2WD Cargo Fatbike with mid drive rear & front hub

wardo78

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Sep 8, 2020
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Hello All,
I did several searched but come up empty handed. I am looking to build a fat mid tail cargo bike for Vermont winter commuting. I am thinking I'll use a Bafang Ultra mid drive for the rear drive. I was wondering about incorporating a low (250 to 350w) motor in the front for an AWD. I wouldn't try to hook it up to the torque sensor on the Bafang, rather I thought both could be run off the thumb throttle since that overrides the torque sensor. What are your thoughts on the feasibility and fussy technical bits that I have undoubtedly missed!

Thanks,
Wardo
 

terry

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May 4, 2020
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I think you might need to use two separate controllers rather than running 2 motors of 1 controller.

I don't know if anyone has explained this yet, but the problem is magnetic induction in one motor feeding inverse flow into the other. It is creating an oscillation back and forth between the two. As one spins faster than the other it acts as a generator to the other. This is demonstrated when you turn one by hand the other rotates in the opposite direction, this means the motors are constantly fighting each other.

If you wish to run two on the same controller you could try either run them in series while doubling your voltage or add some capable diodes to prevent backflow. I would recommend two motor controllers however. One side effect of this is the dynamic breaking, so coasting would be an issue.
 

Moe Ped

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Jul 17, 2020
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You could do one throttle running 2 controllers from one battery and it would work OK.
 

mlx john

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Sep 27, 2020
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I have given this motor disparity some thought and my idea is to individually use 2 motors, 2 controllers and 2 thumb throttles. The thumb throttles could be locked together or individually varied, (as in a tractor's two side's brake peddles).

The other option is to mount throttles on both bar ends, for front/back variable drive to both wheels while on the move. It shouldn't be too complex to ride as you have no clutch to deal with, and might actually be quite fun as you can shift drive to whatever wheel is gripping best.
 
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