Mini drill speed control with stable RPM

[pvit]

This speed control tracks AC brushed motor's RPM via BackEMF and significantly improves tool usability, especially at slow speed.



Hardware should be universal, but PCB was routed only for Hilda 180W and others in the same case. It replaces original board, has self-calibration and does not require manual tune.

Links:

• Github - docs & firmware
• EasyEDA - schematic/PCB/BOM, everything can be ordered in couple of clicks

This project was done "just for fun", to learn how to make modern electronics easy-to-do for hobbists. We also documented all maths, raw logs and algorithm pitfalls here. May be that can save some time to one who decide develop something similar.

Enjoy!

PS. Not tested with 110V models, sorry.

[pvit]

New version of software & hardware:

• Support new grinder models (Hilda 180 is out of marked).
• Single side SMD mounting (more easy to assemble).
• Replaced PID with ADRC.
• Improved calibration.

[Renate]

In the US, Dremel brand (despite not being demonstrably better than the other crap) rules.
The low "numbers" on the "speed" control are practically useless since they have no torque.
I guess that I'll have to take mine apart and see if there is any space for a (reformulated) PCB.

[pvit]

AFAIK, original dremel 4000 series already has "constant electronics" feature. And dremel 3000 series has not enougth room for PCB reroute.

[Benta]

A universal motor does not generate useable back EMF for this kind of thing. I find this highly questionable.
Measuring current consumption of the motor and increasing voltage when it rises might work, but would probably have stability problems. Works great with PMDC motors, though.

[pvit]

A universal motor does not generate useable back EMF for this kind of thing. I find this highly questionable.

https://github.com/speedcontrols/ac_sc_grinder/blob/master/doc/math.md I'd suggest to read doc about math first. It contains details about our implementation, and references to alternatives.