Changing from TMM Torque Sensor to Cadence sensor - how hard is it please?

[LesleyA]

Hi All,

I have a Raleigh Velo XC and posted here about it last year, regarding intermittent problem with pedal assist. Finally took it in for repair this week, and bike shop have advised it is the Torque sensor that as failed - in fact it has actually broken in half. They contacted Raleigh and the Torque sensor is no longer stocked part with them. They have given me the manufacturer details - IdBike based in Holland, so I have emailed to ask if they still supply them and get a price. Today we stripped the Torque sensor out ourselves, and have superglued the broken side plastic back together. Leaving to cure overnight and will try it tomorrow. I am wondering if it would be possible to change the TMM to a cadence sensor on the crank. Would this need a whole new controller etc, or would the signal still trigger the motor from the cadence ring if wired into the circuit? I have just the exact same bike listed on eBay and it seems to have the TMM disconnected (see below) and has had a cadence sensor added, so looks like someone else has had the same problem. Any advice appreciated, thanks

 

[thelarkbox]

Just an idea...
But all the sensors on my ebike kit are hall effect sensors that respond to magnets..

on that basis alone i think its worth a punt your dodgy sensor is also a hall effect sensor,
Worth checking out at least, unless someone in the actual know comes along and shoots me down..

if so it may just be a case of how to hold a different sensor in the correct place..

 

[guerney]

Today we stripped the Torque sensor out ourselves, and have superglued the broken side plastic back together. Leaving to cure overnight and will try it tomorrow.

If that doesn't hold, perhaps try the stronger superglue+baking soda combination, or the even stronger superglue+graphite? Be very careful, it sets very fast and you'll need acetone to get any that's bonded to your fingers (also strips paint and dissolves some plastics).

 

[saneagle]

It's most likely strain gauges glued to a piece of metal. To replace it with a normal pedal sensor should be easy enough. You'd have to change the controller too, and get an LCD to match the controller. Check the number of pins in the motor connector to see you need a sensorless or sensored controller, and count how many wires join the battery to the controller to be sure your battery will work with any controller.

 

[thelarkbox]

It's most likely strain gauges glued to a piece of metal.

Well that tells me..

 

[LesleyA]

This is the Torque sensor I have and the 2 broken plastic sections are where the red crosses are. Not sure if glue will hold still allow the movement needed to trigger the sensor power.

 

[Woosh]

The plastic is not load bearing, its job is to hold the magnet. If the sensor head is still working then the sensor should work.

 

[guerney]

If it worked until the plastic broke again, I suggest superglueing it back together as you did before, plus add a bit of reinforcement. However, reinforcing plastic that small would be fiddly. After cleaning it with isopropyl to remove oil/grease, I'd hold it horizontally and make a tiny mound of fine grain bicarbonate of soda (sold as "food grade" on ebay) on one of the breaks which is presently being held together by superglue, using a small flat screwdriver blade as a spoon... and flatten the mound a bit... then while making sure it made no contact with anything, apply a small drop of superglue. It'll harden within a few seconds. You could do this on the opposite side. If the resulting hard plastic bulge was too large, you could stick some fine grit abrasive paper onto a table using double sided sellotape, and very carefully grind it down a bit. Superglue spurts and runs all over the place, so this could all get very messy. Superglue + bicarbonate of soda is tough and rigid, and a devil to remove.

Alternatively, you could try Araldite or hot glue? Bulk it up a bit around the repaired break and grind it down?

 

[saneagle]

If it worked until the plastic broke again, I suggest superglueing it back together as you did before, plus add a bit of reinforcement. However, reinforcing plastic that small would be fiddly. After cleaning it with isopropyl to remove oil/grease, I'd hold it horizontally and make a tiny mound of fine grain bicarbonate of soda (sold as "food grade" on ebay) on one of the breaks which is presently being held together by superglue, using a small flat screwdriver blade as a spoon... and flatten the mound a bit... then while making sure it made no contact with anything, apply a small drop of superglue. It'll harden within a few seconds. You could do this on the opposite side. If the resulting hard plastic bulge was too large, you could stick some fine grit abrasive paper onto a table using double sided sellotape, and very carefully grind it down a bit. Superglue spurts and runs all over the place, so this could all get very messy. Superglue + bicarbonate of soda is tough and rigid, and a devil to remove.

Alternatively, you could try Araldite or hot glue? Bulk it up a bit around the repaired break and grind it down?

If it's a strain gauge one, you can't reinforce it because it needs to bend with the torque.

 

[guerney]

You can't reinforce it because it needs to bend with the torque. That's how it works.

Like I said, it can be ground down. A very fine layer might be all that's required to prevent it breaking. If the OP's time isn't too expensive, overall it's cheap to try.

BTW grinding down superglue + bicarbonate of soda with a needle file can clog it up, so file a stick of chalk first. Makes it easier to remove - lightly tap the file against something. Also makes for gentler filing, because less material is removed per stroke.