These 3 inch diameter by 1.32 inch width mecanum wheels are designed for use in FIRST Tech Challenge: their small form factor, built-in connection to Actobotics hubs, light weight, and traction are an improvement over commercially available mecanum wheels. We are using them on our 40 lb robot this season, and they have held up well to date, though we periodically tear a silicone roller. We mostly drive on ½” foam mats. For longer life or if you want to drive on a different surface, you might consider using a stiffer silicone rubber for the rollers.
Making these wheels is a fun project that will introduce you to the wonderful world of casting silicone in 3D printed molds. The possibilities are endless. We hope you enjoy these wheels!
You will need a set of 4 wheels, 2 right and 2 left, to drive a robot.
Bill Of Materials (for a set of 4):
2 x hub side left (mecwheelhubside.stl)
2 x hub side right (mirror mecwheelhubside.stl in your slicer)
2 x screw side left (mecwheelscrewside.stl)
2 x screw side right (mirror mecwheelscrewside.stl in your slicer)
Top of roller mold (rollermoldtop.stl)
Bottom of roller mold (rollermoldbot.stl)
See the attached pdf for non-printable parts, sources, and tools.
eSun PETG for wheels
We print the wheels in PETG with 3 perimeters, 20% infill, gyroid pattern. We have printed the molds in PLA and PETG. Whatever filament you have on hand will probably work fine for the molds.
We print with supports on the baseplate only, with the larger flat side down.
To Make the Rollers
Print the two roller mold parts in PLA or PETG. Remove the supports.
Assemble the molds by screwing the aluminum spacers into the two halves of the printed mold pieces with the ½” 6-32 bolts. Block up the seam between the mold halves with the sulfur-free clay so that the silicone does not leak out.
Mold ready for assembly!
Mix up a batch of Moldstar 30 according to the package directions. For these molds, you will need about 30 grams of silicone to completely fill the four cavities, so pour 18g of each part as a little will be left in the mixing containers.
Pour the silicone into the cavity in the top of the mold. The silicone will take a while to flow down into the 4 molds, so you will have to go slowly.
Wait 6 hours.
Unscrew the hex screws from the bottom of the mold, and pry the silicone out of the top of the mold. An awl or small screwdriver will help getting the silicone off the bolts that will be covered in silicone. You will have to break the four small cylinders of silicone that lead into the roller chamber to get the plug of silicone out of the top of the mold.
The plug of silicone has been pulled out of the top of the mold
Remove the rollers from the mold, cut off the flashing, vent and inlet pieces, and push the rollers off the aluminum standoffs.
Reassemble the mold and begin again. You will need to pour 8 rollers for each wheel, and probably some extras as the rollers do get a little banged up over time depending on what surface you use your robot on.
The flashing and vent tubes can be cut off once the rollers are out of the mold
To Assemble a Mecanum Wheel
Temporarily assemble the two wheel halves with the Actobotics hub and the 4 x 1.125” 6-32 socket head screws.
Cut 8 pieces of brass tubing to fit between the holes for the rollers. You want these to spin freely, so not too tight, a little over 1.25” worked for us. Sand the edges so they won’t cut the plastic. We slid the tubing over some scrap ⅛” stainless rod and cut it with bolt cutters, then sanded both edges. A dremel would probably work better and be faster. Or try a hacksaw and sandpaper.
Push each of the 8 silicone rollers you made onto the center of one of the 1.25” #8 nylon spacers.
Use the M3 45mm button head screws and M3 nylock nuts to assemble the brass tubing/ nylon spacer/silicone roller assembly into the 8 slots on the wheel.
Good luck! Let us know how it goes or if you have any questions!