BBS02 - Pedals/crankarms vibrate when rolling the bike backwards, sign of a problem?

[paxtana]

This thread is closed due to a surprising amount of hostility.
To all users please be civil to each other, if this can not happen the mod team will have to take further action.

[Circuitsmith]

stts:

" I looked back on that thread where I was helping you out."

Please point out which thread where you allegedly helped me out. I don't recall you ever saying anything helpful to me.

I did see the pictures you posted. And as a recently retired Electrical Engineer, I can confidently say they prove nothing.

Re your talk of trolls, stupidity, and blunders, I suggest you look in the mirror.

[AZguy]

...My 2 cents:
A permanent magnet motor can indeed generate electricity when spun by external means.
However, it cannot charge the battery because between the battery and motor is the commutator circuit, consisting of several power MOSFETs among other parts.
This circuit (Bafang controller specifically) is not designed to transfer electric energy in the reverse direction.

Yup! Right on point

[Circuitsmith]

When I first started reading this thread my first thought was the grease in various mechanisms (freewheels & gears) had simply dried out after sitting several years.
Thus the strange behavior.
That dark grease I'm sure is not high quality stuff.

Then of course came the "tangential debate".
My 2 cents:
A permanent magnet motor can indeed generate electricity when spun by external means.
However, it cannot charge the battery because between the battery and motor is the commutator circuit, consisting of several power MOSFETs among other parts.
This circuit (Bafang controller specifically) is not designed to transfer electric energy in the reverse direction.

[Retrorockit]

That's absolutely normal. if you're in a cross chained gear it may even be the chain trying to slip off at the front chainring. If it doesn't do that then you have a problem. Some thing is broken between the motor and the wheel.

[npt45]

Thanks for the heads up on the waterproofing ideas, it sounds like a worthwhile investment to do.

My motor kit also handily came along with the full Luna ebike toolkit, which includes the freewheel/cassette removal tool... so now time for some youtube education. I've opened up pretty much every bike part, greased bearings, etc, except the rear freewheel is the one thing I haven't touched yet.

[73Eldo]

Let me take a crack at explaining whats happening, maybe I will stumble on a good combo of words that will click, pun intended.

Made up numbers just to make the the math easier and the concept easier to understand.

Lets say the back wheel hub has 4 internal teeth spread out by 90 degrees. The rear sprocket have a tooth called a pawl that will engage the first tooth it comes to and that is when it begins to drive the wheel. For this concept lets say we have a wacky single speed setup that has 42 teeth up front and 42 in the back so 1:1 ratio. One pedal/crank turn = one wheel turn. On a regular bike the crank is solidly connected to the chain ring so you start pedaling chain ring moves chain moves sprocket moves.

From a dead stop worst case within 90 degrees that pawl will catch and begin to drive the wheel. In a real bike there would maybe be at least 24 teeth so 15 degrees? but the concept is the same with my imaginary 4. Again here made up numbers leaving out some ratios and such, lets say our final drive ratio is also 1:1 so 1 crank turn = one wheel turn. Lets say the bike is now moving a 10 rpm and you are not pedaling. The sprocket isn't turning so the pawl just skips across those 4 teeth as they pass by, this is the clicking when you coast. You begin to pedal first at 5 rpm, you are not yet driving the wheel but have reduce the clicking by half. You increase your pedal speed to 11 rpm which you can do because you are not yet engaged to the wheel.

As soon as your crank speed hits 10 rpm you have matched the wheel speed and lets say you just happen to be at 45* right between 2 teeth still nothing happening other than the bike is likely slowing down slightly maybe to 9.9 rpm and you pedaling is still accelerating because its not yet loaded so its really easy. What happens next? You basically have an an object moving at 9.9 rpm and an object right behind it accelerating up to 11. The 11 is going to hit the 9.9 with a bang on some level and there will be some energy loss so we maybe end up with the whole works now engage and moving forward at 10.5 rpm. All good.

So you can see in our example here that from a stop worst case it will take 90* to engage, it just depends on where things stopped. If you were moving you are taking a running start chasing a moving object. Clear so far? Great now we will add in the BBS, again imagining its got the same 90* 4 teeth and everything is still 1:1. See where we are going? From a dead stop we now may have to crank 90* before we start to move the chain at which point we get a little clunk and we may also have to move the chain 90* before we clunk there and start turning the wheel. You can see that having double this slack while moving gives you even more chance to over accelerate your pedaling before it hits.

[ncmired]

And just for people's curiosity, after all this discussion, here is a photo of my setup, though not much help for troubleshooting.

