Turning the knobs

A project log for Apartment HVAC IoT

Bringing analog hvac system into home automation.

PyDrewPyDrew 10/29/2020 at 16:520 Comments

There are two knobs on the control panel. One adjusting the thermostat moves in a 270 degree arc: 135 degrees counterclockwise for heating, 135 degrees clockwise for cooling. The second in a continuous movement at 60 degree indexed positions for off, heat, low cool, high cool, exhaust, vent.

Removing the plastic knob revealed a knob post with a flat, making for a simple, friction fit, 3d-printed.

Moving the thermostat was easy for the NEMA-17 motor.

The heat/cool mode selector, however, required more torque than the NEMA-17s that I had could provide directly. I attempted to solve with a more scientific method of measuring the torque but neither the fancy, digital automotive torque wrench or the mechanical one wouldn't measure that low. Elementary school science of a simple spring scale and a foot-long length of material would have been ideal; but would have to wait until Amazon could deliver the $6 scale.

In the meantime, a stepper motor with a 5:1 planetary gear that originally had been destined to upgrade my 3D printer extruder seemed to do the trick.