Accelerometer Suggestions

[Donut]

Originally Posted by 6600gt

Now I am not saying you are wrong, but how did you arrive at that 9ft/s robot achieving a 1.7g?

This would theoretically mean that, if it could go that fast, it could reach a speed of 54ft/s from 0ft/s in just one second. I thought that such G's might only be "possible" during a full speed collision.

I figured that for a robot with 6" diameter wheels to go at 9 ft/sec, it would have to have wheels spinning at 344 RPM. The CIM motors have a free spinning speed of roughly 5200 RPM, and a torque at stall of 2.4 N*m. Since we have 4 CIMs in our drive system usually, that would give us a stall torque of 9.8 N*m.

Reducing our RPM from the motors to 344, increases our stall torque to 148 N*m (this is ignoring all gear train inefficiencies). Dividing this by the radius of the wheel (.0762 meters) gives us 1942 N of force at stall. F = ma, so we divide the force by the robot's mass of 60.5 kg, and we get an acceleration of 32 m/s^2, which is actually 3.3 gs!

I had originally gotten 1.6 gs, but that's because I used the wheel's diameter in place of its radius.

Of course, this acceleration is actually impossible because the wheel traction would probably never allow for any force greater than 1000 N.

Collisions are much worse; I registered a 1 g acceleration on the accelerometer when it was only 5 degrees from vertical, which meant the impact generated was more like a 12 g acceleration. Driving around with it being used for position I've gotten .5 gs from the Vex robot, which is no where near the power of an FRC bot.