pic: WCD Summer Project

[Chris is me]

I believe the reason Travis is specifically mentioning next year is that it will be the first game with the new control system where anyone would have any reason to build a 6 CIM drivetrain. Some have suggested that the system is more vulnerable to brownouts than in the past. (I'm not particularly informed on this, I don't know if people have tested this etc)

However, at least in the context of the previous control system, gearing your low gear so that your motors draw <30 amps each when traction limited is the right move. It's a conservative number that should help prevent pushing matches from tripping your main breaker. Be careful to manage current draw throughout the rest of the robot as well.

As for the design, it's not too bad. I would remove the lightening pattern from the front and back rails. The square lightening versus a triangle or X pattern is substantially weaker, and most any lightening pattern in 1/8" wall tube is going to result in a weaker and less rigid tube than a 1/16" wall unlightened tube. And it won't even be lighter! If you want to save weight, you can usually get away with 1/16" wall tube for the crossmembers.

While I wouldn't say this chassis would have "little to no" torsional stiffness, a lot could be gained with a structural belly pan for relatively little cost of weight (since you already need something to mount electronics to regardless). The waterjet or lasered aluminum belly pan is a slick way to do it, but a composite like garolite left solid can also do the trick for a lot less machining time. You could also add some standoffs connecting your two gearboxes together at the mounting holes. Also do keep in mind that your manipulator design may also provide some cross bracing, and in that case your drivetrain doesn't necessarily need to be structurally perfect independent of other subsystems.

[GeeTwo]

Originally Posted by Chris is me

Some have suggested that the system is more vulnerable to brownouts than in the past. (I'm not particularly informed on this, I don't know if people have tested this etc)

While we haven't done any intentional testing of the brownout, we have definitely found a difference with the RoboRIO in practical (non-competition) situations. In previous years, we didn't always realize when it was time to change batteries, because there would be different symptoms. We would lose acceleration, or we might drag a bit as we tried to do a kick or other high-current function, but the degradation was usually gradual, until it caused one of the digital components (most commonly our raspberry pi vision processor, but occasionally the D-Link radio, and in one case apparently the cRIO) to reboot. In each case, the failure took several to many seconds for recovery. The roboRIO has a defined brownout sequence, which cuts power to the motors first, then proceeding to other specific busses until the cRIO itself is eventually shut down. In practice, this means that our robot runs just fine at extended practices and demos until the drive system enters a "jitter" phase in which it is energized, draws the voltage down, shuts off, allows the voltage back up, is re-energized, and shuts off again, creating a cycle that executes about 7-10 times per second (based on my non-calibrated biological clock, but with a lot of acoustics experience). In Recycle Rush, this appears to have rarely occurred during a match unless a team was working unusually quickly, or using particularly old batteries. I suspect that in the near future, especially if we get more defensive games, teams will have to monitor battery voltage and total current draw, and implement software limits that prevent or at least limit the impact of these brownouts. The good part of this change is that at least we are much less likely to spend most of a match waiting on a reboot!