Robotics Team Notes: Teaching Relay to Start Smoothly
1The robotics team at Larkfield Middle School built Relay, a robot that carries lunch trays and library books down the school's long hallways. On its first trial run, Relay lurched forward so quickly that a cup of soup slid off its tray. Team members Ottilie Nakashima and Bram Castellucci decided to find out how the net force on Relay and its total mass affect how quickly its speed changes.
2With no load, Relay has a mass of 4.0 kg. To add mass, the pair strapped sandbags into its tray bin. Relay's program sets how hard its wheels push. To measure each setting, the pair hooked Relay to a force gauge tied to a wall and let its wheels push while the gauge held it still. Relay's wheels and motors also rub as it rolls, so friction pushes back on it. To measure friction, the pair towed Relay slowly at a steady speed with the gauge (Table 1). Then they subtracted friction from the wheel push to find the net force.
3Every run started from rest on the same stretch of smooth tile floor, and a motion sensor measured Relay's speed 2.0 s after the start. The pair repeated each run three times and recorded the averages in Table 2. The hallway was cleared during each run, and Relay never went faster than a slow walk.
4Before collecting data, the pair checked that the floor was level. They set Relay down with its motors off and made sure it did not start rolling in either direction. They also marked a start line with tape, so that every run began at the same spot, at least 10 m from the end of the hallway, and a teammate stood at the far end to stop Relay if anything went wrong. After the tests, Relay's own motion sensor kept a log of its speed during real deliveries, so the team could check how it started and stopped with a load on board.
5The cafeteria staff gave the team a requirement for soup trays. Relay's speed may change by no more than 0.25 m/s each second, and it should reach 0.50 m/s within 2.0 s of starting. Relay's motors can push with at most 8.0 N.