Manster

Should an electric tandem with a crankshaft torque sensor for motor control have a sensor for the stoker? I guess there would have to be one for the captain anyway to permit solo rides, in which case would there be a use case for a torque sensor switchable between captain and stoker? Anyone have experience with such a beast?

fooferdoggie 

I have this guy. the problem is the pedals are not locked together. i can freewheel and my wife can pedal without me. if we are not careful we can pop the chain off when starting up. mustache sells a tandem with a rear motor but it is 8000 I saw a custom built using a shimano motor that had more of a normal bike setup it started at 8000 https://www.seattleelectricbike.net/...YaAtPzEALw_wcB it looks easy to put the motor in back but maybe not. https://propelbikes.com/product/mous...edi-27-x2-trk/ but now that ebieks are more established we will see more e tandems.

Leisesturm

Since a tandem is never (ever?) ridden without the Captain, it stands to reason that the Captains cranks must be the ones with the torque sensor. One is enough. There does not need to be one also for the Stoker. Torque sensing on tandems is tricky. If the timing chain is of the conventional kind the Stokers input will throw off the reading of the Captains torque sensor. If IPS then the Stoker ends up just being along for the ride. Seems to me that cadence sensing might be the way to go for a tandem application.

Manster

Tell me more about how the Captain input would be thrown off? I would think a Captain's torque sensor would multiply their torque input regardless of the Stoker's input.

Well, this is one reason I am thinking of adding ability to switch to the Stoker's torque sensor. I'm wondering if it could improve the tandem experience if it makes the Stoker into a "super-Stoker"

Leisesturm

Maybe. What I know is that there are different ways of measuring torque. Some sensors measure only one pedal, others both pedals, others the torque on the chainring and still another, the torque on the chain at the rear cogset. What kind of system are you planning? Hub motor? Mid-drive? I would think a tandem would need a very high torque motor that is also very strong. A hub motor up to that kind of output would be extremely large and heavy. Seems to me a mid-drive would be the best option. There are not many torque sensing options for this application. The only really practical one is the Tongshen TSDZ. One of those would indeed make your Stoker a 'Super Stoker'. As sold, it would not have a left hand chainring, but I can see adding one, and I don't think it would impact the torque sensing. The Captains torque would be added to the Stokers torque (or vice versa). Ideally a torque sensor at the rear cassette would be ideal but this system is not available independent of some models of half-bikes, most notably the 'Juiced Bikes' line of torque sensing hub motor designs. The only downside with the TSDZ is it really is not the most robust e-assist ever made. Still, it looks to be the best solution for your application. If you can do without torque sensing the Bafang BBSHD, also mounted at the Stoker position would have enough power and is built plenty strong.

Manster

As usual for me, I'm starting with the question of what would be ideal and then working towards putting it into practice. A torque sensor behind the stoker (in the stoker's BB as the TSDZ, or the rear cassette) might be the most natural, as \a tandem is driven with the sum of the crew's torque. I was thinking about individual torque (pedal) sensors and where they should or could be located for the best tandem e-bike experience.

Thanks for adding some practicalities. The Tongshen TSDZ looks nice. With an internal torque sensor in the bottom bracket a TSDZ at the stoker with a left drive added looks like it would work well by multiplying the sum of the torque .

What about a TSDZ at both seats? You'd have twice the torque available. You would need to rig the captain to stoker link on the right hand side, but then each crew member would have their own torque multiplier, and their own clutch. Hmmm...

fooferdoggie 

How much power do you need? my bosch powered e bike lets us climb 16% grades and steeper for short runs. this is the way to go the motor in back then the pedals are locked together. https://moustachebikes.com/en/electr...s/samedi-27x2/

Manster

That looks like a nice tandem. How does it ride? The Bosch on that is spec'd at 65Nm/600W. A single TSDZ2 is 80Nm/750W, weighing in at 8lb. Think two would require a beefier drive train?

Leisesturm

Actually ONE of those TSDZ2's really should have an ebike rated chain and steel cassette. Two of them?? Hell yes. Ebike rated timing chain, drive chain and steel cassette. I agree with the other poster though, a single TSDZ2 at the Stoker position should be all you need. IF you absolutely had to have two I would de-rate them both (in the software) to 500W each. You would get much better life and reliability out of them that way.

fooferdoggie 

no it works great. its not as zippy as my commuter bike using the speed version of the same motor. but we have plenty of power and seldom have to use it all but on steeper hills.