# skipping the transmission



## electricwagon (Feb 9, 2009)

Is it unrealistic to do a conversion where the motor is directly driving the driveshaft? This would be a rear wheel drive setup with a 4.11 posi rear. Looking at a DC motor with lead acid batteries.

I'd be happy with a top speed of 50mph. If that is possible, what kind of motor would have the torque and rpm range to pull this off without a transmission?


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## ice (Sep 8, 2008)

I also wonder if that would work...


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## kittydog42 (Sep 18, 2007)

If you are going to go with a direct drive application, one thing to consider is that most DC series wound motors (WarP and Advanced DC, specifically) used on EV applications are self-cooled, meaning that the velocity for the cooling blade comes from the rotation of the motor itself. What this means is that it is more detrimental for the motor to run under a heavy load at low RPM as it would when driving up a hill. To minimize this problem, and to provide reasonable acceleration, you would need to figure out a way to end up with a final drive ratio of between 8:1 and 10:1. This would generally equate to second gear in a manual transmission vehicle. The next problem that you would then run into is that the maximum safe RPM of the motor will not get you past 35-40mph. You would need to select a motor that has a max RPM of over 10,000, to achieve freeway speed. This is why motors such as the TransWarP are not recommended for direct drive applications, but rather for hybrid assist. 

Anybody with a RWD traditional conversion (series wound DC motor with manual transmission) can test this out by putting the car in 4th gear and seeing how it accelerates from a stop, especially on a hill. The high speed test could then be performed by doing the same, in 2nd gear, and noting the top speed. This should make it clear how drive ratio and RPM go together for engineering an EV.


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## judebert (Apr 16, 2008)

There have been drag racers who went with direct-drive motors. The problem, as you specified, is getting sufficient torque on the low end, while still having a high enough max RPM to reach your desired speed.

Without knowing the tire diameter, it will be impossible to determine the RPM of the motor at your max speed. 

Assume a series-wound motor, since it can generate LOTS of torque, so you should be able to accelerate nicely. Assume a top RPM of 4110 for easy calculations. With your 4.11 rear ratio, that means your top speed is wheels at 1000 RPM. With a 185 70R 15 tire, the tire circumference is 79.16", and needs 825.4 revs to go a mile. Since you'll be going 1000 revs in a minute, you'll be going 1000/825.4 = 1.2 miles per minute. That's 72.7 MPH.

That's at least better than your 50MPH requirement. Smaller wheels will reduce your top speed and increase your acceleration.

And acceleration is a problem. You'll need a lot of torque to take off; that means you'll need a lot of Watts (a Watt is one Amp at one Volt). The common solution to this problem is a Zilla2K, which can provide the Watts at up to 2000A. The problem is that those aren't made any more.

The other problem is that batteries don't like to provide 2000A. It can damage many batteries, and the rest don't provide all their energy when they provide it at high currents (see Peukert's Exponent). So you'll want either a LOT of batteries, placed in parallel so they can split up the current, or a VERY high-voltage controller.

I don't know of any really high-voltage series DC controllers right now. You could build your own out of big contactors. (See Contactor Controller.) You could go AC, which supports very high voltages; unfortunately, that's generally pretty expensive. Especially if you get a battery pack that can provide that kind of power for an extended period of time.

Anyway. Possible, even feasible, but often expensive. The guys who do this are drag racers. It's an expensive hobby, where you expect parts to break.


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## MalcolmB (Jun 10, 2008)

Just one point to add to the arguments above. If you halve the weight of your vehicle you also halve the torque (and current) needed for a given acceleration or to climb a given hill (same thing in effect). A single ratio can work well on a motorbike because it's so light. The heavier the vehicle you want to convert, the more important it becomes to use a multispeed transmission.


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## electricwagon (Feb 9, 2009)

judebert said:


> There have been drag racers who went with direct-drive motors. The problem, as you specified, is getting sufficient torque on the low end, while still having a high enough max RPM to reach your desired speed.


I appreciate all your feedback. The max rpm I already knew I'd be ok. I was looking at a large (>200lbs 11-12") forklift motor. At a higher voltage than it was designed for (48v) I figured I'd have no problem sustaining 3000 rpm, which put me at 55mph roughly (195/70R15). Alternatively, there's a 4.85 ratio I could swap, but I'd need a bit over 3000 rpm to achieve 50mph. But I dont know if this setup has enough torque. Hence, I was trying to figure out what ratio is needed in practice.



> And acceleration is a problem. You'll need a lot of torque to take off; that means you'll need a lot of Watts (a Watt is one Amp at one Volt). The common solution to this problem is a Zilla2K, which can provide the Watts at up to 2000A. The problem is that those aren't made any more.


