Polyathlon Robots compete for points in 6 contests to determine the best overall performer. The contests are Simple Line Follower, Advanced Line Follower, Beacon Killer, Beacon Killer with Obstacles, Navigation by Dead Reckoning and Bulldozer. See the rules below which cover each of these events.
These six contests are designed to challenge the robot builder to find the best balance of size, weight, speed, and other features to achieve the highest total score. In 2018 amidst fierce competition, Polymax 9000 was the first Polyathlon robot to come in first place in all 6 contests to achieve a perfect score .
Each robot will receive a score for each contest, and the robot with the highest total score at the end of all 6 contests wins the Polyathlon. A robot does not have to compete in all 6 contests to participate. While the most successful Polyathlon robots tend to be built from scratch, there are many robot kits available which perform well in individual contests. Examples include the Pololu 3pi for Line Following and the Zumo32U4 for Bulldozer.
The rules were last updated in November 2019. Navigation by Dead Reckoning is now a timed event and will be run on the Bulldozer table.
Tips for Building a Polyathlon Robot
Array of 3 Ultrasonic Sensors used to detect obstacles pointing left, right, and straight
Custom-built Line Sensor Array
To compete in all 6 Polyathlon contests, a robot will need quite a few sensors.
Line Sensor. Used in Line Following, a Line Sensor looks at the ground and determines whether it is white or black. While Line Following is possible using as little as one sensor, competitive robots tend to have an array of 8 to 24+ sensors spaced no more than 3/4" apart. Ideally the line sensor will be as wide as possible and as far out in front of the robot's wheels as possible. If all the sensors are mounted in a straight line, the robot may lose sight of the line during a sharp turn and would need to remember on which side it last saw the line. To reduce the likelihood of losing the line during a sharp turn, the line sensors can be mounted in a V shape or in an arc. For a 10" wide robot, a couple of QTR-16-MD reflectance sensors can be a good option. If you are experienced in vision processing, you could try sensing the line with a camera.
Edge Sensor. Used in the Bulldozer contest, the edge sensor is senses the edge of the table so the robot doesn't drive off. Edge sensors should be mounted far forward and as wide as possible sticking out beyond any front wheels, as the robot will need some time to stop itself before any wheels go off the edge. While it is possible to use a Line Sensor as an Edge Sensor, this has caused issues in the past for robots during competition as the lighting conditions may be different than where you practiced. A dedicated Edge Sensor that specifically senses distance is often the best option. The sensing distance is typically 2cm to 10cm depending on how high the Edge Sensor is mounted on your robot. This distance is generally too short for Ultrasonic sensors to be effective, but IR sensors can be used. Sharp makes a series of Digital Distance Sensors with 5, 10, and 15cm ranges that can work well and there are Time-of-Flight sensors with the proper sensing range too.
Obstacle Sensor. Used in Bulldozer and Beacon Killer with Obstacles, an obstacle sensor is used to detect the presence of obstacles within the robot's vicinity. In the case of Bulldozer, the goal is to drive towards the obstacles, while in Beacon Killer any contact with the obstacles is to be avoided. An ideal obstacle sensor would not simply sense that there is an obstacle; it needs to tell your robot where the obstacle is so the robot can decide whether to turn left/right or go straight as needed. Obstacle sensors are often used in an array, with each of several sensors pointing in slightly different directions. Multiple distance sensors can be purchased and configured into an array including options such as Time-of-Flight, Ultrasonic, and Infrared. All-in-one solutions include spinning Lidar systems and the Protractor Proximity Sensor designed by one of our own club members.
Beacon Sensor. Used in Beacon Killer contests, a beacon sensor consists of a sensor mounted on the robot and a separate beacon which the robot must find. Like the Obstacle Sensor, knowing the distance to the beacon isn't as important as knowing the angle that the robot must turn to face the beacon head on. Some beacon designs have a 360 degree field of view, while others accomplish the job with just two sensors facing forward. There aren't many great beacon and sensor options available off-the-shelf so design and/or selection of a beacon sensor can be challenging. The Pololu IR beacon can be a good starting point for beginners, although its low angular resolution can make it difficult for the robot to find once it gets within 1-2 feet. The Lego EV3 kit also includes an IR beacon and sensor but its range is less than the 10 ft needed for Polyathlon. Both of these IR beacon sensors can have trouble distinguishing between the true beacon and a reflection so they should be kept away from walls to avoid confusing the sensor. Prior contestants have achieved good results using technologies such as microwave, polarized light, and vision systems.
Interference. It is important to use sensors that won't interfere with each other during a competition. For example, if a robot's Line Sensor and Obstacle Sensor are both using Infrared Light, it is best to turn off the Obstacle Sensor while Line Following and vice versa. The Beacon Killer with Obstacles contest poses a challenge in that both the Beacon sensor and Obstacle sensor must be active at the same time. It is best to use different technologies for these two sensors so they don't interfere.
Sensor Arrays. When using an array of sensors to determine the location of something, special techniques may be needed to turn the raw data from each of those individual sensors into useful information. Check out the Centroid Algorithm for a great way to make that happen.
The quickest way to tell a novice from a seasoned competitor is to look at a robot's drive train. From the battery to the wheels, a properly designed and well balanced drive train is essential to performing well in Polyathlon. Check out our Robot Drive Systems article for details on how to design a competitive drive train.
Drive System. Differential Drive (a.k.a "tank steer") is the dominant drive system for Polyathlon robots. It is simple to build, allows zero-radius turns, can be very fast and efficient, and parts are easy to find. Wheels are generally preferable to treads as they make turns more consistent and distance travelled can be more accurately calculated using motor encoders.
Battery. Both NiMH and LiPo/LiFePo rechargeable batteries are a good choice for a Polyathlon Robot. Disposable batteries are not recommended as they will cost more in the long run considering all the testing and troubleshooting time involved in getting a robot ready for competition. NiMH batteries are the most robust option for beginners, as most LiPo battery packs will require additional circuitry to monitor and prevent over-discharge and maintain balance between cells. All batteries have some amount of internal resistance and will heat up during use. Be sure to check the discharge rate of the battery is rated at or above the maximum current that the robot may pull: ideally the battery should not be damaged even if both motors are stalled for 10-20 seconds.
Motor Driver. The power flowing from the battery and into the motors is controlled by a motor driver. A typical Polyathlon robot will have 2 motors, so two single-channel motors drivers or a single dual-channel motor driver will be needed. Motor drivers should have forward, reverse, and braking capability and be rated to handle the stall current of the motor without damage. Motor Drivers typically have a PWM and Direction input signal coming from the robot's main controller for each channel. Alternatively, Motor Controllers are also available which take commands from the main controller over serial or I2C and may automate closed-loop speed control of each motor.
Motors and Gearbox. The motors turn electrical power into mechanical power. It is possible to use Stepper Motors and Brushless DC motors, although Brushed DC motors are the most popular choice. Small motors typically operate at high speeds and with low torque, so a gearbox is used to trade speed for torque. The gearbox ratio needed will change depending on the torque and speed of the motor and the size of the wheels. Studying popular robot kits of similar size as your own robot is a great way to get a better idea of what motor and gearbox combinations may work for you.