A Crust-Cutting, Carrot-Chopping Robot

[3DprintedLife] sure does hate bread crust. Not the upper portion of homemade bread, mind you — just that nasty stuff around the edges of store-bought loaves. Several dozen hours of CAD later, [3DprintedLife] had themselves a crust-cutting robot that also chops vegetables.

This De-Cruster 9000 is essentially a 2-axis robotic guillotine over a turntable. It uses a Raspberry Pi 4 and OpenCV to seek and destroy bread crusts with a dull dollar store knife. Aside from the compact design, our favorite part has to be the firmware limit switches baked into the custom control board. The stepper drivers have this fancy feature called StallGuard™ that constantly reads the back EMF to determine the load the motor is under. If you have it flag you right before the motor hits the end of the rail and stalls, bam, you have a firmware limit switch. Watch it remove crusts and chop a lot of carrots with faces after the break.

This is far from the dangerous-looking robot we’ve seen lately. Remember this hair-cutting contraption?

9 thoughts on “A Crust-Cutting, Carrot-Chopping Robot

  1. So how does the firmware limit switch (flag) work as the article claims “have it flag you right before the motor hits the end of the rail and stalls”? It detects back EMF from the motor being under increased load, and therefore will register the same load *until* it stalls, and *then* it will flag.

    Am I missing something here?

    1. It actually flags right as you make contact with the hardstop (not before). When you make contact, the stepper will gradually see increased load before it eventually skips steps. Stallguard allows you to identify this increasing load and stop driving the motor before it actually skips any steps. Works very well as long as the hardstop is indeed a hard stop and not a squishy stop!

    2. You’re right I think the article has a typo, stallguard flags after contacting the hardstop but before the motor stalls. So the motor actually won’t lose any steps while performing a sensorless homing routine!

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