# Two Golf cart motors -> KitCar?



## Woodsmith (Jun 5, 2008)

Hi and welcome.

Are you thinking of the motor being in the hub with a wheel attached or are you thinking of the motor inboard with a flexible drive shaft to the wheel?

The former would put a lot of unsprung weight into the wheel, the latter would allow the motors to be fixed to the frame and the wheels to be suspended.

Also, what plans do you have for gearing down between the motor and the drive wheel?


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## Resonance (Aug 30, 2011)

Thanks Woodsmith,

Preliminary gearing looks like about 5:1 . If the motors are frame mounted and one set forward of the other (concentric is too wide) , the gearing could be used to re-center the drive gears to the drive shafts. Both the Porsche 944/924 and Mercedes 300d series have suitable rear half shafts and unbolt-able rear suspension components available in junk yards.

The thought is to let the decades of golf-cart R&D prevail and use thier motor/batteries for an e-car of short range, fair performance. 40miles, 75mph, but not at the same time.

Or is it more sensible to have one mid mounted 11" motor driving the differential of above mentioned donors? The wieght, friction, $$ and gearing gets complicated.

Thanks!


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## rwaudio (May 22, 2008)

Resonance said:


> Thanks Woodsmith,
> 
> Preliminary gearing looks like about 5:1 . If the motors are frame mounted and one set forward of the other (concentric is too wide) , the gearing could be used to re-center the drive gears to the drive shafts. Both the Porsche 944/924 and Mercedes 300d series have suitable rear half shafts and unbolt-able rear suspension components available in junk yards.
> 
> ...


I'm working on a 944 conversion and although there is a ton of room in the back once you remove the transmission/gas tank/hatch floor. I think it would be easier to do an 11" motor in the front and use the existing drive train. Remember that the 924/944 are rear transaxle cars so there is no rear diff to connect directly to. I do think that the galvanized bodies of the 944's make them great donors though, as they will last a very long time. 

Good luck with your design.


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## Resonance (Aug 30, 2011)

A full 944 conversion - smart. Strong AND light chassis. Already set for high torque loads, lots of choices for bushings/shocks. Possibly cheap if you find one with a blown motor. and best of all, LOOKS AWESOME!

I restored a '82 944 a while ago and have all the tools - might make more sense even on the bottom line than a multi-motored golf-cart based car. I still see Sterling kitcars (very cool) available but at a price point similar to an '80s 944....

Any projections on your cost, 0-40mph time, 'nice driver' range ?
The car was designed light by Porsche for performance - a good start...


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## rwaudio (May 22, 2008)

Resonance said:


> Any projections on your cost, 0-40mph time, 'nice driver' range ?
> The car was designed light by Porsche for performance - a good start...


I'm looking at 0-60mph in 5 seconds or less, a "nice driver" range to 80% of 100km and a cost of 20k. I will have a fairly small battery pack, partly because I don't "need" a huge range, and I also don't "need" a huge pack to get high power out of the A123 cells.


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## Drahcirdk (Sep 5, 2011)

Hi, this is my first time posting on these forums. I don't really have any answers to add, but I do have some other questions related to this. 

I have been thinking about doing a similar project, mounting 4 golf cart motors to a frame (maybe a sandrail or something else light) which would each then drive one wheel of the car. What I am not sure about is how to connect the motors to the wheels. As you said, a ratio of 5:1 (or around there) would be best if it is going to be just a single ratio. I have heard of people using a chain drive, which would be simple, but I would be worried about the extra maintenance/attention that would require.

The other question I had was the controller, and how to limit wheel slip. I had thought about using one controller per motor, or using a larger controller to power several motors in parallel (or series, or even switching between the two). If you used separate controllers, loosing traction with one wheel wouldn't keep the others from still performing as normal (providing the batteries could handle the draw). Ideally you would have some way of slowing down the wheel that lost traction so it wasn't wasting energy. 

What had you thought about doing on those points for your conversion (connecting the motors to the wheels and the controller set up to use)?


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## Sunking (Aug 10, 2009)

Got a golf cart motor in mind. Golf Cart motors is kind of meaningless. They run a gauntlet in varieties from high torque with low RPM up to speed motors but not a lot of torque 

I have a EZ-GO modified cart made for speed that can top out around 28 to 30 mph on a flat paved surface.

I think the real challenge for you will be the cost. OEM motors run from $400 to $800 each, and controllers another $400 to $700. 

I am not sure but I do not think you can series wire two motors and run it with one controller. Maybe someone else knows and has done it.


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## Resonance (Aug 30, 2011)

Thanks for the excellent feedback Folks.

