Al did a great job of covering electrical sources of brownouts, which were the most common reason for brownout I saw. There was one non-electrical source of brownouts -- drivetrain designs. Specifically, six-wheel drop-center (i.e., KOP chassis) drivetrains with AndyMark
AM-0970 pneumatic wheels, or similar.
Teams needed to pay particular attention to robot CG and tire pressure to keep the turning current low.
One test I use is to put the robot, with battery and bumpers installed, on carpet. Put a sheet of paper underneath each of the corner tires, and pull it out. If the force needed to pull the sheet out varies dramatically, you need to balance the robot.
Another way to check is to put the robot, with battery and bumpers installed, on carpet, and try to turn the robot by pushing on the corner of the robot with your finger. If you can't turn the robot, it's probably going to take a lot of energy to turn.
Don't bother doing either of these tests on a hard surface. The results don't replicate the actual field. Don't have a piece of real field carpet? Ask the Regional Planning Committee about getting some leftovers after the event. Or go to the carpet store and buy a remnant of a low pile carpet made of the same material as the field carpet. It won't be exactly the same as the field, but close enough to test it.
Here's what we did. First, we used a similar tire, but with a smooth profile
like this. Second, we paid close attention to robot balance, ensuring that the CG of the robot was near the center. Third, we ran the center tires on each side at 30 PSI and the outer tires at 10PSI. This caused the center tire to be bigger, and helped with turning energy.
Our drivers could tell instantly whether the pit crew had forgotten to set the tire pressure.
I also saw a couple four wheel pneumatic tired robots -- they had the same difficulties as the six wheel ones, but are fundamentally difficult to fix.