A team at Texas A&M has published the design of RoboBall III in IEEE Transactions on Field Robotics — an inflatable sphere meant to explore lunar craters that wheeled rovers cannot reach. The robot has neither wheels nor legs: it moves by shifting an internal pendulum that changes its centre of mass.
Key takeaways
- 1.8 metres across, 150 kilograms, costing about $250,000
- Only two actuators, both internal, sealed off from dust and temperature
- Climbs 20-degree slopes and bounces over obstacles
- The spherical shell protects the electronics from 93°C down to minus 240°C
- Mission target: Shackleton crater at the Moon's south pole
Drive with no wheels and no legs
Instead of motors in wheels, RoboBall shifts an internal pendulum. Moving the mass throws the sphere off balance and sets it rolling — the same mechanism steers direction and speed on a slope.
A simplified flow of RoboBall's pendulum drive. Editorial diagram based on the mechanism described by IEEE Spectrum — the paper does not present a schematic in this form.
The design has two consequences. First, the sphere cannot tip over, because it has no upside down. Second, both actuators?Actuator: The component that converts energy into motion — in robotics usually a motor with a gearbox. It is the most common failure point, because it works mechanically and is exposed to dust and temperature. sit inside, so lunar dust and temperature swings never touch them — and those are the two factors that usually kill hardware on the surface.
Five years and three versions
The work is led by Rishi Jangale and his team, and the idea itself dates to 2003 and Robert Ambrose, a former NASA robotics engineer. The current third version runs on batteries.
| Parameter | RoboBall III |
|---|---|
| Diameter | 1.8 m |
| Mass | 150 kg |
| Actuator count | 2 (both internal) |
| Maximum slope | 20° |
| Temperature range | 93°C to −240°C |
| Unit cost | about $250,000 |
The figure matters, because at that order of magnitude a mission can carry several units rather than one.
Why a sphere in a crater
Shackleton crater at the south pole has walls too steep for wheeled rovers. A sphere copes for a simple reason: as Jangale puts it, there is no better shape for rolling down a hill. The design handles rocky ground, soft terrain and steep slopes, and testing was done in a quarry.
Why it matters
Crater exploration is stuck on hardware too fragile and too expensive to risk sending down a steep wall. RoboBall inverts the problem: instead of protecting a complex machine, it simplifies the machine down to two actuators inside a sealed shell.
What's next
- The paper appeared in IEEE Transactions on Field Robotics and contains a hypothetical mission plan, not an approved flight
- The team tested the design in a quarry — there is no information on vacuum or reduced-gravity testing
Sources
- IEEE Spectrum — The Best Way to Explore Lunar Craters Is a Giant Robot Ball
- IEEE Xplore — IEEE Transactions on Field Robotics
