4 Mar
2010
4 Mar
'10
2:14 p.m.
On Thu, 04 Mar 2010 10:27:43 +0000
Jonathan Gazeley <jonathan.gazeley(a)bristol.ac.uk> wrote:
On 04/03/10 10:20, James Morris wrote:
Instead of directly trying to measure RPM, measure milliseconds per
rev. then invert it. Once you have your first reading, then start to
average over 2/3 revs. gives you a pretty fast responding figure with a
simple setup.
Also, use a short range photocell on the spokes (say 50mm). Easy to
mount, reliable results with minimal effort. As these can usually
respond up to 10-30kHz you won't have to worry about pedalling too
fast :)
--
Will J Godfrey
http://www.musically.me.uk
Say you have a poem and I have a tune.
Exchange them and we can both have a poem, a tune, and a song.
On Thu, March 4, 2010 09:48, Jonathan Gazeley
wrote:
Yes - I have a cycle computer that can measure cadence. However, I
typically pedal between 60 and 90 rpm which means my reading would only
be available for sampling every 0.7 - 1.0s. It would work, but in the
space of one second my cadence can vary a lot if I'm accelerating so the
sound of the rising revs would be jumpy.
Also, if I suddenly stopped pedalling, it might take up to a second for
the sampler to register and kill the engine noise. I don't think it
would be a very satisfactory experience, which is why I was thinking of
mounting 10 or so magnets around the chainwheel, to be able to sample
the cadence every 0.1s. 1. A sensor that can measure my cadence. A simple
magnet switch that
triggers once a revolution won't be enough to measure the cadence with
sufficient resolution, since my cadence is usually between 50 and 80
rpm. I would probably need to mount multiple magnets spaced equally
around the chainwheel and have a single sensor on the frame. Then I have
to get it to supply this information to my control program.
Cycle computers which measure cadence work with a single magnet on the
crank and can measure cadence in that range and above. I think the fastest
RPM I ever got was (only a vague memory) around 120 (maybe?) when I was
being silly trying to see how fast I could pedal.