Bike Power

[chil]

I want to set up a bicycle with the rear wheel lifted from the ground and a dynamo fitted so that I can power something that shows how much energy is being put out.
There would be three bikes and the object is for cub scouts to pedal for a given time to see who does the most. The measure can be anything that is visual .Help pleas.
I have asked this same question on How It Works

[dizmouk2009]

A low voltage/wattage light bulb? or something that plays a tune?

[dizmouk2009]

Or a water pump, so that when they pedal it throws water around all over. That could be classed as fun as well.

[chil]

Hi dizmouk,
the water idea sounds great I could measure how much they pumped,but I dont know how to power the pump from the bike. Do you know how much power I can get from a bicyle dynamo and what size pump it would power. I have toyed with the idea of taking the tyre off and putting a belt around the wheel to drive something bigger.

[beso]

The bicycle dynamo can't consume enough power. They are only a few watts. For a human a one kilowatt capacity. We can pedal a few hundred watts.

I like the sound of using a pump because its pressure is easily contolled by throttling the flow. Pressure times flow is a good measure of power and are both easy to measure in simple mind occupying kinds of ways. They can calculate where the best performace lies.

Also no electricity involved which makes it safe and fun.

Get an old swimming pool pump as this will be about the right size. One end has a fan. Remove the fan and mount a small sprocket on the shaft. Hook that up to your bike chain. The rotating mass of the electric motor helps smooth out the motion.

If you mount the pump on spring you can measure the chain tension and with the linear speed of the chain, calculate the mechanical effort. More good maths and science.

By comparing the effort against the output power they can find the pump's operating efficiency at different pressures and flows. Bound to keep even the Einsteins among them busy. And the rest will have a lot of fun and might even learn something.

[wildwood]

If you want it more simple, you can buy those small pumps that are designed for emptying fish pools etc. driven by attaching it to an ordinary electric drill. It has a hose pipe at each end for an garden hose. It would be easy to make something so the pump is driven by the bicycle, then measure the time it takes each scout to transfer the water from one waterdrum to another. Or, how much water in 5 minutes - this can be measured with a wooden stick with 100mm marks on it.

[beso]

The fish tank pump is unlikely to do enough power. Also, being designed to be driven axially it will not have the structural integrity to be driven from the side.

Another way to drive a shaft is through running the bike tyre on a small wheel attached to the pump shaft. The advantage of this method is they can use any bike without having to do any modifications. It also provides high rpm which would better match the normal operating conditions of the pump.

Use a second wheel next to the drive and run the bike wheel between them.

[chil]

Thanks Guys
I am now looking at building two machines. I like the idea of the pool pump as this will be cheap,and I will look out for an old swimming pool pump. I have also been given a couple of car alternators so I now also want to experiment with them. Oh well good job Iv'e got some spare time.

[solera]

Put an ammeter on the output from your dynamo, your car alternator will give you a dc output, should be worth seeing the muscle development after the bike rides.