noviceBuilder said:
I'm actually struggling to see how this isn't a problem on all torque sensing mid-drives. Consider the TSDZ2. The torque is sensed on the BB spindle, the motor drives that spindle as a consequence, the torque of which is sensed, and so on. Why doesn't the TSDZ2 spin out of control? Does the system subtract the motor's contribution of torque from the measured torque?
as noted by another poster, it detects the torque in a place in the system before the motor's input. usually that's the crankshaft--the same place that many of the independent torque sensors put the sensor, like tdcm, thun, sempu, etc. if the motor were driving the actual crankshaft, then it would need to sense the pedal torque before that point--if it's driving it at the rigth crank / shaft interface, then the sensor has to be left of taht point, to sense (like the thun) the leftside pedal torque via twisting of the shaft. (i don't know exactly where the tsdz2's sensor is).
back when i was doing middrive stuff on my first big cargo bike, the crazybike2, i worked out several different torque sensing system designs, but each time i realized most of teh way thru working it out that the motor would input torque to the sensor and thus make it useless (dangerous even). i would have had to redesign the whole drivetrain to create a path for pedal power to feed into the drivetrain before the motor's input point, to have a place i could detect pedal input without the motor taking over.
in the tsdz2 (and similar) there isn't any place in the system to measure the motor torque prior to the pedal torque (not that there coudn't be, but there just isn't), so it doesn't ahve a value to subtract from anything.
there *is* a possibilty to have a battery-powered sensor with a remote wireless (radio, bt, etc) connection that is actually in the *pedals*, such taht it detects the force of pressing down on them, but it doesn't detect rotational force, or direction, so it would operate the system just as easily if just standing on the pedals as if actually pedalling with some force. it would work about the same if there was a motor driving the cranks as not, because the mtoor driving the cranks would take some pressure off the pedals depending on the cadence and the motor speed and force, so if it is setup right for the rider, the motor would cancel out the rider's force on teh sensors, just enough so the rider would keep the system active at whatever level they were going for. that might be a little complex.
but you'd have to design and build taht system yourself, cuz i don't know of such a system being commercially produced. (i think at one time there *were* pedals that could sense torque (pressure, really) for training cyclists, but i don't know what kind of effort would be needed to adapt them to your process.
[strike]I must be missing something fundamental.. because I don't even see how there can be mid-drives with a throttle (instead of PAS) and no pedaling. AFAIK, the freewheel mechanism is in the rear cassette and there is only one chain between the front & rear sprocket. So when a mid-drive motor turns the front sprocket how can it not cause the crank arm & pedals to turn too?[/strike] (edit: nevermind.. the answer is that the chainwheel has a freewheel mechanism)
yes, there is a freewheel in most of them. coaster-brake versions of such systems do not have a freewheel, or the brake wouldn't work...and thus those will make the pedals turn along with the motor.
some other middrives like the stokemonkey were designed without crank freewheels, because they drive the left side of the cranks via one chainring, and that passes thru the crankshaft to the rightside chainring and outputs to the rear wheel. since it passes thru the crankshaft, which connects both cranks together, it also forces the cransk to turn...like a tandem bike system does. (hence the name; the system acts as the stoker rider, though it's mechanically a little different chainline). this is pretty much how my powerchair-motor-driven system worked on crazybike2, back before i went dual hubmotor with it.
I was assuming the torque sensor was ultimately outputting a throttle control. You seem to imply that I can't simply expect the throttle output to be compatible with the controller's throttle input, is that correct? I hope the
cycle analyst v3 can essentially use any torque sensor input to control any motor.. maybe that's a bad assumption.
torque sensors don't generally output a throttle-compatible signal. i haven't experienced any that do.
the reasoning behind them not doing so make sense, because gearing, cadence, crank length, rider strength and needs, etc., will all affect how the system needs to respond to the sensor, and if they just output a simple throttle signal they wouldn't be adjustable enough to do this for a wide range of riders, bikes, and sitautions. you'd have to have what amounts to a significant portion of a ca v3 inside the sensor, programmable by some external method, to make them adjustable. easier to just send the "raw" signals out to something else (the controller, usually), that can be setup by the rider to match their needs.
so usually they output a voltage corresponding in some way (dfferent for each sensor type) to the torque value itself, *and* a cadence data stream, which may be pwm, or may be simple pulses for each rotation, and either a direction signal or just not outputting anything when pedalling backwards. each one is different.
see the http://ebikes.ca pages about torque sensors for more detail on the signals and such.
https://www.ebikes.ca/learn/pedal-assist.html#methods-of-torque-sensing
https://www.ebikes.ca/getting-started/pas-options.html#torque-sensors
https://www.ebikes.ca/learn/pedal-assist.html
ther'es another page with even better info but i can't find it right now.
but anyway, yes, the ca can take whatever torque sensor input, along with it's cadence sensor (or a separate one if the sensor you choose does not have one), and convert that to a throttle output, based on the settings you choose. see the ca3 product info page on ebikes.ca for the details of how the ca does what it does and how to set it up. (it's a process).
