[cajunfj40]

Hello again thingstodo,

*WARNING * another long-winded post!

No worries, that's basically my default mode...

If you are using separate controllers, I don`t think you need any electrical alignment. If you are still looking to do one controller - I would be interested in your results.

I agree. I'd also be interested in my results - it'll take a while to get there if I try it! I'm a MechE, so this isn't my natural turf.

I don`t know of any research on-going at the moment to drive multiple motors of any type in Field Oriented Control or sensorless vector. If the nerds are not arguing about it - there must be an obvious problem or two

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I've seen a few papers out on the 'net, but without the EE background I can't tell what's BS and what's not.

You can run the motors in parallel from one drive. I have 4 running in parallel on a machine that runs on rails. There is nothing critical about it - we ran one at a different horsepower for a month when we ran out of spares. But it is volts per hertz. You don`t maximize torque per motor, you waste a bit of power, the motors heat up more than they *REALLY* need to. It DOES give me 4 wheel drive, one motor and gearbox per wheel, with no need for limited slip or differentials. Each motor gets the same frequency, so if it has no traction .. even if it`s up in the air ... they spin the same speed and whichever wheels have traction take the available power. The others just spin the same speed .. or about the same speed. A motor under load spins slightly slower than a motor spinning unloaded.

How does the picture change when the motors are mechanically connected? Can you put it into a torque-vector mode of some sort, perhaps by adding a resolver/encoder, to get the maximum torque available and less heat? Does it require a bit more exacting "matching" of the two motors?

With a modern dual-signal hall effect sensor, you could .. in theory .. send the same throttle signal to each controller. The controllers *COULD* fight if one of them saw the signal as slight regenerative braking while the other saw the signal as slight acceleration .. but the calibration curves for the throttle should take care of that. There`s always a bit of deadband around `coast`. That should take care of it.

The OEM EV drives (besides Tesla) appear to use CANbus to give them their throttle reference. Sending the same signal to multiple controllers should be quite easy to do.

That's close to what I was thinking with "twinning" the throttle or similar.

Going back to a Jack Rickard (EVTV) video - you would need some sort of limited slip arbitration, or ABS maybe, so that you do not break loose one rear tire while accelerating through a turn.

This is thinking way beyond my ability to actually do something about, but a lookup table based on steering input, throttle input, wheel speed sensor input and possibly a suspension angle sensor input would give the necessary ratios for splitting up the torque commands to the 4 wheels, if using separate motors. No need if they are on the same shaft, though.

EVTV has such a controller - they call it GEVCU - and it`s open source so you can see how they do it, or write it yourself.

I'll just have to poke around once I am closer to being able to buy parts and see if anyone has sniffed the appropriate CANbus commands to run the donor inverter(s) I decide on.

As I guess I did not really explain above - the throttle is a torque setpoint. If you lose traction, it still tries to drive the motor to the requested torque. That`s what the ABS is for. Or limited slip algorithmn.

Is this true for OEM EV drives, then? If so, I still only need to worry about keeping the two motor/drive setups balanced enough that the "deadband around 'coast'" can handle it.

If I lived in the US, I would purchase leaf wrecks for the EV parts. $5K appears to be the going rate. You get the motor, the battery pack, the charger and the DC to DC converter. At least $10K in parts if you were to buy them. If someone figures out the CAN commands for the BMS and the controller - that`s an extra bonus. I think you have room in that beast for 3 leaf motors coupled end to end. You could keep the rest of the drive-train as is and twist drive shafts if that`s what you wanted to do ...

I am definitely considering the "whole wrecked Leaf" donor route. Not sure I want to go into the "parting out a Leaf" business, as I've no space to store more than one donor at a time. I should be able to sell the rest of each carcass to a salvage yard, though. There's a thread, I think on diyelectriccar.com, with a guy who tore an entire Leaf driveline out and figured out how to get it running without the rest of the car, and paring it down to the minimum. No special CAN controller.

Making things work with OEM parts has some advantages:
- if you sell it eventually, the new owner can find parts and has confidence that he can
- you can go and buy a part off the shelf to get back running ... if you need to .. or you can get another wreck or buy something from a wrecker
- Comparatively little issues with `that company is out of business, or the part is obsolete so you can`t fix it`.

Much like using newer, common Chevy/Dana/Etc. parts to modify an old FJ-40.

The alternative, for me, is Open Source. I`m not dedicated to building the boards, or soldering, or writing the program myself. But if you have the schematics you can troubleshoot it yourself. If you locate something that died - like an IGBT - you can buy a replacement and put it in, or get someone at a maker space to put it in. You have the power!

The software may not be as bullet-proof as an off-the-shelf product .. but it may be better .. depending on the guys doing the open source. If you see some new feature in a car in 2 years .. and you want it badly enough .. you can add it!

I like the idea quite a bit, so long as the 'hassle-factor' of fixing code doesn't overwhelm the rest of it. I like the "built, not bought" ideal, but when time is at a premium and I enjoy the mechanical stuff far more than the code/electrical side... We'll see.

Boy - I do rant on, don`t I?

As I mentioned above - long-winded is my default mode, so no worries!

I will follow your build with interest!

When I finally do get the rig, I'll try to put a build thread on here somewhere. Might start outside the EV forum at first, depending on budget.

I'll likely keep asking questions here and there on this forum as I get ideas I want to check.

Thanks!