Omniwheels

Brief

Upon inspecting where most of the robot's weight was, we identified the omniwheels to be the primary suspect. Each of the old metal wheels weighed 74 grams, and with 3 of these, they contributed to nearly a fifth of the robot's weight. We underwent several iterations to develop a new 3D-printable omni wheel that weighs just 15 grams.

Development

We researched current solutions other teams have used. The most notable was Team Orion's, which used two layers of silicone rollers with multiple 3D printed plates and an embedded nut for a grub screw.

Team Orions omni wheel

We attempted to recreate this design, first, as a proof of concept. However, we quickly changed to a different design, as we couldn't find a reliable way to cut the rubber tubing required for the rollers. Instead, we developed our own version, based on GTFRobots' 50mm omni wheel, which featured a ring of 18 rollers, with each having what resembled rubber o-rings.

GTFRobots 50mm omni wheel Team Athenas 50mm omni wheel

We still took inspiration from Team Orion, for their embedded M3 nut which allows a reliable grub screw thread to mount to the motors. This design saw more success. We made a simple jig to cut plastic rods for the roller axles and used 11mm o-rings to add grip to the rollers. However, these rollers seemed to keep sliding off the roller. We even tried super glue, but this only caused the o-rings to rip off instead of completely sliding off. So we iterated over the design once again, using a fully PLA-based roller, with rounded teeth that resemble a spur gear. This style of roller simply didn't provide enough traction, even on the carpet of the field - the wheel kept skidding. Even TPU didn't solve the problems. So we knew to continue with o-rings but with some changes. Instead of a 'V' shaped cutout around the roller to house the o-ring, we moved to a 'U' shape, which more tightly hugs the o-ring and prevents it from escaping. Already, this was far more reliable, with o-rings only occasionally sliding off. For extra security, we used super glue after which the o-rings don't come off.

The new omniwheels weigh just 15g, which is a reduction of 59g over the old wheels, and are significantly lighter than the GTFRobots 50mm omni wheels. Over three wheels, this results in a weight reduction of 177g, which is more than 10% of the robot's total weight.