Electric bike, Strange power anomaly

[pappajohn]

Out on my bike yesterday and noticed something odd.
3rd gear of 5 and 2nd level of assist just tooling along on the level and slowed pedaling to slow down a little..... And it didn't!!!!
The motor maintained the same speed even though the pedals were only just rotating and zero load.
Stopped pedaling and the motor stopped as it should.
Tried again but this time braked slightly rather than fully stop pedaling and the motor again stopped as it should.
Not complaining as effectively I have a throttle bike as long as the pedal crank is turning a bit, albeit a fixed throttle, which is CE certified as a pedal assist bike.

 

[SuperMike]

Are you sure or on the fall down juice again, Uncle PPJ.

 

[Geo]

He's only a pint and a half from perpetual motion Mike

 

[pappajohn]

Come on chaps, not a drop has passed my lips since Saturday night.
Sunday was a blur but back to my sober self by Monday.

 

[Guigsy]

My wife games her electric Brompton all the time. It has a motor in the front wheel and it has no idea what gear you're in. All you have to do is turn the pedals and it'll keep pushing. She just windmills along while the bike does all the work. Telltale sign that she's cheating is you can hear when the freewheel in the rear hub engages if she accidentally pedals fast enough to do a bit of work.

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[pappajohn]

My wife games her electric Brompton all the time. It has a motor in the front wheel and it has no idea what gear you're in. All you have to do is turn the pedals and it'll keep pushing. She just windmills along while the bike does all the work. Telltale sign that she's cheating is you can hear when the freewheel in the rear hub engages if she accidentally pedals fast enough to do a bit of work.

Not a fault on mine then.
I did notice if I change up a gear or go up a slight incline and make the motor work harder it can't, it just gets slower unless I put some effort in as well.
Whatever the rate of work the motors doing when I slow pedal is the limit... No more, no less.

 

[Guigsy]

I think ebikes with the motor in the bottom bracket can infer how hard you're pedalling and adjust their power to match. Most bikes with wheel mounted motors effectively just add a fixed amount of power regardless of how hard you're pushing.

 

[Lenny HB]

Has it got crank sensors? could be the Cadence sensor playing up.

 

[Guigsy]

Has it got crank sensors? could be the Cadence sensor playing up.

They have, but all they detect is that you are turning the cranks. They have no idea what gear you are in, so they don't know whether the speed you are turning the cranks is actually doing any work. They can't detect how hard you are pushing. It's just an on-off switch the same as a throttle button.

 

[Lenny HB]

I think ebikes with the motor in the bottom bracket can infer how hard you're pedalling and adjust their power to match. Most bikes with wheel mounted motors effectively just add a fixed amount of power regardless of how hard you're pushing.

Very true, if you want to use Turbo mode on a Bosch you really have to put some effort in or it will tell you to sod off. ?

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[Guigsy]

Very true, if you want to use Turbo mode on a Bosch you really have to put some effort in or it will tell you to sod off. ?

Yeah, I'm under the impression that the Bosch type bottom bracket mounted systems can be much smarter.

The modes on the e-Brompton (and I assume most other hub mounted ebikes) just sets the power level it kicks out when it comes on. It is smart enough to blend the power in and out smoothly, but it is just 'on' when you pedal (regardless of effort and cadence) and 'off' when you stop/freewheel. Don't get me wrong, it's perfectly adequate 99% of the time. However, don't try to 'track stand' on an e-Brompton (it accelerates off when you were just trying to balance).

 

[Neil Bedwin]

....and if you squeeze the brake lever you operate a switch that turns the motor off even if you are still peddling.

 

[pappajohn]

Has it got crank sensors? could be the Cadence sensor playing up.

Yes, it appears to have a Hall sensor on the crank housing and a perforated wheel on the pedal crank.

 

[pappajohn]

They have, but all they detect is that you are turning the cranks. They have no idea what gear you are in, so they don't know whether the speed you are turning the cranks is actually doing any work. They can't detect how hard you are pushing. It's just an on-off switch the same as a throttle button.

That's exactly it.
If I change up a gear the load on the motor becomes too much so it slows unless I switch to a higher level of assist..... Or but some leg effort in.

 

[pappajohn]

if you want to use Turbo mode on a Bosch

The Bosch motor and electronics probably cost more than this complete £600 bike.
It's going to be pretty basic electronics.

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[Neil Bedwin]

Sounds to me like everything is working as it should.

If I am in level 5 (the top) then the motor wants to power me to 15mph no matter how fast the pedals go round. If I lower the power level then the speed decreases unless I add leg power.

So if you were on the flat and peddling then it powered you to the speed you were doing.

I find as I approach a junction I change down a few gears, turning the crank helps the down shift.....and makes the motor drive me forward! Have to be gently on the brake at the same time so the motor is disengaged.

 

[pappajohn]

....and if you squeeze the brake lever you operate a switch that turns the motor off even if you are still peddling.

Yes, I know that which is why I mentioned it to say it was working as expected... But thanks for pointing it out anyway.

 

[Guigsy]

My wife thinks her e-Brompton is brilliant... and so do I as we can ride together.

However, I tend to spin the pedals pretty much all the time and then adjust the amount of effort I'm putting in. When I ride her bike, it interprets this as 'motor=on' all the time, so I can end up accelerating when I wanted to slow down. Maybe I'd get used to it, but the few times I've ridden it, I get annoyed with it. Wife thinks I'm just being awkward (she's probably right).

I've also got a reasonable mountain bike that I take trail riding (mud, armour and falling off type riding). If I get an e-MTB, it's definitely going to have to be a Bosch type system.