Forum Administrator. The Water Rocket Achievement World Record Association 
I guess it's that clear casing they have lets the light in. I'll have to try the UV-LEDs in the next unit I fabricate. 
Bibbleycheese wrote:Here is LS-Op1 on the launchpad. Unfortunately, even though the optical detector works perfectly well on the bench, in the field it fails.
The problem appears to be in the way the PICAXE chip interprets the data from the comparator.
Although it seems to supply a good digital upside-down / not upside-down signal, the PICAXE will not accept this - either interpreting a high or a low all the time.
I've tried switching the PICAXE input from digital to analogue - and this gives reliable results on the bench, but outdoors it fails 3 out of 10 times - which is no good. I've tried tweaking the analogue level at which the PICAXE triggers, but still no improvement in reliability so far.
What I'm going to try is build a more sensitive detector array using UV-LEDs spaced further apart, and see if this will improve the quality of the signal. I could also try routing the output from the comparator through a gate to clean-up the digital signal - but it's back to the breadboard for now.
That might be an option.U.S. Water Rockets1 wrote: The place where you are standing to do your testing may not be reflective. When you launch the rocket the field of view widens and perhaps there are reflective surfaces on the ground that come into view and confuse the sensors.
You might consider a sensor that is looking at a different part of the spectrum. Perhaps an infra-red sensor would pick up the heat from the ground better than it would see it in the empty sky. Or perhaps a sensor looking for UV would see more scattered in the atmosphere than reflecting from the ground. The concept is workable, as opposed to be mercury switch idea, which physics has proven to be impossible.Bibbleycheese wrote:That might be an option.U.S. Water Rockets1 wrote: The place where you are standing to do your testing may not be reflective. When you launch the rocket the field of view widens and perhaps there are reflective surfaces on the ground that come into view and confuse the sensors.
I was launching over grassy scrubland on a particularly overcast day. There's a good chance that there wasn't enough difference in the light levels from sky and the ground.
I learned a new word from Mythbusters - the episode when they debunked the Moon landing conspiracy; and the word is Albedo.
When I've been testing the sensor, it seems I've been luck enough to have a sunny clear sky above, and dark green grass below. On my launch site, on the day I went to try the unit out in flight, it was completely overcast and guess what - I didn't test the thing was working before launching.
Fail to plan - Plan to fail!
So I dug out the old photographic light meter and next time I'm over there I'll take some measurements.
But I like your point about widening field of view. And now doubt is beginning to flash a fin.
This might mean that actually, like mercury switches, optical apogee detection will be at best unreliable in flight.
I hope not.
Now what I'm hoping is someone out there has some video footage of an optical apogee detector working in flight.
Anyone?
