# electric motor booster



## HyperUniverse (Jun 23, 2011)

Hi,

I have an old van VW T4 Syncro (4x4), and for the last 3 years I have been driving it only in 2wd mode, as the viscous coupling going to the rear axle was damaged and I've removed it.

I am thinking to install an electric motor to power the rear axle, so I can have 4x4 traction again.
It won't need to be working all the time, just in the winter, and probably when I need more acceleration going up a hill.
So I don't think of a big battery pack, and not even a big motor.
I won't be moving the van just on the electric motor only (except when the front wheels will be stuck in the snow).

Has anybody got a suggestion for me what motor to use, how many batteries?

Thank you.


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## dougingraham (Jul 26, 2011)

This is a difficult problem to solve. You only want to use the AWD when conditions are bad. Without some mechanism to keep the front and rear drives in sync you will create a somewhat dangerous control situation. I suspect your best course of action is to fix the viscous coupling and continue to drive it on the ICE. Alternatively you could convert the whole thing to an EV. Having both systems generally means you attain only some of the pluses because you are carrying around a lot of stuff you don't need. The OEMs spend millions of dollars to combine both systems in one vehicle and call it a hybrid. These tend to have dubious advantages over their non hybrid siblings and often at high cost.

I think you could make something that would work pretty easily as long as you are on dry pavement. Getting both systems to play together nicely under adverse conditions is something entirely different. My suggestion is to pick one or the other drive system. I would prefer you convert the vehicle to an EV but this may not be able to accomplish your goals for the vehicle.

Best Wishes!


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## jwiger (Oct 18, 2014)

I'm pretty sure you can electronically sync curtis controllers to drive two motors at the same speed. Perhaps he could do an awd system this way without the physical coupling between the front and rear. Although I suppose just feeding a matched throttle signal to both front and rear would give a pretty simple division of power.

I wish I had the know-how to design that throttle mux I have in mind. It could be used for differential throttling.


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## Duncan (Dec 8, 2008)

Hi Hyper

Don't worry about synchronizing the front and the back - the ground will do that very well,
If you think about it every two wheel drive vehicle is an extreme example of how unimportant that is with 100% of the power going to only two wheels

It's actually worse than that - 99% of cars have an "open" differential so the ground is the only thing that makes the two wheels on the same axle get the same amount of torque

Bigger problems
The cheapest way to get enough grunt to make a difference would be a DC motor - effectively a re-purposed forklift motor
BUT a brushed motor should not be driven with no current through the brushes - it will wear out very fast
So a DC motor would need some type of clutch to disengage it when not being used

An AC motor does away with that problem but they tend to be more expensive


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## HyperUniverse (Jun 23, 2011)

Duncan said:


> Hi Hyper
> 
> Don't worry about synchronizing the front and the back - the ground will do that very well,
> If you think about it every two wheel drive vehicle is an extreme example of how unimportant that is with 100% of the power going to only two wheels
> ...



Thanks all for answering,

Well then I am lucky......my van has this kind of clutch already in the rear differential.
When the rear wheels are moving, the propshaft doesn't move.
But if I turn the propshaft by hand, then the rear wheels start to spin.
(just a clarification.......a section of the propshaft is already taken out to disengage the faulty VC, so now the rear wheels are spinning freely, but the propshaft stays fixed)

So, no problem about that.
About other problems mentioned here.......I don't worry about anything.

Now where can I find such DC motor, and how powerful do you think it should be ?

Thank you.


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## jumpjack (Sep 9, 2012)

The electric power you need depends on the ICE power you currently have: it should be at least the same (just convert HP to kW).
The more the current, the more the torque is.
The more the voltage, the more the speed is.
At same power, the more the voltage, the less the current (and torque) is.

Also, forget brushed motors, they cost in maintenance and are less affordable than brushless.


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