Controlling two motors - AWD Lawn mower project


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8:04 AM
May 17, 2021
Hello, I am new here looking for technical advice from Germany.

I am planning to mount an additional electric front wheel drive on my petrol lawn mower (ride-on) tractor.
The tractor has a rear wheel drive which sometimes does not have enough grip to climb on the hilly terrain I have to mow, there are more expensive all-wheel drive models that solve this problem, but I plan another solution.

My idea is to buy 2 pcs of so-called electric wheelbarrow kits, these are geared high-torque BLDC hub motors, I am looking at those with 15 inch tyres mounted, These have enough torque (50-70Nm per wheel, so up to 140Nm for the whole front drive) at starting/low speed that would perfectly solve my problem if I mount these instead of the current (free-wheeling) front wheels. I plan to go for a 48V / 500W version per wheel, and a 48V 15-20Ah battery pack. (The battery capacity is not an issue, maybe can be even lower, I will need the extra grip of the electric front drive only for some minutes on occasions , not the whole time mowing)

My questions:
Is it OK I use the electric wheels at undriven state (either all power cut-off or with the controller input in neutral), would they free-wheel without a significant drag? is it Ok for the controller's electronics that they rotate? Or perhaps a future upgrade: Could I use these wheels to regeneratively charging the battery?

I will have separate controller per wheel, but need to exactly synchronize their rotation speed. I plan to use the same analog input line split parallel into the two controllers (left + right wheel). The analog control would come from my electronic board with a microcontroller driving a DAC outputting the 0-10V signal, the microcontroller would sense the either the rear wheel's rotation with an encoder or the throttle position, have not decided yet, will try perhaps both. So I will not have to manually adjust the front wheels speed, will have only a RWD/AWD main switch.

- Do I get there very same rotation when the analog input is at the same voltage level?, are these controllers reliable in this way?
- Are there controllers with digital input (RS232/UART/Can bus/etc) that would accept a Speed/sine wave Frequency value as input, instead of the inherently less precise analog control?
- I plan to sense the steering wheel position so I could calculate turning radius of the vehicle and apply the needed speed difference between the inner and outer wheel in curves (an electronic / software version of a differential) What do you think, does it worth the hassle, or is the skid negligible on a grassy/soft terrain anyway?

Thank you all who can help with any clues/ideas.
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