Bicycle Dynamo powered by model I.C. engine

[Brian Rupnow]

Today I tested the bicycle generator (dynamo) that was sent to me by a fellow member. Not knowing what voltage this thing produces, and not having a voltmeter, I robbed a 2.9 volt rated battery out of a flashlight and jerry rigged a pigtail and alligator clamp to the bulb and the output terminal of the dynamo. I have a small cogged drive belt that I salvaged off something, and holding a 1" pulley in the milling machine chuck and pulling the belt tight I was able to light the flashlight bulb.  This satisfies me that the dynamo does indeed produce electricity. It did need to be rotating at a pretty respectable rpm to light the bulb, but I don't have actual figures on the rpm.  I intend to machine a 0.8" diameter flat pulley with side flanges on it to press fit onto the knurled end of the dynamo, and use the same belt that is in the picture to drive the dynamo from the 2" diameter starter hub on my side valve engine. This will give me a ratio of 2.5:1, so if the engine is rotating at 1500 rpm, the dynamo will be revolving at 3750 rpm. I have to design and fabricate a mounting base for the dynamo and a belt tightening mechanism, as I want the dynamo and its base to be a "composite unit" separate from the engine.--Stay Tuned!!!

[Brian Rupnow]

I think I have most of this sussed out now. I have a short length of 24DP rack left over from when I built the sawmill, and I will build the mounting plates from 3/4" aluminum. The sprag will be a bit of 1/4" square steel key stock. I want to be able to start the engine with the belt loose under "no load" conditions, then tighten the belt gradually until the revs come up on the dynamo. The sprag will hold the belt tight. I haven't modeled the release mechanism yet. I have to go out and buy a bulb and holder yet.

[Roger B]

That's a much more sophisticated system than I used (a piece of wood pivoted on a woodscrew) 

Having tried this with a much smaller capacity engine (2.5cc) many years ago I am following with interest   

[Steam Haulage]

Hi Brian,

These dynamos were designed to be powered by the bicycle rider, the faster you (or me whilst I was at school) pedalled the brighter the light. The power is transmitted to the dynamo by the serrated rotor pressing on the sidewall of the tyre by means of a spring mounting. The mounting for the dynamo would have facilities to hold the rotor away from the wheel in daylight hours. In the winter months the police would be enforcing the lighting regulations. For getting to school battery lamps were beyond the average schoolboy's funding capabilities and these units were very common. Tyres were available with a track moulded into the side wall, without this you could go through a tyre in a couple of winters. There are still some in use for their original purpose.

To find the necessary speed think of the serrated drive rotor against a 24 inch diameter bike wheel with the bike moving at a maximum of 30 mph, ( UK speed limit in built-up areas) to get the speed in sfm and work from there.

I'm afraid the sums are beyond me at this time in the evening.

Jerry

[Nerdz]

For what its worth, why not use a 1/4-20 "lead screw" to adjust tension?

[mklotz]

I'm afraid the sums are beyond me at this time in the evening.

circumference of wheel = pi *24 in = 2*pi feet

30 mile/hr * 5280 feet/mile * 1/60 hr/min * 1/(2*pi) revolutions/foot = 420 rpm

[Allen Smithee]

I've made several on-board generator systems for large model aeroplanes simply using a cheap brushless outrunner motor and three diodes connected to a regulator circuit. The idea was to enhance safety by making the on-board batteries a back-up system rather than the primary flight control power supply. It's very easy to do, and you can simply select a motor which produces the required voltage at (say) 20% engine rpm. The biggest one I did could deliver 30A at 6v (one on each engine of a 170" span, 90lb AUW B26 being built by a friend as a commercial order for a wealthy colonial customer) to drive a total of 29 servos, an electro-hydraulic retractable undercarriage system, landing/nav lights and the ignition systems of the two engines via four isolated DC power busses. These were simply driven with tothed belts from a ring-sprocket behind the prop driver of each engine. We did consider trying tio make them starter/generator units, but that would have needed a much chunkier belt system and we were tight for space, so we didn't bother.

The model has been flying reliably for five years now, and the customer reports that the onboard generators have made it much less sensitive to battery health (which has been an issue on several of his other large models).

AS

[Brian Rupnow]

I made the pulley and pressed it on. That went well, but the pulley was so smooth the belt slipped badly. Next trick was to go all around the pulley with my automatic punch and "upset" the metal to give a little something for the belt to grip. If I was smart instead of good looking, I would have knurled it while it was still in the lathe.---Nah, that wouldn't have worked. I just checked and the knurling tool is too wide to fit between the flanges.

[Brian Rupnow]

There was a bit of method to my madness!!! By building and installing the pulley first, I was able to start the engine this morning and drive the dynamo via drive belt from my engine itself. Remember, the only test done previous to this was to drive the dynamo from my milling machine arbor. At any rate, even at half throttle the engine doesn't even grunt, and the lightbulb lights up like the lighthouse at Rhodes!!!---A very positive result!!! I needed to check this out before I wasted time building any of the other parts. Now that I know the engine drives the dynamo with no problem, I can proceed.

[Roger B]

  

[Nerdz]

Im curious to know how much current/voltage it produces under different loads. You pretty much have a small back up generator.

[Brian Rupnow]

I believe everything that has been said about the effort to pedal a bicycle with one of these installed on it. I used to own one many years ago. Fortunately, the engine seems to run it with no problem.

[Brian Rupnow]

I am always pleased when whatever I build looks like the 3D model. The only change I made is that I didn't but the large radius on the bracket holding the dynamo, because I may need it to have a flat top for mounting the bulb. I haven't totally worked that out yet, but I will tomorrow. So far--So good!!!

[ths]

I like that belt tensioning system Brian, very neat indeed. Hugh.

[Brian Rupnow]

Thanks Hugh---Of course there is more to this than just mounting the dynamo itself. The squeeze bolt is going to morph into a handle, and I have added a bulb, bulb socket, and bulb socket support. The only remaining unknown is the release handle for the sprag.