• SpaceBok – a four-legged planetary exploration robot is being developed to hop across complex terrain on other planets
  • The idea is to change how astronauts explore the Moon, who spend most of their time hopping around rather than walking.
  • To test it scientists decided to build the world’s flattest floor and play a live-action game of ping pong.
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A dog-like robot being developed to hop across complex terrain on other planets has been used to play a live-action game of ping pong in its latest phase of testing.

The idea behind the project is to change how astronauts explore the Moon. Astronauts spend most of their time hopping around rather than walking.

The European Space Agency (ESA) built SpaceBok – a four-legged planetary exploration robot which hops, much like a Springbok.

Designed and built by a Swiss student team, it is currently being tested using robotic facilities at ESA’s Automation and Robotics Laboratories (ARL) facilities in the Netherlands.

The robot is being used to investigate the potential of ‘dynamic walking’ and jumping to get around in low gravity environments.

SpaceBok could potentially go up to 2 metres high in lunar gravity, although such a height poses new challenges.

ETH Zurich/ZHAW Zurich
SapceBok jumping in simulated lunar gravity. Source ETH Zurich/ZHAW Zurich

Once it comes off the ground the legged robot needs to stabilise itself to come down again safely – like a mini-spacecraft. So, like a spacecraft. SpaceBok uses a reaction wheel to control its orientation.

This can be accelerated and decelerated to trigger an equal and opposite reaction in SpaceBok itself, explained team member Philip Arm.

“Instead of static walking, where at least three legs stay on the ground at all times, dynamic walking allows for gaits with full flight phases during which all legs stay off the ground. Animals make use of dynamic gaits due to their efficiency, but until recently, the computational power and algorithms required for control made it challenging to realise them on robots,” said Hendrik Kolvenbach from the Swiss Federal Institute of Technology in Zurich Robotic Systems Lab.

The team looked at the conventional methods satellites uses to control their orientation using what is SpaceBok’s legs incorporate springs to store energy during landing and release it at take-off, significantly reducing the energy needed to achieve those jumps.

The team is slowly increasing the height of the robot’s repetitive jumps, up to 1.3 metres in simulated lunar gravity conditions so far.

To simulate the vanishingly low gravity of asteroids, the SpaceBok team made use of the flattest floor in the Netherlands – a 4.8 x 9 metre epoxy floor smoothed to an overall flatness within 0.8 millimetres, called the Orbital Robotics Bench for Integrated Technology (ORBIT), part of ESA’s Orbital Robotics and Guidance Navigation and Control Laboratory.

And to test it they decided to play ping pong.

SpaceBok was placed on its side, then attached to a free-floating platform to reproduce zero-G conditions in two dimensions. When jumping off a wall its reaction wheel allowed it to twirl around mid-jump, letting it land feet first again on the other side of the chamber – as if it was jumping along a scaled-down single low-gravity surface.

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