Ball mills and beanbags lead to a prototype for lunar wheels
Planning a lunar road trip? If you are, you’ll need wheels that can absorb the impact of the moon’s rocky surface without bouncing wildly in its low gravity. And for inspiration to build such a thing, you need look no further than ball mills and beanbags. Especially if you are Mechanical Engineering Professor Peter Radziszewski.
Ball mills are standard technology in mineral processing: ore is placed in a rotating cylinder with metal balls which grind it into a fine powder. “Ball mills absorb energy really well,” says Professor Radziszewski, a specialist in mineral processing.
.“So we thought, ‘What if we fill a lunar wheel with balls?’ That would absorb energy, giving great shock absorption, but we would still need to make the tire surface flexible.”
Enter the beanbag. The weekend after discussing the potential of a malleable ball-filled wheel with doctoral student Sudarshan Martins, Professor Radziszewski took his son’s Spiderman beanbag and screwed a hub through its centre. A prototype was born.
Iron rings and chainmail
To provide the required flexibility (rubber is too bouncy and would degenerate quickly in a vacuum with high temperature variation), they fixed upon chainmail. And so they came up with the iRing, a chainmail-sheathed wheel filled with a space-appropriate material (or, in a smaller terrestrial model, peas).
The name iRing refers to the looped rings of the chainmail as well as the Iron Ring graduating engineering students receive in Canada.
“The iRing has some interesting advantages,” Professor Radziszewski says. “Its traction is equal to or better than that of an equivalent rubber tire, and you can tailor how much particulate you place in the wheel according to how much traction you need.”
“It conforms to surfaces because it is about 80 per cent filled with particulate. And when it rolls quickly, the particulate centrifuges, creating a void between it and the rim and allowing the wheel to dissipate energy when it hits rocks.” The disadvantage, though, is that it consumes about twice the energy of a rubber tire. “So on flat surfaces you won’t go as far with the same energy,” he says.
“But for travelling uphill, the wheel’s rolling resistance is not as important as its ability to carry the vehicle’s weight.”
The lunar wheels project — a collaboration with the Ottawa-based Neptec Design Group and the Canadian Space Agency (CSA), along with funding by the Natural Sciences and Engineering Research Council of Canada (NSERC) — has involved a large, diverse team.
“Undergraduates are very good at designing and building things,” Professor Radziszewski says, “and graduate students are very good at analysis and simulations.”
“We created a dynamic where, as part of their fourth-year capstone course, undergraduates design and build prototypes and test equipment, and then our graduate students use these to validate models and feed back into the design process.”
So far, about 60 students have taken part, as well as Mechanical Engineering Professors Damiano Pasini, Vince Thomson and Larry Lessard, and Electrical and Computer Engineering Professor David Lowther.
With another year to go on the Neptec contract, about 20 more students will likely join the roll of iRing designers.
Professor Radziszewski says there is no guarantee that McGill’s iRing wheel design will one day roll across the moonscape.
“Our goal is to identify the most appropriate wheel for the rover,” he says, “and in doing that our team is evaluating various designs generated by students and the Neptec Design Group’s other partners.”
“But the iRing is certainly competitive ― and it’s definitely new, so we have a real shot at it.”
“What we have done, quite literally, is reinvent the wheel!”
Extensive media coverage
Media reports about the iRing prototype have gone viral. Professor Radziszewski and his students have been interviewed about its potential use, both in space and here on earth, by French-, Italian-, English- and Chinese-language television, internet and print journalists from Canada and abroad.
Print and online coverage