On Fri, 02 May 2014 12:53:09 -0500, Tim Wescott
wrote:

On Fri, 02 May 2014 08:53:21 -0700, ggherold wrote:

On Thursday, May 1, 2014 11:20:44 PM UTC-4, Tim Wescott wrote:
On Thu, 01 May 2014 10:15:48 -0700, ggherold wrote:
snip
What's your detector?

Could you use an LED and photo diode?

It's in a very uncontrolled environment both for dirt and for light
(it's gotta work in full sun, in just about every conceivable
orientation), and there's no room to shoot light through an aperture --
it would have to be reflective.

Hi Tim, I've never done light detection in full sunlight,
so I may be full of ****. But there is some nice 3M retro reflective
tape that Phil H. (of SED) turned me on to. As long as you have enough
dynamic range in the detector (to take care of full sun) cna't you you
then AC couple the signal? (White leds are blinding these days.)
(Will it kill you if you get a few false counts as full sun blinks
through the spinner onto the detector. That's going to be a very small
solid angle)
I've no answer for dirt and grease.

I am starting to think in terms of opto -- but usually the decision tree
for industrial equipment for optical vs. magnetic starts with "will there
be dirt on the surfaces?" -- if the answer is "yes", then the following
box says "use magnetic sensing".

The spinner comes with big lightening holes, much larger than the magnet
I'm thinking of using. I'm considering making up some high strength
epoxy putty with some chopped carbon fiber strand and microballoons, and
holding the magnet in with that. It's kind of a cro-magnon solution, but
it may work.

Now, if only someone made rare-earth magnets in the form of little
screws, I'd be all set!

A sort of left hand turn off the topic but why not just use an optical
tach for setting static speeds and (perhaps) and acustic tach to
calculate the increase in rpm when flying?

One example:
https://play.google.com/store/apps/d...viery.rpmgauge
--
Cheers,

John B.
(invalid to gmail)