how do throttles and sensors function?

Rexlion

Active Member
Region
USA
City
Tulsa metro
Some questions for you ebike owners, from an owner-to-be:

On ebikes with a throttle, does it engage in a binary manner (either full-on or full-off), or does it add power incrementally like an automobile's accelerator pedal? Or are there some variations from brand to brand between these two methods of working?

How do cadence sensors apply power? Do they add more power the faster one pedals, or less power? (I read in one thread that Yamaha motors provide less power as cadence increases, so I'm wondering if this is unusual.)

Speaking of sensors, I have learned that some mid drive motors (such as Brose) feature a shift detector that very briefly interrupts power while shifting, to take pressure off the mechanical parts. I understand and think this is sensible, but a local salesman told me that Bosch motors don't have a shift detector and don't need one. Is this correct, and if so, why wouldn't the Bosch need one; is it (I'm just guessing) because the Bosch has so much lower torque than most other mid drives?

TIA.
 

scrambler

Well-Known Member
Region
USA
City
Bay Area, CA
Throttles are gradual, they apply power incrementally by generating a variable voltage usually between 0 and 5V, which the bike controller converts into a power level. The controller maps the voltage range of the throttle to a power range that can vary depending on preset levels (like 0 to 200W or 0 to 1000W...)
That said how smooth that power curve is depends on the throttle HW and the controller.
The two main types of throttles sensor are potentiometer based and Hall sensor ones. The two functional types (regardless of sensor) are thumb throttles (can be rough on the edges) and twist throttle (the smoothest)

The basic principle of a cadence sensor is an ON/OFF switch that applies a chosen level of power when the pedals turn. Changing the power being applied is mostly done by changing Pedal Assist level on the controller.
That said some controllers can add a level of intelligence over that which can create some variation of power based on the Cadence and the bike Speed. But given that the sensor information does not tell how hard you are pedaling, it will never feel quite right in all situations.
Two basic and opposite scenarios for doing that are:
  1. If the cadence slows down the system assumes you are struggling and provides more assist. That can be counter intuitive if you like to downshift into a lower gear for more power.
  2. If the cadence increases, the system assumes you downshifted because of struggle and provides more assists. That can be counter intuitive if you like to stay in the same gear and pedal harder.

To provide a more natural and intuitive Pedal assist, the system must also incorporate a Torque sensor that detects how much effort you apply on the pedal, and a good controller to blend the information of both sensors to determine the Power assist level.
 

Rexlion

Active Member
Region
USA
City
Tulsa metro
BMZ/Brose motor has no shift sensor features.
Unless you are just making it up.
Maybe I have misunderstood the specs I read on the Ride1Up Prodigy with Brose mid drive. On their website they state:
Shifters
Shimano 9-Speed Trigger Shifter, Electric Shift Assist Sensor
I took this to mean that it had a shift detect that would momentarily stop power during the shift. Or does it mean something else altogether? I'm not sure.
(Btw I didn't care for the implication that I might be telling an untruth. A bit of tact would go a long way....) ;)
 
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harryS

Well-Known Member
Throttles are analog. Most of them vary the voltage between 1.6 to 4.5 volt. High voltage = more steam.

Cadence sensors put out a digital pulse train, which is shaped so the receiver can tell if pedals spinning forward or backward. For most controllers, the detection of the proper pulse train is like an on/off signal. Spinning the pedals faster might help the bike move faster, but doesn't affect motor speed. I've kind of proven this to myself by lazily turning the pedals with the wheel off the ground and watching the speedometer. Faster crank speed doesn't change the wheel rpm on my controllers,

Bromptom, by the way, spend a lot of time trylng to put some smarts into their cadence sensor. All it got them were lots of recalls for bikes that had a mind of their own when the pedals were moved.
 

AHicks

Well-Known Member
Region
USA
City
Snow Bird - Summer S.E. Michigan, Winter Gulf Coast North Central Fl.
Agree with @harryS on the cadence sensor function. Bottom line, it tells the controller when the crank is turning, so the controller can turn the power to the motor on and off safely. In addition, the controller may be set up to count the number of pulses from the cadence sensor prior to tuning on the power to the motor. This to prevent accidental starts. If the bike is stopped with a magnet just getting ready to provide a pulse, and you bump the pedal climbing on or off, it will likely startle you as the power comes on for a second. The controller is easily programmed to avoid that by waiting for 2 or more pulses from the PAS sensor. There's a LOT more to the controller, but no point in going there now.

Shift detectors/sensors are sort of a deluxe feature. They do detect shift cable movement, and shut the power to the motor off for a split second. No, you don't have to have one, just like you car will drive fine without power windows. For folks used to riding derailleur equipped bikes, the shift detector is no big deal. You may not even notice it's there most of the time. For those struggling with their first derailleur equipped bike, or coming back up to speed from long ago experience, they're a nice feature.
 

