# Rear axle/ 2 motors?



## speff (Feb 8, 2008)

I would like to build a electric car, weight is a little high 3300 lbs.
To cut down on weight and do something different, would like to ditch heavy rear axle and make my own. Would having 2 electric motors work? One for each rear wheel, gearing them down accordingly. When making a sharp turn will that ruin the motors, they would be fighting each other?

Having a solid axle will not work. will suck power in turns.

Thought of having only left rear tire power car? will car want to push to right a little?

I know I will have only 1 speed with this setup. 40 mph is fine


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## Telco (Jun 28, 2008)

It should really only be an issue if you do a lot of tight, long corners so long as the two motors are not physically connected to each other. But, you'd not be able to just attach the motors to the suspension and use them as axles. You'll need to use some sort of independent rear suspension to support the vehicle weight, or have extra beefy motors capable of holding the weight, along with a suspension redesign. Either way will add a lot of cost to the project, and not a little weight. On another board I post to involving S10 trucks with V8 engines there is a member who has installed an IRS unit out of an early 90s Thunderbird, and he said he is looking at a 50/50 weight ratio on a vehicle that normally has an 80/20 weight ratio. 

Not knowing exactly what vehicle you are using other than it being a RWD vehicle, I'd suggest just spending the money on installing the motor where the transmission would normally reside, use a driveshaft and just drive the existing rear end. That being said, there is a project on this board somewhere where the posters are working out an in-hub motor setup.

If you'd posted what vehicle you are converting it would be easier to make recommendations. In the Chevy world there are different rear ends that can be put into just about any vehicle, and the different rear end types use varying amounts of power to turn the rear gears depending on how hefty they are, ie it takes more power to turn a heavy duty 14 bolt rear end used in 3500 series trucks for hauling 5 tons or more than it does in a corporate 10 bolt used in lightweight cars. And, unless the rear end has some sort of locking differential, solid axle rear ends are normally very simple jobs that only drive one tire. These are the most common rear ends, and will transmit all power to either tire via the path of least resistance, and are known as open differentials. You can tell this rear end easiest by just flooring the vehicle from a dead stop, if it only leaves one tire mark then it's the cheap rear. That rear end will also use the least amount of power of that class of rear end, with the posi units it will take more power. One notable exception is the factory (GM) G80 (RPO code in the glove box) locking unit, which only locks up when a certain amount of wheel spin is used. It normally acts as an open differential, but will lock both rear wheels together if one wheel spins too much. This is helpful if you are stuck in the mud or on ice.


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## speff (Feb 8, 2008)

Telco, thanks for reply, motors will not be used as axles, would maybe use chain drive (of correct ratio) motors would be mounted to axle, and never thought of motor vibration?

Yes, I thought of a warp 9"-11" mounted where trans would be, but just trying to get the most eff. A 10 bolt open rear axle will work fine, will only be slight power loss. 10 bolt would be easiest, and can also gear change fairly easy, ratios from 2.73 up to 4.88.

The car will be a 1967-1969 camaro convertible and have restored several of these last 32 years. Trying to fing just somewhat of a rust free shell.


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## freecarforum (Feb 4, 2009)

"the motors are not physically connected". this can be a good reason!

Used Cars


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## Telco (Jun 28, 2008)

That would be a pretty cool project. Personally I prefer the Firebird to the Camaro, but the Camaros are nice too. 

If you decide to go ahead with eliminating the rear axle, it might be possible to use a front wheel drive car's front suspension as a vehicle support. They are set up to allow wheel movement and weight support, without putting any weight on the CV joint or requiring the engine to move with the wheel. You would still need to use a half shaft to connect the electric to the wheel though. Going at it this way will eliminate the most unsprung weight, and will probably be a lot lighter and will be a lot smaller than conventional IRS systems since you have to be able to fit an entire engine and transmission between the front wheels. You can use a tie rod end mounted from the electric motor frame to the steer arm on the spindle to keep the wheel pointed correctly, and this will allow toe-in alignment of the rear end.

You could probably also wire the motors to work in a series/parallel configuration, with a switch to allow you to run them in either mode. This would make for an electric transmission. Series would be first "gear", parallel would be second "gear". There's plenty about the concept on this board, just search series-parallel.


Freecarforum, thanks, I didn't notice that, corrected.


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