Setting a speed limit on bafang mid drive

[chris_n]

Fixing magnets to spokes at the right distance and keeping them there is tricky

Really, can't say in something close to half a century of riding bikes with magnets on spokes (whether for speedo or motor control) I've ever had one move unless it has been physically contacted by something else e.g. loose branches / hedgerows when off road etc.

 

[guerney]

Really, can't say in something close to half a century of riding bikes with magnets on spokes (whether for speedo or motor control) I've ever had one move unless it has been physically contacted by something else e.g. loose branches / hedgerows when off road etc.

Quite, I meant if I had to make mounts or mounting ring for just the small flat magnets...

Fixing magnets to spokes at the right distance and keeping them there is tricky, I'd have to make consistent mounts,

...which I initially assumed @Saneage was initially referring to.

You should have said: I bought a box of 100 spoke magnets from Aliexpress for about a tenner about 8 years ago, and I've only used two.

The only time my magnet becomes misaligned, is when I encounter particularly deep potholes particularly violently - no suspension on my bike, aside from the recent suspension seatpost and Crivit pneumatic "Air Comfort" saddle which has a built-in button pump.

28 for £14.86 inc. shipping

Universal Bike Speedometer Magnet | Universal Magnet Bike Wheel - Universal Wheel - Aliexpress

Smarter Shopping, Better Living! Aliexpress.com

vi.aliexpress.com

Cool! Cheers, bookmarked. I had no idea they were so cheap. Are the magnets as strong as the Cateye supposedly are? I may order a few, after trying four (three Catyes ordered plus Bafang's kit speed magnet), and after I have deterimined the upper limit of magnet signal number allowed by firmware, if someone spurs me into action by posting proof rozzers are seizing bikes after doing no-load speed tests of pedal assist. Until then I probably can't be arsed. Dumb test - all it'd take is for the fuzz in question hopped up on cocaine, donuts and steroids to fit you up by turning the pedals too damn hard. I know all about what they get up to, my mate was with the Met, and that stuff is just the tip of the horrible iceberg. I daren't commit the other stuff to text. The Met turned him into a right **.

 

[saneagle]

Quite, I meant if I had to make mounts or mounting ring for just the small flat magnets...



...which I initially assumed @Saneage was initially referring to.




The only time my magnet becomes misaligned, is when I encounter particularly deep potholes particularly violently - no suspension on my bike, aside from the recent suspension seatpost and Crivit pneumatic "Air Comfort" saddle which has a built-in button pump.




Cool! Cheers, bookmarked. I had no idea they were so cheap. Are the magnets as strong as the Cateye supposedly are? I may order a few, after trying four (three Catyes ordered plus Bafang's kit speed magnet), and after I have deterimined the upper limit of magnet signal number allowed by firmware, if someone spurs me into action by posting proof rozzers are seizing bikes after doing no-load speed tests of pedal assist. Until then I probably can't be arsed. Dumb test - all it'd take is for the fuzz in question hopped up on cocaine, donuts and steroids to fit you up by turning the pedals too damn hard. I know all about what they get up to, my mate was with the Met, and that stuff is just the tip of the horrible iceberg. I daren't commit the other stuff to text. The Met turned him into a right **.

If they're not strong enough, you can stick a plain disc magnet on top. The magnets are very cheap on their own.

 

[guerney]

If they're not strong enough, you can stick a plain disc magnet on top. The magnets are very cheap on their own.

I can try 2, 7, or 14, for 14 spokes on the speed sensor side. I've ordered 7 of the cheapos, I can use the remaining 3 as unusually effective fridge magnets - the same fate awaits all of them, if things don't pan out.

 

[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.

What maximum current does your Shimano controller draw?

If the government wanted to restrict maximum output power, they have oodles of highly paid experts and would have done so.

I can get my acoustic bike's wheel spinning at 60kph by hand, this no-load speed test is absurd.

 

[matthewslack]

What maximum current does your Shimano controller draw?

