ICRS / Vex
What is VEX?
VEX is an organisation which hosts international competitions for students interested in robotics. This year, the Imperial College VEX team were tasked with designing robots for a game called VEX Toss-Up. The Toss-Up game is played with two teams, a red team and a blue team, each having two robots.
The objective is to score points by placing your team’s coloured (red and blue) large balls and small balls (Buckyballs) in scoring zones. The opposition’s score can be reduced by removing their balls from the goals. Additional points can be scored by a robot hanging from the coloured hanging bar at the end of the game. The game is explained in more detail in this official VEX video: https://www.youtube.com/watch?v=3euUzfn0TwI
Each robot has a VEX cortex microprocessor, and is allowed a secondary processor if needed. Games last two minutes, consisting of one minute where the robots operate autonomously followed by a second minute of manual control.
Basic Mechanical Design
The two robots have to fit into specific size limits at the start of the games. One robot must fit into a 15 inch (38cm) edged cube and the other must fit into a 24 inch (61cm) edged cube. The robots can expand out of these size limits after the game has begun. The robots were designed to expand upwards to place balls in the elevated scoring goals whilst still being lightweight and fitting within the size limits at the start of a games.
The robots were built from aluminium in order to keep weight down so the robots would be more agile. Present on the arena floor are barriers and bumps which impose size constraints on the robots. We designed both robots with high ground clearance in order to drive over the bump. The 15 inch robot was designed to be short enough to fit under the 12 inch (30cm) barrier. The large robot was designed to pick up both Buckyballs and large balls so it had rollers with rubber flaps down low for Buckyballs and smaller rollers higher up for large balls. The rollers also hinged horizontally to allow room for the large balls. The small robot was originally designed to only pick up Buckyballs so it only had low rollers/flaps. But at the competition we added metal bars wrapped in rubber bands to allow it to pick up large balls too, this is shown in figure 2.
The robots were also designed in CAD using the Autodesk Inventor software to allow easy reassembly after repairs and transportation.
Basic outline of sensors
The robots used a combination of ultrasonic sensors and a webcam to get information about the arena, and use that as a basis for a mixture of procedural and deterministic autonomous code. Both robots used the VEX cortex as a main processor which handled the processed data from the sensors and controlled the robot. Each robot also had a Raspberry Pi, which communicated wirelessly with a laptop for programming and debugging purposes. Each Raspberry Pi used its general purpose IO pins to control four ultrasonic sensors, and used the USB port to take image data from a standard webcam – processing the image to find colour features corresponding to the balls.
Big Bang Fair
In addition to testing done in labs, we also took the robots to the Big Bang fair in Birmingham where VEX were running the high school UK championships. VEX had installed arenas which we could use to calibrate the limits for the sensors. Testing was less successful than hoped for, due to background wireless signals from all the stalls at the fair interfering with the wireless communications used to download new code to the robots. However, progress was made on the autonomous mode, and the drivers had a chance to practise with the controls and work on strategies.
The World Championships were held in Anaheim, California, where sixty universities from around the world were competing. Testing, practising and calibration were done on the first day, with the remaining three days spent playing ten matches and continuous development. Though the team had issues with equipment being damaged in transit, we placed 30th. This was despite substantially greater funding and experience many of the other teams had.
We wish to give a huge thank you to the Department of Electrical and Electronic Engineering, The Faculty of Engineering and the Old Centralians’ Trust for funding the project, it wouldn't have been possible otherwise.
2013-2014 Team Members
- Adam Heywood (Team leader)
- Micheal Hart
- Erwei Wang
- Ben Windo
- Thomas Collingwood
- Mikheil Oganesyan
- Patrick Mabin
- David Salmon
- Rebecca Simpson
- Johan Arulnesan
- Ahmed Ibrahim