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Pedal assist stopped working on new ebike

Old 11-12-20, 08:31 AM
  #1  
gadgetadam 
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Pedal assist stopped working on new ebike

I put 36 miles on my new ebike and the pedal assist stopped working. When I started to pedal yesterday the motor was intermittently engaging while I was accelerating while pedaling and after about 15 seconds the motor stopped. The throttle still works. I emailed the company and I'm waiting for them to reply but I wanted to try to figure out what's wrong with it before they diagnoses it and send out replacement parts. Since this ebike stuff is new to me I need to learn it.

It has hydraulic brakes with a feature to disengage the motor when the brakes are applied.
It has a cadence/torque sensor on the rear dropout next to the cassette.
The motor controller is in the frame.

I'm not sure if the brake switches are normally open or normally closed but I disconnected them to test and no change.
I disconnected all of the electrical connectors and reconnected them just to make sure nothing came loose.

I'm not sure if the controller receives input from the cadence/torque sensor or not.

What does everyone think the problem might be?
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Old 11-13-20, 08:37 AM
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Moe Zhoost
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The sensor on the back is a speed sensor, not a cadence sensor. Check to see if it's aligned properly with the magnet and is at the proper distance away. Does your bike have a PAS sensor mounted at the bottom bracket, near the crank? If so, check its connection.

Also, the make/model of your bike would be useful.
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Old 11-13-20, 09:44 AM
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Moe Zhoost
It's a Juiced Bikes CrossCurrent X.

This model does in fact have a cadence/torque sensor on the rear dropout.
https://www.juicedbikes.com/products...nt=18177155205

Since my post I looked at a few things.
https://1drv.ms/v/s!AhWV8e0N_605wYJG...NcxUg?e=jrGr65
It seems the small cog of the cassette is right up against the sensor in the video above. There should be a gap no further than the width of a nickel there. I can't even put a piece of paper between the two! As you can see in the video there isn't any gap and I feel somehow the rear wheel may have shifted breaking the sensor. Juiced Bikes has documented that if you hear a knocking noise when pedaling you should re-seat the wheel. I didn't do that as I thought it might have been normal since I'm new to ebikes and that adds to my suspicion that something shifted and broke the sensor.

I'm still waiting back to hear from Juiced Bikes and hopefully they'll send out a new part soon.
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Old 11-13-20, 11:15 AM
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Moe Zhoost
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Originally Posted by gadgetadam
Moe Zhoost
It's a Juiced Bikes CrossCurrent X.

This model does in fact have a cadence/torque sensor on the rear dropout.
https://www.juicedbikes.com/products...nt=18177155205

Since my post I looked at a few things.
https://1drv.ms/v/s!AhWV8e0N_605wYJG...NcxUg?e=jrGr65
It seems the small cog of the cassette is right up against the sensor in the video above. There should be a gap no further than the width of a nickel there. I can't even put a piece of paper between the two! As you can see in the video there isn't any gap and I feel somehow the rear wheel may have shifted breaking the sensor. Juiced Bikes has documented that if you hear a knocking noise when pedaling you should re-seat the wheel. I didn't do that as I thought it might have been normal since I'm new to ebikes and that adds to my suspicion that something shifted and broke the sensor.

I'm still waiting back to hear from Juiced Bikes and hopefully they'll send out a new part soon.
Thanks. It's interesting that they have a dropout mounted cadence/torque sensor. It appears to measure cyclical stress from flex between the frame and derailleur mount. I had never seen one of these.

It certainly does not look like either the rear wheel or sensor is correctly installed or spaced. My bet is that the cog is hitting the mount slightly causing it to sense flex incorrectly. I'd try a test by adding a thin spacer to the axle to move the cog away from the sensor and see if that makes a difference. You may not be able to do that if the drop-out spacing is tight.

Good luck.
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Old 11-15-20, 03:05 PM
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I agree. There must be a washer missing. You need more room to get the chain over the smallest cog. Maybe the axle is pressing too hard on the sensor. It's amazing how they can measure cadence with that.

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Old 11-19-20, 10:37 AM
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Originally Posted by Doc_Wui
I agree. There must be a washer missing. You need more room to get the chain over the smallest cog. Maybe the axle is pressing too hard on the sensor. It's amazing how they can measure cadence with that.
I wondered myself. Here's how. So the 'width of a nickel' spacing sounds about right and if that is off it might indeed mean that the wheel is crooked in the dropouts or that the area has collected grime or dirt. That's what I would check before assuming anything is broken.
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Old 11-19-20, 10:47 AM
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Leisesturm and everyone else. Juiced Bikes got back to me. They're sending me a new sensor AND washers. Either I'm a one off, part tolerance/manufacturing is off, or this is a known issue. It seems they agree the cog is way too close to the sensor. It's not grime and dirt as the bike only had a total of 36 miles on it before it stopped working. Even after taking the wheel off and putting it back on there isn't any change so it wasn't shifted during transit. As for comments about the chain needs space the chain only goes around 1/2 of the cog not the entire thing. The sensor is on the other 1/2 of the cog so no room has to be taken into account for the sides of the chain.

Anyway I'm hoping the part they think is bad really is so I can pedal assist. It gets boring riding around with the throttle and not pedaling.

Thanks everyone.
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Old 11-19-20, 12:25 PM
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So you are saying that what looks like the smallest sprocket in your video is not intended to carry the chain, but is part of the sensor used by the bike to measure wheel speed and torque.
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Old 11-19-20, 01:01 PM
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Originally Posted by gadgetadam
Anyway I'm hoping the part they think is bad really is so I can pedal assist. It gets boring riding around with the throttle and not pedaling.
Maybe you could temporarily disconnect the sensor in order just to pedal along with the throttle?
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Old 11-19-20, 05:47 PM
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I can pedal and use the throttle at the same time but the amount of power isn't automatic based on my speed and torque.
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Old 11-19-20, 05:52 PM
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Doc_Wui
It carries the chain but the position of the sensor isn't at a position near the cassette where the chain is.

Blue is the 11 tooth cog
Red is the chain
Black is the sensor.

This means the sensor only sees the 11 tooth cog on the cassette, not the chain.

Did my crappy drawing help? I did fail drawing in High School.
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Old 11-20-20, 09:23 AM
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Aha. I got it now. It's interesting to get such a close up of the teeth on the gears. We can really see how they are cut at different angles to facilitate chain movement to the other gears.
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Old 11-20-20, 09:48 AM
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Originally Posted by Doc_Wui
Aha. I got it now. It's interesting to get such a close up of the teeth on the gears. We can really see how they are cut at different angles to facilitate chain movement to the other gears.
Yea, I didn't think my phone would take such detailed videos so close to something. It was pretty interesting how the teeth are cut out differently and angled along with paper/cardboard fibers in the video(as I was trying to see if a thin piece of packaging cardboard would fit there that is less than 1 mil thick).
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