Low-budget EV - Multiple motors & mechanical PWM

6283 Views 6 Replies 5 Participants Last post by nimblemotors, Feb 6, 2011

spaine

Discussion Starter · Feb 4, 2011

I am looking for input on a low-budget build I am considering.

I am using input from a few other threads, including:

Multiple small motors

Mechanical PWM

I would like to combine these 2 concepts in to an effective, yet practical approach for those on a limited budget. I plan on using my VW bug as a test platform, assuming this proves to be practical. For the motors, I am considering using several (number yet to be determined) starter motors. The quick specs of the motors are 12V, 1HP. Now, I want to be clear that I know the draw backs of using smaller motors and that these are not ideal motors. I also know that these motors are made to be run a short amount of time, so part of the plan is to cool them.

I am thinking of a gear on the transaxle shaft (not the large flywheel gear) and these starter motors mounted around this gear with gears of their own. To cool them, I would either use an electric fan or a fan driven by the input shaft of the transaxle (so the cooling was proportional to the speed of the motors). the electric fan would have less drag on the system so would probably be the best bet. I would use a large fan shroud to focus the air on the motor system and draw it in through the fresh air intake at the top of the engine compartment.

For the controller, I really like the idea of a mechanical PWM. I am aware of the limitations of this device, but I really like the fact that it is a serviceable part. With the electronic controller, sure you have more efficiency, but you never know if/when it will decide to leave you stranded. With a mechanical part, it could be serviced on the side of the road (to a limited capacity) and possibly get you back home. Also, the reduced cost would make it more that possible to carry a spare - something VW drivers are all to familiar with doing.

This is the design in its most basic form and I now ask for input to refine the concept and hopefully move into the fabrication phase. I have all the tools required (mill, lathe, welding equip, etc).

Thoughts?

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alvin

· #2 · Feb 5, 2011

Try to find a forklift junkyard. The motor in my truck is an 11 inch GE from a Hyster forklift. They sold it to me for $50. I only cleaned it (the outside) and painted it. After 2000 miles it is still working. The output shaft is splined and I went back and got the pinion gear from the lift to make the coupler. They also gave me the pump motor from the lift.

This might be cheaper and easier than several starter motors.

alvin

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bumblebee

· #3 · Feb 5, 2011

spaine said:
I am looking for input on a low-budget build I am considering.

I am using input from a few other threads, including:

Multiple small motors

Mechanical PWM

If you're looking for high power at a low cost, you may as well just pick up an EPC industrial controller.. they run on 12 volts, and handle a billion amps

They might not be pretty or fancy, but at about a dollar an amp, you can't go wrong!!!!

I get nervous with mechanical PWM's... too much current to switch that way

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Woodsmith

· #4 · Feb 5, 2011

I made a mecanical PWM controller to test the principle. It worked ok with an electric window motor but it was arcing and wearing rapidly. To make one that would work it would need to be quite well made but even then it would have a very limited life.
Simon designed his one to use in a Robot Wars competitor, a very different animal to a car.

I wouldn't recommend it but you are welcome to try it and shoot some video of it in action for us.

The use of starter motors is also not recommended as they are short duty motors designed for a few seconds of use very intermittantly. If all you were doing was nudging your car a few feet at a time a couple of times a day then fine but anything that constitutes a drive will cause you more problems and headaches then just getting a proper traction motor.

A forklift motor is fairly cheap to obtain and you would only need one of them and less cable to connect it.
You might even be lucky and find a usable control package from the same forklift.

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nimblemotors

· #5 · Feb 6, 2011

Sounds interesting, as long as you can get the parts cheap, why not give it a shot? If nothing else, it'll be a great story on what not to do!

I considered building a big multiple motor setup using surplus $10 3hp motors, and overdrive them 10x. Could at least get a kickass launch while the gas motor turbo has time to spool up.

The starter gears are horrendously noisy, you should consider chains, which are also noisy, but better, or as I was thinking of, using a planetary gear from a transmission where you have 4 motors each powering on of the planetary gears inside the outer gear, which is the output.
A controller for a multiple motor might be as simple as powering 1/x of them, full-power all motors running.

Crazy fun to build stuff that isn't really practical.

spaine said:
I am looking for input on a low-budget build I am considering.

I am using input from a few other threads, including:

Multiple small motors

Mechanical PWM

I would like to combine these 2 concepts in to an effective, yet practical approach for those on a limited budget. I plan on using my VW bug as a test platform, assuming this proves to be practical. For the motors, I am considering using several (number yet to be determined) starter motors. The quick specs of the motors are 12V, 1HP. Now, I want to be clear that I know the draw backs of using smaller motors and that these are not ideal motors. I also know that these motors are made to be run a short amount of time, so part of the plan is to cool them.

