3D-printed wheel or gear slips on the motor shaft: D-shaft and set screw fixes

A round bore on a shaft with a flat will slip. Print the D shape of the shaft and add a set screw against the flat.

What the message means

The torque goes through the contact between the hub and the shaft. A bore a little too large or without the flat has no grip.

Fix it in this order

1. Measure the shaft diameter and the flat with calipers.
2. Print a D-shaped bore and test the fit. Allow a small clearance for your printer.
3. Add a nut trap and a set screw that presses on the flat of the shaft.
4. Use a metal hub or a coupling for high torque.
5. Avoid glue on the shaft if you may need to remove the wheel.
6. Check that the hub wall is thick enough, so it does not crack.

If you see this, do this

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servo torque calculator, robot drifts to one side.

Last reviewed: November 2026. These are the usual causes and the order that finds them fastest. Test on your own board; clones and cables differ.