Sawppy the Rover’s PLA Wheels Deformed Under Heat

Sawppy tearing up its right-front steering coupler was the most obvious attrition from spending a day showing off to JPL employees. There was another problem less visible to casual onlookers: Sawppy’s wheels were slowly deforming under the southern California sun. By the end of the day, some of the wheels were decidedly out of round.

Out of round PLA rover wheel

The 3D printers that printed Sawppy’s parts were loaded with Monoprice’s PLA plastic filament. PLA plastic is relatively cheap, easy to print, and rigid which makes the material good for prototyping mechanical components. Part of why it is easy to print is that it is easy for the print head to melt the material for extrusion then quickly solidifies into the proper shape. The downside of this “easy to melt” behavior is that it doesn’t take a lot of heat before PLA plastic softens. Sawppy’s thin delicate wheels couldn’t hold their shape after spending a few hours on sun-heated concrete and asphalt.

Earlier tests indicated the rigidity – and corresponding brittleness – was a weakness of printing these wheels in PLA. Now we can add lack of temperature tolerance to the list. It was not surprising but still mildly disappointing to see PLA distort.

Given this experience with brittleness and deformation under summer sun, we have motivation to look into a more ductile plastic material that is less likely to deform in the summer. The first candidate is ABS plastic, which I’ve tried to print before without much success. The second candidate is MatterHackers PETG, which is a favorite among local makers.

Now I have motivation to give it a try.

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