I want to keep this as simple as possible, that doesn't sound like it 

I was thinking good old contactor controller.

I only have to travel 10 miles in one direction at most so I dont need that much lead. I think I can get the glider to around 2200lbs. Add electric motor, vacuum pump, brackets, wiring and batteries weight.

If that doesn't work, then I'll have to forego the steel cage approach and think "outside the box" and go for a light 3 wheeler.


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## rfengineers (Jun 2, 2008)

The cooling problem is easily solved by using a fan to circulate air through the motor. Net Gain makes a cover for their motors to allow for this.

The torque issue means you need a larger motor,e.g. an 11-inch instead of a 9-inch, for the same weight car. Generally, the larger motor means a lower top RPM.

I considered this route for my current project, a 1961 Sunbeam Alpine. I decided, after building the "Learning Experience" (http://www.evalbum.com/2283), to use the transmission.


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## electricwagon (Feb 9, 2009)

kittydog42 said:


> Anybody with a RWD traditional conversion (series wound DC motor with manual transmission) can test this out by putting the car in 4th gear and seeing how it accelerates from a stop, especially on a hill. The high speed test could then be performed by doing the same, in 2nd gear, and noting the top speed. This should make it clear how drive ratio and RPM go together for engineering an EV.


Well, 4.11 is a pretty high ratio (and 4.85 even moreso). a 3ish:1 is more typical in differentials in rwd, and I've seen pretty low 2.x ratios in Mercs but they might make up for it in tranny gears. What is a typical 2nd gear ratio? It seems that this could vary wildly.


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## electricwagon (Feb 9, 2009)

rfengineers said:


> The cooling problem is easily solved by using a fan to circulate air through the motor. Net Gain makes a cover for their motors to allow for this.
> 
> The torque issue means you need a larger motor,e.g. an 11-inch instead of a 9-inch, for the same weight car. Generally, the larger motor means a lower top RPM.
> 
> I considered this route for my current project, a 1961 Sunbeam Alpine. I decided, after building the "Learning Experience" (http://www.evalbum.com/2283), to use the transmission.


So, on the sunfire you didn't use a tranny? that has to be an interesting twist on a transaxle fwd car. Or are you saying that based on that, still using the transmission, you'd never try a conversion without tranny? I also see that your final weight is 300kg heavier than a stock sunfire, I am a bit surprised by that, with only 10 batteries. I would have expected you'd end up with a lighter vehicule in the end?


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## rfengineers (Jun 2, 2008)

electricwagon said:


> So, on the sunfire you didn't use a tranny? that has to be an interesting twist on a transaxle fwd car. Or are you saying that based on that, still using the transmission, you'd never try a conversion without tranny? I also see that your final weight is 300kg heavier than a stock sunfire, I am a bit surprised by that, with only 10 batteries. I would have expected you'd end up with a lighter vehicule in the end?


No, I DID use the transmission. I normally (almost always in fact) drive the car in third gear. Acceleration is great in third (even starting out on a hill) but not too impressive in fourth.

What I am saying is: based on my good experiences with using the transmission in my EV the "Learning Experience" I am sold on the concept of using a transmission.


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## rfengineers (Jun 2, 2008)

electricwagon said:


> So, on the sunfire you didn't use a tranny? that has to be an interesting twist on a transaxle fwd car. Or are you saying that based on that, still using the transmission, you'd never try a conversion without tranny? I also see that your final weight is 300kg heavier than a stock sunfire, I am a bit surprised by that, with only 10 batteries. I would have expected you'd end up with a lighter vehicule in the end?


I believe the car is 300-pounds heavier, not 300-kg.

The battery weighs 860-lbs.


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## electricwagon (Feb 9, 2009)

rfengineers said:


> No, I DID use the transmission. I normally (almost always in fact) drive the car in third gear. Acceleration is great in third (even starting out on a hill) but not too impressive in fourth.


This is a good reference. 4th gear means an overall ratio of 3.62 while 3rd is 5.2, so with my 4.11 that might be a bit off, but with a 4.85 that should be almost like your 3rd gear.

It gives me some data. Anybody else want to contribute some comments on 3rd / 4th gear acceleration from standstill?


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## rmay635703 (Oct 23, 2008)

electricwagon said:


> Is it unrealistic to do a conversion where the motor is directly driving the driveshaft? This would be a rear wheel drive setup with a 4.11 posi rear. Looking at a DC motor with lead acid batteries.
> 
> I'd be happy with a top speed of 50mph. If that is possible, what kind of motor would have the torque and rpm range to pull this off without a transmission?


