How is purely torque-sensing PAS actually implemented?

[mschwett]

Regarding "cadence sensing". For what it's worth, any system I've messed with have had cadence sensors that only tell the controller the crank is moving, that's it. They DO NOT tell it anything else. Nothing I've messed with anyway. Anything that has to do with speed is measured by a speed sensor. I've never seen, or heard of anything that would do both (sense crank movement AND measure how fast it's turning). -Al

that’s strange! the “cadence“ sensors on my bikes have always fed an actual numeric value to the head unit. otherwise the data logged is not of much use. i guess (some) eBike/kit manufacturers saved a few pennies by simplifying the sensor?

 

[AHicks]

that’s strange! the “cadence“ sensors on my bikes have always fed an actual numeric value to the head unit. otherwise the data logged is not of much use. i guess (some) eBike/kit manufacturers saved a few pennies by simplifying the sensor?

Different type sensor? Typical of the PAS sensors I've seen is a 3 wire affair, with a hot, ground, and sensor output. Each time a magnet passes the sensor, you get a pulse on the sensor wire. The controller, from a stop, will count those pulses, and at a predetermined number, will turn the power to the motor on. When the crank stops turning, the pulses stop, and the controller turns off the power. Controllers with a "sensitivity" adjustment let you vary the number of pulses sent prior to the motor being powered on.

Speed is generally measured internally within the motor, and /or externally with a magnet mounted to a spoke. Some, like the Bafang mid drives, have several speed sensors and get pretty complicated pretty quickly....

 

[mschwett]

Different type sensor? Typical of the PAS sensors I've seen is a 3 wire affair, with a hot, ground, and sensor output. Each time a magnet passes the sensor, you get a pulse on the sensor wire. The controller, from a stop, will count those pulses, and at a predetermined number, will turn the power to the motor on. When the crank stops turning, the pulses stop, and the controller turns off the power. Controllers with a "sensitivity" adjustment let you vary the number of pulses sent prior to the motor being powered on.

Speed is generally measured internally within the motor, and /or externally with a magnet mounted to a spoke. Some, like the Bafang mid drives, have several speed sensors and get pretty complicated pretty quickly....

right, but the sensor type you describe would (in combination with a measurement of time!) be sufficient to generate RPM. i’m guessing they’re all like that, and the controller or display side deals with the simple math and averaging if needed.

i thought you meant it only returned a “spinning” or “not spinning” voltage state, which would be less useful!

 

[PCeBiker]

right, but the sensor type you describe would (in combination with a measurement of time!) be sufficient to generate RPM. i’m guessing they’re all like that, and the controller or display side deals with the simple math and averaging if needed.

I would think that if the cadence sensor is on the crank, it could only know the RPM of the crank.
The controller/display would need to know what gear you are in, and all the gear ratios as well as wheel size and time to generate an actual ebike speed?

 

[mschwett]

I would think that if the cadence sensor is on the crank, it could only know the RPM of the crank.
The controller/display would need to know what gear you are in, and all the gear ratios as well as wheel size and time to generate an actual ebike speed?

cadence in cycling is crank RPM, so all you need is a sensor at the crank. as you note, for speed other information is needed which is usually provided by a sensor at the rear wheel, in combination with tire circumference. some bikes let you adjust this value, some don’t. any street legal ebike will have some way to measure speed, so that the assist can be cut off…

 

[scrambler]

All bikes have a speed sensor. Combined with a crank cadence sensor, the controller can deduct what gear you are in (apart from ghost pedaling)

 

[Kayakguy]

You can buy a torque sensor from Grin ebikes at ebikes.ca. along with their Cycle Analyst display unit. The sensor installs in your bottom bracket and puts out a signal for your pedal pressure. The Cycle analyst converts that to a voltage that most hub motor controllers can recognize as a throttle voltage.
.
https://ebikes.ca/getting-started/pas-options.html
.
However, I am sure the ultimate systems would take into account how fast the pedals are spinnning, the speed of the wheel, and combine all of this into a more pleasureable pedaling experience. Not happening with the above,
.
I am fiddling with a middrive kit, made by Tong Sheng, that uses torque sensing. I didn't get it running til November, so cold weather has limited my trials. The system works, but I.m not sold on whether the added complexity is worth it,

My Ariel Rider C class uses a Tongsheng that is alleged to have both torque sensing and cadence sensing. Works very well. I can definitely feel the torque feed-in as I go up through the PAS levels. Not sure about the cadence sensing, but I tend (intentionally) to maintain a 70 rpm pedaling cadence, or at least I try to. All seems quite satisfactory. I also notice that torque sensing adds power as I add power. Vigorous pedaling yields more torque input. Desultory (i.e. half-assed) pedaling not so much. This is especially good if exercise is the goal.

