Just wondering how you guys would determine the speed of your robot if you wanted a pretty exact number.
Tape measure+stopwatch+calculator 
*Originally posted by Caleb Fulton *
**Tape measure+stopwatch+calculator**
That’s really it.
Just one other thing to remember, will your robot be stopped when you begin timeing, or will you let it get up to speed (have it start before the line)? - This wouldn’t have as much of an effect the further the distance, but I’m assuming that you’re only going to have it go 30-40 ft, in which case, it would make a difference.
If you wanted to do it with calculations, you can figure it out theorhetically. You need the diameter of your wheels. With this, you can find out the circumference of your wheels with:
Circumference = (Diameter) * (pi)
Then, you need to figure out what speed your output shaft revolves at. You can figure this out with:
Shaft speed = (Motor free speed) / (Gearbox & sprocket reduction)
Then, just multiply the shaft speed (rev/sec) by the wheel circumference (ft/rev) to get the speed (ft/sec). For all practical purposes, I would multiply the speed # by 0.90 or 0.95 to take in account a 90-95% drivetrain efficiency. You’re not going to get 100% of the motor speed to your robot wheels.
For example, last year we used the Chiaphua motors geared overall 30:1, with ~7" diameter wheels (including traction material). The Chiaphua rotates at approximately 5400 revolutions per minute, or 90 rev/second.
Circumference = 1.83 FT
Shaft Speed = 3 rev/second
Speed = 5.5 ft/second
Of course, the most accurate way is tape measure + stopwatch + calculator, as said above. Get your robot up to speed, and let it go for 50FT (the longer, the better, the less error). Time how long it takes to travel this distance, and divide the length by the time.
we measured the distance of our practice playing feild 38ft and then ran a stop watch. it did 38’ in 4.1 seconds, so that would be 8 ft/second and change.
Bad