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

AI Thread Summary
Using two hub motors for an e-rickshaw can eliminate the need for a mechanical differential, which is heavy and inefficient. Wiring the motors in series may allow for equal current and torque, theoretically mimicking a differential, though practical issues like one wheel over-speeding could arise. Alternatively, wiring in parallel presents challenges with slipping and inefficiency during turns due to the motors' natural resistance to speed changes. The discussion also touches on the inefficiencies of using PWM with H-bridges and the complexities of regulating speed without separate controllers. Ultimately, the simplest setup suggested is to wire the motors in series, assuming they are identical DC motors, to maintain consistent torque.
KDP
Messages
25
Reaction score
7
TL;DR Summary
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?
 
Engineering news on Phys.org
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?
 
KDP said:
inefficient
Why do you say that? Inefficient in what way?
 
berkeman said:
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.
1753820189340.webp

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.
 
I have recently moved into a new (rather ancient) house and had a few trips of my Residual Current breaker. I dug out my old Socket tester which tell me the three pins are correct. But then the Red warning light tells me my socket(s) fail the loop test. I never had this before but my last house had an overhead supply with no Earth from the company. The tester said "get this checked" and the man said the (high but not ridiculous) earth resistance was acceptable. I stuck a new copper earth...
Thread 'Electromagnet magnetic field issue'
Hi Guys We are a bunch a mechanical engineers trying to build a simple electromagnet. Our design is based on a very similar magnet. However, our version is about 10 times less magnetic and we are wondering why. Our coil has exactly same length, same number of layers and turns. What is possibly wrong? PIN and bracket are made of iron and are in electrical contact, exactly like the reference design. Any help will be appreciated. Thanks. edit: even same wire diameter and coil was wounded by a...
Thread 'Beauty of old electrical and measuring things, etc.'
Even as a kid, I saw beauty in old devices. That made me want to understand how they worked. I had lots of old things that I keep and now reviving. Old things need to work to see the beauty. Here's what I've done so far. Two views of the gadgets shelves and my small work space: Here's a close up look at the meters, gauges and other measuring things: This is what I think of as surface-mount electrical components and wiring. The components are very old and shows how...
Back
Top