Mark I:
Mark I was the first prototype of a series of autonomous airships built by the The Robot Group. The airship utilized an undercarriage constructed of aluminum rods and plastic with two gimble-mounted toy motors driving two small propellers and a water ballast tank connected to an electric water gun pump. The gimble powered by a geared-down Futaba hobby servo motor, was movable through one axis to provide multiple angles of pitch for the propellers. The on board control system was based upon a Motorolla MC68HC11EVB development computer controlling the toy motors via relays and the Futaba gimble via Pulse Width Modulated (PWM) signals. The control program generated movement based upon random selection of time intervals and movement selections. The computer and motors were powered by a bank of generic NiCad batteries, providing power for an extended flight of approximately one hour. The ballast pump was operated by a radio-controlled mechanical switch.
The envelope for the Mark I was constructed of Mylar survival blankets taped together with Mylar tape. When inflated, the envelope measured approximately six feet long by four feet tall by three feet wide. It carried a payload of approximately three pounds, which was roughly equivalent to the weight of the undercarriage and a handful of coins (additional ballast).
The Mark I airship was developed at a cost of approximately $200 and the time investment of approximately 50 man hours. It was first exhibited at RoboFest 1 in the fall of 1989 at Discovery Hall in Austin, Texas.
Problem areas were observed in the Mark I airship which would cause the retirement of the ship and redesign of a new airship. The problems that arose with the design included:
The most major improvement to the airship was the nature of the control system. The motor control was changed from relays to PWM(speed as well as directional control) using high current FET H-bridges. A new program was written which accepted high level movement commands via an RS-232 communications link to a ground based computer. A small cable linked the ground station with the Mark II.
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The computer blimp project continued with The Robot Group members finding solutions to previous airship design flaws. The Mark II airship was designed with improvements in control and ballasting. A new envelope was constructed of raw heat-seal polyethylene. This greatly improved the tightness of the seams as well as the appearance of the machine. The new envelope was much larger, in anticipation of providing the lift necessary for the improved undercarriage, approximately five pounds. The motors were replaced with high RPM disc-drive motors and the small propellers were replaced with much larger, higher speed propellers.