I am thinking of a gear on the transaxle shaft (not the large flywheel gear) and these starter motors mounted around this gear with gears of their own. To cool them, I would either use an electric fan or a fan driven by the input shaft of the transaxle (so the cooling was proportional to the speed of the motors). the electric fan would have less drag on the system so would probably be the best bet. I would use a large fan shroud to focus the air on the motor system and draw it in through the fresh air intake at the top of the engine compartment.

For the controller, I really like the idea of a mechanical PWM. I am aware of the limitations of this device, but I really like the fact that it is a serviceable part. With the electronic controller, sure you have more efficiency, but you never know if/when it will decide to leave you stranded. With a mechanical part, it could be serviced on the side of the road (to a limited capacity) and possibly get you back home. Also, the reduced cost would make it more that possible to carry a spare - something VW drivers are all to familiar with doing.

This is the design in its most basic form and I now ask for input to refine the concept and hopefully move into the fabrication phase. I have all the tools required (mill, lathe, welding equip, etc).

Thoughts?

Save

spaine

Discussion Starter · #6 · Feb 6, 2011

Thank you for all of the input so far.

Woodsmith & Alvin:

I agree about the arcing issue, and that is one of my main concerns at the moment. I have also looked in to finding a forklift motor, but the only scarp yard in the area doesn't have one, hence why I am looking for other alternatives.

Bumblebee:

What is an EPC industrial controller and where can I find information on them? A quick google search didn't provide anything obvious, but then again, I don't know what I am looking for.

nimblemotors:

I have looked into largely available DC motors in my local area and have not had much luck. Do you have any information on the 3hp motors you mention?

I too have thought about using a planetary gear system. The problem I have found is the cost associated with such a system. I have not considered a chain, however. I don't like the possibility of the chain breaking and allowing the system to "run away" when the load suddenly is absent. With the gearing, there is less possibility of 100% of the load suddenly disconnecting from the system. I would probably use gears with a slight helix to them, since they are much quieter.

I also like your thoughts on dividing up the power/motors. One option I was considering is to vary the distribution of the power, much like the PWM does. In other words, divide the power to the motors so that only one motor is receiving power at any moment in time. This will allow me to lower the current flowing through the mechanical parts and reduce the wear on them. Think of the concept of how a distributor on an ICE only delivers power to one cylinder at any one time, yet the system is always receiving power. This variation will essentially vary the duty cycle of each motor from 0 to 100% so that when full throttle is applied the cycle time for each motor is at its lowest (closest to a direct connection to the battery).

I hope i am explaining this well enough. I am still trying to wrap my brain around how to mechanically achieve this...

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nimblemotors

· #7 · Feb 6, 2011

If you go to surpluscenter.com sometimes they have some cheap motors.
These were treadmill motors, but sold out long ago.
There are 12v winch motors I bought a new one recently on ebay for $90 I think, here it is, $84 http://cgi.ebay.com/ebaymotors/NEW-...ptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories
4.6hp. Get four of these and run them at 48v, and you'd make some power for a short time. But then you are $400, a big used forklift motor is a lot cheaper.

I suppose you can buy starter motors at the junkyard pretty cheap?
Hmm, picknpull.com has them at $27, not that cheap really.

For gears, take apart any automatic transmission (bad ones are free, gears are still good usually) and you'll find the planetaries.

Another thought for you if you want to play around is to make your own motor.

spaine said:
Thank you for all of the input so far.
I have looked into largely available DC motors in my local area and have not had much luck. Do you have any information on the 3hp motors you mention?

I too have thought about using a planetary gear system. The problem I have found is the cost associated with such a system. I have not considered a chain, however. I don't like the possibility of the chain breaking and allowing the system to "run away" when the load suddenly is absent. With the gearing, there is less possibility of 100% of the load suddenly disconnecting from the system. I would probably use gears with a slight helix to them, since they are much quieter.

I also like your thoughts on dividing up the power/motors. One option I was considering is to vary the distribution of the power, much like the PWM does. In other words, divide the power to the motors so that only one motor is receiving power at any moment in time. This will allow me to lower the current flowing through the mechanical parts and reduce the wear on them. Think of the concept of how a distributor on an ICE only delivers power to one cylinder at any one time, yet the system is always receiving power. This variation will essentially vary the duty cycle of each motor from 0 to 100% so that when full throttle is applied the cycle time for each motor is at its lowest (closest to a direct connection to the battery).

I hope i am explaining this well enough. I am still trying to wrap my brain around how to mechanically achieve this...

Save

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