, and provide something for the magnets to push against to transfer the torque against the end plates and mounting points, so that the shaft and armature spin, rather than the body of the motor.

I expect it's similar if not identical in wound-field motors. 


An expert should also jump in here, but that's the first things I can think of that could be a problem with removing motor material.


What weight have you removed from elsewhere in the vehicle? What is left that you might be able to remove?

I doubt you'd be able to remove more than a few pounds of material from the motor safely, if any. That would not be worth the risk of compromising it, to me.
________
AVANDIA SICKNESS


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## bipole (Sep 8, 2009)

Amberwolf said:


> Some questions to ponder before you do that:
> 
> What weight have you removed from elsewhere in the vehicle? What is left that you might be able to remove?......



A finished GTM weighs about 2350lbs. Engine, exhaust, radiator, coolant, tubing, hoses, fuel tanks, fuel, wire and ECM add up to about 650lbs omitted. I would say removed, but they were never there since this is a scratch build.

I used an earlier Porsche 930 transaxle which is about 30lbs lighter and much stronger (survives up to about 750 ft-lb reportedly) than the G50 in the standard build.

I trimmed the set of brake caliper brackets of 2 lbs total. I cleaned off all the casting parting lines and smoothed all the aluminum A-arms resulting in about 1.5 lbs removed from each corner (lots of work). I researched my front tires and managed to find a set of Continental Extreme Contact DW's that were 6 lbs lighter each than the tires I had and have a decent rr value of .012. All together 20 lbs lighter on the suspension/wheels.

I'm down to about 1650 lbs now before adding electrics. Pictures of all this stuff are in my 'bucket'.

What's left to attack:

The rear glass is 18 lbs, I could replace that with polycarbonate to save maybe 12 lbs. Unfortunately the glass a substantial amount of rigidity to the hatch structure so I'm not sure if I want to go that route. Glass doesn't scratch that easy either.

The seats are 15 lbs a piece and I just added seat warmer elements to the drivers seat so I'm up a pound there, totally worth it! There are lighter seats, but not by much.

I'm not willing to go without a stereo or A/C.

I don't want to mess with the chassis unless racing sanctioning body rules dictate. In that case it would probably be adding a pound or two.

I just lost about five pounds, got a german shepherd puppy, been walking/running her around. I really don't have any more to lose.

The rest is predominantly electric items, the motor the heaviest by far and the only one that likely can be lightened. It looks like I'll be using a 13" GE weighing over 300 lbs. I have room for a siamese 9, but the price of the GE was pennies compared and these seem to work well for Dennis Barube.

I'd like to have the charger onboard, but now that I think about it, I think I'll make it removable. Thanks for spurring the thought!


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## Amberwolf (May 29, 2009)

Have you got interior insulation, carpeting, dashboard coverings/etc? 

You might be able to trim down the motor, but I think that they probably have good reason to have the steel there in the amounts they do. You might ask Jim Husted or major about trimming down on the motor--they'd know more than me, for sure. 
________
WEB SHOWS


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## Bowser330 (Jun 15, 2008)

Bipole,

you should also consider blocking off the front bumper opening (mouth) because that will cause some undesired drag. 

Weight reduction efficiencies are better noticed at lower speeds where as aerodynamic efficiencies are noticed at higher speeds..

Theoretical battery pack of lithiums..

100 cells (200AH & 6.4kg each)

320V
200AH ([email protected])
640kg (1400lbs)


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## major (Apr 4, 2008)

bipole said:


> Can motors be lightened up a bit?
> 
> If I wanted to trim some off the outside are there any negative consequences to performance?


Hi bipole,

The outside shell (the heavy steel tube) of the motor is called the frame or yoke. It is a critical part of the magnetic circuit of the motor. There may be some sections of that which are not run to the magnetic limit, but it would be a difficult machining process to remove that material, not a simple turning or milling operation.

