Date: September 2019
Created By: Alex Gronlund, Christian Weaver, Joseph Allen, Samuel Ryckman, Erick Eickhoff
Purpose: Compete in the NRC Combat Robot Competition
Features: Spinning at 400rpm, lightweight design, custom PID motor controllers.
This robot was constructed to compete in the Combat Robot event at the 2020 NRC competition. The goal of this competition is to construct a 14" x 14" x 14" 3lb beetleweight robot. Two robots fight head-to-head in an enclosed 8’x8’ arena until one of the bots becomes immobilized. The robot we designed for this was a full-body spinning robot. It is circular and the entire robot is designed to spin at approximately 400rpm. The primary weapon is a tooth sticking out of the side to hit the other robots.
Mechanically, the idea behind this design was to put as much mass as possible behind the weapon so that we could maximize damage. With a weight limit of 3lbs, if mass is split between the weapon and drivetrain there would be a tradeoff between weapon effectiveness and controllability of the robot depending on how the mass was split between the two. By making the entire robot the weapon, all the mass is simultaneously part of both the weapon and the drivetrain. For the chassis, the main components and the selected materials are as follows:
This design was tested for durability and effectiveness with a prototype constructed from similar materials and dimensions. In the testing, the design held up quite well despite using weaker materials, and the weapon proved very effective.
Electrical and Programming
The planned electrical system for this robot is show in the diagram below. Brushless motors with integrated drivers were chosen for the primary drive motors. An Arduino Nano 33 BLE was chosen as the controller since it has a fast processor and a built-in 9-dof IMU. For controlling the robot, the Xbee remote controllers our team developed would be used.
Since the robot would be spinning at a high rate of speed, very accurate motor control was needed to achieve reliable movement. To make this happen, the team decided to develop a custom motor speed controller. The device would be controlled through i2c and manage the speed of the motor using a PID controller algorithm. The planned design for this controller is shown below.
Some testing was done using a prototype with promising results. We simulated rapidly changing the motor speed to a set value as well as varying the motor speed in a manner which would be similar to when the robot is translating and spinning at the same time. The controller was able to perform both of these tasks reasonably well (see video in gallery), but no testing was done with the motor on an actual robot.
Another portion of the work revolved around getting the robot to drive in straight(ish) line while spinning. Early on in the first semester we were able to get the robot to do this but at a low speed. The rest of the two semesters was spent trying to make this work at much higher speeds but due to some finicky hardware and a shortened time due to Covid-19, we were not able get this working by the end of the school year.
At the moment, the robot is partially manufactured but the control systems are largely still unfinished. We will likely plan to compete at the NRC again next year, so we are quite certain that we will be able to finish this bot by then. We look forward to seeing how it fares in the arena!