Two steps. First the Motor Lab: measure your own motor and find its torque and speed. Then the estimate: will the motor drive your legs, and how far will the robot walk in 15 seconds?
Your design is saved in this page's link. Copy link gives you a link to paste into Google Classroom or your notebook. Opening it brings everything back.
Step 1 · Motor Lab
Put a spool on the motor shaft and time it lifting a known mass. Heavier masses slow the motor down. Four lifts are enough to draw the motor's torque–speed line.
Lift tests the numbers filled in are example data
The numbers filled in are example data. Replace them with your own. A row only counts when mass, height and time are all filled in.
Speed against torque
Stall torque is found by extending the line. Don't hold the motor stalled to measure it. Most power comes at half the stall torque and half the no-load speed.
Step 2 · Torque and speed
Now put the motor and the legs together. The motor slows down as the load goes up, so a heavy robot or a leg that bobs a lot walks slower, or stalls.
Torque at the crank
Speed and distance
How good is this number? The biggest guesses are linkage efficiency and slip. After a test run, adjust linkage efficiency until the predicted distance matches what you measured. Then use the page to compare design changes.
Using it on your project
Run the Motor Lab with your own motor and battery pack. Type in your spool diameter, your no-load count, and your lift times. When the status says OK, switch the motor numbers to Motor Lab.
Bring in your leg. On Leg and Foot Path, press Send to Motor and Speed. Or pick Estimate by hand and type in a stride and a duty factor.
Weigh the robot. Mass matters more than anything else on this page.
Read the two checks. Torque: is the peak well under the motor's stall torque? Traction: can the feet push harder than anything that drags?
After your first real run, calibrate. Change linkage efficiency until the predicted distance matches the distance you measured. Write both numbers in your change tracking.
Then compare changes. Lighter body, another leg per side, a gear reduction. Predict first, then test.
It's an estimate, not a promise. Your walk score comes from your best real run against the benchmark, 90 cm. A robot that curves, tips or slips will fall short of this page's number.
How the estimate works
Motor. Speed falls in a straight line from the no-load speed to zero at the stall torque. Extra gearing multiplies the torque and divides the speed.
Lifting. Each crank turn, the motor lifts the body by the body bob, once per step. Work = weight × rise.
Drag. Anything that slides takes work too: friction × the weight on it × the distance moved.
Torque. Average torque = (lifting + drag work) ÷ linkage efficiency ÷ 2π. The peak is higher, because the load comes in bursts.
Speed. Crank speed = no-load speed × (1 − average torque ÷ stall torque). If the peak torque is more than the stall torque, the crank stops.
Advance per turn. With a foot always down, each turn moves the robot stride ÷ duty factor. With gaps between steps, it moves one stride per leg on a side.
Traction. The feet can push with grip × the weight on them. If the drag from sliding parts is more than that, the feet slip and the robot goes nowhere.
