Cytronex pedal assist - motor cuts in and out then stops

[Slimjim]

Also added as comment to Alan's post. Thanks in advance for any advice.

I am in the process of fitting my brother's two year old Cytronex kit to a different bike. The kit is prewired, and intact, apart from missing the crank magnets, and the brake lever magnet.

The kit has the ni-mh bottle battery, which is reported as fully charged (by the correct charger) after a three hour top up.

Also fitted/wired are front and rear lights, which work from the second thumb switch.

Some Cytronex kits have a bike computer, buy this one doesn't, and I can't see a spare/unused plug for one in the harness.

There are two 'hall effect' sensors, one red and one black.
Also a reed switch (I think it is - small black tubular sensor) for brake activation. I don't have the brake lever magnet, and will be fitting this kit to a bike with hydraulic brakes.

I've been told that the black hall effect is for a wheel speed sensor, and it is wired through the harness to the motor controller.

The red hall effect is apparently the pedal-assist sensor.

The motor is a 180W Tongxin front hub, 175rpm, 29 inch wheel.

I have temporarily fitted the kit to the intended bike.
I only had a couple of spare 'wheel magnets' from old bike computers, so I taped these 180 degrees apart to the small chainring, and taped the red sensor to the frame/chainstay.

When I switch the system on (thumb button shows red light), and spin the cranks, after a few revolutions the front hub will start to turn, but only got half a rev. Then cuts out. Then cuts in. And out. Etc for a few seconds. Then stops reacting.

I've tried various combinations of repeating this test with a magnet against the brake sensor (one orientation stops the motor turning at all, the other orientation results in the same on/off clunking). And also with and without a spoke magnet on the back wheel, so that it spins past the black sensor when I turn the cranks.

The effect is always the same on/off for a few seconds, then nothing.

I don't have a user manual unfortunately, and can't find a wiring diagram online.

My brother thinks I might need a new red pedal-assist sensor. Possibly I also need to fit the correct number of magnets (although obviously I can spin the cranks faster to get a higher frequency pulse from just two magnets).

Any suggestions for how to test the red sensor? The rubber sheath has pulled back from the sensor, exposing three coloured wires, but their insulation seems intact. If i hold them straight I seem to get a note immediate response, but the wheel still atops after a few turns so I can't prove this.

Also, should the black sensor be mounted at the front wheel - I.e. does the motor controller use a feedback loop to check motor speed, hence if it's not measuring the correct motor speed (because the black sensor is on the un-motored wheel), does the controller error?

Also, the brake lever sensor doesn't seem to need a magnet near it to let the motor drive, unless that just worked because I had placed the magnet against it in the wing orientation?

Any advice on the logic of the system would be very useful, before I spend money on a new red sensor.

I'll order some magnets, and continue to try with the black sensor on the motored front wheel.

Thanks, Adam.

 

[Slimjim]

Also added as comment to Alan's post. Thanks in advance for any advice.

I am in the process of fitting my brother's two year old Cytronex kit to a different bike. The kit is prewired, and intact, apart from missing the crank magnets, and the brake lever magnet.

The kit has the ni-mh bottle battery, which is reported as fully charged (by the correct charger) after a three hour top up.

Also fitted/wired are front and rear lights, which work from the second thumb switch.

Some Cytronex kits have a bike computer, buy this one doesn't, and I can't see a spare/unused plug for one in the harness.

There are two 'hall effect' sensors, one red and one black.
Also a reed switch (I think it is - small black tubular sensor) for brake activation. I don't have the brake lever magnet, and will be fitting this kit to a bike with hydraulic brakes.

I've been told that the black hall effect is for a wheel speed sensor, and it is wired through the harness to the motor controller.

The red hall effect is apparently the pedal-assist sensor.

The motor is a 180W Tongxin front hub, 175rpm, 29 inch wheel.

I have temporarily fitted the kit to the intended bike.
I only had a couple of spare 'wheel magnets' from old bike computers, so I taped these 180 degrees apart to the small chainring, and taped the red sensor to the frame/chainstay.

When I switch the system on (thumb button shows red light), and spin the cranks, after a few revolutions the front hub will start to turn, but only got half a rev. Then cuts out. Then cuts in. And out. Etc for a few seconds. Then stops reacting.

I've tried various combinations of repeating this test with a magnet against the brake sensor (one orientation stops the motor turning at all, the other orientation results in the same on/off clunking). And also with and without a spoke magnet on the back wheel, so that it spins past the black sensor when I turn the cranks.

The effect is always the same on/off for a few seconds, then nothing.

I don't have a user manual unfortunately, and can't find a wiring diagram online.

My brother thinks I might need a new red pedal-assist sensor. Possibly I also need to fit the correct number of magnets (although obviously I can spin the cranks faster to get a higher frequency pulse from just two magnets).

Any suggestions for how to test the red sensor? The rubber sheath has pulled back from the sensor, exposing three coloured wires, but their insulation seems intact. If i hold them straight I seem to get a note immediate response, but the wheel still atops after a few turns so I can't prove this.

Also, should the black sensor be mounted at the front wheel - I.e. does the motor controller use a feedback loop to check motor speed, hence if it's not measuring the correct motor speed (because the black sensor is on the un-motored wheel), does the controller error?

Also, the brake lever sensor doesn't seem to need a magnet near it to let the motor drive, unless that just worked because I had placed the magnet against it in the wing orientation?

Any advice on the logic of the system would be very useful, before I spend money on a new red sensor.

I'll order some magnets, and continue to try with the black sensor on the motored front wheel.

Thanks, Adam.

Oh and in case I sound too lazy to just put the spoke magnet and black sensor on the front motored wheel and try it..... I took the kit back off the bike this afternoon to sort out the wiring as the premade harness, inside the black plastic conduit, doesn't fit the longer GT frame I'm mounting the kit on. Hence when I thought about fitting the spoke magnet to the front motored wheel, unfortunately I had already stripped the kit off and packed the bike away.

Thanks again, Adam

 

[Slimjim]

Oh and in case I sound too lazy to just put the spoke magnet and black sensor on the front motored wheel and try it..... I took the kit back off the bike this afternoon to sort out the wiring as the premade harness, inside the black plastic conduit, doesn't fit the longer GT frame I'm mounting the kit on. Hence when I thought about fitting the spoke magnet to the front motored wheel, unfortunately I had already stripped the kit off and packed the bike away.

Thanks again, Adam

OK ignore the above post, I think I've realised my school boy error.
Whilst bench testing the kit, I held the hub horizontally with the axle in a vice. Spinning the wheel in the vice must have knocked the three magnets off (or the spacer washer I fitted to allow the hub to clear the suspension forks wasn't thick enough) and I presume the motor or controller needs the signal from these. I'll fit new magnets to the hub, and fit the black sensor to the fork ends....