pic: Ira's Senior Project

[Sylvia]

Ok, so I'm new to 1712 (as you know, Ira). Next year I'm going to be one of the team members using "Runt" to learn. I have to know next year's robot's drive's expected behaviors before testing (i.e. speed, torque, amp draw, etc.)
Kressly had me review Ira+Andy baker's calculations with me, changing variables and such to force me to learn (which is good, as I know NOTHING)

Here are my primitive calculations. Did I screw up?

The robot speed @ normal load = 4200 RPM
Gearbox Ration is 12.75:1
Gearbox to Wheel Ratio is 1:1
Wheel Diameter is 4 inches.

I was asked to change to a 24-tooth sproket on the output shaft of the gearbox, making the gearbox to wheel ration 2:1, then change the wheel diameter to 6 inches. My calculations were:

4200 RPM / 12.75 = 329.4117647 RPM output
329.4117647 x (2/1 gearbox to wheel ratio) = 658.8235294 = RPM wheels are driven at
658.8235294 RPM / 60 = 10.98039215 RPS (duh)
Circumference = d(pi) = 6(pi) = 19.44
10.98039215 RPS x 19.44” = 213.458823396 in/s
(213.458823396 in/s) / 12 = 17.77 ft/s

[Rich Kressly]

...and as you give feedback, please remember this is purely a theoretical setup. Our biggest interest as a team is in students (with Sylvia as a leader) learning how to calculate correctly so we get to know expected outcomes that can help us make better decisions in the future ...

[Andy Baker]

Originally Posted by Sylvia

My calculations were:

4200 RPM / 12.75 = 329.4117647 RPM output
329.4117647 x (2/1 gearbox to wheel ratio) = 658.8235294 = RPM wheels are driven at
658.8235294 RPM / 60 = 10.98039215 RPS (duh)
Circumference = d(pi) = 6(pi) = 19.44
10.98039215 RPS x 19.44” = 213.458823396 in/s
(213.458823396 in/s) / 12 = 17.77 ft/s

Sylvia,

All of this is correct. Good job on the calculations. Here is some advice:

1. Set yourself up a simple Excel file to do these calculations. Once you get your equations determined, then you can change a few variables (wheel dia., sprocket size, etc.) to get final speed results.

2. You don't need to track any decimal places past the tenths for this application.

3. Your 17.8 ft/sec makes sense, but it's too fast. Ira's setup was giving you about 5.8 ft/sec. If you increase the speed (by 2x) of the wheel by putting a larger sprocket on the gearbox, then you get 11.6 ft/sec. Also, if you increase the wheel size to 6", then that 11.6 is multiplied by 6/4, which results in 17.4 ft/sec.

What is the speed you want to go?

Keep it up,
Andy

[Sylvia]

Ok, I'll look into the advice
Thanks!