SMUD Solar regatta 2017
The Regatta is an annual competition held Rancho Seco Recreational Area near Sacramento, California. There are high school and college level competitions, in multiple categories over a weekend.
Sprint - Solar only 100yd straight line race from stationary start.
Slalom - Solar only course navigating a close set of buoys with 180* turn at end.
Endurance - No solar, battery only powered race. Do as many counterclockwise laps of a course in 25 minutes. Ends require 180* turns, and there is a mandatory driver change-over after 10 minutes. Maximum battery capacity is 180Wh (~432 watts for 25 minutes = 12v@36amps). Start and driver change allow a shove from a single person in the water.
Gearbox
I was responsible for the drivetrain for this year.
We started with a helicopter brushless outrunner motor capable of ~800watts continuously (while weighing only 200g). Since the panels only give around 500watts, we were comfortable with the motor selection, despite it's diminutive size.
With a 770kv rating (~9000rpm at 12v), we needed a significant speed reduction to drive a propellor in water. To achieve this we selected helical spur gears again designed for an R/C helicopter, allowing a 7:1 gear reduction. Under 50% stall load, this should provide a prop speed of ~700rpm, which is appropriate for the air (!) propellor we decided to use.
We ran out of time to fully test and optimize the ratios and prop selection before the competition.
Results
Sprint- We managed to get the fastest sprint time of the day on our very first attempt, with some cloud cover!
Endurance- We did reasonably well in the endurance race, despite having a battery without enough capacity to deliver the current we needed to run at near full speed, and damage to the rudder system on launch (see video below). We came away with the 3rd longest distance.
Slalom - The hull shape is certainly not conducive to tight turn radii, but we still managed 3rd place.
