One thing to keep in mind is that speed is not just a function of gear ratio. It also depends on the diameter of the wheels you use, the friction of your drive train and the weight of your robot. Study the information in the VEX Speed Charts to understand how fast you can go with certain combinations of gearing and wheels.
Last year, the fastest robots I personally watched were 723 (which I think was running 7:3 with 4" wheels), 575 and 418 with 3:1 with 2.75" wheels, and 417 with 16:5 with 2.75" wheels. All were fast and responsive BECAUSE they were very lightweight. The three Exothermic robots were right around 8 pounds, less than half the weight of the average VRC robot. Even at this weight, they used a drive train with six motors to get enough torque to turn well. The extra torque also gave them great acceleration, which is something you won’t see with a heavy robot geared up high.
Of the really fast robots from last year, I really liked how 575 moved because of its software and its very good driver. As Kendalls wrote, it takes great software to make a fast, maneuverable robot. Watch video of FTC matches to see really fast robots that are totally uncontrollable. Big motors do NOT make a good robot – only the right drivetrain with the right software and good drivers works well.
The robots listed above have theoretical top speeds of 3.6 to 4 feet per second. We experimented with some gearing at around 5 fps, but even with light robots they were too sluggish to rely on, and with the motors bogged down we were clearly sucking too much power and straining the motors.
Just remember it’s not just the gearing that determines how fast you can go, and how fast you can go in a useful, controllable way:
- Wheel diameter
- Weight of the robot
- Configuration of the wheels (a short wheelbase will improve your maneuverability requiring less power to turn the robot)
- Number of drive motors
- Skill and experience of the driver
- The quality of the driving software.
I know I’ve posted this before 3-4 times, but it’s a great 30 seconds of what you can do with a fast robot, a good driver, and software that allows an otherwise twitchy robot to handle well. Watch the robot that starts on the far left corner of your screen, it starts with an empty mechanism and picks up three cubes from the other side of the field and then scores them in three different goals in 24 seconds. I also saw this robot pick up a cube from the floor and score it in the high goal with four seconds left in a match. http://www.youtube.com/watch?v=aIsQckNv9zM
(By the way, make your fast robots extra tough and reliable. Hitting the wall or another robot at 3.5fps is a great way to knock battery cables into resetting the robot. Ask me how I know. )