Could eddy currents be causing this riding through treacle effect

[MikeS]

Is the eddy current effect big enough to cause an appreciable braking effect if something is 'sticking' in the motor? Presumably when the motor is 'off' then the magnets must be moved away from the coils to avoid this effect, but how do the manufacturers achieve this, and can it go wrong.
My Active Line Plus Bosch motor has started giving me a 'riding-through-treacle' effect at irregular intervals and I have no idea what triggers it or what frees it up, but it's as if someone switches on a dynamo - effect comes on over about 2 or 3 seconds, then I need usually about 25% more effort than normal to pedal the bike. Sometimes the effect is very strong but most of the times it happens it's very subtle and pointless to demonstrate to the dealer who will just say 'it's when the electric assistance stops' or 'it's a heavy bike to pedal without any assistance'. I know I am not imagining it because most of the time (all of the time for the first 1200 miles), the bike was a dream to pedal with the motor switched off.
I have had a dealer in York do the Bosch diagnostic and it showed no stored errors. I have checked everything at the back end but I am pretty sure the problem is within the motor as the bike freewheels perfectly well.
Any suggestions would be welcome
Mike

 

[vfr400]

There's a ratchet/ clutch between the pedals and the motor so the motor doesn't turn when you pedal on your own. The only possibility is that it's faulty and somehow keeps re-engaging when it shouldn't, but I don't think there's much chance of that, though not impossible.

I think more likely is that you have a knackered bearing.

 

[MikeS]

Thanks - you mean in the motor? There’s no unusual noises coming from it?

 

[Artstu]

There's a ratchet/ clutch between the pedals and the motor so the motor doesn't turn when you pedal on your own.

My Bosch Classic has that however I'm pretty sure it doesn't work as the way you describe, it would be possible for the motor to turn and provide drive without turning the cranks but if you're rotating the cranks then the motor is turning too, even when switched off.

 

[vfr400]

My Bosch Classic has that however I'm pretty sure it doesn't work as the way you describe, it would be possible for the motor to turn and provide drive without turning the cranks but if you're rotating the cranks then the motor is turning too, even when switched off.

No, that's not right. Firstly, the motor turns only when there's pressure on the pedals. Secondly, if you switch off the power, you can pedal the bike normally without turning the motor.

On the CX motor, it still disengages, but when you pedal, you have to still be engaged with the secondary reduction, which is why it has its characteristic drag.

 

[vfr400]

Thanks - you mean in the motor? There’s no unusual noises coming from it?

I would have thought that if the clutch was faulty and randomly engaging, you'd get occasional loud mechanical noises, like clacks or clacking, when it was half engaged.

Did you inspect behind the chain-wheel and did you unclip the chain to test the bearings?

 

[Artstu]

Secondly, if you switch off the power, you can pedal the bike normally without turning the motor.

Having had the motor apart I can't see how that is possible?

 

[vfr400]

Having had the motor apart I can't see how that is possible?

I think you need some new glasses then. Here's a picture of it and an explanation of how it works half way down the page.

Bosch Active Line 3

Here, I share technical solutions that arised during the development of my solar-bike.

www.avdweb.nl

 

[Artstu]

I think you need some new glasses then. Here's a picture of it and an explanation of how it works half way down the page.

Bosch Active Line 3

Here, I share technical solutions that arised during the development of my solar-bike.

www.avdweb.nl

Thanks, clearly an improvement over my Classic motor which I guess was designed 10 years ago.

 

[MikeS]

It feels like an electrical resistance but your bearing theory has merit too as often it happens in one of the assisted modes. Not so obvious and more like the motor has kicked down one level for a while
I have disconnected the chain and turned the pedals and not noticed anything amiss but then it only happens every now and then anyway
Mike

 

[MikeS]

After another 30 miles today, I am convinced it's some kind of electrical effect resisting me pedalling. VFR400 - have you any other ideas about how this could be happening because I'm going to have to give the bike to Halfords who will undoubtedly tell me they can't replicate the problem, then they will send it to their Bosch service centre who will put the diagnostic on and say that there are no error codes.
But it's driving me mad. When it's OK I can pedal the bike in 7th or 8th gear at 19 or 20mph on level tarmac with very little effort. When the problem kicks in I am struggling to do 10mph in 5th gear on the same level stretch. And that's with the motor switched to off.
Mike

 

[Deleted member 25121]

After another 30 miles today, I am convinced it's some kind of electrical effect resisting me pedalling. VFR400 - have you any other ideas about how this could be happening because I'm going to have to give the bike to Halfords who will undoubtedly tell me they can't replicate the problem, then they will send it to their Bosch service centre who will put the diagnostic on and say that there are no error codes.
But it's driving me mad. When it's OK I can pedal the bike in 7th or 8th gear at 19 or 20mph on level tarmac with very little effort. When the problem kicks in I am struggling to do 10mph in 5th gear on the same level stretch. And that's with the motor switched to off.
Mike

If this happens with the motor switched off it's unlikely to be an electrical problem unless it wasn't really off? Maybe try with the battery removed?

