Cranks rotating when the wheel turns

[geekeasy]

With traditional bikes this happens but isn't an issue. With an e-bike it becomes a problem because when you're walking the bike, the cranks turn, and the motor kicks on.

So.... why are my cranks turning when the rear wheel turns?

Is it an issue with chain tightness or something? And note, this is an XP Lite so it's a single speed bike.

Here's a video showing the issue:

 

[Chargeride]

Sticky freewheel pawls obviously, or something jammed between cogs and spokes, only an issue these days with hub drives and basic cadence sensors.

Its only a matter of time before theres a video of a riderless ebike cruising down the street

 

[6zfshdb]

This also happens on my hub drive Pedego when walking the bike backward, and I'm told it's normal. I simply turn off the power to avoid any issues.

 

[harryS]

Cranks always rotate backwards when rolling the bikes backward. until they jam against a kickstand.. Happens to me every day when I roll the bikes out from storage, If they rotate when rolling forward, probably a sticky rear gear.

Power should be in zero assist when rolling an ebike anyway, especially if the bike has a throttle. Before I made that a habit, I've had them pop wheelies when walking them. One bike swung around like a discus and launched itself. Battery mount broke off. Real bummer.

 

[geekeasy]

Sticky freewheel pawls obviously, or something jammed between cogs and spokes, only an issue these days with hub drives and basic cadence sensors.

Its only a matter of time before theres a video of a riderless ebike cruising down the street

Small powerboats and jetskis come with "kill switches" so they won't move without someone on them.

Maybe e-bikes should do the same....

 

[mfgrep]

Small powerboats and jetskis come with "kill switches" so they won't move without someone on them.

Maybe e-bikes should do the same....

Nah. A torque or cadence sensor eliminates the need for a kill switch.

 

[geekeasy]

Nah. A torque or cadence sensor eliminates the need for a kill switch.

Except in this case it doesn't: The bike rolling forward turns the cranks, which engages the cadence sensor, which turns on the motor, which moves the bike forward....

Unlike the powerboat, the bike is likely to quickly fall over and stop. But still it's a bit of an issue.

 

[mfgrep]

Except in this case it doesn't: The bike rolling forward turns the cranks, which engages the cadence sensor, which turns on the motor, which moves the bike forward....

Sensor needs replacement. A kill switch could also fail

 

[PCeBiker]

Sensor needs replacement. A kill switch could also fail

It's not the sensor.
The crank is moving when it shouldn't.

Fix your sticky freewheel.

 

[geekeasy]

Fix your sticky freewheel.

Suggestions on fixing it?

And the answer could just be replacing it because the OEM one is obviously really cheap and low quality.

 

[PCeBiker]

You've got a one speed, so your hub guts probably look like this,..

The spring loaded one-way ratchet pawls are binding and not ratcheting.
They need to be cleaned or lubed or replaced if they're damaged.

The wheel has to come off and the hub taken apart to get at the mechanism.

 

[PCeBiker]

This also happens on my hub drive Pedego when walking the bike backward, and I'm told it's normal.

That doesn't sound right to me?

Will your Pedego also "Go" if you bump the pedals backwards while stopped?

Even my cheap cadence sensor hub bike won't activate when the pedals are rotating backwards.

 

[Gionnirocket]

Thanks! This really helps clarify things. I found the part number for the hub motor and the entire unit is only $50 on Alibaba so it doesn't surprise me that it doesn't work optimally.

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Seems like I'm just going to live with this minor issue, and then maybe someday upgrade the motor to a Bafang (recognizing that's a big project).

As @PCeBiker said.. If you're handy, I'd try cleaning / lubricating it.

 

[geekeasy]

As @PCeBiker said.. If you're handy, I'd try cleaning / lubricating it.

I deleted my comment above. I shouldn't be having these conversation before coffee. Above he said "remove the wheel" not "disassemble the wheel".

Looks like there are just a half-dozen hex bolts holding on the cover. Opening it up, cleaning it, and adding good lube shouldn't be too bad at all.

 

[PCeBiker]

Your hub motor is fine.
It's the single speed ratchet assembly that attaches to it that you need to clean or lubricate.

It looks like that motor doesn't include the single speed gear??


You might be able to remove the wheel and just spray some lube all up in there to get it going again?

You'll make a big ole mess, but you can clean that up and maybe get it going without removing the single gear from the hub motor?


The ratcheting mechanism can get really bad and not engage when you pedal forward, then your pedals just spin and aren't mechanically connected to the wheel.

 

[PCeBiker]

I found another picture that should help,..

That gear should spin freely in one direction and grab in the other direction.

When your gear is "spinning freely", there is so much drag that it pulls the chain and pedals with it and that activates your cadence sensor.

 

[6zfshdb]

That doesn't sound right to me?

Will your Pedego also "Go" if you bump the pedals backwards while stopped?

Even my cheap cadence sensor hub bike won't activate when the pedals are rotating backwards.

No. Both the torque and cadence sensors on the Pedego do not function when the crank turns in reverse.

 

[PCeBiker]

Looks like there are just a half-dozen hex bolts holding on the cover. Opening it up, cleaning it, and adding good lube shouldn't be too bad at all.

Here's some more pictures that should help,..

The freewheel/sprocket/ratchet assembly is probably threaded onto the hub motor like in this picture.
(Same idea, but you've got a motor instead of just an axle.)

You probably need special tools to unscrew your assembly?

We didn't have the special spanner wrench when we were kids, so we used a flathead screwdriver on an angle into the little hole, and pounded the Hell out of it with a hammer.

 

[PCeBiker]

No. Both the torque and cadence sensors on the Pedego do not function when the crank turns in reverse.

That's strange.
I wonder how rolling backwards is different than pedaling backwards?

I'd would think that both should activate the cadence sensor backwards?

Perhaps that's so if you start rolling backwards on a hill while you're on the bike, the power turns on for safely?

 

[geekeasy]

Here's some more pictures that should help,..

The freewheel/sprocket/ratchet assembly is probably threaded onto the hub motor like in this picture.

Again super useful. Any reason to not just replace the super cheap OEM freewheel with a still cheap ($30) Shimano 1200 freewheel?

Spending $30 for a better part seems like a much wiser choice than trying to service the crappy one.