Looking for a torque sensor with a unique set of requirements

I currently have a Sempu 115mm spindle-width torque sensing bottom bracket. I'm going to soon upgrade the gearing on my custom velomobile built on a KMX framekit with a Schlumpf HS drive with a triple chainring set, which uses a special bottom bracket, meaning I'm going to need to use a different type of torque sensor. Torque-sensing PAS is important to this build and I require it for a series of reasons, some of them legal reasons. Whatever torque sensor I use must be compatible with my Cycle analyst v3 computer and must be something I can fit to my current build.

Anyhow, I've come across the following:

https://idbike.com/sensors

I have a Leafbike 1500W motor and the axle width is limited. So limited I cannot fit a Grin torque arm on the chaindrive side of the motor for regen. So I'm not sure this will work. But it's a distant possibility.

What types of non bottom-bracket torque sensors exist that are readily available? Ebikes.ca had a list (https://ebikes.ca/learn/pedal-assist.html), but most of their links are defunct. I've come across lots of sites with links, most of those links out of date linking to products that no longer exist.

There is this project, if you are willing to DIY:
https://endless-sphere.com/forums/viewtopic.php?f=3&t=67086&hilit=torque+sensor&start=25#p1687815

https://onedrive.live.com/view.aspx?resid=4BE668230430EFDD!2790&ithint=file%2Cdocx&authkey=!AJJC5hfnmnV612M

I have only read the document thru once, but it appears relatively easy to make and use, for anyone with minimal electronics skills, and some mechanical fabrication skills.

It outputs a straight up throttle signal, as described, so as long as the version of firmware you have in the CAv3 has the option to do a custom sensor with a voltage range that fits a typical throttle, it would work on the torque sensor input.

Alternately you can use it as an actual throttle, if that works for your purposes, paralleled with the handlebar throttle, as given in the document. If you need cadence PAS at the same time, that won't work, AFAIK (I don't remember if the CAv3 can be setup to require cadence PAS sensor input to enable throttle control).

If wasn't stuck on unpaid leave I'd buy the parts and build one to put on SB Cruiser and test it out (since paralleling with the actual throttle would eliminate the need for at least one of my Nano Tidbits that I don't yet know how to program since the CAv3 doesn't allow operation of pure torque mode).

Thanks for posting this. I definitely need it to record cadence as well. I'd have to re-design this to accept input from a cadence sensor as well. I'm hoping I can find an off-the-shelf plug and play solution, given my time is quite limited and I have a bunch of parts sitting around that I haven't had time to install.

If you need cadence, don't worry about redesigning it, just use it as input to the Cycle Analyst's torque sensor input (it works basically like the BeamTS so if you already have that one in the CA settings just use that, otherwise use a custom one that fits the range you setup on this one).

Then use any old cadence sensor (which you can buy or make) and use that as input to the CA's cadence sensor.

Torque sensors are generally one of 2 designs:

Cantilevered Pressure Sensor, where a lever is displaced by chain tension, and a Thin Film Pressure sensor at the other end varies resistance. Low cost and low resolution. Has erratic control at lower speeds due to chain tension variances.

Direct measurement through a torsion beam that accurately measures displacement (input force). Thun/NTSC are the only ones I know for sure, probably a few others too. They also measure rotating speed which provides a more intuitive power control to the motor. I'm a Thun fan FWIW, so I'll stick with a 3x10 on the FS26. On a 3x20 derailleurs can get a bit long.

Triketech said:

Torque sensors are generally one of 2 designs:

Cantilevered Pressure Sensor, where a lever is displaced by chain tension, and a Thin Film Pressure sensor at the other end varies resistance. Low cost and low resolution. Has erratic control at lower speeds due to chain tension variances.

Direct measurement through a torsion beam that accurately measures displacement (input force). Thun/NTSC are the only ones I know for sure, probably a few others too. They also measure rotating speed which provides a more intuitive power control to the motor. I'm a Thun fan FWIW, so I'll stick with a 3x10 on the FS26. On a 3x20 derailleurs can get a bit long.

Click to expand...

Do you have links to examples of either that I can actually buy? Everywhere I've searched for THUNs they have been out of stock. This has been the case before all the supply line disruptions, which made me think they've been out of production for years. I settled on a Sempu 115mm because it was the only torque sensor BB I could find that could work with my front derailleur, but now I need a non-bottom bracket solution to accomodate the gearing range I need the Schlumpf for.

So the triple chainring is an absolute requirement?

A schlumpf is a gearbox at the BB, so anything that replaces the BB won't work.
http://www.schlumpf.ch/hp/schlumpf/faq.getriebe.engl.htm

Another "DIY" solution is to use the Sempu as a jackshaft within the chainline, but that would likely be a complicated mess, as you would have to go back from the left to the right again using another jackshaft, since the Sempu (AFAIK) detects torque thru the shaft twist (if it doesn't, then I am probably thinking of the TDCM).


The THUN only detects torque on one side (left?) while the others do it on both.


Erider and NCTE are the other two BB type solutions I know of.


The only ones I know of that are still available anywhere that are not BB solutions are the ones you already found in the OP, where it clamps to or replaces the dropout. At least one generation of the Stromer bikes used this type of sensor, and I think Juiced used them too, for at least some bikes. (no idea if they were the same brand).

The other solutions I have found are DIY, like the one I linked.

FWIW, the dropout solution from Idbike requires that it *be* the dropout, because AFAIOS it is sensing the forward pull of the axle (by the chain tension on the rear cluster) in the dropout relative to the rest of the metal of the bracket, which then clamps to the bike frame.

So to use it on your trike, you would need to remove the dropout on the side you are sensing torque from, and replace it with their unit, bolted to the remaining part of the frame.

Or machine your dropout/frame so that it looks like their dropout/module, then install their sensor into the spot for it in your modified dropout. (assuming the metal of your dropout/frame will bend/warp the same way as theirs in response to chain tension on the axle, to cause the sensor to output the same way).


I don't know what effect the hubmotor's axle rotation torque will have on the reading the sensor gets from the chain tension, if any.

Thank you amberwolf for the information. I'm surprised there are no torque sensors available that can mount to the frame and read the chain tension.

E-HP said:

So the triple chainring is an absolute requirement?

Click to expand...

Yes. My build is intended to be pedalable with the motor shut off up a steep hill at walking speed, and also pedalable with the motor on at highway speeds with human power still adding motive force. The Schlumpf HS drive with a 38-56T front chainring range and 11-34T 7sp freewheel on a Leafbike 3T wind hubmotor built into a 16" moto wheel with a Mitas MC2 16x2.25" tire would give me the gearing range needed to do 4 mph up a steep hill at 60 rpm cadence, to careening down the highway at 108 mph at 140 rpm, and anything in between. My next body shell is going to be sufficiently aerodynamic that I'll be able to turn the motor off and cruise ~25 mph on ~150W with the motor's cogging torque drag included, or turn the motor on and cruise 60 mph on ~1kW with human power accounting for about 20% of the motive force. The vehicle is going to weigh around 100 lbs and the electric motor is going to be modified with cooling holes/ferrofluid/fans/heatsink fins and run with an ASI BAC4000 controller set at 10 kW peak and 250A phase current, allowing it to perform like a car when the motor is in use. At 72V, I'm expecting a top speed around 70 mph, but once high voltage FOC controllers of about 1-2 lbs enter the market, I will be upgrading to ~130V for triple digit top speeds. The battery pack is going to be ~2.5 kWh of Panasonic 21700 cells.

there is a prototype

https://endless-sphere.com/forums/viewtopic.php?f=2&t=113925

regards
stancecoke