A Combot (short for "combat robot") is a remote-controlled machine with attached weaponry designed to damage or destroy another robot in a fight. Under the student organization iRobotics, the Combots division consists of four teams that each build their own combot and demonstrate them in showmatches during Engineering Open House in the spring, alongside visiting robots built by individuals, alumni, and teams from other universities.

Robots entered into competition are limited to 30 pounds. After a short discussion, our team decided on a drumbot design, which uses a vertically spinning toothed drum to strike opponents. Following this, we began looking for appropriate components (keeping in mind power, weight, size) to add to the Bill of Materials, and CAD modeling of confirmed components began.

A partial capture of the BOM.

Design of the robot's drivetrain came next. We had seen in previous years that robots with a frontal weapon tended to necessitate placing the drive wheels all the way to the rear of the robot just to fit the weapon motors and pulleys in. However, with the center of mass of the robot so far forward due to the weight of the weapon, traction on those wheels was often loose, and driving was erratic. We solved this problem by making the robot wider than usual, leaving a large enough gap between the drive motors to run the weapon belts through to motors placed in the rear. This allowed for a more balanced weight distribution on the drive wheels, and a more controllable robot.

The frame of the robot was designed to be built up from a series of stacked flat plates, cut on a waterjet and bolted together. This allowed us to round the corners of the robot, preventing any corners which would present a vulnerable surface. Internal components such as motors and shafts were to be attached to milled mounts, sandwiched between the plates.

Completed CAD model.

With the CAD complete, fabrication began. Nearly all the parts were machined on the waterjet out of various thicknesses of aluminum plate, with only the weapon made of steel. The 30lb weight limit was a major consideration, with our robot tipping the scales at over 29lb after completion.

The waterjet-cut base plate of our robot.

After I applied a galaxy-themed paint job to the plates, assembly began. Bolts were slotted through each hole, then the rest of the parts dropped into place. Electrically, the weapon and drive motors ran on two separate circuits, powered by two separate batteries. Control was done through a standard RC airplane receiver and remote, which allowed for some tuning of drive characteristics.

Not quite final assembly and testing, but the final configuration.

You can watch the entire competition and view the bracket here: