[fox46]

The past three years I've been involved with a couple teams using 6 motor drives:

2011

Cybergnomes#2013: 4x CIM + 2x RS775 on Single speed 8x8 drivetrain, 1xRS550 arm stage 1, 1xRS375 arm stage 2, pneumatic gripper.

2012

Cybergnomes#2013: 4x CIM + 2x RS775 on Single speed 8x8 drivetrain, 2x RS550 shooter, 1x AM9012 Conveyor, 1x Window motor pickup retract, 1x RS545 feeder, 1x RS375 Azimuth control.

Ramferno#3756: 4x CIM + 2x FP0673 on single speed 10x10 drivetrain, 2x RS550 shooter, 1x window motor feeder, 1x RS550 conveyor, pneumatic pickup retract.

2013

Cybergnomes#2013: 6 CIM drive single speed on 6x6 drivetrain, 2 MiniCIM on climber, 1 MiniCIM Shooter, BAG Motor Azimuth control.

Never once did we experience a main breaker trip. All machines since they were single speed drivetrains were geared to operate at the limit of traction. They had great acceleration, good *controllable* speed and phenomenal torque. As far as pushing power, they were on-par with the 2 speed 4 motor drivetrains. However, when in a prolonged shoving match they did eat much more power than the 2 speed drives. The behavior we noticed is that if the drivetrain managed to stall (was designed to break wheels free first but on a weakened battery it would occasionally happen), since no three DC motors are exactly the same (why BrianC was getting different current draws during no load) it seemed that the 40A auto-resetting breakers would trip in a cascade fashion. One would go (highest draw motor) which would increase the load on the other two whose breakers would respectively follow suit.

Personally, I think 3 motor 2 speed is a waste of money unless you can generate enough traction through mechanical interaction with the carpet to warrant it. Single speed 3 motor has the benefit of being able to compete with multiple ratio transmissions if geared properly because we are all limited by weight. Remember: force of friction (traction) = normal force (weight) x coefficient of friction (gum rubber on carpet in best case). Since we can't use studs or an apparatus to "claw" at the carpet, every robot is more or less limited in traction by its weight. Where the single speed shines is its ability to go whistling across the field, HIT a robot thus exceeding its static forces of traction with the carpet by overwhelming it with momentum and then "freight train" it across the field without ever letting up or shifting.

That being said... 3 motor 2 speed would allow you to wrestle with other robots without using as much power and with very little worry about tripping any breakers.

Instead you can worry about peeling the tread off your wheels and incurring penalties for damaging the field surface.

For this year, we are again building some very power-hungry robots and I am somewhat concerned about power draw myself but if past experience is any indicator, there shouldn't be too much to worry about. We may be implementing some current-saving techniques like shutting down the compressor or even two drive motors while reloading *the primary weapon* but all in all I would not be too worried.

One thing to mention though, keep an eye on your batteries. 6 motor drives WILL bring a frail battery to its knees during competition so be wary of that old grey battery that your team has had kicking around from 3+ seasons ago.