Setting a speed limit on bafang mid drive

[guerney]

I have exactly the same issue. Have you managed to find a way around it? I find it hard to explain to police why the motor is still running when it passes 15mph maximum speed limit.

When riding, pedal assistance on my BBS01B conversion stops abruptly at 25kph, which can be hard on the old knees if unprepared: Change "Stop Delay" and Stop Decay" parameters if you want a similarly unpleasant cease of assistance experiences:

https://edrivenet.com/bafang-programming/




I very much doubt the police are testing pedal assist top speed, with the driven wheel raised off the ground... but if they ever do, simply reduce speed limit to 10kph, or whatever speed tests relevant, for absolute certaintude of stress-free legal pedelecing? Although riding your bike would become a miserable experience, this would be offset by reduced police fear levels. What the resultant despair managed this way may be, varies with the individual. I'd certainly feel deep despair pedelecing at 10kph, such much be managed lest it overwhelm - we must strive against all odds to find silver linings in every situation, while knowing full well it's dark before things go completely black.

 

[Grigoriy]

When riding, pedal assistance on my BBS01B conversion stops abruptly at 25kph, which can be hard on the old knees if unprepared: Change "Stop Delay" and Stop Decay" parameters if you want a similarly unpleasant cease of assistance experiences:

https://edrivenet.com/bafang-programming/

View attachment 62470


I very much doubt the police are testing pedal assist top speed, with the driven wheel raised off the ground... but if they ever do, simply reduce speed limit to 10kph, or whatever speed tests relevant, for absolute certaintude of stress-free legal pedelecing? Although riding your bike would become a miserable experience, this would be offset by reduced police fear levels. What the resultant despair managed this way may be, varies with the individual. I'd certainly feel deep despair pedelecing at 10kph, such much be managed lest it overwhelm - we must strive against all odds to find silver linings in every situation, while knowing full well it's dark before things go completely black.

I've tried your settings with exactly the same result - after 15mph motor slows down considerably but still spinning and you can hear it working. This might be a problem to explain that to police when they'll stop your and check maximum speed by lifting back wheel. So war I couldn't find any solution to stop motor spinning exactly at 15mph.

 

[guerney]

I've tried your settings with exactly the same result - after 15mph motor slows down considerably but still spinning and you can hear it working. This might be a problem to explain that to police when they'll stop your and check maximum speed by lifting back wheel. So war I couldn't find any solution to stop motor spinning exactly at 15mph.

Are the police testing maximum speed like that? If this really worries you, reduce speed limit to below 15.5mph/25kph in small increments until you judge it to pass such a daft copper roadside maximum speed test?

The prospect of coppers doing such a stupid roadside test hasn't worried me enough to do a no-load speed limit test on my own bike, but I might try at some point out of interest. Who goes nowhere pedelecing on their driveway stationary with the rear wheel spinning in the air?

 

[Peter.Bridge]

I've tried your settings with exactly the same result - after 15mph motor slows down considerably but still spinning and you can hear it working. This might be a problem to explain that to police when they'll stop your and check maximum speed by lifting back wheel. So war I couldn't find any solution to stop motor spinning exactly at 15mph.

I don't think this will ever work, even if the motor stops at exactly 15 mph, an unloaded wheel will be massively accelerating when it gets to 15 mph and the motor cuts out and end up hitting a ridiculous top speed. I tried this with a TSDZ8 , set to 25 km/h max assist speed and the max speed registered was about 60 km/h with the back wheel raised and using a throttle. The motor didn't kick back in again until the speedo went below 25 km/h

 

[matthewslack]

I would expect a 'wheel in the air' test to be continued for long enough to establish the cutoff speed: long enough for any overshoot to work itself out. If your motor is still assisting above 25 km/h after say 5 seconds then there is clearly a problem somewhere.

 

[guerney]

If a cop wanted to test my bike like that, I'd insist he ride it. Then I'd expect he'd offer to buy my most excellent bike.

 

[matthewslack]

I don't think this will ever work, even if the motor stops at exactly 15 mph, an unloaded wheel will be massively accelerating when it gets to 15 mph and the motor cuts out and end up hitting a ridiculous top speed. I tried this with a TSDZ8 , set to 25 km/h max assist speed and the max speed registered was about 60 km/h with the back wheel raised and using a throttle. The motor didn't kick back in again until the speedo went below 25 km/h

What gears have you got on that bike?!! And what maximum cadence does the TSDZ8 manage? I'd need to be at 130rpm with 700c, 38T/11T to read 60km/h.

That degree of overshoot is in my view a clear fail. Remember the wording: "...progressively reduced approaching 25km/h, and cut off completely above...". Overshoot to 60km/h shows an algorithm acting too slowly and far too late.

I am not clear whether the Woosh 250W labelled TSDZ8 is of different spec to the 750W ones. A big overshoot from full throttle on a 750W motor would be understandable.

 

[guerney]

What gears have you got on that bike?!! And what maximum cadence does the TSDZ8 manage? I'd need to be at 130rpm with 700c, 38T/11T to read 60km/h.

That degree of overshoot is in my view a clear fail. Remember the wording: "...progressively reduced approaching 25km/h, and cut off completely above...". Overshoot to 60km/h shows an algorithm acting too slowly and far too late.

I am not clear whether the Woosh 250W labelled TSDZ8 is of different spec to the 750W ones. A big overshoot from full throttle on a 750W motor would be understandable.

There isn't that level of overshoot in use on the road, so how is a no-load speed test relevant?

 

[guerney]

I've tried your settings with exactly the same result - after 15mph motor slows down considerably but still spinning and you can hear it working.

What speed does the assist work up to? On which gear?

