Using a torque sensor in an eccentric bottom bracket?

[samwake]

Hello, I'm planning to get a Bakfiets Aero (part way down here http://schoolruncentre.co.uk/cargo-bike-bakfiets/) and have it fitted (by the dealer) with a Heinzmann Directpower front motor. The tricky part seems to be that the Aero model has vertical dropouts so uses an eccentric bottom bracket for chain tension, and this means that fitting a torque sensor BB (TDCM or Thun - apparently the latter is more forgiving in cable routing etc?) is either difficult or not possible.

Do you think it should be possible to fit a torque sensor into an eccentric BB housing?

The alternative is to use a PAS, but we are hoping for a torque sensor to give easier, more immediate power on hill starts and smoother, more efficient battery use.

Thanks

Sam

 

[amberwolf]

https://www.google.com/search?q=ecentric+bb+adapter&ie=utf-8&oe=utf-8#q=eccentric+bb+adapter&tbm=shop

 

[Chalo]

If the cable lead of the BB is long enough to exit the eccentric shell with a little latitude for chain adjustment, to me it seems like it would be easier to set up a TDCM in a roomier shell like that than in a normal threaded shell. The eccentric adapter would of course have to have an opening through which the cable can pass.

I haven't set up a Thun, so I can't speak to that.

 

[samwake]

Thanks. Would the requirement the TDCM sensor has to be mounted level be a problem? I don't really understand why the TDCM needs an accurate levelling, since I assume it works whatever angle the bike is ridden at? Once used in an eccentric shell it would presumably rotate with the shell when chain tension needs to be adjusted? Would it need rotating within the eccentric housing to regain a level any time the eccentric was adjusted?

 

[Chalo]

There's no assurance of level in a normal threaded BB shell, so I don't think a change of orientation in an eccentric shell would make any difference. It's not measuring orientation; it's measuring strain in the BB spindle.

 

[icerider]

The Bionx motor has a similar orientation requirement. That is because the Bionx torque-sensor strain gauge measures the BEND in the axle from the chain forces on the sprocket.

The Bionx system is tolerant of some misalignment -- say plus or minus 30 degrees or so.

It isn't unreasonable to expect the BB torque sensors to have the same kind of tolerance to variations from the specified alignment.

Upside down might be a problem if the controller cannot "invert" the signal from the torque sensor.

Mounting perpendicular to the specified orientation may result in a signal too small to be useful.

All of this discussion presumes that the torque sensors ARE sensitive to orientation and that the requirement isn't there simply to make sure that the cabling exits in the desired direction.

 

[amberwolf]

Some torque sensors require a certain orientation with respect to the chain tension, so see the installation guides for the particular sensor about that part.