hissingnoise
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Modifying the Electronic Controls of a Pedal-assist Bicycle. . .
A friend has been attempting some modification of one of these 'battery-powered' bikes!
He got it as a mobile exercise 'thing' and now finds that he is often miles from home by the time his exercise regimen has lost its dubious appeal,
and he figured that by bypassing the magnetic sensor on the pedal assembly, he could switch between 'pedal-assist' and powered biking at will thus
motoring home when he'd had enough of leg-waving.
So, thinking the black box beneath the battery was some kind of electro-mechanical regulator, he exposed its innards, only to be confronted by a
fairly complex piece of circuitry of a kind he knows nothing about.
He asked me to find some info that might help with his 'project', but so far I've drawn a blank. . .
Does anyone here know anything about these contraptions?
Oh, and as caveat I should add that what he is attempting is technically illegal as these bikes are normally exempt from regulations.
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not_important
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Tough question to answer. A little research showed that there are two main classes of sensors, one responds to speed/rotation rate only while the
other senses applied torque. Some models also monitor the selected gear ratio. Some include the motor controller logic as well, being based around a
device like the Freescale 56F8xxx production with multi-channel PWM for driving a brushless polyphase AC motor and multi channel ADC.
My suggestion is that your friend do a better job planning their routes so they do not get so far from home as to make the return pedaling all that
bothersome.
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hissingnoise
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Thanks n.i.---route-planning was my suggestion, too, but he brings a camera with him and when he spots a possible shot in the distance route-planning
goes out the window. . .
I'm using better search-terms now (info dribbling in) but as you say; it ain't easy.
Hooking sensor and magnets to a small, battery-driven motor with a switch could be a last recourse, but bypassing the sensor would still be the ideal.
. .
[edit]
The other thing that occurred to me was that he could possibly, by switching, bypass the controller altogether and power the motor straight from the
battery, but when the motor would strain uphill he'd need to dismount and walk.
And that's assuming that full battery-current/voltage wouldn't overload the motor.
[Edited on 19-11-2009 by hissingnoise]
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densest
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A detailed photograph (tiff/pnm only, jpeg would be unusable because of lost detail) of the controller board and sensor assembly
might let us reverse engineer enough to give suggestions. The pictures would only be useful if all the text on the chips was readable. Repeat after
me, no compression, no jpegs...
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hissingnoise
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No compression, no jpegs, jgeps, pesjg. . .
There will be *some* details for sure!
Next week?
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JohnWW
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Who makes battery-assisted bicycles, and how much do they cost? What sort of batteries do they have? What are their top speed, and range before
recharging, without also using the pedals? Do they use regenerative braking and downhill recharging to top up the batteries?
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not_important
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A Web search on the phrase "battery-assisted bicycles" will answer many of your questions. One dealer in several suppliers is at http://www.nycewheels.com/bikes.html
In much of the developed world, to be classed as a bicycle and thereby avoid vehicle registration and licensing of both the cycle and driver, the
bicycle will not move without the rider pedaling. Those which do run without pedaling are usually classified as motorcycles.
A few models do use regenerative braking, monitoring the motor speed vs that the pedals to determine if braking is needed. These look to be the high
end models, generally torque sensing for both quicker starts and better braking determination.
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JohnWW
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Thanks, Not_Important. I might add that a typical fit human cyclist cannot transmit power at a rate of more than about 0.1 hp (75 watts) through
pedals. Battery-powered electric motors, small enough to be mounted along with a rechargeable battery and small inverter on a bicycle with a
sufficiently strong frame and wide tires also fitted with pedals, are available which could deliver several times this power, up to about 1 hp.
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hissingnoise
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I finally got an image of the electronics from my reluctant cyclist---I don't know useful it is, though!
Does it make sense to anyone?
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not_important
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It would help to know what the large black, red, yellow, green, and blue wires connect to.
With the small amount of information given, we don't even have the make and model of the bike, I'm guessing that the 6 power semiconductors along the
top are part of a 3-phase motor drive. If I'm correct there's no way to just simply bypass the controller, as it is part of the motor. Instead it will
be necessary to figure out how to fool the sensor or the electronics that read it, makinfg it appear as if the rider is madly pedaling away.
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hissingnoise
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Quote: Originally posted by not_important  | | Instead it will be necessary to figure out how to fool the sensor or the electronics that read it, makinfg it appear as if the rider is madly pedaling
away. |
Yeah n_i, I was thinking along broadly similar lines!
But how to go about it seems difficult because with me, knowledge of electronics is 'limited'.
A small b.p. motor rotating magnets (mag. stirrer?) past a second sensor might have merit.
And the info given is pretty thin but I'll get him to take a series of detailed pics that'll show what goes where and with legible print
hopefully.
[edit]
Ooops! I'm repeating myself now. . .
[Edited on 8-12-2009 by hissingnoise]
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not_important
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A sketch might be better than photos, in terms of the general wiring.
Rather than adding a second sensor, which could be difficult to integrate into the existing gear, it could be simpler to simulate the pulses from the
sensor with something like a 555 feeding through a network to match it to the sensor. I would suspect the use of a Hall effect switch-mode sensor for
just picking up a rotating magnet - reading RPM if you will. But if it is a torque sensing model, it would be more difficult to fake.
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Vogelzang
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Maybe someone over here http://www.ratrodbikes.com/forum/ would know
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