Mechanical Design

Mechanically, our project is a cable-actuated robotic system that moves a board using four wires. These wires get spooled and unspooled by stepper motors attached at the corners of a frame we built out of 2x4s that provide rigidity to the system and put it at a height that is appropriate to shoot at.

Final System Frame

Frame

The frame is constructed using 4 cut 2x4s connected to 2x6s at the base, providing a sturdy and reliable foundation for the system. To enhance stability and reduce lateral movement, two horizontal cross beams were added: one at the midsection, serving as a mounting point for motor brackets, and another lower down to further distribute the load evenly. The corners are reinforced with L-brackets, ensuring the 2x4s remain securely fixed and minimizing any potential wobbling during operation. This design prioritizes simplicity and efficiency, using scrap stock for all materials to keep costs low and promote sustainability.

Backboard

The backboard is a foam core board cut to 8” by 10” with holes in the corners and in the middle at the bottom. Each hole in the corner is reinforced to prevent tearout by a hammer-in threaded insert and then a nail or screw can be used to provide a pin to attach the wire to the backboard. We found that using a rubber band at this attachment can be very helpful to account for over tensioning in the system. The holes at the middle bottom of the backboard are ½” in diameter, which allows for the two ends of our aluminum rod to fit in and then we used adhesive to attach it to the back of the hoop to prevent sliding and wobbling.

Motor Mount and Tensioner

Motor Mount and Tensioners

Finally, each motor is attached to the wood frame with a 3D printed motor mount and wood screws. The motor mount is designed such that a NEMA 23 stepper motor with 3D printed spool attachment can fit into it snugly and be screwed in to lock it in place. It has a guide hole on a corner tab to help keep the cable from spooling abnormally. We realized later in the project that a helpful feature for our mechanical system would be a cable tensioner so that our motors could unspool wire very quickly while keeping tension. The mechanical team created a 3D printed piece that snap fits onto the motor mount and uses two spools, one on a sliding shaft with a spring so that, when the motor gives out line, the spring snaps back and tensions the line again.