Your Motor, Measured
Measure a motor's speed and torque at a few loads and see its real speed-torque line beside the published one. Worn motors and cartridges drift, and this shows by how much.
Inputs
Run the motor at full power and load it by different amounts: a lever on a spring scale, a brake, or the robot pushing into a wall. At each load, read the speed and the torque the motor reports: Motor.velocity(rpm) andMotor.torque(Nm) in VEXcode, or get_actual_velocity() andget_torque() in PROS. Spread the loads from light to heavy.
Fill from a robot log (CSV)
A CSV the robot saved to its SD card, or any spreadsheet saved as CSV. It’s read on this device and isn’t uploaded anywhere.
Results
Free speed, from your line
—rpm
Of the published free speed
—%
Stall torque, from your line
—N·m
Of the stall torque in the site’s figures
—%
How straight your readings are
—R²
Readings used
—
Show the numbers behind this chart
Your readings, and the speed each line gives at the same torque.
How this is calculated
A DC motor’s speed falls in a straight line as the load on it rises: fastest with no load (free speed), stopped at its stall torque. The page fits the straightest line through your readings (least squares), then reads off where it crosses each axis.
speed = free speed − slope × torque stall torque = free speed ÷ slopeWith your numbers
What this doesn’t cover
The torque is the motor’s own estimate, worked out from its current, not a measurement at the shaft. The ends of the line are extrapolated past your lightest and heaviest loads, so they’re only as good as the readings. VEXos also limits current, which flattens the heavy end of a real curve.
Make a notebook page
Turns this calculation into a dated engineering notebook page: the setup, data, results, figures, working and sources, numbered and cited. You add the goal, the decision and the reflection in your own words, plus photos and sketches. Print it, paste it into Google Docs, or download a Word file or slides.
Save this run, and compare
Keeps what is on screen so you can change something and see both sides of the change. Saved in this browser only, never uploaded.
Sources & assumptions
Published: each cartridge’s free speed, and 2.1 N·m stall torque for the 100 RPM cartridge. Derived: the 200 and 600 RPM stall torques, from the same motor behind different gearing.
Every reading is yours; the line is derived from them.
- VEX Robotics: V5 Smart Motor & Gear Cartridges (276-4840) — checked August 2026
- Purdue SIGBots Wiki: VEX Motors — checked August 2026
Where this goes next
Explore further on the full mapWhere the answers on this page can be used, and which tools could have given you the numbers it asks for.
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Your Motor, Measured
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