nowholeself
1 W
I'd like to fashion my own bottom bracket torque sensor. The bottom bracket tube is 46mm ID, though I can go bigger if necessary. The current spindle is 19mm, though I may switch to a 22mm. Ideas? Threads?
DIY Bottom Bracket Torque Sensor?
- Thread starter nowholeself
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I don't know of any threads for one yet. There are threads like the TSDZ2 big thread that show and describe the sensor that's in that design, which might help. Basically it uses an analog hall sensor (similar to those in a throttle; there are many types of them) and a magnet near it in the shell / shaft that when the shaft deforms from torque the sensor detects the change in the field. It's likely that many of them work like that.
But you could also do it like the Stromer (and others) do, which is having a slit in the rear dropout and a hall sensor on one side and magnet on the other, or a strain gauge across the slit junction, that detects the change in torque by the deformation of the frame there.
IIRC the BionX detects the torque along the motor axle with a strain gauge, detecting deformation from the pulling of the chain on the freewheel.
There used to be one called the BeamTS that had a roller on the chain that detected chain deflection and output a throttle signal. Not available anymore, but it shouldn't be too hard to design one based on that idea. (I'd planned on one like that way way back for CrazyBike2 more than a decade ago but I never worked it out fully--it would've been a potentiometer mounted to the pivot of a springloaded roller on the top side of the chain, and the voltage on the pot would've been detected by an op-amp and amplified and turned into a throttle signal, calibratable with pots on the op-amp...there are better ways to do it but that would've worked).
Do you want to detect torque on just one side of the pedals? (like the THUN) Or on both? (like the TDCM) Do you want it to be agnostic to the orientation of pedal torque to chainline? (the TDCM, for instance, requires specific alignment of sensor to chainline / etc).
But you could also do it like the Stromer (and others) do, which is having a slit in the rear dropout and a hall sensor on one side and magnet on the other, or a strain gauge across the slit junction, that detects the change in torque by the deformation of the frame there.
IIRC the BionX detects the torque along the motor axle with a strain gauge, detecting deformation from the pulling of the chain on the freewheel.
There used to be one called the BeamTS that had a roller on the chain that detected chain deflection and output a throttle signal. Not available anymore, but it shouldn't be too hard to design one based on that idea. (I'd planned on one like that way way back for CrazyBike2 more than a decade ago but I never worked it out fully--it would've been a potentiometer mounted to the pivot of a springloaded roller on the top side of the chain, and the voltage on the pot would've been detected by an op-amp and amplified and turned into a throttle signal, calibratable with pots on the op-amp...there are better ways to do it but that would've worked).
Do you want to detect torque on just one side of the pedals? (like the THUN) Or on both? (like the TDCM) Do you want it to be agnostic to the orientation of pedal torque to chainline? (the TDCM, for instance, requires specific alignment of sensor to chainline / etc).
The stumbling point for installing a torque sensor in my mind, is where are you going to plug in/connect the wires coming from the torque sensor?
Installing the torque sensor is the easy part. Now you get to pick out a controller that's able to translate the signal coming from the torque sensor into something useful. The controller on the bike now most likely has no place to plug in a torque sensor, or ability to translate the signal.
Installing the torque sensor is the easy part. Now you get to pick out a controller that's able to translate the signal coming from the torque sensor into something useful. The controller on the bike now most likely has no place to plug in a torque sensor, or ability to translate the signal.
That's easy--just design it to output a throttle signal (like the BeamTS, the Sempu, etc). Then you plug it in in place of the throttle.AHicks said:
Or you use the Cycle Analyst v3 to convert the TS signal into a throttle signal.
nowholeself
1 W
Thank you for your detailed replies AmberWolf. I'll likely be sticking with an ASI BAC855 controller, which I assume can accommodate the sort of signals the TSDZ2 would be sending. I'll be sure to check out that thread. If you know of a page or section in that thread that gives a sort of "how-to", please let me know.
nowholeself said:
There isn't a how-to; the TSDZ2 is a complete BB-mounted middrive system with integrated controller, pedals, etc. I dont' recommend using one because it has a terrible design for the crankshaft, which virtually guarantees it will break off while pedalling at some point (sooner the harder you pedal).
That thread (and at least one other somewhere about the above problem) just happens to have pics that show that sensor, and some description of it.
It's possible that the separate TSDZ2 open-source firmware thread may have info on how they made the controller read that torque sensor, but I haven't read it so I don't know.
Regarding the ASI controller, you shouldn't assume anything, but should verify what kind of signals it can use for control input--otherwise you may end up with a sensor design that requires an external conversion unit to work with your controller. The Phaserunner is based on an ASI 8xx series AFAICR, and it does not have any direct TS input that I am aware of (but I have not studied it in detail, so perhaps this is incorrect).
Unless you always are pedalling really slow, you need a cadence sensor in addition to the torque sensor, unless you want a system that gives you less assistance the faster you pedal. The faster you pedal, the less torque you manage to put into the pedals, so you need to use the rpm and calculate wattage once you get past a certain rpm. The CA does this very well. Most (or maybe all?) the bottom bracket torque sensors that you can buy now have a cadence sensor, and the tsdz2 as well.
That depends on your gearing range as well as your speed range.HrKlev said:
amberwolf said:That depends on your gearing range as well as your speed range.HrKlev said:
Yes, you are probably right
However, as you pedal faster, with the same amount of torque, you are putting in more effort/watts, but the assistance level stays the same. So the assistance level feels declining. Its not the best feeling you can have on an ebike
I did try to wire the torque output to the throttle and tune it, but it was back to normal power-based again pretty soon.
One way to fix that would be to create the system in a way that assists less at the lower speeds so that the curve of assist vs human input remains the same across the speed range from zero to max.
I don't know how to do that, but it should be possible.
I don't know how to do that, but it should be possible.