 

[Jeremy McCreary]

@Court just reviewed my bike, the 2023 Surface 604 V Rook:

Surface 604 V Rook Review | ElectricBikeReview.com

Price: $2599.00 | Model Year: 2023 | An approachable deep step-through electric bike that comes in two frame sizes and three colors! Includes aluminum alloy fenders, sturdy rear rack, integrated lights, and two battery size options for extended range. Relaxed handlebar, adjustable angle stem...

electricbikereview.com

There I learned that the torque sensor in my right rear drop-out is the TMM4 by IDbike. Their product page makes no mention of cadence-sensing capability.

Still, the TMM4 measures drop-out strain due to chain pull. And that strain must include a ripple due to pedal rotation. The slight surging I get at low pedal pressure on high PAS tells me that the TMM4 can pick up at least some of this ripple. If so, a suitable controller might be able to process the TMM4 signal for cadence.

Short of that -- or a cadence sensor hidden elsewhere -- I'm back to thinking that my Rook controls motor current on crank torque alone.

Whatever the bike's doing, it seems to be working. Aside from the occasional surging -- again, slight -- the power delivery's so smooth and natural that it's hard to see much room for improvement.

 

[linklemming]

@Court just reviewed my bike, the 2023 Surface 604 V Rook:

Surface 604 V Rook Review | ElectricBikeReview.com

Price: $2599.00 | Model Year: 2023 | An approachable deep step-through electric bike that comes in two frame sizes and three colors! Includes aluminum alloy fenders, sturdy rear rack, integrated lights, and two battery size options for extended range. Relaxed handlebar, adjustable angle stem...

electricbikereview.com

There I learned that the torque sensor in my right rear drop-out is the TMM4 by IDbike. Their product page makes no mention of cadence-sensing capability.

Still, the TMM4 measures drop-out strain due to chain pull. And that strain must include a ripple due to pedal rotation. The slight surging I get at low pedal pressure on high PAS tells me that the TMM4 can pick up at least some of this ripple. If so, a suitable controller might be able to process the TMM4 signal for cadence.

Short of that -- or a cadence sensor hidden elsewhere -- I'm back to thinking that my Rook controls motor current on crank torque alone.

Whatever the bike's doing, it seems to be working. Aside from the occasional surging -- again, slight -- the power delivery's so smooth and natural that it's hard to see much room for improvement.

Your correct in that its hard to find TMM4 info that talks about a candence sensor.

That being said, it can be seen clearly in their own pic (the square nub thingy)
https://surface604bikes.com/products/2020-torque-sensor

Looks identical to the Juiced (look at both pics)
https://www.juicedbikes.com/products/juiced-bikes-current-series-torque-sensor?variant=18177155205

The cadence sensor (at least on the juiced) is the square thing next to where the wire meets the sensor.

The clearance between the smallest cog (11t on the juiced) and the cadence sensor is 'critical', get that clearance wrong and you will be introduced to the concept of surging...maybe thats your problem

 

[mclewis1]

I get there could be a rotational sensor there along with the strain (torque) measurement, and it's position on the rear dropout will measure wheel speed. But how can there be a measurement of pedal cadence without being certain what gear your in? ... and even then it's a calculation and an assumption based on the initial setup of the hardware (gearset) and that the shift sensor is working as it's supposed to.

I'm also not buying this idea of measuring ripple ... yes technically I get how that might work but with all the variables on an ebike (environmental and mechanical) I can't see that being an solid dependable capability (and not a big complex bit of code).

Am I missing something here?

 

[AHicks]

Any "cadence sensor" I've ever seen is there to tell the controller if the crank is turning - or not - to turn power to the rest of the system on and off. They have nothing to do with anything else. Stop pedaling and the power goes down. Start, and it's turned on.

 

[Jeremy McCreary]

This Juiced page suggests that they use the cadence info coming from this rear drop-out sensor only to determine  if you're pedaling, not how fast. Makes sense, because the only speed you could get from this setup would be cassette speed -- which by itself gives you neither crank nor wheel speed.

Not sure how taking this yes-no pedaling info into account would improve power delivery over torque-sensing alone. But one thing's for sure: It cannot give the motor contol system rider power (= crank torque x crank speed in appropriate units), as Grin's bottom-bracket sensors and CA3 display/computer do.

Addendum: The one benefit I can think of is when the chain bounces on a rough road. If you weren't pedaling at the time, the control system would know to ignore the resulting strain signal.

 

[mclewis1]

Any "cadence sensor" I've ever seen is there to tell the controller if the crank is turning - or not - to turn power to the rest of the system on and off. They have nothing to do with anything else. Stop pedaling and the power goes down. Start, and it's turned on.

Yup, and with some systems it can be a bit more nuanced than that. My setup (PAS only, no torque and managed by the Grin Cycle Analyst) differentiates between pedaling backwards, slow rates (power won't come on if you just re position the pedals), and ramps up the power as I spin the cranks faster. So it's using more information from the crank mounted cadence sensor rather than just motion on/off.

So it appears that a "cadence sensor" can be implemented in a variety of ways and is used to measure a few different motions, and ultimately the various types of system controller logic uses this data differently.

 

[AHicks]

This Juiced page suggests that they use the cadence info coming from this rear drop-out sensor only to determine  if you're pedaling, not how fast. Makes sense, because the only speed you could get from this setup would be cassette speed -- which by itself gives you neither crank nor wheel speed.

Not sure how taking this yes-no pedaling info into account would improve power delivery over torque-sensing alone. But one thing's for sure: It cannot give the motor contol system rider power (= crank torque x crank speed in appropriate units), as Grin's bottom-bracket sensors and CA3 display/computer do.

Addendum: The one benefit I can think of is when the chain bounces on a rough road. If you weren't pedaling at the time, the control system would know to ignore the resulting strain signal.

Jeremy, it's about just how sophisticated the controller software really is. MOST geared hub bikes sold come with a really mickey mouse controller just smart enough to get the (basic) job done (a damn shame). Others, like some of the aftermarket stuff from KT and Grin, offer WAY more sophistication, not to mention their abilities to be customized by the owners.

The controller on your bike is sort of unusual, and would fall between the extremes above.

As far as the torque sensing, pretty sure there are differences from one system to the next, but the basics are generally along the line of once the controller senses the crank turning, the amount of power going to the motor IS controlled by the torque placed on the drive train by the rider, using input from the torque sensor.

I have 2 torque sensing bikes, both Bafang powered. The first one, powered with an Ultra (torque monster), taught me to NEVER EVER climb aboard that bike unless my hand was on the brake (lesson learned twice!!, even a dog will only burn it's nose once!). Hand on brake assures no power to the motor when your weight is placed on the pedal! The second bike is an M600 powered bike. This bike can be mounted without concern of a false start. Point being, even though they are both later model M series Bafangs, there are still slight differences in the controller software. I blame that on the fact these bikes, and their electronics, are still in their infancy. As the industry matures, betting we'll see features not available now, some standardization regarding sensor layouts and wiring that make a little (lot?) more sense than what we have going on today. Kinda like comparing a Model T to the new Vette they just introduced..... My thoughts anyway, FWIW. -Al

 

[Jeremy McCreary]

As far as the torque sensing, pretty sure there are differences from one system to the next, but the basics are generally along the line of once the controller senses the crank turning, the amount of power going to the motor IS controlled by the torque placed on the drive train by the rider, using input from the torque sensor.

Very helpful, Al. Now that you mention it, makes sense to disable torque control when the pedals aren't turning. I'll have to test this on my bike and report back.

Don't feel bad about getting burned twice. According to my wife, our dog's more trainable than I am. And the dog's not all that good at even basics like sit, stay, drop it, and come. Pretty sure it's a control thing on the dog's part.

 

[smorgasbord]

The TMM4 is an interesting device.

You've probably already seen the spec page on it, which includes:

Supply voltage:	5 V
Output voltage:	0,1 V- 4,9 V
Measuring range sensor unit:	120 Nm ( High sensitivity) / 300 Nm (medium sensitivity)
Sensitivity TMM sensor unit:	40 Nm/V (High sensitivity)/ 100 Nm/V (medium sensitivity)
Tolerance on sensitivity:	< 3 %
Allowable range ZTV (zero torque value):	0,5-2 V
Temperature influence:	< 1 mV/ ºC
Electrical disturbance:	< 10 mV
Effect of moisture:	< 10 mV
Operational temperature:	-10 - 60 ºC
Storage temperature:	-40 - 85 ºC
Durability:	At least 10 million cycles
Protection Class:	IP66 >> protection aigainst water and dust

Here's IDBike's 3D CAD animation on it:

From the EBR Strommer forum, where Strommer claims how it is mounted (greased/torqued) really matters: https://electricbikereview.com/forums/threads/tips-to-improve-tmm4-torque-sensor-reliability.37699/
So, that might be a tip to bookmark as you perform maintenance in the future.

