Smart exercise bike computer. Part #3: Power measurement

RE: Smart exercise bike computer. Part #3: Power measurement

jw0752 — Sun, 20 May 2018 05:17:41 GMT

Hi Yuri,

I like your experiment and your approach. It is possible that you want radians per second in your equation for power instead of revolutions per minute. This should give you 1 RPS = 2 Pi radians per second. Notice you also want the angular velocity in a time frame of seconds not minutes. The work done by the pedal is torque times the change in angular distance. Power is work done per second or as you stated torque(in newton meters) times angular velocity (in radians per second). The method you are using is a pretty good way to estimate the power but also keep in mind the static friction causes the torque needed to start the pedal to be higher than the amount needed to keep it turning. Even if you can put a generator on the bike and measure its power output you will still be ignoring the parasitic losses due to friction before the power gets to the generator. The importance of the power calculations should allow you to make comparisons though even if they are not perfect. I will enjoy watching your progress.

John

RE: Smart exercise bike computer. Part #3: Power measurement

DAB — Fri, 18 May 2018 20:46:23 GMT

Very good post Yuri.

DAB

RE: Smart exercise bike computer. Part #3: Power measurement

genebren — Fri, 18 May 2018 14:48:45 GMT

[mention:bcf467be9bf04982b313a2229455ef3a:e9ed411860ed4f2ba0265705b8793d05],

Nice update to your design challenge project. I think that adding the generator, with variable loading, could be an excellent method of determining work done. I have seen some pretty clever approaches, were the energy generated is captured and pushed back onto the power grid (through an appropriate power inverter). What fun to get exercise while generating electricity.

Keep up the good work!

Gene

RE: Smart exercise bike computer. Part #3: Power measurement

mcb1 — Fri, 18 May 2018 12:43:02 GMT

A real issue indeed.

I was looking at your earlier post and the images provided.

[View:/resized-image/__size/614x407/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-d1c8b9c3-69e8-4bfa-92b7-7b9e60192b43/contentimage_5F00_187362.png:614:407]

I resume the round item nearest the front is what your pedalling rotates, and the band just behind is connected to the tensioner so it acts as a brake.

If you were to use a round wheel connected to a motor, (similar to the below ... it was the best I could find) you should be able to rotate this and measure the current when it is rotating at a constant speed.

[View:/resized-image/__size/99x74/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-d1c8b9c3-69e8-4bfa-92b7-7b9e60192b43/contentimage_5F00_187363.jpg:99:74]

As you adjust the tensioner, it should change.

This may give you a more scientific figure (or a bigger headache)

Mark