Robotics Team Notes: Pip Bumps Into Things
1The robotics team at Linwood Middle School built Pip, a small robot that carries library books and lab supplies between classrooms. With its tray, Pip has a mass of 6.0 kg. It rolls on smooth wheels and steers itself down the halls with a camera. In its first week on the job, Pip bumped into a rolling supply cart, a recycling bin and, once, a student's leg. No one was hurt, but coach Mr. Delroy Hutchins asked eighth graders Astrid Mensah and Joaquim Fairbanks to study the forces in a bump and to design a safer robot.
2First, the pair tested bumps with rolling carts on the smooth hallway floor. They loaded each cart with books to a measured mass. With its standard rubber bumper, Pip drove straight into the resting cart at 0.8 m/s. A switch in the bumper cut Pip's motors the moment it touched anything, so during each bump the only strong sideways pushes on Pip and the cart came from each other. A thin force sensor behind Pip's bumper recorded the largest force on Pip during the bump, called the peak force. A phone filmed each bump from the side, next to a meter stick, so the pair could find how much each object's speed changed. Each bump was repeated three times, and Table 1 shows the averages. In every bump, Pip either kept rolling forward more slowly or stopped. The pair also bumped Pip into Cart X, a cart of library returns whose mass they did not know.
3Next, the pair tested hallway safety with a shin dummy, a padded post bolted to the floor with a force sensor behind its padding. Pip drove straight into the dummy with different bumpers and top speeds (Table 2). Mr. Hutchins gave three criteria. The peak force on the dummy must be 65 N or less, so a bump would not hurt a person. Pip's top speed must be 0.5 m/s or more, so deliveries finish between classes. With its bumper, Pip must be 60 cm wide or less to fit through the gap beside the lab benches. The bumper wraps around the front corners, so it adds its thickness to both sides of Pip's 50 cm body.
4The school is also building a second robot, Quill, which has a mass of 12 kg. In narrow halls, the two robots could meet head-on.