At 09:18 AM 5/22/2011, you wrote:
> > The PowerTap used a special hum that had a strain guage in it to measur=
e
> > torque.
>
>Now that would be an exceedingly clever trick :-)
>
>I assume that the hum measured the force with which the chain tension
>pulled the axle forwards.
>If so that would be chain force rather than torque per se, with torque
>inferred from chain centre to axle radius.
>
>It's not instantly obvious to me
>how you'd measure pure torque in a hub. No doubt enough thinking would
>suggest a way.

Obvious way is to split the hub in some way, connect the two halves with a
torsion bar, mount (a) strain gauge(s) on the torsion bar. We only need one
component of the torque vector.

Here's one that uses standard 350 ohm strain gauges:
http://www.futek.com/files/pdf/Product%20Drawings/FSH00322.pdf


If there was a volume market, there would be cheaper ways.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the rewar=
d"
speff@interlog.com             Info for manufacturers: http://www.trexon.co=
m
Embedded software/hardware/analog  Info for designers:  http://www.speff.co=
m



--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.