Rexlion

Active Member
Region
USA
City
Tulsa metro
Agree with @harryS on the cadence sensor function. Bottom line, it tells the controller when the crank is turning, so the controller can turn the power to the motor on and off safely. In addition, the controller may be set up to count the number of pulses from the cadence sensor prior to tuning on the power to the motor. This to prevent accidental starts. If the bike is stopped with a magnet just getting ready to provide a pulse, and you bump the pedal climbing on or off, it will likely startle you as the power comes on for a second. The controller is easily programmed to avoid that by waiting for 2 or more pulses from the PAS sensor. There's a LOT more to the controller, but no point in going there now.

Shift detectors/sensors are sort of a deluxe feature. They do detect shift cable movement, and shut the power to the motor off for a split second. No, you don't have to have one, just like you car will drive fine without power windows. For folks used to riding derailleur equipped bikes, the shift detector is no big deal. You may not even notice it's there most of the time. For those struggling with their first derailleur equipped bike, or coming back up to speed from long ago experience, they're a nice feature.
Some nice detail there, thanks. I have read some stuff (somewhere) in the last few days which made it sound like the clutch pawls or whatever inside the motor can get worn or damaged faster if there's no shift pause, but I can see how a person who's accustomed to shifting derailleurs would sort of have the habit ingrained of letting off pressure.

BTW, I hope you are spending time up north this summer. SE MI is baking pretty good this year from what I hear (I grew up near Standish). I was in Munising in mid June and it hit 90 on the Superior shore the day I was there! 😬
 

AHicks

Well-Known Member
Region
USA
City
Snow Bird - Summer S.E. Michigan, Winter Gulf Coast North Central Fl.
Some nice detail there, thanks. I have read some stuff (somewhere) in the last few days which made it sound like the clutch pawls or whatever inside the motor can get worn or damaged faster if there's no shift pause, but I can see how a person who's accustomed to shifting derailleurs would sort of have the habit ingrained of letting off pressure.

BTW, I hope you are spending time up north this summer. SE MI is baking pretty good this year from what I hear (I grew up near Standish). I was in Munising in mid June and it hit 90 on the Superior shore the day I was there! 😬
The bigger picture is that you want to avoid big shock loads on the entire system when shifting. It will happen to most of us human types on occasion, and the system is built heavy enough to handle that, it's just the constant noisy gear bashing you want to avoid.

Yes we summer here in MI. We've had some really dry weather lately. All the grass has gone dormant. Still, I'll take whatever we get up here to avoid the summer Florida humidity. I don't tolerate that well at all!
 

Rexlion

Active Member
Region
USA
City
Tulsa metro
Say, what about the torque sensors? I assumed that more torque would be applied the harder one pedals. But today I watched a review video on this site for the Giant (now Momentum) Lafree E+ with Yamaha SyncDrive Life mid drive, and they were showing the "auto mode" which does add power as one pedals harder... but they made quite a big deal of this feature, as if it were not present on other mid drives. Yet all the other mid drives (AFAIK) have torque sensors, too. Does the Yamaha motor do this and the others can't, or did all the others add the "pedal harder, get more power" feature since the time of that video (2019), or what?

I did catch where they said that the motor has an accelerometer and a slope detector to help evaluate how much power to supply in auto mode, and I don't imagine any other mid drive mfr adds those features. This system does sound appealing to me. More torque than the Bosch, and better reliability than Bosch from what I've read here.
 

PedalUma

Well-Known Member
Region
USA
City
Petaluma, CA
@scrambler is spot on. I take exception to one point. Yes, a twist throttle is smoother than a thumb throttle but (and this is a large but,) they can be a safety hazard. Unlike a motorcycle and electric bike does not make any sound when it is on. It is easy to forget that it is on while walking it through a door for example. If you accidently twist the grip while walking the bike it will go flying. I am up in the North Bay and putting the final touches on a torque sensor bike with all red wire housings today. This essentially puts the throttle function into the pedals.
 

JES2020

Well-Known Member
Region
Other
but I can see how a person who's accustomed to shifting derailleurs would sort of have the habit ingrained of letting off pressure
The thing is there is a lot more torque going through the system so it is a lot easier to mangle the chain and or gears by leaving out the shift pause, with mid drives.The internals of the motor don't care as much.
BTW I ride my Trek without pausing between shifting and it has no issue with it, (hub motor).
 
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AHicks

Well-Known Member
Region
USA
City
Snow Bird - Summer S.E. Michigan, Winter Gulf Coast North Central Fl.
Say, what about the torque sensors? I assumed that more torque would be applied the harder one pedals. But today I watched a review video on this site for the Giant (now Momentum) Lafree E+ with Yamaha SyncDrive Life mid drive, and they were showing the "auto mode" which does add power as one pedals harder... but they made quite a big deal of this feature, as if it were not present on other mid drives. Yet all the other mid drives (AFAIK) have torque sensors, too. Does the Yamaha motor do this and the others can't, or did all the others add the "pedal harder, get more power" feature since the time of that video (2019), or what?

