Eliminating a differential of an e-rickshaw by using 2 motors.

[KDP]

TL;DR

I would like to design an electric rickshaw with two hub motors on the rear wheels and no differential. Is this best accomplished by having the motors in series or parallel and are complex speed controller algorithms required?

A mechanical differential is heavy and inefficient. To try and design an efficient e-rickshaw I would like to use a hub motor for each rear wheel. My initial enquiries suggest that wiring the motors in series would theoretically emulate a differential by maintaining the same same current and torque in each motor during the turn, but some sources suggest this is problematic in practice with one wheel over speeding. If the motors are wired in parallel they both see the same voltage but motors naturally resist being sped up or slowed down which might cause slipping and inefficiency during turning. Ideally I would like to avoid the complexity of having separate speed controllers and steering sensors. What is the simplest reasonably efficient set up?

 

[Baluncore]

Assuming the motors are identical DC motors, wire them in series. The currents will then be the same, so the torques will be the same, which is the electrical equivalent to a differential. It is unlikely that a wheel will spin, if one does, you might switch the motors into parallel.

How will you regulate the speed?
Will you use PWM of an H-bridge?

 

[berkeman]

inefficient

Why do you say that? Inefficient in what way?

 

[sophiecentaur]

Why do you say that? Inefficient in what way?

That's a can of worms (pardon the pun). I always 'knew' that the hypoid gear in a normal diff is less efficient than the other gears because of the extra friction due to the sliding component of relative motion. I remember having to buy special oil for the diff. I found this figure which sort of confirms my memory.

But the comparison with electric motor drive will not be straightforward because of the series resistance in the power supply (could it be really low? perhaps).

The value for a worm gear is not encouraging except when you need it to work just one way. So a screw won't work its way out of a wall unless you're really unlucky.