RoboTeam Twente is a multidisciplinary student team from the University of Twente and Saxion University of Applied Sciences in Enschede. For years, the team has competed in the RoboCup Small Size League (SSL), where squads of small, fully autonomous robots play soccer against each other. Now the team is taking on its most ambitious challenge yet: building a Mars rover to compete in the European Rover Challenge (ERC) in Kraków, Poland. In both projects, Xsens sensors give the robots their sense of motion: the MTi-3 AHRS in the soccer robots, and the Xsens Avior family in the rover.
RoboTeam Twente's soccer robots sprint across the field, turn and line up passes. To do this, each robot needs to know at every moment which way it is facing and how it is moving. Humans do this with their eyes, inner ear and sense of balance; the robots need sensors.
For this, the team uses an inertial measurement unit (IMU), which measures linear acceleration, rotation and the magnetic field. On their own these signals mean little. Fused together, they form an Attitude and Heading Reference System (AHRS), which tells the robot its roll, pitch and heading in real time. The team has used Xsens AHRS sensors in its robots for years, and will use them again in its new rover.
Small size, big decisions
The team's SSL robots are compact, fast and fully autonomous. They decide to accelerate, brake and rotate in fractions of a second, so the control loop needs orientation data that is both accurate and immediate. At the same time, every component has to fit within the league's strict size limits.
The inner compass of the soccer robots is the Xsens MTi-3 AHRS. With a footprint of roughly 12 by 12 mm, it fits comfortably on a crowded PCB, which matters in a competition where every square millimeter counts. Just as important, the MTi-3 fuses and processes all raw sensor data on board. That leaves the robots' controllers free to focus on what wins matches: precise driving, sharp turning and staying on target.
Moving on to Mars
Drawing on its experience with compact, precise robots, the team is now building a Mars rover for research purposes. This is a big step up in complexity. A soccer robot has one job; the rover has several autonomous subsystems, and each one must know how it is oriented and positioned: the rover body, a robotic arm, a drill and a small scouting drone.
For the rover's navigation, the team plans to use either the Xsens Avior RTK GNSS/INS or the Xsens Avior Dual Antenna RTK GNSS/INS. Both fuse inertial and GNSS data in a compact module, delivering precise and reliable position and orientation. Where the MTi-3 was chosen for its size, the Avior is chosen for its performance:
At 36.8 by 40 mm, the Avior is larger than the MTi-3, but the rover has room to spare. That is a small price for the performance it delivers, and its wide choice of interfaces makes it straightforward to integrate into the rover's design.
More than driving: arm, drill and drone
Beyond driving, the rover performs several other tasks that depend on inertial sensing.
Robotic arm. Xsens IMUs serve as a reference for the arm's kinematics. This allows accurate control of the end-effector's position during sampling and maintenance tasks.
Drill. An IMU lets the drill stabilize and level itself before drilling, so each borehole starts at the right angle.
Scouting drone. An Xsens Avior AHRS keeps the drone at a stable attitude while it scouts the surrounding area.
Looking ahead
From a soccer robot that fits in your hands to a rover built to explore, the core question stays the same: where am I, and which way am I facing? Together with Xsens, RoboTeam Twente is working towards a rover that can truly rove, sample, maintain and scout, on the surface of Mars and here on Earth alike.
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