If the government wanted to restrict maximum output power, they have oodles of highly paid experts and would have done so.

Remember mine's the weakest motor, 40 Nm, the most I ever saw, momentarily, was 13A pulling away uphill before it settled back to normal 3 to 4A.

 

[guerney]

Remember mine's the weakest motor, 40 Nm, the most I ever saw, momentarily, was 13A pulling away uphill before it settled back to normal 3 to 4A.

What voltage? That's a heady 468W @36v and a cop gut-busting 624W @48V! Stones, throws, glass houses etc. I recall you said you might be writing letters if DJI claimed a 250W rating for their new motor.

The DJI will be interesting to watch come to the market, because it seems to be just as powerful as BBSHD.

Are bike manufacturers really going to claim a 250W rating for it? I might be writing letters if that happens.

If they do, it's legal. Unless you write a million letters which appear to be from different people on the electoral register, possibly.

 

[matthewslack]

What voltage? That's a heady 468W @36v and a cop gut-busting 624W @48V! Stones, throws, glass houses etc. I recall you said you might be writing letters if DJI claimed a 250W rating for their new motor.



If they do, it's legal. Unless you write a million letters which appear to be from different people on the electoral register, possibly.

My general point is at that at some point change is likely because the nuttiness of the test for compliance will be rumbled by someone who can't look past it.

Imagine if some company got the manufacturer of those 1000, 1500, 2000W dinner plate direct drive motors that we are all so quick to criticise to produce a 250W marked version? There's nothing to stop that, because it would pass. That's the nuttiness, and all nuttiness eventually fails or gets bottled as a brown spread.

 

[guerney]

My general point is at that at some point change is likely because the nuttiness of the test for compliance will be rumbled by someone who can't look past it.

Imagine if some company got the manufacturer of those 1000, 1500, 2000W dinner plate direct drive motors that we are all so quick to criticise to produce a 250W marked version? There's nothing to stop that, because it would pass. That's the nuttiness, and all nuttiness eventually fails or gets bottled as a brown spread.

I doubt it, the man won't do anything to stymie commerce, particularly in the current worrying economaaaAAARRRRGGGHH: Amazon completely legal oil cooled pavement going cargo liner behemoth toe flattening pedelecs, for example. I fear your letter writing will be in vain, but if it stops your inkjet cartridge drying out, have at it. I use dot matrix, the same ribbon is usable for many years. Include mention of Shimano ebikes. Also, "Guerney says hi". They're used to hearing from me about space graffiti obscuring views of extinction level event asteroids.

 

[saneagle]

My general point is at that at some point change is likely because the nuttiness of the test for compliance will be rumbled by someone who can't look past it.

Imagine if some company got the manufacturer of those 1000, 1500, 2000W dinner plate direct drive motors that we are all so quick to criticise to produce a 250W marked version? There's nothing to stop that, because it would pass. That's the nuttiness, and all nuttiness eventually fails or gets bottled as a brown spread.

You still have this weird idea in your head that there's some sort of power limit. there isn't. We already have weird dinner plate motors that can drag 500kg up a 14% hill, and they're perfectly legal and certified OK to use under EN15194.

 

[matthewslack]

You still have this weird idea in your head that there's some sort of power limit. there isn't. We already have weird dinner plate motors that can drag 500kg up a 14% hill, and they're perfectly legal and certified OK to use under EN15194.

So here's a new angle for you!

Is there any motor that cannot pass the 250W rating test used by EN15194?

All motors that fail when tested at 250W pass, because they can only be rated at less than 250W.

All motors that pass at 250W pass unless they are retested at a higher number than 250W, which the procedure does not require.

Therefore all motors pass!

 

[guerney]

I'm going to write a dot-matrix letter to Cedric asking if he'll rate his Lynch motors 250W:

https://en.wikipedia.org/wiki/Lynch_motor

Lynch Motor Company | Lynch Motor Company Ltd

Lynch Motor company engineer and manufacture brushed DC electric motors for boats, cars, industrial machinery and robotics.

www.lynchmotors.co.uk

 

[saneagle]

So here's a new angle for you!

