Motor Knob


To control the operation of electric windows, one of the options is to use a rotary knob to control the position of the window(s) being operated. Turning the knob is mirrored by the movement of the window with a rotary encoder picking up the direction that the knob is turned.

If one embeds a low-torque stepper motor, then the knob can be animated, especially during a flick-to-close/-open operation;  and to provide intuitive control to arrest window motion.

Such a control device may be used for other than the control of electric windows. It can be applied anywhere where its desirable for an operator to intuitively exercise proportional motion in an actuator.

The good thing about the Internet is that one can easily discover that others have already done part of your “original work”  work for you. 😉  Here’s a description and demonstration by Franck Fleurey of how to use an old hard drive stepper motor as a rotary encoder.

So at first glance, such a control knob looks feasible. Assembly and the main components of the master window control motor knob:

Explosion diagram of version 2 of the Motor Knob

Perimeter light guides are illuminated by PCB-mounted LEDs

  • Press larger bearing into end plate (black)
  • Press larger bearing onto shoulder of spindle (silver).

    Version 2 Motor Knob - Assembled

    Version 2 Motor Knob – Assembled

  • Feed stator wires (not shown) into the hollow spindle through the side hole, towards the front of the spindle. Press stator pole assembly onto spindle.
  • Press smaller bearing onto spindle
  • Press rotor poles (red) into knob housing (grey)
  • Slide rotor and knob over stator then clamp end plate onto knob using screws (not shown).
  • Clip lens sections (shown white) into the bezel’s ring.
  • Assemble pads onto PCB (green).
  • Slide assemble PCB and pads over the shaft of the bezel ring until it clips onto the ribs.
  • Feed stator wires through bezel shaft and plug into PCB.
  • Feed power and LINbus wires from PCB through the centre of the spindle.
  • Press bezel ring shaft into the spindle until it clips in. (Keyed)
  • Secure knob to panel using a screw through the hollow spindle.
  • Clip the centre push-button into the bezel.

At an overall diameter of about 50mm, the knob should provide enough space internally for a LINbus node (using SMD components) directly on the internal PCB, sensing knob rotation, driving the stepper motor, monitoring the 5 switches and driving at least 8, perhaps as many as 16 LEDs.

Embedding the node in the knob massively simplifies external wiring.

Window control knobs for two windows, such as one mounted overhead above the rear seat passengers, would  have only 2 pads; one for left, another for right. And of course, 2 lenses. It’s simple enough to press two buttons at once to select both windows for opening/closing.

A control knob for a single window requires no buttons at all, just the rotary knob and a lens to show operational status/location lighting.

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