Mobile Robotics Platform

For this particular project, I was called in as a robotics consultant to aid in the design, build and implementation of a mobile platform for a robotic prop being used in a performer's tour. With a very tight deadline, unusual constraints, and the unique issue of sourcing components during the peak of FIRST FRC competition season, this was definitely an interesting one.

Design Requirements

Seeing as the platform was a sub-system of a larger robotic assembly, and it would be operated with a live performer by non-technical staff, most of the core requirements were put in place for safety (speed reduction) and ease of operation/maintenance while on tour. 

Typically, with a robot being operated by humans in close proximity to other humans, adding appropriate control features to ensure safe operation is recommended. However, doing so does require controllers and advanced hardware, all of which would be very difficult for a non-technical operator to diagnose and fix in the field. For this reason, it was determined that all the motors (for the platform and main robot prop) had to be "controlled" with direct analog input, not a micro-controller.

In addition to the analog control, only two robot operators would be present on the tour, requiring that all the motors would have to be controlled using only the input from two handheld remote control units. This is an especially challenging constraint; the robot needs more actuators than there are joysticks, so getting the desired motion and maintaining ease of operation without a micro-controller was a significant hurdle with this project.

Finally, we were given a little more than two weeks to take the robot from a concept to a finished system. For designing, building and testing a custom robot, two weeks is really not a lot of time so using as many off the shelf components as possible was made a priority. If something broke, or malfunctioned, there most likely would not be enough time to re-fabricate custom components, or source specialized electronics.

Mechanical Design and Drivetrain

Due to my experience with mobile robotics from my own work with FIRST, as well as my graduate studies, it made the most sense for me to handle the mobile platform, while the other engineers on the projects dealt with the mechanisms for the stage prop itself. Initially, we had considered designing it totally from scratch, but I suggested using a chassis from AndyMark (a common chassis choice for FIRST FRC robots) as the kit would supply everything we needed to get the platform together. This would also significantly cut down on design time, as it's a platform I'm intimately familiar with, and allow for as much time to test and fine tune as possible before shipment. 

The platform utilizes dual DC motors to drive each side of the robot, a drive-train commonly referred to as tank drive. This is one of the most mechanically simple drive-trains to implement with few parts to break, so it was the ideal choice for this task. Tank drive utilizes one joystick to drive the right motor of the platform "forward" or "backward", and the other to drive the left motor in the same way. This allows for full linear and rotational control, and is fairly simple for drivers to operate, unlike swerve or mecanum drivetrains (which are awesome, but much more complicated). Gearing for the motors was chosen so that under full throttle, the whole unit would not move at a dangerous speed, and also to increase the torque output. 

After the drive-train was completed, custom components like battery shelving and mounting plates for the main prop were designed and fabricated. The timing of everything meshed really nicely, and we were able to assemble the full platform in one (very long) day! 

Control and Electronics

In addition to just the mechanical design, all the electronics, and the method for controlling the robot without any on-board microcontrollers, had to be designed and sourced. The biggest issue with controlling the platform arose from the chassis being designed for classic tank drive, which requires two joystick for full control of the platform. As mentioned in the requirements, only one joystick on the remote could be dedicated to controlling the platform, so we had to get a bit creative here.