Design Concept
Instead of doing a wheeled robot, we decided to take a risk and do a hovercraft.
Challenges
Generating enough lift to keep the craft airborne while providing enough thrust to propel the craft forwards proved to be a considerable challenge. While we had run initial tests to confirm that we would be able to accomplish both with a decent amount of weight on the body of the craft, we drastically underestimated just how much the finished product would weigh. Between visual indicators (LEDs, servos), sound, bumpers, and all other additional functionality, our craft came in at 8lbs, 4.4 oz. This is nearly TWICE the weight of hovercrafts that have been attempted in past years.
The Solution
We characterized the current draw of our thrust motors at different duty cycles, and determined that we would need larger than average fuses. We wound up putting a 7A fuse on EACH thrust motor so we could run them at 100% duty cycle.
With the thrust motors running at 100% duty cycle, drawing ~5A each, we were already taxing our existing set of batteries considerably. One set of batteries was not capable of supplying enough current to also power the blower fan providing the craft's lift. Since we needed additional mass on the craft for weight balance purposes anyway, we decided to add another set of batteries (14V) dedicated to powering the lift fan.
For good measure, we made slight modifications to the underside of the hovercraft architecture in order to allow additional airflow (AKA cut some of it out with an Exacto knife).
Our last ditch efforts provided to be successful, and we were able to get our hovercraft to function at the competition.