Radio, GPS, attempted liftoff

Turns out I goofed with the airframe; the thickened undercarriage nearly covers the motor mount screw-holes, not leaving enough room for the screw heads. When I was trying to assemble it anyway, I ended up breaking off the tab on one of the undercarraige struts.

For some reason the motors ship with two long screws with smaller heads and two shorter screws with large heads (and have a total of four identical screw holes). By using only two screws with smaller heads I was able to mount the motor and assemble the airframe. (I used superglue to reattach the broken off tab.) I wonder if TAP carries 3/16" acrylic...

So anyway, I mounted a motor, and strapped down a battery for good measure, and hooked up the XBee to the Propeller chip, and made a little test program that turns the numbers 0-9 (when received over the XBee radio) into 0%-90% motor power. Around 60% or 70% the platform wants to pull into the air (totally off-kilter of course, since there's only one motor mounted). At 90%, it's really pulling hard. This is with one of the batteries strapped on. With four rotors and two batteries -- especially two smaller batteries than what I'm using now -- I'm pretty sure it will have no trouble getting airborne.

(You can't really tell, but the unit is lifting up against my hand.)

I wonder how ESC input corresponds to actual propeller RPM. Seems like it more corresponds to power output, and it adjusts RPM as necessary to hit the target power level? That could be annoying, especially for things like yaw control where I really want to adjust the RPM directly. But the next level would be to use something like the mikrokopter BrushlessCtrl ESC instead of my off-the-shelf ESC, and that's complicated and fiddly. Other people manage to fly with off-the-shelf ESC using servo inputs, so I should be able to as well.

Also, I got the GPS module hooked up and wrote a test program to echo GPS data over the radio. (I had to change the radio config from 9600 baud to 57600 baud to accommodate the data!) The GPS says I'm at
37° 25' 57.41" N, 122° 8' 43.18" W which is by far the most accurate fix I've ever gotten from my living room. In fact it seems to know exactly *where* in my living room the sensor is located, which is pretty impressive given that it's indoors. I'll need to turn down the update rate to 1Hz (or less?) for every message except $GPGLL -- getting the entire NMEA dump 5 times a second is pretty overwhelming.