Here's a steerable blimp using an RCX. The maker wants his next version to use an autonomously-programmed NXT with a single mylar envelope that could theoretically fly for days.
Here's the builder's full description:
"Using an RCX, 3 Motors, the Infrared Remote, Large trash bags, and lots of helium, my son and I created a steerable blimp.
Two of the motors controlled propellers (made from a LEGO propeller with larger blades made out of packaging plastic). The third motor controlled the tilt of the two propellers.
Each propeller can be separately controlled. For example, to rotate the craft, one propeller would be driven forward and the other backward.
Metal washers were used as ballast to try to achieve neutral buoyancy so the propellers could be used to raise or lower the craft as well as move about the room. Helium leaked out of the trash bags fairly quickly so the ballast had to be frequently adjusted.
With one load of helium, we had about 2 hours of flight time (starting with a lot of ballast and then removing it bit by bit over the two hours).
The use of the Infrared remote was a bit of a challenge as the controls were not very intuitive (e.g., frequently tilting the rotors in the wrong direction). Also, maintaining the line-of-site needed for the remote was a challenge.
In my next version, I'm planning to make the following changes:
- Use an NXT instead of an RCX and use bluetooth to remotely control the craft.
- Set up more intuitive controls.
- Replace the trash bags with one large mylar envelope. This should greatly increase the flight time from hours to days or even weeks.
- Set up one of the propellers to have the opposite pitch to have the two props cancel each other out when spinning in a vertical position.
- Add sensors and program the NXT for independent control."