[PSUBS-MAILIST] toy update, crude attitude control

[David <buchner@wcta.net>]

  Hey, all. I'm returning after recovering from a dead hard drive. I 
don't care how often you do back-ups: reinstalling software and copying 
over files is a giant pain, especially now that 30 gigabyte disks are 
common.

  So here I am fulfilling my role as frivolous aquarium-scale p-subber. 
I still haven't finished the boat I started by taking apart two 
miniature r/c speedboats, but Clara and I were wheeling through the 
Wal-Mart toy dept waiting for Mom, and stumbled upon a $9 submarine.

  It's super-tiny, just 2 inches long (the packaging bills it as the 
World's Smallest R/C Submarine). It's one of these deals that only has 
two thrusters, starboard and port -- and diving and surfacing is 
supposed to be controlled by angling that thrust up and down, in this 
case with little vanes on a guard around the prop of each, which you 
set by hand before putting it in the water. So you get forward+dive or 
reverse+surface.

  Of course I didn't like that -- because that makes it impossible to 
hang out near the bottom. And the prop shafts kept getting fouled with 
aquarium plants and the guards made it impossible to clear -- so I 
carefully cut those off. It also is intended to be positively-buoyant, 
so that it surfaces with a dead battery -- so I weighted it to be as 
close to neutral as possible.

  So here's the deal. My little submarine's depth is actually much more 
controllable now than it was. Not all that controllable, but still 
better, and good enough to be fun. The trick is to give short bursts of 
power, and its high center-of-gravity results in a rocking motion. I 
wait for the nose to be pointed in the direction I want to go, and then 
apply forward thrust. I keep wondering just how half-assed this method 
would feel, driving around in a human-scale version. For that matter, 
in a small enough vehicle, I could do all the attitude control by 
shifting my own weight. Hmmm...




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