Kybernetes is a test platform for autonomous navigation I developed with the Robotics Society of UC Merced. It has competed in Robogames 2012 and 2013, taking second place in Robomagellan in 2013 (see http://nathanielrlewis.com/?p=24). Development was started in 2011 with a budget of $2,500.
Since design, construction, and software had to be handled in a four month timespan (December 2011 – April 2012), Kybernetes was built with off the shelf parts to speed up development. Robomagellan is an outdoor and off road challenge, so the vehicle needed to have a chassis capable of overcoming rough terrain. Observing the competition in the past, repurposed RC vehicle chassis were quite popular among competitors. No combustion based engines are allowed in Robomagellan, so we used a Traxxas E-maxx (Traxxas #3903). It’s a robust vehicle with independent suspension, four wheel drive, and a large weight capacity for its size. It is sold by almost every hobby shop in the country, making replacement parts easy to acquire in a hurry. To make the chassis more suitable for a robot, some modifications were made – the transmission shaft was extended forward so that a quadrature encoder could be mounted to the transmission cover and as the stock suspension was to weak to support the additional weight of the electronics, it was stiffened. Spring stock was purchased at Orchard Supply Hardware that was the same diameter as the standard shocks on the chassis and cut into segments the same length as the E-maxx stock shocks. To reduce the amount of electrical noise from the motors and to decrease energy usage, the stock dual brushed motors have been replaced with a singular 1660 Kv brushless motor (Hobbyking S3674-1600) and the speed controller replaced with a bidirectional brushless controller (Turnigy Reversible 60A ESC). Note – most brushless controllers are unidirectional, I made this mistake when purchasing a controller, so be careful. The stock E-maxx also feeds the drive motors 16.8V from two battery packs and is capable of reaching 45 mph. The brushless controller is only fed 8.4V from one battery pack, and the modification drops the top speed to a more sane 10 mph (still makes catching it in the event of failure difficult).
In an effort to spatially partition the components in Kybernetes, all the electronics related to motion are mounted directly on the chassis. When competing in Robogames 2013, we noticed that the 6V lines coming from the BEC circuit in the ESC became noisy when the robot was accelerating. It would cause the servos to rotate to one extreme and then come back under control. To fix this situation, the battery that feeds the ESC is also fed into an external 6V switching regulator (LM2596) to provide power to the steering servos.