Thanks, pictures of people's e-bike conversion projects are almost always helpful, and not just for technical/reference reasons.

[npt45]

I did check the chain when pedaling, and it starts moving every time within ~1cm, in all conditions, so I think that confirms the motor freewheel should be ok. But also, every time the chain moves, the rear wheel turns. So, both are working in that sense. Only while rolling do I get that clunk, which I presume must be in the rear hub, so I assume the whole rear freewheel itself is turning with the wheel, and doesn't let the pedals/chain engage until they "catch up" in rotation speed, and then it clunks when engaging.

I thought these systems were supposed to be pretty waterproof, even for riding in rain? (not that I am, I'm only out in nice weather) I do recognize the need to better protect the motor wiring/connections though; if I had that shrink tubing stuff I would have used that, instead of multi-layers of elecrical tape as now. That may be a future improvement project as well. Actually, in my area the bigger issue is getting sand up into everything - I'm regularly brushing off the drivetrain, but surely miss some, and sand certainly can't be good for wear.

[npt45]

And just for people's curiosity, after all this discussion, here is a photo of my setup, though not much help for troubleshooting.

[npt45]

The whole bike is just as it was since it was new (minus new brake pads and shifter cable), and has always worked well. The motor definitely isn't loose at all. The rear freewheel appears normal, and the rear wheel spins alone and freely with the freewheel clicking.

It's a weird thing, which is why I'm puzzled with it. I have never felt on any other bike (or this one until recently) a "double click" or delayed double engagement when pedaling, which is why I originally assumed it may be something within the motor. But, I don't have any sense of a problem when using the motor, either pedal assist or straight throttle, it's only tied to my own pedaling, as described above. On further closer inspection, I feel like the issue is somewhere in the rear freewheel, that the first initial click I feel is the normal engagement of the crank ams to the drivetrain (which I never felt before adding a front chainring freewheel via the motor, but as expected), and the 2nd clunk is the inside rear freewheel engaging. The question is more why it's so noticeable and with such an odd delay in it.

[73Eldo]

Good line of questions. Did you have to do any mods or swapping in the rear wheel area on this bike or is it all as it was when it was a regular perfectly functional bike?

[AZguy]

FWIW, as mentioned before, I'm too old to waste even two neurons "debating" trolls, whose toolkits seem to primarily consist of insults and personal attacks

OTOH I will point out misinformation that I *know* to be untrue, in particular if it is likely to waste somebody's time

[AZguy]

I'll keep my nose out of the tangential debate, though the idea of charging by rolling backwards is interesting, albeit I imagine pretty inefficient, like, I'd rather just ride home by normal pedaling at that point.

Anyway, I opened and greased the main gear side this evening with the SCH-100 grease, and wow, so much quieter, definitely worth doing. It had some dark grey factory grease in there, not a ton, but enough to not be dry. The rolling backwards bumpity feel on the pedals is still the same (and minor, as it was even before), so I'll lean toward assuming it's normal and ignore it.

For the other delayed clicky engagement issue, I tested more carefully (bike in place, rear wheel up). With a non-spinning rear wheel, going from pedaling backwards to forwards, I feel an immediate catching in about 1cm, and the wheel starts turning. If I keep pushing at this point, I don't get the 2nd loud click. But if the wheel is then already spinning and I do the same thing with the pedals, I feel the clunking engagement after about 30-40 degrees of rotation; and if I pedal realllly slowly, the arc grows to maybe 90-120 deg of rotation before it happens, but mashing the pedal hard it happens in maybe 20 degrees rotation. Oddly though, If I'm riding/rolling at speed, and I repeatedly turn the pedals backwards a bit and then slowly forwards, while not engaging the drive train with any force at all, I get the loud clunk in the crank arms every time in about 30-40 degrees. Since it all seems in some manner correlated to the rear wheel spinning condition, it makes me suspect that it may be something in the rear hub freewheel, but I'm still surprised I feel such an obvious click through the pedals.

Well it sounds like everything related to the motor is most likely normal

I don't really understand the scenario where when the wheel is already spinning... typically with a derailleur setup the rear freehub/freewheel will be disengaged (clicking) when the wheel spins forward so there's no movement with the ring and the behavior would be the same if the bike is stationary - is the ring turning when you move the rear wheel forward?

[73Eldo]

Does this clunk seem to change depending on how hard you are pedaling? Any chance the whole unit is shifting in the bottom bracket a bit or the crank arms are not tight? Does it do it in any gear? The apparent rhythm to it makes me think its not an internal thing with the BBS unit. Again hard to diagnose for sure online but thats just the direction I am thinking now.