The net result of simply cutting away part of the steel frame could be a loss of torque. And it could be significant. If you do that, you might as well just get a smaller, lower torque motor to start with 

major


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## bipole (Sep 8, 2009)

major said:


> Hi bipole,
> 
> The outside shell (the heavy steel tube) of the motor is called the frame or yoke. It is a critical part of the magnetic circuit of the motor. There may be some sections of that which are not run to the magnetic limit, but it would be a difficult machining process to remove that material, not a simple turning or milling operation.
> 
> ...


Thanks Major, that's exactly what I needed. I'll add those terms to my vocabulary. I guess I picked up the 'housing' word on Husted's site.

If I can get the DE and CE Plates on a lathe, I'll clean them up a bit, nothing too drastic, they'll be easy to polish up after a small cut.


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## bipole (Sep 8, 2009)

Bowser330 said:


> Bipole,
> 
> you should also consider blocking off the front bumper opening (mouth) because that will cause some undesired drag.
> 
> ...


Yep, planning on doing some aero mods and that big hole at the front is top of my list. The car looks sleek, but some educated folks have concluded that the Cd is near .42 , CdA about 18. I don't think I need any openings up front. The car's underside is almost completely smooth and a front splitter might help a little.

I'm thinking quite opposite on the battery pack although that one would drive a long way.

95s12p A123 26650 cells. 80kg (176lb), 1435A @ 52c. Yes, I want to drive them hard!

This is getting quite off subject, I guess I should get a build log going so all can throw their input my way. All constructive input is very welcome btw. Thanks!


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## bipole (Sep 8, 2009)

Amberwolf said:


> Have you got interior insulation, carpeting, dashboard coverings/etc? .........


Yes, have all those, they are not that much weight and serve to make the car comfortable, so I'm keeping them. I'm adding a bit of dynamat on some of the larger aluminum panels to deaden them down a bit. I want to hear the gearbox, tires and wind, but no rattles!

I have a '67 Camaro that I drag race as well as drive on the street. I might just be growing old, but it's just plain noisy! It ran consistent 9.50's at 144 mph with the old nitrous'd small block. This year she got an all aluminum 565 big block and is tore down for orange paint. Hoping to get her into the high 8's next summer,.....uh, make that fall, as usual, too many projects.

Before I get bashed here, I'm converting it to E-85 this winter for what that's worth environmentally. To help balance out the carbon footprint I drive a Honda Insight and hypermile to a 84.8 mpg lifetime average. Yes, I tend to take things to extremes, isn't that how we're supposed to live?


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## DavidDymaxion (Dec 1, 2008)

Dennis Berube (world's quickest 1/4 mile electric dragster, he has run in the 7's!) tried shaving down his motor, to save weight. He lost enough power the vehicle was slower.


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## Woodsmith (Jun 5, 2008)

Maybe if motor weight is that great an issue then perhaps changing to a set of Agni 95 motors would be good. I think I read somewhere they were about 25lb a peice @ 10kW @ 60v.


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## bipole (Sep 8, 2009)

DavidDymaxion said:


> Dennis Berube (world's quickest 1/4 mile electric dragster, he has run in the 7's!) tried shaving down his motor, to save weight. He lost enough power the vehicle was slower.


Well, there we go, that settles it!

Thanks!


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## Duncan (Dec 8, 2008)

Hi
Major has told us that the steel "'yoke" is part of the magnetic circuit
it occurs to me that the steel in front of the armature and behind it is probably not as important
on my motor this steel is about 10mm thick
if you have a big enough lathe some of this could probably go
you would probably only need a couple of mm for strength! (maybe 5mm?)

Leave the band around the field coils and armature for the magnetic field


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## major (Apr 4, 2008)

Duncan said:


> Hi
> Major has told us that the steel "'yoke" is part of the magnetic circuit
> it occurs to me that the steel in front of the armature and behind it is probably not as important
> on my motor this steel is about 10mm thick
> ...


Hi Duncan,

No, it is not that simple. It is probable that in certain areas, all of the steel in the yoke is needed to support the flux, including the overhangs. Flux, like a fluid, will completely fill the cross section of the pathway. Shave down that cross section, and you'll increase the flux density. Get that flux density to the point of saturation, and you start loosing torque.

