Knock to move

The wall lamp is a pendulum arm on a brushless gimbal motor, with no buttons or switches. The arm is the only input, so the motor that moves it also has to notice when someone hits it.

Knocks are read through the motor’s own encoder. One knock steps the arm one position the way it was pushed, and a quick second knock sends it to that side’s end. Matter over WiFi covers the light for when getting up to knock on a lamp isn’t an option.

The light

The head I’m still designing puts a small light at the end of the arm, facing a row of colored plates on the wall. The room sees only light reflected off the plate the arm points at, so moving the arm changes the color.

Why a cycloidal reduction instead of a planetary gearbox?

At rest the motor driver sleeps and friction in the reduction holds the arm, so staying put costs no power. That needs enough torque to move the arm and enough friction to hold it. Direct drive and a printed planetary reduction came first. The printed cycloidal reduction, at a higher ratio on the same motor, does both.

Electronics

The lamp reuses the desk lamp’s control board and a fork of its firmware, which adds knock detection and a USB serial console for tuning the arm live.