Two Motors (left & Right), one controller:
Two DC motors in series will experience the same current through each (Ohms Law). If one is on the inside radius of a turn (smaller radius), it will turn slower than the outside one, being coupled with the tires to pavement. The current stays the same in each motor, but the voltage across each is proportional to the load on each, providing power (power=voltage times amperage)- more Ohm's Law) differential similar to the mechanical differential on a standard setup.
The DC controller, if controlling amperage only, 'sees' both motors as one current draw and applies current per the throttle setting and draw of the seen 'single' motor (usually across a series shunt). AC, PWM, Induction motor controllers have a vastly more intimate knowledge of the motor and would not be appropriate for a dual-motor-series configuration.

This dual-series motor could be modeled with an RC electric car with a simple DC Brushed current controller; if you can find anything but brushless nowadays.

It would be GREAT to have this reviewed by a DC Controller Engineer who is familiar with the the violent world of 1000 amps!

Coupling to drive shafts; my hope is to get junk yard parts of performance cars. Yet I think no custom car is built without some custom machine shop work and welding (mine or hired). To couple an electric power system to the wheels, I'll be welding electrical drive components to standard automotive components at some point. Its the nature of the hobby, yes?

A123 has a wide selection of batteries, even LiPoFeMg. What model # or product line is in the E-Car scale?
Thanks


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## rwaudio (May 22, 2008)

Resonance said:


> A123 has a wide selection of batteries, even LiPoFeMg. What model # or product line is in the E-Car scale?
> Thanks


http://www.a123systems.com/products-cells-prismatic-pouch-cell.htm 20ah pouch, LiFePO4 very low impedance, very stable voltage, but hard to connect together.


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## MalcolmB (Jun 10, 2008)

Hi Resonance
I'm converting a classic Mini, using a couple of series wound motors to drive the front wheels in the way you describe. The motors are mounted face to face across the subframe and are each connected by a chain reduction to sprockets on the end of each drive shaft. The ratio is just over 4:1, which is the highest I could manage in the limited confines of a mini subframe. I would have preferred closer to 5:1.

The motors are connected in series to a single controller and work just as you describe on the bench. I've not tested it on the road yet. I've asked a lot of people about how well this is likely to work and the consensus is that it will work fine with the motors in series. This of course means you need a battery pack and controller that can supply twice the voltage needed by a single motor. I also intend to try running the motors in parallel, as this would let me use a lower voltage pack and controller. Running in parallel may be more problematic as slight differences in resistance could cause one motor to 'hog' more current, so it's important to make sure the motors are matched and cable length is identical. I have found references to industrial applications where motors are run in parallel and it seems that if this is going to work at all it's most likely to work with series-wound motors because of their behaviour under load.

I started down the two motor route partly because I happened to come across two identical motors going cheap and partly because of the novelty value  If I was to do another Mini conversion I think I would go for a single motor mounted above a diff with a belt drive, or perhaps two (short) motors mounted either side of the diff to balance the load on the diff input bearing.

My Mini build thread is here: http://www.diyelectriccar.com/forums/showthread.php?t=52461


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## Drahcirdk (Sep 5, 2011)

If one of the wheels were to loose traction, would its voltage increase at the cost of the other motor? If so, would you have to worry about burning out the motor due to too high of voltage? And wouldn't you loose power to that wheel, even though the amps stayed the same?


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## MalcolmB (Jun 10, 2008)

Drahcirdk said:


> would you have to worry about burning out the motor due to too high of voltage?


Yes that's a possibility. The worst case I've considered is a failure in the drive train to one wheel, so that one motor is free to overspeed. The simplest way I can think of protecting against that is to use an rpm switch that senses motor shaft speed and switches a resistor across the throttle if motor rpm rises too high. The resistor would be selected to drop the controller voltage to a safe level, but still allow you to manouver out of harm's way using the other motor.

Edit: Not sure if this would work with all controllers, but I think it would work with an Alltrax, where the throttle setting commands a given speed/voltage.


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## Resonance (Aug 30, 2011)

Thanks for A123 link -i look forward to their 110kW packs- the management electronics are very cell-design dependent and hence better supplied by the Mfg.

The original thread of two golf-cart motors and deep cycle lead acid is based on being able to find them surplus, broken, etc, by virtue of their prevalence; where people golf.; eg everywhere.

I'd be happy to rewind a motor, change the brushes, bearings or fix a couple controllers if they came my way. - I get a kick from taking "junk" and turning it back into its $400 dollar value again. ;-)

The ultimate GREEN, if you will.


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