FIRST Tech Challenge

Over winter break I took SKIDADDLE apart into pieces that each do one job. Controllers now only ask for accelerations: one along the path, one back onto it, one for heading, each with a weight and a priority. A scheduler runs whichever are active, and a default controller brings the robot to a stop when none are. A new allocator turns the requests into motor space and hands out each motor's remaining headroom, highest priority first and shared by weight within a priority, so correcting off the path can come before speeding along it without any motor going past its limits. The look-ahead, before the most expensive part of the loop, became a precompute: when a path is made, one backward pass finds the fastest speed the robot can enter each turn at, so the loop only reads it.

Planning in motor space means a turn's sideways acceleration comes out of the same wheel budget as speeding up and slowing down. Road Runner limits acceleration only along the path, so on a tight hairpin at the same limits its plan asks for more grip than the wheels have, falls behind and overshoots the end. With its limit lowered to 30 in/s² it stays within 9 in; SKIDADDLE stays within 4.5 in and stops 0.7 s sooner. It isn't ahead everywhere: on sharp corners Road Runner with the lower limit tracks tighter, and the rework doesn't correct sideways error yet, so it can stop a few inches off the end point.

SKIDADDLE is a path-following library for FTC robots, written in Java, that I built to fix inefficiencies in Road Runner, the usual FTC path library, and get better paths. It plans with a physics model of the robot, and I derived all of its math by hand, myself, without AI or earlier work to build on. A path, a cubic Bézier for autonomous or a Hermite spline built on the fly in tele-op, is flattened into straight segments by adaptive De Casteljau subdivision, and a curve whose turns would need more than the robot's acceleration is relaxed until they don't. Every loop it splits the robot's velocity into a convergent part, toward the goal, and a transverse part, everything else. It first spends its acceleration budget cancelling the transverse part, then speeds up the convergent part, so from any starting position or velocity the robot converges on the path. A look-ahead over the stopping distance sets the fastest speed for each corner, and the robot switches segments when its braking distance says it must. Heading is a separate controller, and the result goes through PIDF and feedforward to the four wheels. A simulator draws the field and graphs every step.

FTC rules ban streaming camera images to the driver station during a match, but telemetry text is allowed, so Live View sends the robot's camera feed as text. Each frame is shrunk and converted to the Lab colour space on the robot, then drawn with Braille characters as pixels: each character is a 2×4 block of dots, and Floyd–Steinberg dithering decides which dots are on, so shading survives with only on and off. To keep the message small, colour is added only for the game pieces: runs of characters that match the yellow, red or blue samples are wrapped in a colour tag, and only the 100 longest runs are kept. The text goes out as HTML telemetry ten times a second. It gave our drivers a view of what the robot could see during matches, within the rules.

As captain I set up a new way to build our robot: two robots developed in parallel. While the CAD was being finished, we assembled the drive trains. Software then got the first robot, a bare drive train, to test on, while mechanical integrated the first feature, such as the lift, on the second. Once that feature passed our definition of done, the teams traded: software integrated the feature and kept developing, and mechanical moved on to the next feature, like the arm, on the other robot, and the trading continued all season. Software was always testing on a competition-ready robot while mechanical kept building, our drivers got more practice before the robot was feature complete, and we would have had a robot ready for competition even if mechanical badly missed a deadline.