UW Robotics Team

Fall 2017 to present
PCB Design, EMI Testing
University Rover Competition preparation

We are currently designing and building an autonomous rover to compete in the University Rover Challenge in Summer 2018.

End Effector

As part of the challenge, the rover is required to pick up and store various samples and artifacts. I designed the end effector board for the rover, which controls a motor to open and close the claw, and allows the end effector board to communicate with the arm and the shoulder boards via I2C, CAN, and UART.

You can find the schematic capture files, pcb layout files, and Gerber files here.

PCB Design

After creating the schematic, I designed the PCB layout for the board. I aimed to mitigate interference by keeping PWM signals far from communication signals, and I used a copper pour with vias around the voltage regulator for thermal relief.

Safety Board

I also designed the safety board for the rover. The main functions of this board are: Undervoltage protection, overcurrent protection and current monitoring (using I2C), and temperature-dependent fan control for the board box.

Microcontroller - For overcurrent protection, the MCU reads from current sensors using I2C, and flips the relay if there is a current spike (This is a software solution).
Temperature-dependent fan control - the IC outputs a higher frequency PWM signal at higher temperatures.
Undervoltage protection - samples the battery and uses a mosfet to control the relay if the battery depletes below 11V (to prevent damage to the compoenents)

EMI Testing

For this competition, we want to run all of the wires from the shoulder up to the end effector on the inside of the arm. As such, I performed electromagnetic interference testing to determine if the PWM signals should be shielded.

Procedure

To do so, I simulated an I2C communication protocol using two Arduinos, and wrapped the wires tightly around the wires that control the motor for the arm. Then I ran the arm and checked the interference on the oscilloscope.

First, I took control measurements of the SCL and SDL as a baseline.

Next Steps

From testing, we determined that the PWM wires should definitely be shielded. We will conduct further testing with shielded wires to see what else can be done to mitigate interference.

Overall, this term we are focused on more testing (relays, heat sinks, etc.), and we will be soldering and debugging the PCBs that were designed last term.