That flux path in the yoke is complex, meaning there is not a constant flux density everyplace in the yoke. And areas which have a low flux density could be trimmed. But you would need a complicated flux map, which would most likely require a magnetic finite element analysis model. And this would require detailed knowledge of the entire magnetic circuit. The motor manufacturer is unlikely to give you this, so you would have to saw the motor in half to measure it. Then after all that, it would take a pretty complex machining operation to whittle off just the right steel. Not a simple "put it on a lathe" type of deal.

Regards,

major


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## pylon (Nov 10, 2009)

I think that installing a 300lbs motor in a 1600lb car, is
like putting a dump truck motor in a sports car. In an electric 
car the power is in the batteries anyhow, put the weight there.
The agni 95 motor twined is definately a good idea. There is
a mini truck weighting about 2000lbs that is on that evalbum site with
twin agni. The 95 model can put out 35KW each. They require vigorous
air cooling, but so what. Air cool it with a big blower motor just
like vw's bugs are, light and airy. This solution is over 200lbs lighter,
that is a lot of grinding!


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## bipole (Sep 8, 2009)

pylon said:


> I think that installing a 300lbs motor in a 1600lb car, is
> like putting a dump truck motor in a sports car. In an electric
> car the power is in the batteries anyhow, put the weight there.
> The agni 95 motor twined is definately a good idea. There is
> ...


 
I checked out the AGNI motor site. They do look great for what they are, I couldn't find the weight spec on them though.

I didn't post my performance goals in this thread but 70 KW is nowhere near what I'm shooting for. More like 250-300 KW and range is not so important, 30 miles would be fine. Looking to achieve sub 4-second 0-60 times. That kind of KW would take minimum seven AGNI's and managing that many motors would be, uh, complicated. I like simple, hence the large single motor.

As for the fan, I have a Porsche 914 blower, which is probably the same as the Vdub fan. It is power hungry though, maybe a temp switch and route the ducting to take advantage of some aero pressure differential so the fan is not needed much at speed.

Thank y'all for your input!


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## Sutitan (Feb 23, 2009)

I remember browsing Jim's albums online, and he did shave down a motor. you can read his comments to get more insight on what he did at http://hitorqueelectric.com/gallery...2_GALLERYSID=4690c0b22b7a547474c7b8ccc7786ffc . I think this is what you guys were talking about. hope this helps.


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## major (Apr 4, 2008)

Sutitan said:


> I remember browsing Jim's albums online, and he did shave down a motor. you can read his comments to get more insight on what he did at http://hitorqueelectric.com/gallery...2_GALLERYSID=4690c0b22b7a547474c7b8ccc7786ffc . I think this is what you guys were talking about.


Taking this approach, you never know until it is too late  Try putting that steel back on to get back the torque you shaved off.

Yeah, there might be a pound here and there you don't really need. But where exactly is that. What I'm saying is that it isn't going to be circular. Now I respect Jim and what he does. And he gets feedback from the horse's mouth. So, do you know for a fact that the motor in the picture was used in a max torque application and put out as much after the lathe as prior to it?

Regards,

major


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## Yabert (Feb 7, 2010)

Hi all

So after two years, I come back with the same question:




bipole said:


> Can motors be lightened up a bit?
> I'm mainly referring to series wound DC motors since that is what I'll be using. I know the all the copper is there for a reason, how about all the steel? I'm guessing the steel housing size is selected by the manufacturer from some commercially available pipe size and wall thickness that will accommodate the internals and end bolt threads. If I wanted to trim some off the outside are there any negative consequences to performance?


Any new comment or idea will be welcome!

You can see my motor housing. It weigh 60 lbs without modification and I can remove 13 lbs (22% of the weight) when I performed pocket or when I trim it.
The pocket can be between each stator and the trimming can be stop where the stator began.

How I can know if this modification reduce drastically the torque of the motor?

Thanks!


