There are few things in this world more disappointing than Wonderbread-style sliced white sandwich bread. This mushy, flavorless bread is pretty much the worst possible way to hold sandwich ingredients together, and yet kids all over the country are forced to eat it day after day. The only consolation is that moms cut off the awful crust, which is a disgrace to the bread crust name. Unfortunately, kids eventually grow up and don’t have moms around anymore to cut off their bread crust. That’s why Andrew DeGonge (AKA 3DprintedLife) built a completely custom robot to de-crust his sandwiches for him.
After making a sandwich, such as a classic PB&J, DeGonge only has to toss it onto a platform on the robot and it will handle the rest. An overhead knife comes careening down to slice the crust off of one side of the sandwich, then the platform rotates and the cutting process repeats. Two more clean slices later and the sandwich is crust free! Alright, so those slices aren’t exactly clean, but that’s mostly because the knife is terrible. A sharp knife with a completely flat edge would work much better. This machine is also capable of other routines, like chopping carrots or dicing onions. Impressively, the robot isn’t just following predefined motions — it uses computer vision to actually target the food that needs to be knifed.
That computer vision is handled by OpenCV running on a Raspberry Pi 4 Model B with a connected Raspberry Pi Camera Module V2. DeGonge created a simple card to calibrate the camera view, which essentially translates pixels into millimeters that the robot understands. To cut off crust, a bounding rectangle is drawn around the sandwich and the machine is told to bring the knife down several millimeters inside of the rectangle. The robot is controlled by a very sleek board that DeGonge designed that is based on high-quality Trinamic stepper drivers. That board cost DeGonge just $27 to build (at a quantity of 10), which we think is very deserving of some applause on its own. The rest of the robot was constructed in a fairly typical manner with a combination of aluminum extrusion and 3D-printed parts. Now DeGonge no longer has to rely on his mom to cut the crust off of his sandwiches!