Blade RPM

[Tudorbug]

Folks:

Is there commercially available a device that will measure shaft rpm for a set of blades while mounted up on a tower?  (I think of a device used on an expensive bicycle to measure wheel rpm and thus miles per hour consisting of a source on a spoke and an adjacent sensor on a fork of a wheel.)  I would prefer to purchase one rather than cobble one together myself.

But, if not commercially available is there a design that I could use to fabricate one with?

I thank you, David

[zeusmorg]

 You mentioned a bike computer. Most of them do not directly show RPM's but this one does, and it's cheap.

http://www.dealextreme.com/search.dx/search.bicycle computer.

 Extend the wires, and you're all set! of course you may have to get creative with the mounting..

I bought 3, one for my 'bent trike..

[imsmooth]

Why don't you check this out.  it should help out.

http://www.mindchallenger.com/wind/wgpage5a.html

[brokengun]

Whatever you do, don't use a wireless bicycle tachometer. I just used one today and the readings were severely effected by the magnetic field produced by the rotor magnets.

It's odd because those wireless ones are a bit more expensive and such, but the way they transmit data is just too sensitive. Definitely use a wired one if you decided to go down that path.

[Tudorbug]

Folks:

I am grateful for your helpful comments.  I had purchased two of the devices noted by Zuesmorg and then began to worry about extending the cable so far down the tower.  I was considering a wireless option when I read brokengun's comment so I won't go that route.

More study on extending cables will be needed.  We have a 20 foot tower at the moment.

Thank you very much, David