It's been awhile! I started grad school recently, so I've been a bit absent for the past year or so. But I'm finally back to making :) I made some wheels for my first robot this semester, and I wanted to share them with you all. Here goes!
Stuff You'll Need:
- 1/8" ball endmill
- 1/4" ball or flat endmill
- 3in x 6in x 1.5in block of machine wax*
- 3D printer**
- (2) 1.5" 4-40 screws + nuts
- Needlenose pliers
- (2) Disposable Cups
- Tongue Depressors (or other stirring sticks)
- Plastic sandwich bag
- Exacto knife (with a sharp blade)
Things To Note:
* I used machine wax, but you can also mill moulds from foam or MDF. Just make sure you seal them and add some kind of release compound so you can get your piece out later.
** I used a 3d printer for this iteration of wheel hubs, but you can also make them with other materials like wood!
Step 1: Make a 3D Model
Make a 3d model that accurately describes how your wheel (tire and hub) will attach to your motor shaft. Pay attention to dimensions, especially motor shaft diameter and length. I recommend making a test print for the motor shaft hole diameter. Be sure to have some super glue on hand if your press fit comes loose.
I designed my wheels in Rhino for Pololu Micro Metal Gearbox motors. I have included my Rhino files for the wheels and the motor shaft hole size test. Content in this Instructable was made from the Rhino files.
If you use Fusion, here is a file to get you started: Fusion360 Wheels
Step 2: Print Hubs
Create STL files for your wheel hubs and print. My stl file is attached for your convenience.
I found that brim adhesion for FDM printers works best. Use a knife to cut away any strings or unwanted artifacts.
Step 3: Prepare Mould File & Toolpaths
I used a 3in x 6in x 1.5in piece of machine wax to create a negative mould from the wheel model. Please reference the wheels.3dm file for the mould geometry.
Use CAM software to generate the toolpaths for the Shopbot. I recommend the following:
- Rough cut with 1/4" ball endmill.
- Radial finishing pass with 1/8" ball endmill. (This gives some faux "treads")
- Drill with 1/8" bit.
I have added the gcode for my mould. Mould-25endmill.SBP is for the 1/4" endmill. Mould-125endmill.SBP is for the 1/8" endmill and drill.
Step 4: Mill Wheel Mould From Machine Wax
Wear safety goggles! PROTECT YOUR EYES! Prepare the ShopBot for milling. Mount the wax block on the machine bed with hot glue along all edges. Make sure the wax is secure. Run the job!
The mould should come out beautifully clean. Here are a few examples of wheels moulds I made.
Be sure to countersink the drill holes from the bottom. Otherwise your screws will be too short to clamp the hubs to the mould.
Step 5: Pipe Silicone Into Mould
Clamp the 3d printed hubs to the wax mould using the 1.5" 4-40 screws and nuts.
Using the disposable cups and stirring sticks, mix a small amount of OOMOO (about 1/3 to 1/2 cup).
Transfer the mixed OOMOO into a sandwich bag. Snip a corner off the bag and carefully pipe the OOMOO into the mould (like frosting).
Let the silicone cure.
Step 6: De-Mould and Trim
Use the needlenose pliers to gently pull the wheels out of the mould.
Trim off the excess silicone with an exacto blade.
Step 7: Press Fit and Go!
Carefully press fit the wheels onto your motor shafts.
And you're done! Happy rolling :D