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## major (Apr 4, 2008)

Yabert said:


> So after two years, I come back with the same question:
> How I can know if this modification reduce drastically the torque of the motor?


After 2 years, I'll give the same answer. Don't. Unless you model the magnetic circuit in a finite element analysis program, you'll never know. After that, it ain't going to be that much weight savings.

If you do what you show, save even more weight and get the next size smaller motor to start with because that is the torque you'll end up with.

Why do you guys think you know better than the engineer who designed the motor? Do you think he used extra material because he owned stock in the steel company? Maybe because it was necessary for the proper operation of the product 

You could probably take out half the copper as well. Maybe shave the comm down to half length. 

Regards,

major


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## EVfun (Mar 14, 2010)

What small fraction of 1% will this shave off the total vehicle weight? Do you happen to be a bicyclist? (the phrase "weight weenie" is coming to mind  )


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## DIYguy (Sep 18, 2008)

I think Jim mainly turns the yoke to clean it up and be able to do a nice paint job or chrome. That is what I did with mine also. Just a skim. Weight saving was not the purpose and no significant amount of material was removed.


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## Yabert (Feb 7, 2010)

major said:


> Why do you guys think you know better than the engineer who designed the motor? Do you think he used extra material because he owned stock in the steel company? Maybe because it was necessary for the proper operation of the productmajor


 
I don't pretend be a great motor designer! I only think than this type of motor are design like this because it's a simple and cost effective way to do. It's also an overbuild design for run hard and fine in a forklift for 8h a day for 15 years!!!
My EV will need probably 10% of this required.
For me it's like compare a tractor engines with todays cars engines.





> After 2 years, I'll give the same answer. Don't. Unless you model the magnetic circuit


So, anyone know what is the tipical magnetic circuit for a serie wound DC motor? Something like this one bellow?


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## major (Apr 4, 2008)

Yabert said:


> So, anyone know what is the tipical magnetic circuit for a serie wound DC motor? Something like this one bellow?


Hi Yab,

Yeah, something like that, except in 3d. And you need to know the exact geometry of the steel circuit and excitation from the electric circuit for your load profile. See those light green areas in the yoke near the outer edge centered over the poles? That would be about the extent of "excess" steel in that case. 

And the heavy steel frame on the motor is not there to make it last 20 years for 16 hours a day. It is there to provide the magnetic circuit which ultimately gives you torque. Maybe forklift designers don't really care if the motor is heavy, but generally the motor manufacturer does and is likely to make the motor with as little material as necessary to get the job done. Then he lets the forklift designer put a 2 ton battery and one ton counter balance weight on the truck.

But hey, go ahead and whack away. Like I said before, you end up with less torque, and it is a lot harder to put that steel back on it 

major


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## albano (Jan 12, 2009)

Yabert said:


> I don't pretend be a great motor designer! I only think than this type of motor are design like this because it's a simple and cost effective way to do. It's also an overbuild design for run hard and fine in a forklift for 8h a day for 15 years!!!
> My EV will need probably 10% of this required.
> For me it's like compare a tractor engines with todays cars engines.
> 
> ...



Got it right, thank.


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## Yabert (Feb 7, 2010)

major said:


> But hey, go ahead and whack away. Like I said before, you end up with less torque, and it is a lot harder to put that steel back on it


Hmmm!!! One more time, I'm resolve to your idea.
Because I don't have the chance to try it and put a new housing if it not work, I think I will focus on reduce the weight of the none magnetic device like the front and rear flange.
But I don't understand someting!! Why Kostov (a great electric motor manufacturer (for me)) put many hole directly in the magnetic flux of the armature??


http://www.diyelectriccar.com/forums/showthread.php/kostov-11-inch-dc-motor-construction-34775.html


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## major (Apr 4, 2008)

Yabert said:


> But I don't understand someting!! Why Kostov (a great electric motor manufacturer (for me)) put many hole directly in the magnetic flux of the armature??


I'd venture to say they would have a much better motor without the magnetic bottleneck in the dbs*,

*dbs = motor shop talk for the area where they have those cooling holes.

major


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