Sojourner/Fall/2018
Motor Driver 3DoT Breakout Board
Author/s: Brandon Leinert
Table of Contents
Introduction
The Sojourner project is designed to use 6 motors for each of the wheels. The 3DoT board that is used to operate the robot only has two motor drivers onboard. Therefore, an additional breakout board is required to operate the 4 additional motors. Rather than use the PCB design from last fall that resolved this issue, a new custom board was created that did not need an additional I2C I/O expander, and also was designed to fit the new pin layout of the 7th generation 3DoT board.
Design
To complete the design of the breakout board, the student used Eagle CAD along with Arxterra’s breakout board guide as a reference [1]. The design for this custom board was based on the discontinued Sparkfun MiniMoto [2] which features the DRV8830 as the motor driver. The benefit of basing the new design on the MiniMoto was that the DRV8830 has a programmable I2C address, which allows for up to 9 unique drivers to work on the same I2C address bus.
With the intended goal of fitting 4 H-bridges on one breakout board, the student’s original design placed each DRV8830 on the same side and in close proximity to the resistors required for the drivers operation. This led to the flawed arrangement in which only 3 drivers fit on the top side of the 1250 mil x 825 mil PCB, while the last driver was placed on the bottom. While this initially seemed better than the alternative of stacking two breakout boards that each had two DRV8830s, further efforts were made to fit all four drivers on the same side.
After consideration, the four drivers were arranged in a single file row, and traces were moved to the bottom of the board as necessary. With this adjustment, the final design helped with removing unnecessarily long traces, and provided aesthetic improvements thanks to its design symmetry.
Conclusion
The new breakout board has been designed and updated in a way that reduces the size requirement of the project’s electronics, and eliminates unnecessary components such as the I2C I/O expander. Also, understanding that the design was based on a retail electronic component, there should be no problems with the operation of the four motors.