Help building a hub motor generator

[electricpedals]

Hi

we are from UK based electricpedals.com who specialize in building human powered installations.

We're working on a new project that takes conservation films to parts of Africa where there is no electricity:

http://electricpedals.com/2011/09/15/our-pedal-powered-field-cinema-is-going-to-dr-congo/

Anyway present we are using one of our bicycle generators:

http://electricpedals.com/bicycle-generator/

Which are hugely inefficient and of course rely on a bicycle being available.

What we would like to build is a generator based on a hub motor.

There is a really good video describing what we'd like to do here:

http://www.youtube.com/watch?v=OD1gSx92DuM

So key question:

1) In order to exclusively use the hub motor as a generator, do we need a hub motor without an internal controller?

2) We to generate not more than 100watts DC, so which motor would you recommend?

Thanks for your help!

Colin

[Bikemad]

Hi Colin andto the forum.

A speed controller is not required, but you will need to use suitable rectifier diodes to convert the AC output to DC.
I'm assuming you would also need some form of voltage regulation to provide a stable output voltage for your battery or electrical devices that it will be powering.

I would suggest the minimotor might be the best hubmotor to use that should suit your requirements:

It is small, compact and probably the cheapest and lightest of the GM hubmotors.

The minimotor has a built in gearbox which should produce a higher output at a lower pedal rpm than any of the direct drive hubmotors, but unfortunately for you, it also has an inbuilt unidirectional clutch (freewheel device) which prevents the motor from being driven in a forward direction by the wheel.
Because of this, you would need to drive the motor in a reverse direction to enable it to work as a generator. This would mean that a fixed gear (without a threaded freewheel) would need to be secured to the motor casing by some method other than the threaded boss, otherwise it would simply unscrew itself under load.
This could be achieved by reversing the axial orientation of the motor and fitting a purpose made sprocket to the brake disc mounting holes.

If it was being fitted to something similar to your home made energy cycle (see attachment) the motor could be installed in its normal position and simply move the chainwheel to the opposite side of the frame to line up with a sprocket mounted on the brake disc side of the motor casing.

Alan

[electricpedals]

Hi Alan,

thanks for the comprehensive reply!

Well you've answered quite a few questions for me having recently fitted one of the mini motors to a standard bicycle and noticing that it only seems to work backwards! Imagine my frustration in not understanding why! Also, at that point I had no idea that this forum existed.

So I think you're right, we'll cut the mini motor we have on the existing wheel off and give it a try. As you pointed out, we'll have a look at the brake disc mounting.

One other question, I noticed that along with the three main wires, there are a load of smaller, I assume control wires. Can I assume we ignore these?

In terms of voltage regulation, this is the easy bit! We'll use a 58Farad ultra capacitors to smooth out the voltage and give us a little storage and either a charge controller or relay to prevent over charging.

What we are looking to build is a fully collapsible generator that can be used out in the field, i.e. congo, uganda etc., So it will need to be super compact and light. Quite an interesting problem to solve!

Thanks
Colin

p.s. have you build anything like this before? Sounds like you have?!

[Bikemad]

I noticed that along with the three main wires, there are a load of smaller, I assume control wires. Can I assume we ignore these?
p.s. have you build anything like this before? Sounds like you have?!

Colin,

The five small wires (Red, Black, Yellow, Green and Blue) are connected to the three Hall Effect Sensors, which are only used to let the speed controller know the exact position of the magnets, so it knows which sets of winding to energise. As you won't be using a controller for your intended use, these wires can simply be ignored.

I once considered building a wind generator just for fun, but I had (and still do have) too many other things on the go. I seem to start lots of things, but never manage to finish everything I start!

If you're interested, and would like to get a better idea of what goes on inside the minimotor, take a look at this post where I've tried to explain how the epicyclic gears and unidirectional clutch actually work.

Early minimotors did not have the ability to bolt a brake disc on, the attached picture below shows a later minimotor casing with the brake disc fixings.

I also found this superb diagram that Perbear produced which shows the all important dimensions for the brake disc mounting bolt holes:



Alan
 

[DirtyGinge]

Hi All

you could take the motor apart, and freeze the clutch, mechanically welding etc?, then the bike could run as standard without changing sides......

Regards

[electricpedals]

Hi Alan,

I read the article, and thanks for that... yeah it was a bit heavy but I get the general principles! Definitely one for the bookmark!

Regarding reversing the motor to act as a generator, I shall look to see if it's possible to use a fixie wheel sprocket and lock nut. Seeing as this type of arrangement is all the rage here, it might prove to be a good option and avoid any machine work.

In terms of the output I have the 36v version MBG36R. Do you see any issue in configuring this to generate a rough constant of about 15v DC?

I don't suppose you know if a wiring diagram to go from the 3 wires AC to 2 wires DC? As you can see, it's all a bit new!

Thanks
Colin

p.s. I'll write back an keep you up-to-date!

[electricpedals]

Hi All

you could take the motor apart, and freeze the clutch, mechanically welding etc?, then the bike could run as standard without changing sides......

Regards

Thanks mate, I'll leave it to the experts to comment one whether this is possible or not. Looking at the previous post and all those nylon gears, I'm not sure that it's easily possible!!?

[DirtyGinge]

yesterday I did a test, unplugged my battery and cycled ( on a non GM controller)
 
The Magic Pie will generat 20V at 10MPH, I drew off about 1 amp of power with all my lights and accessories, there was no dimming at all, so I reckon there was plenty more amps available, but have no way to test unfortunately...

I know the DD pie is heavy as most DD are, but mechanically, there isnt much to go wrong if you are in the middle of nowhere.....