Motorized bicycle project

I assume you're in the US, so this may be of limited use, but I expect the US has something similar:

I would encourage him to ride the non-motorized bicycle. Better yet, they make a bike that attaches to the rear of an adult bike so you and him can both ride and pedal together.

The paybacks in health will stay with him all his life.

I wish I had a link for what I am describing, perhaps someone else can.

Wes

I think you'll only have about 1/4 of the power at 12 volts (assumes the resistance of the motor is more or less constant once its running). That's about 1/16 hp to drive the bike. With so little power, you won't get into any trouble, but may well be dissapointed. If you did have enough power to drive the bike at the speed you suggest, you would need some sort of speed control.

Interesting idea about reversing to apply the brake, but again, this system would apply FULL brake, all at once!!!!

Pete Stanaitis

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Ignoramus26157 wrote:

Remember, it is a kid's bicycle. He weighs about 40 lbs. I did some quick power calculations. The most power I can put out is go up a stairs, skipping every other step, briskly. That amounts to 150-200 watts from a 190 lbs man and is a quite extreme effort.

A 40 lbs kid riding a bicycle, on a 40 lbs bike, uses a lot less power than that. I would say, safely 2/5 of that based on weight, further divided by perhaps 3 due to efficiency of bicycle. So, we get approximately 20 watt of a "boy on bicycle" output. This 1/4 HP motor, turned into a 1/16 HP motor, would deliver 46 watt, which is plenty or maybe even too much (acceleration too sharp).

I would rather err on a safe, low power side here.

I'll see. 12v motor drives are available. I think that I can start without one.

Good point. Reversing can be done through a series resistor.

His bike also has a handle actuated brake (not working at the moment).

He needs a speed control Otherwise he can't approach anything except full tilt. And full tilt will be much faster going downhill, slower going up. I doubt that the motor will be able to produce a panic stop, or even a quick stop--and if it can, then he will have too much braking most of the time.

I remember recently seeing a guy with an electric assist on his bike and I stopped him to ask about it, the battery pack was fitted to the seat stay and was about 14" high x 2" wide x 3" deep and the power unit was in the front hub like a drum brake hub. very neat installation and he said it had a range of about 30 miles. I can't remember the maker unfortunately. Regarding your output estimates, I recall some years back with the man powered flight and the gossamer albatross figures being given and an extremely fit person, such as the top class amatuer cyclist involved, might be able to achieve 1/2hp for the duration required, whereas most normal fit people would do maybe 1/4hp and then only for limited periods. For good output the tour de France and I expect other races these days, many racers are fitted with telemetry and the average and instantaneous outputs are sometimes given, very impressive, but in a different league to the rest of us.

I think a motorized bicycle is a somewhat vicious machine for a six year old to handle. Since you like to make things, why don't you take it a step farther and build him an electric car. All you need is four small bicycle wheels, a simple welded frame and a "horseless carriage" body that resembles a 1903 Olds or the original Ford.

Jerry

It would be vicious if it would go fast, which I want to avoid. I would want the max speed to be approximately his brisk, leisurely speed.

I suggest a twist grip control like a motorcycle that would return to the off position when released for safety in emergencys. I would also use a caliper type brake. if he has to reverse the motor to stop that will also stop the motor and cause it to overheat. Engineman

You need this Iggy:

Graham, it is a nice kit, but it is for adults (26" wheels).

Better yet, a multispeed rear sprocket set, and chain drive to the rear wheel with freewheel on the motor sprocket. Mount the motor assembly on a rear "carrier" type frame. That way you can pedal to assist, pedal with no power, or run under power.

Or install 2 freewheels on the rear wheel. Then motor and pedals are totally independent.A bottom bracket race can be pressed into duty to couple 2 freewheels as it has the same thread as the rear wheel hub where the freewheel fits, Space the first freewheel out with a bottom bracket lock nut so you have about half thread left for the bottom bracket race- and thread the second freewheel on. Not good for high power or a big man's bike, but plenty strong for a 40 pounder.

Then make him a "chopper" bike, and run it on 12 or 24 volts to reduce the speed.

Brian Lawson

On Wed, 20 Jun 2007 22:33:31 -0500, with neither quill nor qualm, Ignoramus25967 quickly quoth:

It's also for sale only to AU, and even if it weren't, can you imagine the shipping costs to get it here? They want $75AUD to ship it locally in AU.

- Metaphors Be With You -

see:

And here is the drive for it:

--Andy Asberry--

------Texas-----