Need advice on how torque sensors work.

[Jeffb]

I'm in the middle of planing out my next enike build. I need advice on how torque sensors work.
How many wires out and the purpose of each.
In what form is the signal sent like is it a simple resistance change with torque?
You can be as technical as possible as I repair aircraft flight systems. If I had a link to any middrive sensors it would be helpful.
I'm wanting to learn what the sensor output is.

 

[Snoop]

I’ll admit I have no idea what I’m talking about and this is definitely not in my “wheelhouse”. I found this, which might help you though.

Electric Bike Torque Sensor Kit

This Electric Bike Torque Sensor Kit works with almost all bikes with 68-73mm bottom bracket. It is compatible with 24V or 36V or 48V 350W motor ( not included in this Torque Sensor Kit ). The torque sensor measures your actual force on the pedal, the harder you pedal, the more power given to...

www.elecycles.com

 

[Snoop]

Regarding how they work, I guess Cadence Sensors work by a simple magnet which moves around with each pedal, essentially acting like a “switch.” Even I can figure that out, LOL.

A Torque Sensor uses more complex technology to sense pedal pressure. Here is an interesting read on the subject:

E-Bike Torque Sensor Technology Comparison

How does different torque sensor technologies compare for e-bike/pedelec application? What is the best solution today and in the future?

sensitivus.com

For me, it’s mostly gibberish, but for a flight mechanic, it might be like reading the Sunday funnies for you.

 

[CloneWerks]

Snoop. Yes you got it right. A cadence sensor is a series of magnets going past a hall-effect sensor. Unless someone does a lot of additional programming it's mostly an "on/off" switch that simply indicates IF you are pedaling and how fast you are pedaling which is why motors running from a cadence sensor are typically programmed with a bit of lag and a slow lead-in to prevent abrupt power changes that would throw the rider off balance and cause a crash. A typical cadence sensor picks up about 12 measurement pulses per revolution.

A torque sensor measures IF you are pedaling, and also HOW HARD you are pushing on the pedals. Light pressure means light assist, heavy pressure means higher assist. A typical torque sensor monitors on the order of 100 cadence measurement pulses per revolution AND around 500 to 1,000 torque/pressure samples per second.

More details on how the torque sensor type system works can be found here.

 

[Train Dan]

I'm with Snoop; much like the law of gravity, it's enough to know it works, without fully understanding why.
My bike has the Bosch system, and it is both responsive and virtually seamless.
The only time I can occasionally 'feel' the boost is in lower gears and a downhill.
It has put this codger back on a bike, and for that I'm happy.
Dan

 

[Jeffb]

Maybe I need to reword my question. I'm wanting to know exactly how the signal from the torque sensors is output. Is it a variable voltage like 0 for no pressure to 5v full pressure? Or maybe a digital signal. I have a bosch torque sensor and true to bosch they don't publish much info on how theirs work.
I do know the difference between a cadence and torque sensor. I am wanting to get into the weeds

 

[Hoggdoc]

Maybe I need to reword my question. I'm wanting to know exactly how the signal from the torque sensors is output. Is it a variable voltage like 0 for no pressure to 5v full pressure? Or maybe a digital signal. I have a bosch torque sensor and true to bosch they don't publish much info on how theirs work.
I do know the difference between a cadence and torque sensor. I am wanting to get into the weeds

If you have a sensor can't you use a oscilloscope to check the output? I would bet its a variable voltage that the controller interprets when applying power to the motor.

 

[CloneWerks]

Maybe I need to reword my question. I'm wanting to know exactly how the signal from the torque sensors is output. Is it a variable voltage like 0 for no pressure to 5v full pressure? Or maybe a digital signal. I have a bosch torque sensor and true to bosch they don't publish much info on how theirs work.
I do know the difference between a cadence and torque sensor. I am wanting to get into the weeds

It is my understanding that different manufacturers use slightly different systems (I.E. not all "strain gauge" systems are read in the same way) and the methodology and programming inside the signal processing modules are tightly held trade secrets at this time.

 

[Train Dan]

Cadence would sense/measure the number of strokes you're making, as an average, which seems a more primitive system.

 

[MWRider]

In regards to Torque Sensing, Seems like it would be pulse width modulation with the signal being something a simple as a potentiometer being actuated by by the movement of a spring loaded crank relative to origin to increase the signal voltage. At least,that is the way that I would do it.

 

[SteveK]

What happens when your down stroke is stronger on one side for some reason with the torque sensor? Does it deliver a jerky assist?