In the vanishingly unlikely event that anything in this idea is novel, please hereby consider it public domain. Conclusion: Best of following meanderings seems to be a sprocket in the top chain run which deflects the usually straight chain run somewhat and which can move verticlly wrt chain. Sprocket loads a load cell which allows chain tension to be measured from frame. c c c sss =3D=3D=3D=3D=3D cs O s|||||||||||||||<-Loadcell c sss =3D=3D=3D=3D=3D c c c c chain s idler sprocket |||||||| sliding sprocket mount rod =3D=3D=3D=3D channel/tube for rod to slide in Loadcell Load cell __________ 1. There is no bogus pressure. If you apply a force to the pedals then power delivered is foot velocity x force. ir standing on the pedals IS delivering energy and doing work. IF the pedal falls when you do this you will need to apply energy to your body to lift it again to repeat the cycle. Standing on the pedals and eg pulling on the handlebars to increase force is just transferring energy from one system to another. Work =3D force x distance =3D F x d Power =3D work per unit time =3D F x d / t d/t =3D Velocity V. Power =3D F x V Close enough (a few %) to be useful kg "force" x RPM x crank length =3D Watts. This works because the various units and magnitudes cancel 'just so' Easily derived. 2. I haven't tried this, but measuring chain tension would allow you to use tension x chain velocity =3D power (!!!) This is top/drive chain tension. Chain tension can probably be measured by using a sprung idler on the top chain arm and telemetering it's position. Movement can be small. You could use eg a Teflon or UHMWPE "slipper" and a sprint loaded plunger or an idler pulley or sprocket on a rod in a tube with a load cell at the base of the tube. Idler sprocket losses can be smallish. Deflection can be about zero if a load cell is used. Triangle of forces (Google knows) issues mean you may waant the chain to angle a moderate amount, which is not how you usually want a top chain to go. Strain gauges on the pedal crank would give good torque measurement. Accessing them from the frame may be annoying. Could use own battery and an opto of slip rings of local processing on the crank with result only sent by opto or whatever. It would be quite easy [tm] to use inductive power transfer from frame to crank to power the electronics and gauge and any number of ways to get data bask. Strain gauges on pedals give a similar result. Spoke stresses, crank disk stresses, and wheel rim stresses would have energy input components but a complex mix of forces is liable to be present. In all cases there will be losses between source (rider) sink (road) and measurer. These may be substantial depending on equipment used. Of all these the idea of an idler with enough bend in the chain to allow trying to avoid measuring tan (infinity). (Chain tension required to stop a force applied at 90 from line of chain from deflecting sideways approaches infinity as deflection approaches zero (draw a picture). 3. Force sensor integrated into chain with eg RFID data recovery sounds doable and fun but harder. Russell McMahon On 22 May 2011 22:18, V G wrote: > > Just a thought. > > I wonder if there's an easy way to calculate the power output of a human > pedaling on a bicycle. The only idea that comes to mind is some sort of > method to sense the torque applied to the wheels, and then calculate the > power output from there using classical mechanics > Or - how about pressure sensors on the pedals? The applied pedaling force= is > directly related to the torque. Human power output can be calculated from > there. But then there's the issue of bogus pressure applied by the body > which doesn't actually go into doing any work (for example, when standing= on > the pedals). --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .