During RobotChallenge Sleipner was using 7 proximity sensors, but this did not work very well. The reason for that is that the sensors had 140cm ± 3% range almost regardless of the surface of the object. Most things were closer than that to the dohyo, so most of the matches were quite random.

The tests in the video below are done with only 3 sensors, but no objects are closer to the dohyo than 150cm. As it turns out this is quite enough even with a simple program. One problem is that the sensors are a bit slow, so while the robots turns at high speed small objects such as the can won’t trigger the sensors. Otherwise, the robot should abort the rotation and attack.

Considerations for the next robot

Sensors are among the biggest challenges when building sumo robots. Good sensors are really expensive and… not that good. My plan is to hopefully get some 200+ fps camera sensor and use an FPGA to approximate the position of the other robot. I’m quite familiar with Xilinx FPGAs and VHLD but I have only seen pretty slow camera sensors with a documented interface and an affordable price.

In general I would like to build the robot without spending too much money on it. Firstly because I’m a student and can’t afford too much (not considering sponsors) and secondly because I like the idea of building a great sumo robot without spending 800€ on maxon motors and lots on expensive industrial sensors. The motors I’m using now are normal BLDC RC car motors for 20€ each and I made custom motor controllers myself. The power output is much higher than for maxon DC motors with similar size. The outrunner BLDC motors I’m going to use for the next robot are even cheaper and have twice as high power output and lower RPM compared to the ones I currently use, so they are perfect for this. As the motors are brushless with sensors and I control the commutation myself they are also used as tachometers with 120 pulses per revolution per wheel, giving me an approximation of the current position on the dohyo. This is also used when turning around at the edge; the turn is not decided by a delay like most other robots, but by the angle difference reported from the motor sensors. Combining this with an all-seeing FPGA-based sensor should result in a really powerful sumo robot.