If using dual DC motors, I think the dual belts is an easy way to go...
That's exactly what I mean by, "dual rear motor setup with an independent belt drive to each wheel." Two motors, two belts, two drive wheels. Sorry if I wasn't clear enough. By "function of a differential when the car makes a turn," I mean that the outer rear wheel needs to spin faster than the inner rear wheel. You need to control for that since you don't have a mechanical system to do that for you. You actually have to tell that outer wheel how much faster to spin.
If not monitoring the individual wheel speed, I suppose you could look at the electrical load on each motor. You could then use feedback to balance the load between the two motors... that's essentially what an open differential does anyway. Not certain if that's the right algorithm in this case, though. If you're smart about it, you could make an effective LSD. At any rate, once you solve that control problem, seems you have half a TC system.
I think I got your point and you may have missed mine.
Or my point may be wrong.
In any case, I think with Tesla's AC motor they are controlling _exactly_ how quickly the motor spins. They have to create A/C waveforms precisely matched to motor RPMs. With a DC motor it is more of just "give it current and let it spin as fast it wants to". So with dual DCs if you round a corner and one wheel wants to spin at a different rate (since it is trascribing a different arc) then it is OK as one motor speeds up a bit and the other slows down. I don't think (but I could be wrong) that they need any special "simulated differential" electronics to do that. Now the effect may be something akin to "open differential" where you run into traction issues if one wheel is on a slippery surface. That is possibly one reason why the home brew person looking for shortcuts would use a simple dual DC motor setup, and a more sophisticated operation would use a single AC motor with a differential and torque limiting traction control.
It is a lot easier to design an EV that works OK in good conditions, but when you want something that is "user friendly" in all conditions (including on snow and ice) you have to do a lot more work.
Yeah, ya know I read right past the DC distinction you were making since it seemed you missed I was already talking about dual belts.
I don't know what kind of motors they're using in the "wind car." I assumed they were brushless DC motors, which can allow for fine speed control. I just assumed each motor has it's own controller. (This is what I'd prefer they'd talk about rather than body work.)
Yeah, I guess if you used two standard DC motors wired in parallel from the same supply, the reduced load on the outer wheel would cause it to spin faster, making a kind of simulated open differential.
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Last edited by doug; 01-06-2009 at 11:58 PM..
Reason: added "... rather than body work"
"I think swappable batteries are not a good idea myself"
Tesla & PBP seem to be pursuing that idea, but there are still plenty who question if it is ultimately the right answer.
By the way, that was a good interview, but I have trouble getting past the idea that Tesla has already "stole" much of Vince's thunder. His viewpoints would have seemed more fresh a few years ago.
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