SRm uses strain gauges in the crank assembly. Power tap has them in the hub. Polar measures force by sensing chain tension via detecting the vibration of the chain. Chain speed is measured at the rear derailleur pulley, bike speed at the rear wheel, and cadence, as usual, at the crank. The pickup for chain vibration is similar to a guitar pickup (in fact, the developer revealed that their first test of the concept was with an actual guitar pickup, yup, and some duct tape.). It is a common method, apparently, in very accurate scales, to sense tension in a wire suspending the weight, via its frequency of vibration.
How does that guitar pickup work? Oh don't get me started...it's an EM phenomenon, so stop me here....just remember the "yellow dots" thread of years ago, and ask me to drop it! Paul. ----- Original Message ----- From: "Greg Franks" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Thursday, March 28, 2002 09:36 Subject: Re: [obc] Cycle Computer > Gilles Lamenoise wrote > > > What kind of computer is there that can give me: speed, cadence, grade > > or altitude, power? > > Getting power is the tough part. You have to measure force someplace, > so this means either a custom rear hub or custom cranks so that you > build in a strain guage. It's not impossible, but its not cheap either. ------ Club Office: [EMAIL PROTECTED] (613) 230-1064 Web/mailing list: [EMAIL PROTECTED] http://www.cyberus.ca/~obcweb Newsletter: [EMAIL PROTECTED] http://www.cyberus.ca/~obcweb/Newsletter ==^================================================================ This email was sent to: [email protected] EASY UNSUBSCRIBE click here: http://topica.com/u/?aVxiDo.a2i8p1 Or send an email to: [EMAIL PROTECTED] T O P I C A -- Register now to manage your mail! http://www.topica.com/partner/tag02/register ==^================================================================