It depends on what type of performance you expect, my little comutacar weighs in around 1400lbs plus cargo and is direct drive, thing is you don't start out on a hill very fast and the rearend is geared in the 5.xx's not 4.11 also the tires are 13".
My top speed hovers between 45mph and 55mph with a 72v 10hp D&D motor.
Remember that the rearend ration on most cars is the 3rd gear in most cars.
My acceleration is about 15-20 seconds to 45mph (my batteries aren't very good) Getting up to 50/55 with the batteries I have takes quite a while usually around a minute (depending on temp, cool out and it never gets there) though I am told that with newer batteries the 50mph time would be close to the 45mph time I am getting now.

SO if you can figure out a way of keeping the weight down as much as possible (I wouldn't do direct drive on a vehicle weighing much over 1 ton) and can find a motor that is sized well and very durable you can run direct drive, just take care that your starting amps stay low and you should be fine.

What others here do not mention is that you DO NOT HAVE to have a performance orientated setup to do direct drive, you just need to LIVE with the performance and limitations of the vehicle configured that way, if you live in a flat area and don't care about performance (as I don't) you will be happy with direct drive. Starts out slowly, then quickly then slowly again as you approach top end. You may also have to replace brushes more often in this configuration but around here there isn't much in the way of hills and I have never had brush issues and I do put on a fair amount of miles, it also helps that my controller maxes at a little over 400amps for a few seconds.

Good Luck


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## CPLTECH (Sep 14, 2007)

What is your aversion to a transmission? I do recommend a lighter weight trans lube such as Redline MTL to reduce losses.
-If turning left at an intersection with oncoming traffic, 1st provides a better sense of security vs. 2nd… Unless all your left turns have a left turn traffic signal.
-When going up a steep hill, 1st allows me to slowly climb at 20-25MPH with the motor spinning sufficient to keep cool vs. 2nd. Some here speak of their motors that are destroyed due to prolonged low RPM’s & high amp scenarios.
-If trying to go in the sand or thru soft ground, being able to drop to 1st is comforting… Unless you relish the thought of waiting for a AAA tow.
-Truth is, none of us want you to get hit in the rear. My S10 is not the quickest, but for the most part it does not aggravate the drivers behind.
-These are some of the reasons the everyday tried & true EVers use a transmission. Choice is yours.

94 S10 28 hp 9” motor 5sp w/clutch
1st – up to 20
2nd – up to 45
3rd – above 40


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## rfengineers (Jun 2, 2008)

CPLTECH said:


> What is your aversion to a transmission? I do recommend a lighter weight trans lube such as Redline MTL to reduce losses.
> -If turning left at an intersection with oncoming traffic, 1st provides a better sense of security vs. 2nd… Unless all your left turns have a left turn traffic signal.
> -When going up a steep hill, 1st allows me to slowly climb at 20-25MPH with the motor spinning sufficient to keep cool vs. 2nd. Some here speak of their motors that are destroyed due to prolonged low RPM’s & high amp scenarios.
> -If trying to go in the sand or thru soft ground, being able to drop to 1st is comforting… Unless you relish the thought of waiting for a AAA tow.
> ...


I can't drive in first gear. I have trouble keeping my tires from spinning.


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## rmay635703 (Oct 23, 2008)

CPLTECH said:


> What is your aversion to a transmission?


My car never came with one and the other vehicle has it stuck in 2nd to reduce speed.


CPLTECH said:


> I do recommend a lighter weight trans lube such as Redline MTL to reduce losses.
> -When going up a steep hill, 1st allows me to slowly climb at 20-25MPH with the motor spinning sufficient to keep cool vs. 2nd. Some here speak of their motors that are destroyed due to prolonged low RPM’s & high amp scenarios.


 One of my EVs isn't designed to exceed 25mph period, the other once moving will climb any hill above 20mph, around here there are few hills though.



CPLTECH said:


> -If trying to go in the sand or thru soft ground, being able to drop to 1st is comforting… Unless you relish the thought of waiting for a AAA tow.
> -Truth is, none of us want you to get hit in the rear. My S10 is not the quickest, but for the most part it does not aggravate the drivers behind.
> -These are some of the reasons the everyday tried & true EVers use a transmission. Choice is yours


 I don't drive through soft sand normally and when I have it hasn't been an issue. In terms of getting hit in the rear I have never had a situation where HP would prevent it, generally I am stopped behind some other yahoo and the rearender is driving too fast and slides, luckily my electric car is so outlandish I have never had anyone come close to hitting it with another vehicle, though bicycle riders have almost hit it not realizing I was there due to the stealthy noiseless camoflage on it.


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## electricwagon (Feb 9, 2009)

CPLTECH said:


> What is your aversion to a transmission?




It is part of my design requirement. Make it simplest as posible, but no simpler 

Battery pack, contactor setup, motor, diff and vacuum pump for the brakes, manual steering. That's it. Everything else will go. I can drop a ton of weight. Tranny is heavy, 4 speed zf (german made) auto with electronic control. Same you find in a Land Rover.

I was just trying to figure out if anybody doing conversions were skipping the transmission and if a large forklift drive motor would be sufficient.

I'm still reading all I can find on the internet before I commit to my project. The one main objection I've found is people talk about cost, that going for the bigger motor means more cost because of controller and motor, but that's a no go for me. I can find a used 11" motor, contactors plus new batteries for less than the cost of just the machine work required to adapt to the zf bellhousing + coupler + special swivel mount (this is a torque tube setup).

But, I'm still researching, as I said.


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## electricwagon (Feb 9, 2009)

rmay635703 said:


> It depends on what type of performance you expect


Just getting reliably from point A to point B where the distance between the two is 10 miles. If I had found a commuta car like yours, I would just have upped the volts and be driving it instead of trying to make a commuta car out of a regular car...



> SO if you can figure out a way of keeping the weight down as much as possible (I wouldn't do direct drive on a vehicle weighing much over 1 ton) and can find a motor that is sized well and very durable you can run direct drive, just take care that your starting amps stay low and you should be fine.
> 
> What others here do not mention is that you DO NOT HAVE to have a performance orientated setup to do direct drive, you just need to LIVE with the performance and limitations of the vehicle configured that way


Thanks. Sounds like we are on the same page.


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## CPLTECH (Sep 14, 2007)

electricwagon said:


> Tranny is heavy, 4 speed zf (german made) auto with electronic control.


You will find only a few have tried using an auto trans due to complexity and loss of HP.

It is good that you are doing research. Look thru the “Garage” section and the EVAlbum to get an idea what works for others.

We all like to try to build/buy a perfect EV first time out, but in reality it is similar to a new car purchase… “I wish it had _____”. “My next car will have this _____ for sure”.
It took me over a year to decide what direction to go and now that I am there I know of some improvements that would be nice as time & finances permit.


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## rfengineers (Jun 2, 2008)

CPLTECH said:


> We all like to try to build/buy a perfect EV first time out, but in reality it is similar to a new car purchase… “I wish it had _____”. “My next car will have this _____ for sure”.


Hence, the name of my first EV conversion was the "Learning Experience."


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## Coley (Jul 26, 2007)

One safety issue I have with a non transmission/driveshaft build, is the fact that you can never be safe, when the car is just sitting and/or being worked around.

Mine had a controller take off on it's own, while sitting in my shop.
Since I always try to put it in neutral, before I leave the driver's seat, nothing happened to me, the car or my shop.

With a transmission, you have a safe, neutral position that will prevent run aways.

Without a transmission, you can't even test run the motor to check the pot or anything else, without jacking up the drive end of the car and using jack stands.

If you have a failure of some sort along the road, how would you troubleshoot the system, if it might just take off and leave you standing there!!!

My vote is that a transmission is a must......


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## Technologic (Jul 20, 2008)

Coley said:


> One safety issue I have with a non transmission/driveshaft build, is the fact that you can never be safe, when the car is just sitting and/or being worked around.


Parking brakes?

Straight drives can have safety locks as well... on the actual gearing.

But it's easily just as safe as a manual to go transmissionless... and you'll save power, weight, etc

Why can't you just remove the belt from the gears to power test?


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## rmay635703 (Oct 23, 2008)

Coley said:


> One safety issue I have with a non transmission/driveshaft build, is the fact that you can never be safe, when the car is just sitting and/or being worked around.


On both of my cars the F/R contactor is always in "neutral" AKA off when the accelerator isn't down meaning my controller can run away all it likes but if the pedal isn't down it won't drive the motor and if my F/R contactor were to weld, the main contactor can be clicked off as well.



Coley said:


> Mine had a controller take off on it's own, while sitting in my shop.
> Since I always try to put it in neutral, before I leave the driver's seat, nothing happened to me, the car or my shop.


And what happened to your motor? With no load mine would fly apart



Coley said:


> With a transmission, you have a safe, neutral position that will prevent run aways.
> 
> Without a transmission, you can't even test run the motor to check the pot or anything else, without jacking up the drive end of the car and using jack stands.


So?



Coley said:


> If you have a failure of some sort along the road, how would you troubleshoot the system, if it might just take off and leave you standing there!!!
> 
> My vote is that a transmission is a must......


??? Mine can't do that because the F/R stays open and when I did have a problem I found a broken wire and replaced it, in fact my simple system could save me because I can wire around the controller if it fails on the spot, nice trick if you ask me. Not to mention I usually check with a volt and ohm meter to find an issue, running tests are for mech issues.

Also What if your tranny fails? How do you troubleshoot? 

Anyway, In my oppinion either way its moot if something fails your gonna hurt a little.


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