FRC 5026 would like to introduce a handheld motor driver which adapts a Milwaukee M12 battery to 12V + PWM output, perfect for plugging into Falcon 500 motors. We’ve used this over the past season to prototype mechanisms with 1 or 2 motors for intakes, outtakes, conveyers, and more! This is only one way to slice it, of course, and we’ve picked the parts to be accessible to quick freehand soldering. Please feel free to reach out with questions and comments.
Shown here is powering and controlling a DC Motor + TalonSRX (what was on hand today) via PWM signal.
Please use appropriate caution regarding PWM controllers and lithium batteries if you build this!
We have used M12 batteries to power other robot projects. One project we are working on is a cutoff circuit when the voltage drops below a set voltage so as not to damage the batteries.
Love this application!
Yes. I found out the hard way that the DeWalt 20 V batteries don’t have an integrated cut-off circuit. I was using a DC-DC converter to run my old Craftsman drills using some DeWalt batteries and I left it connected over the weekend. The quiescent current of the DC-DC converter drained the DeWalt battery to the point the charger would not charge it.
Where did you find the cut-off circuits? I could make my own but would rather just buy a ready made one.
Yes the M12 battery packs are pretty bare bones inside. That’s part of what makes them straightforward to use here since the terminals can be reached by some standard quick connect terminals. If there are any off the shelf protection circuits for 3S Li-Ion that are the right size to fit right where the terminals are here that could be a very slick update.
For fun, we also have a version of this for DC motors using a cordless drill trigger. There are some files in the links here, but not a full BOM. I could package it more if folks are interested.
What do you use for the contact pins on the M18 batteries? It would be nice to have a little more oomph from those batteries, which we also have. Though, getting a 18V-to-12V converter that can spike up to ~40A without damage has been challenging.
In preparing for the new season, I’ve made a little piggy-back PCB for the Teensy-LC to help simplify assembly and also get simple voltage feedback from the pack to cut off the PWM signal when too low.
Originally, I wanted to add an off-the-shelf BMS to provide both voltage and current protection at the cell level, but that proved to be too much for all the milling about this fall.
Software and build instructions are still in flight but should come in the next few weeks. Sorry for the delay! Hopefully there is still some time pre-season for anyone interested.