Torque Sensor Questions

I would like to fit my ebike conversion with a torque sensor and eliminate throttle entirely. I want to use my bike for exercise as well, so I'm thinking about getting rid of the throttle or cadence sensor (which can be fooled by shifting to a lower gear and pedaling vigorously) will help me be less lazy and retain the biking experience.

Ebikes.ca has several torque sensors: http://www.ebikes.ca/shop/ebike-parts/torque-sensors.html.

- What are general thoughts on using torque sensor only? Is there a possibility of it acting unexpectedly?
- Does anyone have recommendations between Thun vs. Isis vs. TDCM?
- I know Thun and Isis are similar and measure the exact torque exerted, while the TDCM is only useful for scaling the throttle without measuring the exact torque (which I am fine with). TDCM is also $100 cheaper - so that's attractive. Anyone have a good experience with TDCM?

Also, I'm not sure what size to get. I'm getting a Trek Marlin 6 MTB in a week. I can go to the store and have them measure the length for me. It'd be nice to know what exactly to measure

Anyone have any thoughts on THUN vs TDCM torque sensors?

I see that the TDCM sensor has some problems(http://endless-sphere.com/forums/viewtopic.php?f=4&t=37964&start=2075#p872023). To be fair, this appears to be a problem with the THUN sensor as well. Are there any established resolutions to this?

I think a torque sensor is a great addition to any ebike build. I bought the cheaper one from ebikes.ca. You must read and understand the directions and have the right tools or you are gonna have a bad time... Once installed there is a slight learning curve but after I installed mine I used it like 95% of the time and use the throttle to get me out of a jam. There might be some slight surging at first but once you dial it in it will eliminate itself. Also there is a delay when it starts and stops but you will get used to this also. I used mine on an extremely large 60T chainring. Which means I got rid of my front gears. This gave me a very low cadence of 60-80 which is where im comfortable yet. I could also pedal this up past 30mph easy and still have assistance. Another thing you may want to get with the torque sensor is a 3 speed switch. This is so you dont have a fixed assist. You can switch between 3 levels of assist on the fly. I split mines up according to a wattage multiplier.My first positions was 5x assist. This was good on slow trails or within a crowd. 10x is what I stayed in for 20-25mph riding. and 15x is what I used to hang in traffic. Torque sensors can work in two modes. They can look at your cadence or pedal RPM or they can look at the torque you are applying on the pedals. I used the latter. The harder you pedal the more assist you get. The lighter you pedal the less assist. This is very effective in controlling your speed while it still feels natural yet superhuman. The TDCM does measure torque. and it actually measures it on both sides of the crank on both pedal strokes.The Thun can do this so you may need a full revolution of the crank to get it to kick in. The TDCM isnt exact when it comes to interpreting your pedal pressure as human watts the thun is more accurate at this.The thun measures one side. I believe the resolution of the thun is higher than the TDCM meaning it has more magnet poles in the cadence sensor The Thun is made out of plastic. TDCM is made out of metal. Mines had no play in the bottom bracket. Good solid bearings and seals. My experience with the TDCM says go for it. I used it on a Golden Motor Magic Pie @ 66v 65A and close to 5000w. It certainly helped me tame the beast and made it feel like an honest work out.

iluvmylife said:

I see that the TDCM sensor has some problems(http://endless-sphere.com/forums/viewtopic.php?f=4&t=37964&start=2075#p872023). To be fair, this appears to be a problem with the THUN sensor as well. Are there any established resolutions to this?

Click to expand...

A few issues have been identified in the CA V3 (remember - it is officially beta code ). The official bug list was posted a bit ago on the ebikes.ca V3 page. You will find this PAS issue is on the high priority list to be addressed before the official v3.0 production software release.

The V3 'Torq PAS' mode scales assist by both cadence and pedal torque. Using a simple PAS Wheel (Auto PAS mode) gives a fixed assist level when pedaling is detected. In either case, the level of assist can be adjusted with a switch (2 or 3 position) or with a potentiometer (continuously adjustable). However, a planned enhancement (see V3 bug/enhancement list) for v3.1 is the addition of rpm-scaled Assist for a simple PAS wheel. In this new mode, you get more assist with higher cadence (e.g.downshift for a hill). This is sort of half of the torque sensor capability - a poor man's TDCM.

The V3 Guide describes how you can achieve the identical rpm-scaling with the existing firmware and a little trickery. This is what I use and I find it works well when used with a POT to give variable assist levels - certainly not a Thun, but depending on your riding style and terrain is can work quite well for less than $20. You might like to start here and then upgrade to a torque sensing BB if the cheapie approach doesn't do the job.

Awesome! Thanks for your inputs, greatly appreciated!