Large Omni Wheel

thingiverse

This is my design for an Omni Wheel, which I'm using on my robotics platform that's based on the Mars Rover. The Omni Wheel can move in almost any direction it wants to go. It rolls like a regular wheel when moving forward, but it also slides sideways thanks to small rollers along its perimeter. In my case, I needed to use an omni wheel to overcome "scrub drag" during "skid steering" of my 6-wheel platform. Here's a helpful article that explains this: http://curriculum.vexrobotics.com/curriculum/drivetrain-design/drivetrain-terminology.html The Omni Wheel is about 120mm in diameter and consists of several parts, most of which can be 3D printed. The hub is designed to fit onto a 12mm hex shaft motor coupler (like the ones used in the "Wild Thumper" 6WD toy). Here are the 3D-printed parts: * First half rim with integrated hub (the largest part) * Second half rim * Omni Rollers (18 per wheel) * Rim cover (required to hold rollers in place) I laser-cut my rim cover from 1/16" delryn (acetal) resin, but it should be easy to print one as well. I've included an STL file for the rim cover, but I never actually printed it. Here are the other parts: * 18 x 5x24 mm stainless pins/axles for roller axis (http://a.co/hJ0sJgK) * 18 x M3x8 mm (or 10 mm will work) screws * 3 x M4x16 mm (you can use longer) screws * 1 x M4x20 mm screw (for attaching to motor shaft coupler if) Here's how I printed it: Note: Rim_w_integrated_hub.stl is upside down, so flip it before printing. I used PETG to print both rims and PLA for rollers. After printing the rollers, I cleaned up the bottom of the opening a little with a dremel to make sure metal axles can rotate easily inside. It took about 3.5 hours to print the rollers, 3 hours to print the rim with an integrated hub, and 2 hours to print the other half of the rim. Here's how to assemble it: Insert the axles into a roller and push it into each slot of one half rim. Make sure the roller is rotating easily. Place the rim cover on top and screw all 9 M3 screws in place. The plastic holds the screws pretty securely, but if you want an even more secure assembly, you can use longer screws with lock nuts on the ends. Repeat this process for the second half rim. Insert the regular half rim into the rim with an integrated hub. Rotate it so each roller of one half rim is offset (20 degrees) from rollers of the other half rim and all 6 M4 holes of the inner hub align. Just keep rotating it until you see light shining through those holes. Then use three M4 screws to secure both half rims together. There are 6 holes, but three screws will do. At this point, your omni wheel is assembled and can be mounted onto the motor shaft. Other thoughts: This design isn't perfect and hasn't been tested much. You'll probably get better results if you can print rollers with flexible filament or add a rubber coating. The size of the rollers and distance between them aren't ideal either. Smoother rolling and less resistance can be created if the rollers are made longer, but I couldn't find pre-made stainless dowels of that size at a reasonable price. Here's a video of the wheels in action: https://youtu.be/BNUZhnwHvlU