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Knobber

What is it? #

Knobber with ergonomic cap
Basically a low speed rc motor which can be controlled via a microcontroller.
There is a magnetic encoder to sense the motors position and a driver chip - well to drive the motor.

Mechanical construction #

Here are all the mechanical components neatly pulled apart from top to bottom:

  • cap which is the twisting part
  • brushless motor 2204 size from Aliexpress with 260KV
  • mounting plate with 3 heat set inserts
  • encoder magnet holder constructed similar to a plastic dowel
  • circuit board
  • base with cutout for USB

Explosion view

All is screwed together with either M2 or M3 screws.

Electronics #

Probably the easiest component to decide on was the STM32G070RBT6 MCU, since we have about 100pcs. surplus of these at work where nobody needs them anymore 😁.
The other main part was the motor driver to drive the three phases of the motor with sufficient current.
After an extensive search on Digikey and Mouser I found this part, which was in stock, compact and relatively inexpensive.
The magnetic encoder was chosen, because of a few breakout boards from aliexpress I already had laying around with these chips on them.

The schematic was mostly drawn from the microcontroller outwards, whose pin assignments were planned beforehand with the STM32CUBEMX software.

Link to the schematic on Github

Other than that there is only a USB-Serial converter and two RGB LEDs for more input/output capability.

Assembly #

All the boards were assembled by myself by hand with a solder paste stencil and some fine tweezers.

Some people might think this is a very cumbersome task to hand place tiny components, but I really enjoy this and think it’s very meditative.
After working trough the iBOM assembly drawing (also available for Altium) the next step is reflow soldering.

Knobber during reflow

I have thought about getting a toaster oven and converting it to a reflow oven, but the cheap aliexpress hotplate has done its job well so far.
The other side I reflowed with a heat gun.

Software #

Now comes the ugly spaghetti code a hardware engineer slapped together.

The software is currently still very much work in progress, so hopefully this section will be extended or it might diserve its own post at some point.
In the mean time thanks to ftobler on github for adding his self developed RTOS to the project. This makes it a lot easier to add independent stuff to the code (especially when you are a programming noob like me 🙄).

And why the weird name? #

Well.. It’s a knob and a “Trüller” (swiss-german word for twistable thingumabob).
Also the swiss way of pronouncing a harsh “K” just fits somehow.

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