​PuzzleBot
Overview
The electrical system consists of motor drivers for large (1HP) stepper motors, as well as smaller NEMA 17 steppers. When multiple motors are used to drive a single axis, the controls are electrically synced so that software can't cause the motors to actuate separately. The system also needs to control a solenoid, a servo, and a vacuum pump. Since many of these components run off of separate voltages, we also need regulation circuitry that allows a microcontroller's output to control all of the peripherals.
Challenges
We had many problems with power management. Because we used 1HP motors (seen below), small power supplies were not able to supply enough current to drive both motors. We ended up solving this problem by obtaining a separate isolated power supply for each large stepper.
As a result of the amount of power our steppers were consuming, we had problems with the drivers. We had to deal with chips frying, overheating, and breadboards melting (see below). To deal with this, the wire gauge was increased, the power transistors were moved to a perfboard (seen below) and soldered, and we doubled up power transistors to reduce the load on any one. Since we are using MOSFETs, they share loads nicely in parallel. The chips still get warm, but stay well within operating specifications.
We also had to deal with cable routing, since we need to get wires to a gantry arm and head that consistently move. We used the properties of angles to reduce the stress on the wires while making sure that the wires never drag on the ground, which could move puzzle pieces. (seen below)
Design Process
Our team chose to build our own stepper motor drivers from discrete power transistors and gate drivers. This decision was partly economic, since stepper drivers for 1HP steppers are expensive, and partly educational because our team members wanted a more concrete understanding of how stepper drivers work.
We also decided to place all of our control circuitry in one place and route wires to all the individual motors. This decision was made for simplicity, since it was much easier to design and fabricate with all the electronic chips in one place. Splitting up the circuit was considered because some of the circuitry could have been moved onto the gantry arm to reduce the trouble of cable routing.
An Arduino was chosen as the main interface between software and the world. PIC was also considered as a viable platform, but Arduino was chosen because of programming simplicity, plus previous exposure during class labs.