I did catch where they said that the motor has an accelerometer and a slope detector to help evaluate how much power to supply in auto mode, and I don't imagine any other mid drive mfr adds those features. This system does sound appealing to me. More torque than the Bosch, and better reliability than Bosch from what I've read here.
Not familiar with all the intricacies of the other mid drives, so just wanted to mention not all have torque sensing. The Bafang BBSxx series do not have torque sensing, while the other Bafang mid drives do. Properly set up, neither are "bad", but I'd have to give the nod to the torque sensing.
 

PedalUma

Well-Known Member
Region
USA
City
Petaluma, CA
I know that this one is NOT your style. It is a town girly, girl bike for a girl. I made it today. It is the one I mentioned earlier with a torque sensor. I love these housings.
 

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Stefan Mikes

Well-Known Member
Region
Europe
City
Mazovia, Poland
Say, what about the torque sensors? I assumed that more torque would be applied the harder one pedals. But today I watched a review video on this site for the Giant (now Momentum) Lafree E+ with Yamaha SyncDrive Life mid drive, and they were showing the "auto mode" which does add power as one pedals harder... but they made quite a big deal of this feature, as if it were not present on other mid drives.
Actually, these are the sensors offered by Giant/Momentum/Yamaha technology:
  1. Torque sensor: The harder you pedal the more motor assistance you are getting
  2. Pedal rpm sensor: The faster you pedal the more assistance is provided. Actually, the torque and pedal rpm sensors are used in combination; the product of both is the rider's pedalling power (user's input). Calculated rider's power is multiplied by the Boost Factor to provide the right amount of assistance
  3. Speed sensor measuring how fast the e-bike is moving
  4. Motor rpm sensor: for syncing of the motor with the pedalling rpm
  5. Slope detection (specific to Giant): as soon as the sensor detects an incline, more power is delivered by the motor
  6. Accelerometer: depending on the bike acceleration or deceleration, the amount of assistance is regulated
Many premium mid-drive motor systems provide the sensors 1-4. Some add the accelerometer. Some (like Bosch) offer the shift detection. Talking about torque or PAS sensors alone might either refer to very primitive e-bike motor systems, or it could mean lack of of understanding how these things really work by the person expressing such an opinion.

Giant "Auto" technology is pretty unique. Based on the 6 sensors as mentioned above, a Giant e-bike tries to automatically switch between the first three assistance modes to deliver possibly the best motor assistance for given riding conditions. Not that technology works particularly well, no.

Another approach is the Specialized Smart Control technology: For instance, you define the distance to be ridden, expected elevation gain and the amount of the battery charge to be left at the end of the ride. The system transparently varies the assistance to meet the criteria. Or, you can define the expected ride time criterion. Or, the heart rate not to be exceeded during the ride. New feature of Specialized e-bikes is Micro Tune, by which you can precisely tune the assistance as you're riding.
Speaking of sensors, I have learned that some mid drive motors (such as Brose) feature a shift detector that very briefly interrupts power while shifting, to take pressure off the mechanical parts. I understand and think this is sensible, but a local salesman told me that Bosch motors don't have a shift detector and don't need one. Is this correct, and if so, why wouldn't the Bosch need one; is it (I'm just guessing) because the Bosch has so much lower torque than most other mid drives?
Not quite. It is some Bosch motors that include the shift detection. This feature implies added complication. Most of mid-drive motor manufacturers don't spend their time on that feature. It is enough to decrease the pressure on pedals or briefly stop pedalling to ensure a smooth shift.
 

scrambler

Well-Known Member
Region
USA
City
Bay Area, CA
Say, what about the torque sensors? I assumed that more torque would be applied the harder one pedals. But today I watched a review video on this site for the Giant (now Momentum) Lafree E+ with Yamaha SyncDrive Life mid drive, and they were showing the "auto mode" which does add power as one pedals harder... but they made quite a big deal of this feature, as if it were not present on other mid drives. Yet all the other mid drives (AFAIK) have torque sensors, too. Does the Yamaha motor do this and the others can't, or did all the others add the "pedal harder, get more power" feature since the time of that video (2019), or what?
This is just Marketing BS :)
Torque sensors are always used to increase assistance the harder one pedals; this is why they provide a more intuitive pedal assist.

That said, how the controller uses that information, in combination with all the other sensors, can create wide variations on the quality of the pedal assist.
So, one is free to advertise they are doing a superior job at it :)
 

PedalUma

Well-Known Member
Region
USA
City
Petaluma, CA
How torque and cadence interact really impacts the feel and character of a bike. For a tot carrying cargo bike I do not want to whiplash little necks so I will put the power gradually ramping up to a high cadence for smoothness. But for a rock garden jumper I will put it at a low cadence, instantaneous.