Is there any motor that cannot pass the 250W rating test used by EN15194?

All motors that fail when tested at 250W pass, because they can only be rated at less than 250W.

All motors that pass at 250W pass unless they are retested at a higher number than 250W, which the procedure does not require.

Therefore all motors pass!

If a motor can only handle 200w before it overheats, it'll fail the 250w test. Any motor that can handle 250w without overheating will pass. It's pretty simple really.

The test involves a trial run to determine the RPM at which the motor has maximum efficiency (least heat), then the actual rating test is done at that RPM. If it can run at that RPM with a load of 250w without overheating, it'll pass. The problem with ebikes is that they rarely run at optimal efficiency because of the change of speed and slowing down to go up hills. If a motor could pass the 250w test exactly with nothing to spare, it would overheat when actually used on an ebike when climbing a hill. It's for that reason that the engineer has to determine how much headroom he needs - typically a factor of three. Add a fat rider, and the engineer might think about a safety factor of 4 or 5.

When I first started riding ebikes, it was quite common for forum members to overheat their bikes when hill-climbing. Some of the early crank-drives (Yamaha I think) had temperature sensors that cut the power to protect the motor, which was the last thing you wanted when you were half way up a steep hill. Keyde hub-motors were even worse. Basically, those motors were not rated high enough to do the job.

 

[matthewslack]

If a motor can only handle 200w before it overheats, it'll fail the 250w test.

But it is compliant with EN15194 because its rated power is 200W, which is less than 250W. So all motors that can't handle 250W pass.

Any motor that can handle 250w without overheating will pass.

Therefore all motors are compliant with EN15194.

When a number appears in a regulation, it is intended to be functional, not cosmetic. Thus this interpretation of motor rated power is not what the law makers intended.

 

[guerney]

When a number appears in a regulation, it is intended to be functional, not cosmetic. Thus this interpretation of motor rated power is not what the law makers intended.

Gawds you're not talking about the "Spirit" of the law are you? The law is not divinied, it's defined. What's intended is what's been defined.

 

[saneagle]

But it is compliant with EN15194 because its rated power is 200W, which is less than 250W. So all motors that can't handle 250W pass.



Therefore all motors are compliant with EN15194.

When a number appears in a regulation, it is intended to be functional, not cosmetic. Thus this interpretation of motor rated power is not what the law makers intended.

It's not compliant if it overheats in the test. You're still letting the paradigm in your head control your thoughts. The paradigm is that low power is OK and high power isn't, but that's not what the law says. The law says it mustn't overheat and the motor can't be used if it's rated at more than 250w. The rule is perfectly functional and understandable. What makes you think that you know that something different to what was written was intended? That's your own head playing games with you.

I know you have a relatively low powered bike. Are you sure it not some sort of jealousy that's making you think like that?

 

[sjpt]

Gawds you're not talking about the "Spirit" of the law are you? The law is not divinied, it's defined. What's intended is what's been defined.

The law is indeed as defined. However, that does not necessarily mean as intended.

 

[guerney]

The law is indeed as defined. However, that does not necessarily mean as intended.

If they intended to define as intended, why didn't they? They're not lacking resources.

 

[saneagle]

It's all moot because I have it on good authority that they're going to remove the power limit shortly. You'll be able to use any motor you want as long as the bike is limited to 15.5 mph. Effectively, we already have that when you see those Amazon delivery vans that are legal 250w EAPCs. This action has come out of the recent parliamentary discussion about raising the limit to 500w, which would have made no sense when we can already have more power.

 

[guerney]

Well, two Cateye magnets have arrived, they're strong and feel good quality - I'm going to try with two at 180 degrees, then three (two Cateye, one Bafang) at unequal angles, to see how Bafang's algorithm copes with calcaulating speed over what must surely be very uneven bumpy terrain, or extremely incompetently trued wheel with a stretchy rim. Will it throw up errors? I'll have a go when I get a mo.