🔍 What changed
This is the first version of the article, so everything below was added.
Gear mesh is how tightly the **pinion** (on the motor) meshes with the **spur** (on the drivetrain). Get it wrong and you either whine and overheat, or grind and strip teeth.
**The paper trick:** loosen the motor screws so the pinion can move. Place a small strip of ordinary printer paper over the spur gear where it meets the pinion. Push the pinion into the spur so it pinches the paper, then tighten the motor screws. Rotate the gears to pull the paper out. The paper's thickness leaves a tiny amount of **backlash** — just enough free play.
**Check it around the gear:** rotate the spur and re-check the mesh at several spots. Spurs are rarely perfectly round, so set the mesh at the **tightest** point — if it's fine there, it's fine everywhere.
**Reading it wrong:**
- Too tight (no backlash): whining, extra heat, wasted power, premature wear.
- Too loose (too much backlash): clacking/grinding and stripped teeth under power.
A correctly meshed pair makes a smooth, low hum — not a whine and not a grind.