would this work?

[Hangdog]

I have a tandem recumbent I would like to add pedal assist to and was wondering...could you mount a BBSXX to the stoker crank, add a torque sensing BB to the captains crank, disconnect the cadence sensor from the controller on the bbsxx and connect
the bottom bracket to said controller? could the controller be reconfigured? replaced by an external controller? or is this way more complex than it sounds?...just wondering

 

[fechter]

Not sure if you can find a compatible torque sensor, but it would work if you can. For sure it's not terribly difficult to use an external controller with one. Any reason you don't want the BBSxx up front?

 

[amberwolf]

AFAICS, the only catch would be that the torque sensor will only work as long as there is a load on the chain, so you have to gear it so you are always pedalling a little harder than the motor is pulling, in order to generate an output to activate the motor.

This is similar to what I wanted to do for CrazyBIke2's orignal powerchair chaindrive, and IIRC that was a problem I think JustinLE had pointed out me. (been some years, so not sure).

But other than that, I'm not sure of any real obstacles to the idea.

The easiest way I know of to do the torque sensor control is to use a Cycle Analyst v3 to read the sensor and send throttle to a "dumb" external controller replacing the BBSxx internal controller. Ebikes.ca carries the CAv3 and Thun or TDCM BB sensors; there are also other sensors like one that runs on the chain itself if you have to keep your existing BB for some reason; I think they ahve that one too but I forget what its' called.

 

[Hangdog]

Any reason you don't want the BBSxx up front?

no reason I guess other than aesthetics and weight balance, but I doubt it would matter otherwise as they are both on the same equalizer chain.but IMHO if the motor is at the rear position its torque would only be driving the rear chainline which would seem to me to be more efficient.the equalizer chain would then only be used to carry human power and operate the torque sensor

 

[Hangdog]

AFAICS, the only catch would be that the torque sensor will only work as long as there is a load on the chain, so you have to gear it so you are always pedalling a little harder than the motor is pulling, in order to generate an output to activate the motor.

thanks amber wolf but IMHO it would`nt seem to me any different for the sensor to activate the mid drive as a rear hub motor.I think the advantage would be (A) it would be more discrete and (B) you could keep the 40 spoke rear wheel and the 36 spoke front wheel and (C)you would be using the existing rear gearing to maintain efficiency.its intriguing though...haven`t heard of anyone to my knowledge running a torque sensing BBSXX motor yet.the TSDZ2 motor would probably work but at 250 watts is way too underpowered for a tandem bike IMO