# Im a physics student and was told that a mechanical engineer

## Main Question or Discussion Point

Hey

Im a physics student and was told that a mechanical engineer may think or i good idea to help so here goes... (this is what ive posted in the physics forum)

Hello
I have to complete an experimental physics project for high school physics this year and with help of the physics forum member, chroot (https://www.physicsforums.com/showthread.php?t=149893), I have come up with the idea of looking in to a experiment like cycling physiological experiment with a heart rate monitor, like measuring power output at various heart rates.

I like this idea I wish to look into it more, but don’t have a power meter device (they work by measuring torque and wheel speed). I need a way of measuring torque, as I’ve been told torque x rpm = power. So we need to find a way to measure the torque of a bicycle wheel. I already have two types of trainers available (A trainer is a compact stand that attaches easily to the rear axle of your bicycle. The trainer holds your bike securely and provides pedalling resistance for your workout.)

The two types of trainers that I have access to are: a mag type trainer, which makes use of magnetic fields to generate resistance, and also have access to rollers, which consist of three revolving drums on which a bicycle can be ridden.

These trainers already include some kind of resistance device to load the cyclist. So by calibrating this resistance device I could find torque it requires to spin at a specific RPM.

The calibration would is the hard part, I need some way to apply a known torque and measure the resulting RPM. It has been suggested that use of an electric motor to drive the trainer's resistance could be an idea I can measure the motor's current consumption, and calculate its torque. If this idea was used, would I just attach the motor straight on to the wheel?, if so how?

So… my question is does anyone have any ideas of a way to find the torque of a bicycle wheel?
And does anyone else have suggestions / ideas on this experiment?

P.S. there is a rundown on the types of trainers on this website-
http://www.bikeline.com/feature/trainer/index.htm [Broken]

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brewnog
Gold Member
If you're only going to be using the trainer (as opposed to using the bike on roads), I'd definitely try and take your measurements on that rather than the bike.

The way I'd like to do it is as follows:

Remove the loading system from your trainer, and replace it with a dynamo sized accordingly. Build a load bank system using either light bulbs or heating elements of known power consumption, wiring in a voltmeter and ammeter. Connect the two, get your athlete pedalling, and switch on sufficient bulbs/elements to get the load you desire. You can calculate power easily from voltage and current, and torque from power and speed. Obviously you'll need to calibrate this but that shouldn't prove too taxing.

The second way you could do it would be to use the existing loading mechanism on your trainer, and instrument it up with strain gauges, with which you can directly measure the load.

If you would like to get accurate power information with out a lot of hassle, I would recommend finding someone in you are with a power meter on their bike. As you discussed in the other post, a powertap would work well. I am actually a competitive cyclist on my way to try to go pro. I just started training with a powertap about a month ago. If you live in a larger city I think if you go into a bike shop they would be able to get in contact with someone with a power meter to help you out. Or you could put a post on cycling related forums. This way they would also be able to use their software to show you the graphs for Watts, Torque and Heart Rate graphed against each other. The experiment sounds interesting. If you are planning to test a few different subjects I will tell you that your data will probably be very different. There are many websites that go into the details about production of power at Lactic threshold and the other zones of heart rates. I hope this helps, but let me know!