Front Wheel Lock Up

[Caph]

I may be being paranoid here but every time I get up to about 30mph a nagging worry starts up in the back of my brain. Could the front hub motor lock up for any reason with the obvious very dangerous results?

Does anyone know if this is even possible? Or am I worrying unduly?

 

[rog_london]

I may be being paranoid here but every time I get up to about 30mph a nagging worry starts up in the back of my brain. Could the front hub motor lock up for any reason with the obvious very dangerous results?

Does anyone know if this is even possible? Or am I worrying unduly?

I think I can answer that one - and it depends. If the hub motor incorporates a one way roller clutch (otherwise known as a freewheel) then you're almost certainly OK. What happens is that if the power is off the motor can coast to a stop within the hub - which has the additional advantage that there is no drag.

Without a roller clutch, a fault in the controller could lock the motor and therefore also the wheel. The type of fault is the sort which keeps one or more motor windings switched hard on - a blown drive transistor, for example.

How can you tell? Probably the simplest way is just to move the bike backwards and forwards with the power off. If there is some slight resistance when wheeling backwards but not forwards, then you have a freewheel. It might be easier to tell if you can get the front wheel off the ground and move the wheel back and forth - it's more sensitive that way.

Rog.

 

[flecc]

I've never heard of this occurring Caph, and there's very little chance of it. About the only thing that could do this is if a piece of loose material jammed in the orbital gears, but that would have to come from somewhere. The way these motors are constructed means there aren't any bits likely to come loose, and they could only come from the open side of the stator and rotor assembly.

On the typical Hall motors that our bikes have the gears are on the closed outer plain side of the rotating drum of the motor, so there's no path for any loose bits to reach them even if any occurred. In any case, a high proportion of motors use nylon gears which tend to strip rather than lock if any fault condition starts.

Though I've never heard of it, one of the permanent magnet bars of the motor could conceivably come loose, but the stator is so close packed that the magnet bar would just skid across it's surface, making a noise but nothing else.

If you have a look at this page on my website, scroll down to the three photos of a stripped hub motor, you'll see a description below of the relationship of the parts, illustrating the above. The diagram of how it operates is at the top of the page.
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[Caph]

Thanks for that, I feel a lot happier now.

My front wheel has considerable resistance when rolled backwards (and none that I can tell when rolled forwards) so I guess I've got a freewheel.

I think in part I was worried because you can't open the motor to see what's in there. The pictures obviously help in that respect.

 

[rog_london]

Thanks for that, I feel a lot happier now.

My front wheel has considerable resistance when rolled backwards (and none that I can tell when rolled forwards) so I guess I've got a freewheel.

I think in part I was worried because you can't open the motor to see what's in there. The pictures obviously help in that respect.

Jolly good. The Wisper - which has a rear hub motor - also has a freewheel, but it's quite hard to detect by the above test, as the motor seems to have almost no resistance to motion. I guess it does rather depend on how the motor is geared (if at all) within the hub.

Rog.

 

[flecc]

Jolly good. The Wisper - which has a rear hub motor - also has a freewheel, but it's quite hard to detect by the above test, as the motor seems to have almost no resistance to motion. I guess it does rather depend on how the motor is geared (if at all) within the hub.

Rog.

In part this is due to it being in the rear wheel Rog. In a front wheel these same Suzhou Bafang motors show the resistance more as the forks flex very slightly.

On your bike, if you turn it over and slowly pull the wheel round backwards by hand, you'll feel the individual magnet pulls like pulses as the motor rotates. At these low speeds it's this and not the gears that provides the resistance.
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[rog_london]

In part this is due to it being in the rear wheel Rog. In a front wheel these same Suzhou Bafang motors show the resistance more as the forks flex very slightly.

On your bike, if you turn it over and slowly pull the wheel round backwards by hand, you'll feel the individual magnet pulls like pulses as the motor rotates. At these low speeds it's this and not the gears that provides the resistance.
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I know it's there, because if you power the wheel clear of the ground (using the throttle) when you close the throttle you can hear the motor come to a fairly rapid stop, leaving the wheel spinning....

I can feel it OK - roller clutches have a distinctive way of engaging, as there is a tiny bit of slack before they 'lock', although unlike a standard bike freewheel they are completely silent (no ratchet clicking away). This is a general observation not specifically related to bike motors.

I was interested that Caph's motor shows quite a bit of drag when driven in reverse, as that's not the case with the Suzhou motor fitted to the Wisper. Also the very slight amount of drag is hidden quite well by the fact that you're also driving the derailleur, cranks and chain.

Rog.

 

[flecc]

I was interested that Caph's motor shows quite a bit of drag when driven in reverse, as that's not the case with the Suzhou motor fitted to the Wisper. Also the very slight amount of drag is hidden quite well by the fact that you're also driving the derailleur, cranks and chain.

Rog.

The spindle is internally shimmed at assembly to set the lateral location of the stator/rotor assembly in the hub shell and that can vary a bit, affecting the degree of gear meshing into the toothed ring and hubshell wall. When I set up my Q-bike rear hub motor I stripped and reassembled it three times to achieve the best combination of quietness with free running. They still gradually change over time though, and the way the spindle is tightened into the frame can affect the sound and free running.
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[kraeuterbutter]

it happend madeba with his recumband bike (20" wheel in front)

GEFAHR !!! Nabenmotor YPW01 von Specialbikes.at - Pedelec-Forum

the motor locked at 45km/h
it was, because its an discmotor (go to the thread, look at the pics)
a magnet came loose and blocked the motor..
its a geard motor but without freewheeling

motor total damage,
some damage to the bike,
some wounds for the driver

 

[Alex728]

OUCH! (not just the prang, but it must cost €€€ for this unfortunate man)

I have let my German get shockingly rusty (and cheated by using google translate to follow much of the thread) but I would certainly agree with this comment on the incident!

Hallo Markus,

was dir passiert ist, ist natürlich Sch....,

Incidentally, on the pedelecs.de forum does everyone mostly use Hochdeutsch or their local dialects (or a mixture of both as on English forums?)? As an aside it was an Austrian chap in the 1980s called Falco which made me continue with trying to learn some German privately even though I couldn't study two languages at high school (silly British rules in the 1980s) - I wanted to know what he was rapping about!

 

[kraeuterbutter]

hoste holt glick, dass de durt im deitschn Forum olle mehr oda weniga noch da Schrift schreiba, sunst würd da Google Translate jo a nix hölfa..

iam Austrian too...
Falco is meanwhile dead (car accident under drugs influence),
he was internationally our biggest pop-musician
behind my house in vienna theres a staircase named after him, die Falcostiege ("the falco staircase")

for the motors: i feel preety safe on my bafang freewheel front hub..
i think:
when the motor locks -> there is still the freewheel, so no crash
if the freewheel locks -> the motor can still spin, its like having a non-freewheel motor, so not catastrophe, no crash

if motor and freewheel lock at same time (how probable is that ??),
there are still the plastic-teeth of the gears which would rub off and allow the hub-housing still to turn -> so no crash

i think there are many many other things that can go wrong on the bike causing me to crash before the freewheeled bafang would lock..

also non mechanical faults, electrical (shortening phases, blown fets, ...) which can cause a motor to turn very heavy or even block -> there is the freewheel which would avoid a crash

as said, i feel preety safe

 

[flecc]

i think there are many many other things that can go wrong on the bike causing me to crash before the freewheeled bafang would lock..

- - - and the magnet to stator pole distance on the Bafang motors is so small that a loose magnet would just slide along along the pole surfaces anyway, so very unlikely to lock up.
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