I never really learned how to calculate the rpm of drivetrains… does anyone know what the rpm would be for my 6-wheel(4 in.), 4 - motor(200 rpm’s on all of them) drivetrain with 84 tooth gears driving 36 tooth gears in between(3 84 tooth, 2 36 tooth in between)? Any and all help is appreciated. Thanks!
1 Like
This is how you calculate drive speed (rpm)
First you get the
driving/the driven
Then using this fraction you mutiply that by the rpm of the motor.
Your drive is ratio 84(driving):36(driven) and you are running a green motor (200) rpm. The rpm of your drivetrain is 84/36 x 200 which is ~467 rpm. So the rpm of your drive train is 467 rpm.
However, this is just raw rpm and wont give the full picture in terms of speed. The wheel size that you use does matter a little bit in terms of speed, a larger wheel will generally cause your robot to go faster than a smaller wheel. (If they are rotated at the same speed). This is because 1 revolution a wheel will cause it to go 1 of its circumference. The 4 in wheel has a bigger circumference than a 2.75 inch wheel causing it to go faster. You can see the difference between drivetrains in this way by seeing their In/sec. For your drive you have a 4 in wheel so 4pi is your circumference. Next we need to mutiply your circumference by rpm speed and divide it by 60(converting it to seconds. So the final problem is 4pi * 467 /60 is 97.8 Inches/Sec (which is on the fast side)
4 Likes
Thank you! Also, the weight of the robot affects that speed, right?
1 Like
The weight of your robot does affect speed. Since it causes more strain on your drivetrain motors which depending on how heavy your robot is this can cause significantly slower speed. A heavy weight also cause a slower accleratation as your robot has to overcome mote inertia. But weight shouldn’t be something that you should stress when building your robot because usually it doesn’t factor in too much (unless you have >20 pound robot, that is when I noticed a big difference)
Overall, weight does effect speed but not to a point that you should worry too much about it.
2 Likes