So during the last two seasons my team has tried 6 different drive trains including an x-drive, and a tank tread system with a two speed shifter. Some of these were OK and some performed well, but what we consistently seem to find out is that many designs that worked for other teams didn’t even come close to working for us.
So here’s the question, what is the best configuration of motors and wheels that you have found to work for you?For my team we have consistently settled on a 4 motor mecanum drive, at a mid-high speed gearing ratio.
I haven’t used mecs, but we have a X-drive this year with 3.25" wheels on high torque with 4 motors. It gives a decent amount of speed and hasn’t burnt out in a match. You could probably even go faster with a lighter bot.
For a tank drive, somewhere around 1:1.6, or 4" wheels with high speed gearing is the norm for a 4 motor drive.
Throughout the season we had an X-drive with 2.75 omni wheels using turbo, high speed, and then torque internal gearing. The 2.75s are awful and constantly gave us problems, don’t even bother building a drive with them. But on the other hand, 3.25s are amazing for X-drives. Like Kevin_Team472 said, 3.25s with torque drive is a really good setup for X-drives. But at the end of the day, the best drive is one that compliments your lift and most importantly your intake.
Drive has a 1:1.25 gear ratio using high torque motors on it right now, however on our robot that we took to worlds last year we used direct 1:1 high speed with mecanum wheels which worked very well with our 12.5 lb robot.
Direct drive is more efficient than geared, but (at least last year) gearing had the advantage that the gears take up some of the force from changing direction quickly, instead of destroying the motor and/or wheel. This year this should be less important because there is less defensive play, so a simple direct drive will usually be better than gears.
Chain is also good on a tank drive to connect the front and back wheels together, and in most applications on a drive better than gears.
So as an aside, I’ve noticed that quite a few teams have gotten their mecanum drives to strafe very well, however our mecanum drive seems to have a difficult time when it is strafing. I think it might have to do with the weight of the robot, however the last competition we went to another robot of similar weight had optimized their mecanum drive very well. Our robot has a 4 motor mecanum drive at a 12:15 gear ratio, on high torque, our robot also weights 22.8 lb. Does anyone have any tips on how to optimize our mecanum drive?
At least in GA, I saw a huge dominance of mecanum wheels. Well, if the only thing you need to do to strafe is to make chassis wider, then why not do it? However I am still working on a controller for my mecanum base’s strafing in auton. Without a ton of gyro program strafing in auton with mecanum is just pretty shaky. We liked the relatively slower turning speed of mecanums.
As for gear ratio, direct internal high speed mecanum handled our 20+ lbs robot okay, although the base does burn out when we went around crashing into other robots carrying 2 cubes. Generally aggressive driving burnt out that base barely after a match, so I would say internal high speed 4’’ wheel is a decent choice for most regular robots.
Our new robot had less weight and the same base worked better. We gave a power expander just for the base, and we liked how it works. First, base has almost infinite power and battery voltage is a lot more manageable. This makes keeping on track of auton overshoot really easy. I know I know PID theoretically deal with that but I would still wanna know roughly what range of base voltage is safe for my auton. Second, if the power expander somehow glitched before a match, the robot wouldn’t go anywhere!!! So it just costs auton and a few seconds into the match. If your lift died and base went out, good luck!!
