More torque sensor issues ... suggestions?

tbar23

Member
I posted about a torque sensor issue I had back in early March here: https://electricbikereview.com/forums/threads/torque-sensor-question.41234/
Yesterday, I encountered a similar, but different, issue. After the March issue, I have made a practice of calibrating the torque sensor before almost every ride. Here is what I saw when I did that before riding home from work last night:
E8FCBFEE-397E-43A2-90F7-E8A893CB111C.jpeg

I power cycled the Omni computer - no luck. I also found that I had no assist. I quickly pulled up EBR and found out how to get into the service menu and found this:
C7037B61-C116-41BB-822B-208DD6582CB9.jpeg
30AF3993-33C9-4ED4-93E8-A6D8064F70C3.jpeg

The first photo is with no load on the pedals while the second is with some weight. Clearly the sensor was changing based on torque, but the offset looked way off to me. And oddly enough, the “RESET OFFSET” menu item that you see wasn’t doing anything.
@Ravi Kempaiah suggested that I remove the rear axle and re-torque, but that didn’t solve the problem, either.
Out of options, I started to ride home. What a reminder not to gain 50 lbs!!
Before heading home, I emailed Stromer USA with the photos above (my bike shop mechanic had already left for the day).
About 13 miles later, the bike suddenly came alive - in other words, it “fixed itself”. The remaining 8 miles of ride were just like usual with full assist.
When I got home, I went into the service menu again and found this:
E152E6FD-B667-4BAC-A6EC-C40DF7403616.jpeg

(Unloaded) Not only had the sensor output voltage increased by ~900mV, but now the RESET OFFSET button would clearly do something. I could tell that the offset would change to precisely match the sensor voltage when pressed - at least for a few hundreds of milliseconds before the voltage drifted 10 or 20 mV away (as can be seen in the photo).

Needless to say, I am not super excited to ride 2/3 of my commute without assist again - it takes too darn long. But I have no idea why the sensor acted up in the first place and/or why it “fixed itself”.
Stromer USA got back to me and said that the recent firmware update could be reasonable. They sent the last revision of firmware to my bike, and I installed that last night. I’m not convinced that this was the problem since the sensor output voltage, itself, seemed whacky.
Any thoughts?

Thanks!
 

Ravi Kempaiah

Well-Known Member
Check if there is debris/ mud around the TMM4.
If there is mud/dirt clogging the TMM4, it would struggle to revert back to the neutral position and maintain the right voltage.
 

tbar23

Member
Thanks @Ravi Kempaiah - I pulled the rear wheel and cleaned up the sensor a bit. The sticker is starting to peel off (ordered another one from Stromer USA). It is handy to know the service menu secret handshake as now I can at least check on it if things are acting up.
 

bluecat

Well-Known Member
About 13 miles later, the bike suddenly came alive - in other words, it “fixed itself”. The remaining 8 miles of ride were just like usual with full assist.

In almost all cases, the sensor crisis came from manipulations in area of the rear axle. An invisible torsion is sufficient. The "self repair" tells me, the sensor plate is not in perfect position - and then vibrations during a ride have effects.