 

[Peter.Bridge]

What gears have you got on that bike?!! And what maximum cadence does the TSDZ8 manage? I'd need to be at 130rpm with 700c, 38T/11T to read 60km/h.

That degree of overshoot is in my view a clear fail. Remember the wording: "...progressively reduced approaching 25km/h, and cut off completely above...". Overshoot to 60km/h shows an algorithm acting too slowly and far too late.

I am not clear whether the Woosh 250W labelled TSDZ8 is of different spec to the 750W ones. A big overshoot from full throttle on a 750W motor would be understandable.

The motor assist stops at 25km/h, just the wheel is accelerating massively with no load so will reach a ridiculous top speed. The motor isn't driving the wheel at that speed, the gearing is 44t/11t

 

[matthewslack]

The motor assist stops at 25km/h, just the wheel is accelerating massively with no load so will reach a ridiculous top speed

Newton's laws of motion might object to an object accelerating with no applied force. Acceleration stops the moment power is completely cut off.

A sensor might well be triggering at 25km/h, but the power is clearly not being cut off immediately. The algorithm will ramp down the power, when signalled to do so, but clearly is not 'tuned' to handle the TSDZ8 motor response to throttle.

 

[matthewslack]

There isn't that level of overshoot in use on the road, so how is a no-load speed test relevant?

Completely relevant as it demonstrates compliance, and is very easy to perform, so is likely to be used.

The main risk of overshoot is of it being mistaken for non-compliance, to which the answer should be 'give it time to settle down' if ever challenged. That could be helped along by a little bit of rear brake.

 

[guerney]

@matthewslack - have you tried the no-load maximum speed test on your Shimano mid-drive bike(s)? Would your bike be jailed?

 

[guerney]

Completely relevant as it demonstrates compliance, and is very easy to perform, so is likely to be used.

The main risk of overshoot is of it being mistaken for non-compliance, to which the answer should be 'give it time to settle down' if ever challenged. That could be helped along by a little bit of rear brake.

How is a no-load speed test relevant to laws clearly about how the bike functions on the road? A 20" wheel has less momentum than a 26", but in use on the road that doesn't make much difference.

 

[matthewslack]

@matthewslack - have you tried the no-load maximum speed test on your Shimano mid-drive bike(s)? Would your bike be jailed?

You'd hate it!

It is staggeringly good. An incredibly gentle but firm reduction and then cessation of assistance all within 0.5 to 1 km/h of 25.

This is not a hard task for these bikes: they are designed to manage the constant delicate torque adjustments needed by off road riders negotiating wet rocks and tree roots. Speed enforcement is chicken feed.

 

[guerney]

You'd hate it!

It is staggeringly good. An incredibly gentle but firm reduction and then cessation of assistance all within 0.5 to 1 km/h of 25.

This is not a hard task for these bikes: they are designed to manage the constant delicate torque adjustments needed by off road riders negotiating wet rocks and tree roots. Speed enforcement is chicken feed.

I guess not much torque is being detected applied by your hand - hardly a real world test is it? Totally absurd way to test maximum speed, for laws which apply to the road, not wheels hanging and spinning in the air.

 

[matthewslack]

How is a no-load speed test relevant to laws clearly about how the bike functions on the road? A 20" wheel has less momentum than a 26", but in use on the road that doesn't make much difference.

Again, the settled speed attained is what matters. Why would there be a difference between the maximum assistance speed demonstrated in a wheel off the ground test, and a test ride? Surely they give the same answer, provided any speed overshoot is allowed to settle?

The risk comes mainly from the opportunity for misinterpretation of overspeed, but in the 60km/h example I would suggest another risk appears: how can a 250W rated motor manage that?

Much trouble is avoided by not raising suspicions.

 

[Sturmey]

I notice that both the tsdz/vlcd5 and the kt controller hub setup has the facility to fit six magnets on the wheel or in the hubs. ( I am not familar with the Bafang) I notice that with the single magnet setup , there is a delay/lag with the speedo showing the correct speed but to some extent this could be expected as I presume the software has to count the pulses and they are possibly not coming in fast enough with a single magnet. So I am wondering is there some advantage with six magnets? Just a thought (or possibly idle speculation) on a wet day.

 

[guerney]

Again, the settled speed attained is what matters. Why would there be a difference between the maximum assistance speed demonstrated in a wheel off the ground test, and a test ride? Surely they give the same answer, provided any speed overshoot is allowed to settle?

The risk comes mainly from the opportunity for misinterpretation of overspeed, but in the 60km/h example I would suggest another risk appears: how can a 250W rated motor manage that?

Much trouble is avoided by not raising suspicions.

As I said, I haven't tried the no-load speed test on my own bike, but it wouldn't surprise me if there was some overshoot, because in my limiting throttle to 6kph no-load speed test, the Bafang controller isn't terribly good at stopping assist at the designated speed with the wheel off the ground, yet is perfectly fine in use on the road.

If I do the test, I may upload yet another brain deadening video to bore you with.

There's slight overshoot on the road, but never more that 0.4kph, here's assist ceasing uphill:

 

[saneagle]

Again, the settled speed attained is what matters. Why would there be a difference between the maximum assistance speed demonstrated in a wheel off the ground test, and a test ride? Surely they give the same answer, provided any speed overshoot is allowed to settle?

The risk comes mainly from the opportunity for misinterpretation of overspeed, but in the 60km/h example I would suggest another risk appears: how can a 250W rated motor manage that?

Much trouble is avoided by not raising suspicions.

The problem is overshoot that all ebike motors have since the speed measurement is a lagging indicator. The power is on, accelerating the motor, but with no load, the acceleration is so fast that the speed overshoots before the controller gets feedback to switch off the power. The main controlling factor is the angular momentum of the wheel (mass).