Tip Speed & Drive RPM Calculator

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Tip Speed / Drive RPM Calculator:

Select battery type:


NOTE: LiHV will increase your tipspeed over standard LiPo!

Motor kV


Spinning Diameter


Output Pulley Ratio


Motor Pulley Ratio


If you’re unsure of your output & motor ratios instead in the same inputs you can enter:
Number of Teeth – output pulley teeth : motor pulley teeth or
Pulley Diameter – output pulley diameter : motor pulley diameter

Rotational Velocity
Max Tip Speed


Note: this is max theoretical tip speed with a fully charged battery, it will spin slower than this in reality.

Kinetic Energy Calculator

Moment of Inertia at Centre of Mass


MoI at CoM obtained from your CAD program. Ensure you’ve got the correct mass assigned and you’re using the correct axis (the letter of the axis you’re rotating around eg – horizontals would usually be Izz) For everything but drums/beaters just take the axis with the largest value – usually in the format 3.00E+05 g mm^2 (ballpark for beetles)

Max Rotational Kinetic Energy

Rotation Velocity (rpm) = max cell charge x cell number x motor kv / reduction ratio

Reduction Ratio = output pulley / motor pulley

Tip Speed (mph) = rpm x diameter(mm) x pi x 60/1609344
Tip Speed (mph) = rpm x circumference x rotatations x scaling for mph

Tip Speed (m/s) = (rpm x diameter(mm) x pi) / 60 / 1000
Tip Speed (m/s) = (rpm x diameter(mm) x pi) / scaling for m/s

Rotational Kinetic Energy (J) = 1/2 x MoI(kgm^2) x (rpm / 60 * 2 * pi)^2
Rotational Kinetic Energy (J) = 1/2 x MoI(kgm^2) x rad/s^2

Thanks to Rory Charlesworth for the inspiration and calculation help.

Disclaimer: Building, maintaining and fighting combat robots is dangerous and comes with risk that must be assessed on a person by person basis. We cannot be held liable for any personal injury, loss of property or money from partaking in building, maintaining, repairing, testing or fighting combat robots even when following our guides and rulesets.