AWD without differentials?

General Discussion about electric vehicles.
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Re: AWD without differentials?

Post by Punx0r » May 04, 2016 5:51 pm

So likewise "torque steer" would steer the torque, not the vehicle?

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Re: AWD without differentials?

Post by cycleops612 » May 08, 2016 9:40 pm

Just saying, but a trike AWD would be very simple, as the rear could, at worst, just coast around corners while the front steers and pulls it thru the corner.

It seems other methods need trial and error to get right. You know this method works

No mention of controller/s or throttle/s?

Is it really such a problem on a narrow track buggy vs a wider car? I bet pedicabs e.g. dont bother.

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Re: AWD without differentials?

Post by atarijedi » Sep 05, 2016 5:25 pm

There was a company called PML Flightlink that made a BMW Mini with 4 hub motors. Technically it could have a 0 degree turning radius. Company is called Protean Electric now.

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Re: AWD without differentials?

Post by cavallo pazzo » Sep 08, 2016 1:14 am

In my velomobile front motors (Crysta 406) are piloted by two separate controllers with one splitted throttle input, no vectoring or correction of any kind.

In speed control mode it's interesting to say the least.
I was sure it'd be a mess to drive, with inner wheel increasing torque as speed reduces, but that forgets the Ackermann compensation. Technically, inner wheel makes a tighter turn, smaller radius. Well behaved trikes are made accordingly, with higher angle on inner wheel. Apply more torque on a steeper angle and you have increased lateral force, inward of the curve.
Feeling is oversteer, like in a rear wheel drive car.
Or like in a front wheel drive with limited slip diff. Think Ford Focus RS FWD or rally cars.

It's less obvious in torque mode with modern controllers, but it behaves still slightly neutral to oversteer under load.

A real pleasure to drive: modulate power to adjust radius, place to velomobile exactly where you want it with throttle.
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Re: AWD without differentials?

Post by cycleops612 » Sep 08, 2016 4:35 am

Cavello, thanks. Very interesting stuff.

I had wondered along similar lines and guessed at the possible existence of ackerman.

i figured similarly on hardware too.

A hub in each wheel is so elegant it has to be right.

A shared controller is tempting for both wheels, but modest mainstream controllers are so cheap & such a big cheap boost to a weak link (controller current) (48v 20a = ~1kw, ~$20 US for a controller), that a shared throttle & each hub having a controller seemed best.

But you actually did it. Nice one.

Extending the above logic, IF, I am correct & simplicity/economy/total control can be had by decentralising propulsion so lesser mainstream gear will do for each motor, (a bit like electric trains do), then, why not extend that logic to batteries. Each wheel has its own battery of equal voltage, so big current draws are short distance, and wheels gradually equalise/balance their batteries charges intelligently as required. If not for each wheel, then 1 each for front and back of car.

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Re: AWD without differentials?

Post by cavallo pazzo » Sep 08, 2016 7:18 am

It was done that way in 2011.
One 51 V 13.5 Ah on each side, 8 mm² cables to controllers, and one small 8-prong cable to link packs and plug charger, solar, accessories, seat heater, music, lights.

Upgrade is planned with a distribution block, 2 batteries and every electric device on it. A big node to have equal voltage for everybody.
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Re: AWD without differentials?

Post by cycleops612 » Nov 30, 2016 10:23 am

Just saying, but awd w/ hub motors with separate tho co-ordinated controllers, could even avoid/improve on (4 wheel steering) mechanical steering, ala bulldozers.

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Re: AWD without differentials?

Post by cycleops612 » Nov 30, 2016 10:30 am

llile wrote:
liveforphysics wrote:No differentials works great. It's a nice way to save wasting a bunch of power at cruise from churning oil.
Hub motor on all four wheels. Electric motors aren't driving at constant speed, they are driving at constant torque (OK really a torque curve but that's beside the point. would be about constant through a short curve). Turn, and both motors are still applying torque, even if one is going slower. The only use of a differential is to drive more than one wheel with one motor, but with electrics, it would be better to drive each independantly.

I'm using 2WD on a tadpole trike, the principle works there as well.
Well OP, there is your answer. llile isnt theorising, he has done it (check his posts here).

Modify what he does to suit.

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