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May 16, 2009, 04:26 AM
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Myth busting


DIY PHOTO LITHOGRAPHY: BUSTED

So the laser printer isn't dark enough. Even 2 transparencies aren't enough.

Did learn U need to dilute the draino 10:1 or it'll dissolve everything instantly. Keep the draino off your skin or else. The best result used ordinary copier paper & 10 minutes of baking. Need to find someone with a super dark printer.

One other thing. No-one sells transparencies anymore because everyone plugs their laptops into projectors. So that's transparencies & inkjet printers in the list of extinct requirements for DIY photo etching. This is yet another one of those myths which could only work for the 1 guy in outer Gainesville who still uses transparencies & inkjet printers for presentations.

MOUNTING GPS ON A 4X4 INCH ALUMINUM SQUARE: BUSTED

Got it locked indoors & swapped the aluminum in & out. Didn't notice a single difference. Between changing satellite coverage, microprocessor interference, & fuselage conductivity, even if there was a change, U couldn't say "Bingo! It's the aluminum."

When the GPS locks, its sensitivity goes up to the maximum, so any change in signal strength blows up.

Note that our uBlox5 lost its configuration after 3 weeks of no flying. Obviously the settings are what's backed by that battery & not the ephemeris. U better have initialization in software.

GPS ALTITUDE HOLD: CONFIRMED

Ideally U have an SCP1000 away from rotor wash. We just hate copying everyone else & it's another part which can break.

Use a uBlox5 in dynamic model 0.

Mount as far as possible from vertical obstructions.

Mount as far as possible from electronics.

Insulate antenna connection from wood & foam.

Any electronics on top of it jam it. If it suddenly stops working, it probably got stuffed under the IMU.

Use absolute altitude error -> climb rate error -> target collective

GPS can't sense velocity below a certain amount. Clamp climb rate error to a nonzero number & make it bob up & down to get the tightest altitude.

Make a vortex ring state rule to goose the collective if maximum descent rate exceeded.

Go to http://www.nstb.tc.faa.gov/Full_WaasSatelliteStatus.htm & only fly when satellites are directly overhead.

Fly high. It's not fast enough to handle ground effect.

Keep GPS powered & locked fulltime.

For automatic takeoffs, use a big starting collective & small collective ramp. Unfortunately, U have no choice but to tune based on payload & battery. It's just like the space shuttle.

Got the 4 waypoint mission to work over & over with automatic takeoffs & landings.
Last edited by Jack Crossfire; May 16, 2009 at 04:34 AM.
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