How about a problem with brakes or even tyres binding?

Just some thoughts....

 

[vfr400]

After another 30 miles today, I am convinced it's some kind of electrical effect resisting me pedalling. VFR400 - have you any other ideas about how this could be happening because I'm going to have to give the bike to Halfords who will undoubtedly tell me they can't replicate the problem, then they will send it to their Bosch service centre who will put the diagnostic on and say that there are no error codes.
But it's driving me mad. When it's OK I can pedal the bike in 7th or 8th gear at 19 or 20mph on level tarmac with very little effort. When the problem kicks in I am struggling to do 10mph in 5th gear on the same level stretch. And that's with the motor switched to off.
Mike

Even if the motor were jammed solid, you'd still be able to pedal the bike normally without resistance.

 

[MikeS]

If this happens with the motor switched off it's unlikely to be an electrical problem unless it wasn't really off? Maybe try with the battery removed?

How about a problem with brakes or even tyres binding?

Just some thoughts....

Brakes and tyres seem to checkout. No strange noises when the resistance is happening. Also checked whether either disk was hot but they weren’t.
I tried it with battery completely removed and got the same problem. But that seems crazy if my instinct is right about it being an electrical resistance so I’m going to try that again this morning. Of course a dynamo does not need a battery to generate a resistance to you pedalling and that’s what this feels like - as if something in the motor is loose and occasionally moving the magnets and coils close together when it shouldn’t be. What makes me doubt this theory though is that the extra resistance also sometimes kicks when I have one of the assistance modes switched on. This is obviously most noticeable in eco mode.
Mike

 

[Deleted member 25121]

Brakes and tyres seem to checkout. No strange noises when the resistance is happening. Also checked whether either disk was hot but they weren’t.
I tried it with battery completely removed and got the same problem. But that seems crazy if my instinct is right about it being an electrical resistance so I’m going to try that again this morning. Of course a dynamo does not need a battery to generate a resistance to you pedalling and that’s what this feels like - as if something in the motor is loose and occasionally moving the magnets and coils close together when it shouldn’t be. What makes me doubt this theory though is that the extra resistance also sometimes kicks when I have one of the assistance modes switched on. This is obviously most noticeable in eco mode.
Mike

I wonder if the clutch is sometimes not completely disengaging? But even if the motor was then functioning as a dynamo maybe it would only present a significant drag on the pedals if it had a large electrical load.
What happens if you briefly back pedal after feeling the drag, does that clear it?
Are your hub bearings OK?

Just some thoughts, all very odd.....

 

[MikeS]

I wonder if the clutch is sometimes not completely disengaging? But even if the motor was then functioning as a dynamo maybe it would only present a significant drag on the pedals if it had a large electrical load.
What happens if you briefly back pedal after feeling the drag, does that clear it?
Are your hub bearings OK?

Just some thoughts, all very odd.....

 

[MikeS]

That's interesting - so if there's no load (lights) on a dynamo the only resistance it's providing is the frictional losses in the various moving bits?. Obviously in my case there is no electrical load when it's off - except that sometimes it almost feels like the motor is trying to wind me backwards when it's set to 'off'. I am going to repeat the experiments with the battery completely off the bike as that would eliminate any kind of 'reverse ghostly action'
Mike

 

[MikeS]

Back pedalling works OK but it doesn't do anything to relieve the problem which goes away after sometimes 2 minutes or sometimes 10 minutes - and I have no idea what makes it go away.
Mike

 

[vfr400]

To find out what's causing your problem, as soon as it starts, jumpoff your bike,turn the pedals backwards to feel if there's any tesistance there, then lift wach wheel off the ground and spin it to see if there's anyresistance there. There is no other possibility. Once you have the source of resistance, a solution should quickly follow.

I asked you twice already, did you unclip the chain to test how free the crank turns backwards, but you haven't replied. That would have given you an answer to the condition of the bearings, which are the most logical culprit.

 

[MikeS]

To find out what's causing your problem, as soon as it starts, jumpoff your bike,turn the pedals backwards to feel if there's any tesistance there, then lift wach wheel off the ground and spin it to see if there's anyresistance there. There is no other possibility. Once you have the source of resistance, a solution should quickly follow.

I asked you twice already, did you unclip the chain to test how free the crank turns backwards, but you haven't replied. That would have given you an answer to the condition of the bearings, which are the most logical culprit.

Sorry I thought I had replied to that bit. Anyway this afternoon I am going to rig the bike so I can sit on it and pedal without the chain connected. I will report back on whether resistance kicks in at some point. Ref the other points - yes I have done those tests but would have to say they are inconclusive. I don't know how much resistance there should be when pedalling backwards - there's a bit, but it doesn't feel like my problem when pedalling forwards. The back wheel spins freely when lifted off the ground immediately after stopping the bike when I have the pedalling problem. However my gut tells me that the problem is only displaying itself when the pedalling action is loaded so I suspect it's not going to manifest itself in this afternoon's tests.
Thanks - and please keep the suggestions coming as I want to give a concise report with suggestions when I take the back in to Halfords.
Mike