Jerky PAS

[dadalonglegs]

Hi rear-hub-motor-cadence-sensing-pas users. Has anyone of you experienced a 'jerky pedal assist' output?

I have logged 6000+km already, riding my bike to work everyday since the pandemic. The commute is about 7km flat + 7km uphill. It was smooth.

I noticed the jerky behavior (only on ascent) starting yesterday when I installed a rear rack to place my everyday carry (heavy) backpack. Today, I wear back the backpack, like I always do since day one, to see if the load balance was the culprit. No. The motor still gives a sudden jolt of power every now and then during ascent.

I'm not losing power. Instead, I am getting a jerky increase in assistance. I used to climb on PAS 3 (60% power) at 13kph ave speed. Now, to compensate for the jerkiness, I climb at PAS 4 (80%) at 22kph. The jerky behavior feels like you're bumped from behind. Not cool.

I stopped to feel the motor. It didn't give off an abnormal heat nor a weird noise while climbing. I guess the problem is not mechanical, but electrical?

Using throttle-only on ascent works just fine.

When I reached my workplace to park--before I turned the power off, I noticed at PAS 0, there's a pulsing jerk at the motor. So I lift my rear wheel and indeed it was slowly turning. I don't know what's going on now.

Any leads will be appreciated. Thanks.

 

[vfr400]

There are three commn causes:
1. The magnet disc behind the chainwheel has been knocked out of line. The gap should be an even 1mm to the sensor. Wiggle it back into position if it's drifted away or crooked.
2. A magnet has dropped out of the magnet disc, in which case there will be a hole where it should be.
3. The hole in the middle of the disc has worn so that it doesn't grip tight. You shouldn't be able to stop it from turning with light finger pressure. If it's loose, take it off and put some tape on the shaft.

If you have the integrated type sensor that fits inside the bottom bracket, it's sticking, in which case it's best to replace it. You can take them off, snap them apart and clean them, but slipping normally wears them, so it doesn't last long.

Please let us know what you find. Photos are always good for the knowledgebase.

 

[dadalonglegs]

Thank you sir. Based on your description, I think what I have is an integrated type. I'll have this removed and clean and see if it solves the issue. Thank you.

 

[vfr400]

600km with one of them is pretty good. I would have thought that the muddy water would have got in and ground it to nothing before then.

There is a scenario where a throttle can cause your problem, so test by disconnecting it to see whether the problem goes away. If it does, you need a new throttle.