[artdutra04]

Originally Posted by Ctrl Alt Delete

I was wondering if anyone knew of videos that show the capabilities of a VEX Robot. I've seen videos of it doing random things, but I'm looking for a video of a VEX Robot going from one end of the field to another.

If you are looking for videos of last year's FVC robots, check out the videos page on VexLabs. But you can find the speed of a Vex robot without needing a video of a robot, simply by using a few simple formulas. Ahh, behold the power of mathmatics.

The Vex motors spin at roughly 90-100 rpm. On the Squarebot, there is a 60 tooth input gear on the motor, and 36 tooth output gears on the wheel axles. Use the formula r₁•t₁ = r₂•t₂. The r₁ is equal to the rpm of the one gear, while r₂ is equal to the rpm of the other gear. The t₁ is equal to the teeth of the first gear, and t₂ is equal to the teeth of the second gear. You need to know only three of these variables to find the fourth. You know the number of teeth of the two gears, and the rpm of one side. Using the formula above, we get:

100rpm•60t = r₂•36t

When we solve this, we get 166.66 rpm for r₂. But we're not done yet! To find the speed of the robot, we need to know the size of the wheels. The Squarebot uses the small 2.75 inch wheels. Using the formula C = π•d, we can find exactly how far the wheel travels in one revolution. The circumference of the 2.75 inch wheel is 8.64 inches. Multiply 8.64 inches times 166.66 rpm and we get 1439.94 inches, which equals 120 feet. This is how far the robot will travel in a minute. To find how far the Vex robot will travel in one second, divide this by 60 to get 24 inches (2 feet) per second.

Enough math for now...

This is a good rough estimate. Of course, the weight of the robot, the gear mesh efficiencies, etc. will lower this final outcome. But to put this into contrext, the 2006 FVC field is 10' x 14'. Assuming the Squarebot can travel up and down the ramps at the same speed as it travels across flat ground, it would take 7 seconds to drive across the 14 foot length of the field. You can experiment with different size wheels and gear ratios and use these formulas to find the speed of the robot. Just remember, you cannot gear the output wheels too fast or the robot won't move at all because of speed and torque are inversly related. But that is for another day...