DEWBOT XIII Drive Train
One drawback of swerve drive vis-à-vis tank drive is the relative penalty paid for incorporating gear shifting. Tank drive, with two independent powerplants, requires two gear shifting mechanisms; Swerve, with four independent powerplants, requires four. This is a serious design hurdle for a drive train which is already a little avoirdupois.
FRC 1640's traditional 8.30:1 reduction from CIM to 4" wheel has provided power, control and agility, but not speed. Frankly, we've been a slow robot; growing relatively slower as teams adopt more aggressive tank drive trains. Then along comes SteamWorks, with a critical need to run gears across the field quickly. Our old swerve drive is just not up to this!
Fortunately, for the past two years, the team has worked to develop the employment of continuously variable transmission (CVT) as a means of employing variable gear reduction without excessive weight. By relying on pulleys, CVT fits 1640's swerve design philosophy far better than gear-based shifting. In fact, the fit is natural.
CVT Reduction
In past swerve systems, reduction had been managed in two stages: a 3.11 reduction via HTD5 pulleys (18T & 56T) from CIM to coaxial drive shaft; and a 2.67 reduction from the miter gear to wheel via sprockets and chain.
