Unequal power left and right legs

Idris the flat · Nov 26, 2022

I have a permanently weak right leg after a big operation. Considering a motor for my recumbent trike, I've come up against a question that I can't find an answer to:

If I fitted a torque sensing motor, like the tongsheng, will it detect and respond differently to the difference in power on the L/R pedal stroke? I'm concerned that this would give a stuttering output and a very strange ride. Power difference L/R is about 100/60, so not a trivial difference. I guess if even if the software averages out the torque sensor input over a complete pedal rotation, that might still mean that leg + motor combined might be different between the l and r pedalstrokes.

Any clarity gratefully received...

E-HP · Nov 26, 2022

Idris the flat said:
I have a permanently weak right leg after a big operation. Considering a motor for my recumbent trike, I've come up against a question that I can't find an answer to:

If I fitted a torque sensing motor, like the tongsheng, will it detect and respond differently to the difference in power on the L/R pedal stroke? I'm concerned that this would give a stuttering output and a very strange ride. Power difference L/R is about 100/60, so not a trivial difference. I guess if even if the software averages out the torque sensor input over a complete pedal rotation, that might still mean that leg + motor combined might be different between the l and r pedalstrokes.

Any clarity gratefully received...

Not sure if this might be helpful, but when I was deciding on what torque sensor to get, I read this on Grin's info page on the different types. I start from a stop using my right leg, so I made sure not to order the spindle sensor type, but maybe that's what you need:

"Spindle Torque
In these sensors, the torque is measured across the bottom bracket spindle. The torque can be sensed with strain gauges and a slipring to couple power to the spinning sensor, it can be measured optically by the alignment of disks on either side of the spindle, or it can be measured with magnetostrictive technology, such as the early to market THUN torque sensors. The downside with measuring spindle torque is that it only senses the force that the rider applies with the left pedal crank, as the right pedal effort goes directly to the chainring without passing through the spindle. As a result, some extra care is required in the electronics to compensate for the lack of a right side pedal signal."

AHicks · Nov 26, 2022

I can share that I recently picked up a bike that came with a newer version of the Bafang M600 (Evelo Atlas). In PAS 1 at lower speeds/cadence levels (under 10mph?) that bike WILL show each pedal stoke on the watt meter. That said, I am not feeling or hearing any difference, from one down stroke to the next, in the motor's tone or feeling any surging. IMHO, I believe Bafang has that properly filtered. FWIW, -Al

Sturmey · Nov 26, 2022

Idris the flat said:
.........If I fitted a torque sensing motor, like the tongsheng, will it detect and respond differently to the difference in power on the L/R pedal stroke? I'm concerned that this would give a stuttering output and a very strange ride. ......

That's exactly the case with my 36v TSDZ2. I end up using the throttle most of the time. I have the standard firmware that came with bike. Maybe custom software might help, I dont know. My legs tire easily without throttle, as torque sensor need pressure on pedals. I much prefer my hub motor with cadence sensor pas and throttle.

Diggs · Nov 27, 2022

You can stop over at Electricbike.com and chat with AZguy. He pedals with only one leg but mostly rides a BBHSD to my knowledge.

docw009 · Nov 27, 2022

I did fit a T/S Tongsheng motor, with the factory firmware from 2019. For me, the assist was very subtle and I didn't teally feel the motor running til I used the highest assist and it would surge. I connected that to a weaker left leg (sciatica). My fix was to load the OSF firmware which gave more power for less pedal torque, so it's probably maxing out power for the lower torque level on the left side. It also feels better to me.

Unequal power left and right legs

Idris the flat

1 µW

E-HP

10 GW

AHicks

10 kW

Sturmey

10 mW

Diggs

100 W

docw009

1 MW

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