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Coaster brake ebrake cutoff sensor

Posted: Sep 03 2021 2:51pm
by eecsflyer
I am trying to design an e-assist handcycle for quadriplegics who do not have enough grip strength to squeeze a brake lever. We generally use a coaster brake instead. Are there any ebrake sensors that work with a coaster brake? In other words, can detect if the user pedaled backwards and intends to stop the bike?

Re: Coaster brake ebrake cutoff sensor

Posted: Sep 03 2021 4:50pm
by TDB
Done with EN15194 pedelecs that don't have ebrake switches, torque sensor instead and is probably your best option.

Re: Coaster brake ebrake cutoff sensor

Posted: Sep 04 2021 5:07pm
by MadRhino
Easy to fit a momentary switch to the brake hub lever. Those hubs have a torque lever that usually attach to the derailer mount. If you give it 1/4’’ play and a return spring, you have enough movement to trigger a momentary switch.

Alternatively, there are brake light switches that are actuated by cynetic energy sensor (or G sensor if you prefer). Some are pretty cheap and can be used to trigger the ebrake cut-off with very little mod. Then your ebrake is automatically engaged and the brake light automatically lit when you start braking. :wink:

Re: Coaster brake ebrake cutoff sensor

Posted: Sep 05 2021 4:35pm
by TDB
Isn't the torque arm usually attached directly to the axle? Axle can't rotate easily when clamped into the frame.

Re: Coaster brake ebrake cutoff sensor

Posted: Sep 06 2021 10:12am
by MadRhino
TDB wrote:
Sep 05 2021 4:35pm
Isn't the torque arm usually attached directly to the axle? Axle can't rotate easily when clamped into the frame.
Image

Most if them since they exist are clamping to the frame. Many recent models are bolted to the derailer hanger. But, all of them have a torque arm.

Re: Coaster brake ebrake cutoff sensor

Posted: Sep 06 2021 12:58pm
by Chalo
TDB wrote:
Sep 05 2021 4:35pm
Isn't the torque arm usually attached directly to the axle? Axle can't rotate easily when clamped into the frame.
Single speed coaster brake hubs have their torque arms attached to the left side axle cone. They can't move back and forth without loosening the hub and causing problems.

Multi-speed coaster brake hubs usually have torque arms that are captive but not rotationally locked to anything other than the brake expander cone. This could hypothetically be used to actuate something, if as MadRhino suggests you provide a spring return of some kind. Braking force on the torque arm can be very high, so it must be firmly retained.

I once had a plan to use the brake arm of a two-speed automatic coaster brake hub to actuate a cable running to the front brake. I never did work out a good way to extend, travel limit, and spring return the arm for this application, but I guess I could return to the project one day.

Re: Coaster brake ebrake cutoff sensor

Posted: Sep 15 2021 12:43am
by donald56
With disc brakes, always use the 60/40 rule (same as cars). 60% front and 40% rear. This method will give the best stopping with the best chance of not skidding or laying the bike down. This method should be practiced a lot to get the feeling of your brakes and how they react to quick actions and learning how much pull is needed. The disc rotors are designed to prevent locking up but when you loose any amount of traction due to road conditions, sand, gravel, etc.., you will lock up. I often practice slamming the front brake just before the back brake and let the rear brake assist with the front. This is across the board with every two wheeled vehicle and disc brakes,Myloweslife hope this helps.

Yesterday, I had a close call and this method stopped me very quickly and did not slide at all.

Re: Coaster brake ebrake cutoff sensor

Posted: Sep 15 2021 7:48pm
by LewTwo
Chalo wrote:
Sep 06 2021 12:58pm
TDB wrote:
Sep 05 2021 4:35pm
Isn't the torque arm usually attached directly to the axle? Axle can't rotate easily when clamped into the frame.
Single speed coaster brake hubs have their torque arms attached to the left side axle cone. They can't move back and forth without loosening the hub and causing problems.

Multi-speed coaster brake hubs usually have torque arms that are captive but not rotationally locked to anything other than the brake expander cone. This could hypothetically be used to actuate something, if as MadRhino suggests you provide a spring return of some kind. Braking force on the torque arm can be very high, so it must be firmly retained.

I once had a plan to use the brake arm of a two-speed automatic coaster brake hub to actuate a cable running to the front brake. I never did work out a good way to extend, travel limit, and spring return the arm for this application, but I guess I could return to the project one day.
Well if you ever decide to follow through on that ....
Epoxy an strain gauge to the surface of the strap holding the arm. You would also need a small mpu and some electronic glue but it could be a workable scheme.