Tool

Gear Ratio & Speed/Torque Calculator

Ties into Chapter 5, Building the Drivetrain and Chapter 15, Advanced Drivetrains. Pick your ratio for the robot's final weight, then pick your motor count to support that ratio, not the other way around.

Program

Drivetrain motors

11W Smart Motor

11W each · cartridge below

5.5W Smart Motor

5.5W each · fixed 200 RPM

Drivetrain power44W / 55W

11.0W of headroom left. V5RC Override caps drivetrain motors at 55W, always re-check the current game manual.

Mix motor types however you like. The 5.5W runs at a fixed 200 RPM and takes no cartridge.

Cartridge (11W motors)

The cartridge changes the motor's internal gearing, so speed and torque move in opposite directions.

Wheel

Omni wheels

grip about 0.8 on foam

Traction wheels

grip about 0.95 on foam

Wheels go on in left and right pairs, so these move in twos. Odd numbers would leave one side grippier than the other and the robot would pull. Omni wheels roll sideways, which is what makes turning easy, but they give up grip. Swap a pair for traction and your pushing power goes up.

Robot weight (lb)

Grip depends on weight pressing the wheels into the tiles, so a heavier robot can actually push harder, right up until the motors run out.

V5 wheels are named by diameter.

External gear ratio

Driving (on motor)

Driven (on wheel)

1:1, direct drive

Only tooth counts VEX actually sells for V5, so every ratio here is one you can really build.

Estimated top speed

34.0 in/sec

Controllable

Under about 62 in/sec. The book's rule of thumb says this stays controllable on almost any build.

Pushing force at the floor

12.6 lb of push

Grip limited

Your wheels slip before your motors give up. Adding motors will not help here, but swapping omni wheels for traction will. Right now 2 of 8 wheels are traction.

Motors could give

22.9 lb

Wheels can grip

12.6 lb

Average grip across your wheels is about 0.84. Stall torque at the wheels is 4.20 N·m. These assume weight sits evenly on every wheel, which is never quite true.

Speed vs. torque balance

More speedMore torque

Wheels turn at 200 RPM. The 200 RPM cartridge is worth 3x reduction on its own, and your gears add none on top, so the marker sits at 3.00x overall. These are simplified estimates for learning the tradeoff, real friction and robot weight always cost you some of it. Confirm against your own robot before you commit.