I doubt the Rook has an external cadence sensor - you'd see a wire coming from the bottom bracket area to the motor if it did. There's probably a wheel rotation sensor built into the Rook's hub motor and it's probably setup to not provide power until the wheel has already started to turn. Maybe some kind of hall sensor like the Bafang mid-drives use, but adapter for the hub?

 

[PedalUma]

it, makes sense to disable torque control when the pedals aren't turning

You can be stopped at an intersection with your foot on the pedal. My go to motors have something like 24 cadence magnets. One needs to pass pickup before power kicks in. That is 15 degrees or less of crank rotation, so it is very immediate. Some old cadence sensors had six magnets on the crank wheel for the Hall sensor and three had to pass the pickup before it would kick in. That is 180 degrees.

 

[KylerLaird]

So I'm left to wonder: Could the very smooth and natual power delivery really come from pure torque-sensing?

Yes, it can. I'm trying to finish a bike that I started years ago that did exactly this. It was wonderful - just needed a good battery and enclosure for the controller. I used a Trampa VESC. I'm having some difficulty getting it to work at all now, but when I first built it, it was amazingly good to ride - for kids and adults. I even had it do regen braking so it would stop on its own.

I have since experienced cadence sensor (only) assist (Lectra XP). It's horrible. I want torque sensing.

--kyler

 

[Jeremy McCreary]

Yes, it can. I'm trying to finish a bike that I started years ago that did exactly this. It was wonderful - just needed a good battery and enclosure for the controller. I used a Trampa VESC. I'm having some difficulty getting it to work at all now, but when I first built it, it was amazingly good to ride - for kids and adults. I even had it do regen braking so it would stop on its own.

I have since experienced cadence sensor (only) assist (Lectra XP). It's horrible. I want torque sensing.

--kyler

Totally agree with that last statement. The power delivery on my torque-sensing ebike feels natural enough that I have a hard time seeing much room for improvement.

The technical question you quoted (not very well put on my part) had to do with an information void regarding my TMM4 torque sensor. The TMM4 manufacturer states that it also includes a "cadence sensor" but doesn't say whether it reports (a) actual crank speed via chain speed, or (b) just the presence or absence of crank rotation via chain motion?

As I learned from @AHicks , a "purely torque-sensing ebike" (bad term on my part) would need (b) for safety reasons without using (a). A more sophisticated power-sensing ebike would need (a).

Question was, could my ebike achieve its excellent power delivery with just (b)? Still not sure. Thanks for reminding me to look into it again.

 

[scrambler]

Totally agree with that last statement. The power delivery on my torque-sensing ebike feels natural enough that I have a hard time seeing much room for improvement.

The technical question you quoted (not very well put on my part) had to do with an information void regarding my TMM4 torque sensor. The TMM4 manufacturer states that it also includes a "cadence sensor" but doesn't say whether it reports (a) actual crank speed via chain speed, or (b) just the presence or absence of crank rotation via chain motion?

As I learned from @AHicks , a "purely torque-sensing ebike" (bad term on my part) would need (b) for safety reasons without using (a). A more sophisticated power-sensing ebike would need (a).

Question was, could my ebike achieve its excellent power delivery with just (b)? Still not sure. Thanks for reminding me to look into it again.

Is your bike a juiced bike?

From the pages below they mention a 104 magnetic pole per revolution, which would suggest they can measure actual cadence with it.

Pedal Sensor / Torque + Cadence Sensor

Dual cadence + torque sensor hardware for Current-Series E-bikes. Frame-mounted rear dropout torque sensor. Made from a CNC milled block of 7000-Series Aluminum. Built-in high sensitivity digitally processed cadence sensor for near zero-lag startup and improved noise filtered torque-sensing over...

www.juicedbikes.com

Torque vs. Cadence Sensors | Pedal Assist Juiced Bikes

Pedal assist e-bikes often come in two different types: Cadence Sensor & Torque Sensor. Click here to learn about the differences & benefits of each!

www.juicedbikes.com