Unit 3: Force, Torque, Speed, and Gearing

The fast motor problem

A motor can spin beautifully on the bench and still fail the moment the robot asks it to move a real load.

This Unit answers why speed alone tells you almost nothing about whether an actuator can do the job.

Torque Is Not Speed separates the two quantities. Gear Ratios Are Design Decisions shows how transmission changes the operating point. Predict Before You Build turns equations into a testable forecast instead of post-failure explanation.

Numbers should change the design

You will work with force, lever arm, torque, speed, ratio, load, stall behavior, and efficiency. The point is not formula memorization. The point is to predict a design tradeoff before hardware forces the answer on you.

Keep a gearing calculation and tradeoff memo for a bounded robot task.

A strong memo says what you assumed, what the model predicts, where losses were simplified, and which measurement would make you revise the choice.

A calculation is evidence with a boundary

Label calculations as models. Label simulation as simulation. Label physical measurements as physical measurements. Do not blur them together just because the final number looks precise.

Move on when you can explain why a chosen ratio helps one requirement while hurting another.