I posted this in the 1323 tech binder, but I’ve had enough people interested that I’m making a new thread for it. Don’t have the time to sit down to make a cogent summary but I’m happy to answer any questions
Here’s a link to the onshape document
I designed this so I’d be able to build it in my living room; the only tools needed were my 3D printer and a hacksaw. If I had a router I’d’ve built it differently, with polycarbonate plates for the claw instead of a giant (and brittle) 3D print. That’d need either a change to the central differential gear to allow for plates to be bolted directly into it, or a separate coupler part to do the same.
Some caveats to this design:
- This was a project for a couple of weekends. I didn’t follow what I’d consider best practices since it was mostly for fun and to show the mechanisms instead of CAD workflows
- The helical gears on the passthrough axle don’t have steel inserts, so they’re very likely to round over the axle if they experience too much torque (eg stalled motors with a high current limit). Redesigning them to support steel inserts would be good if you want to do this on a real robot
- They also don’t mesh well in the claw body and had a lot of friction. Probably mostly because I don’t have a way to cut the passthrough axle to the perfect length, but it’s impossible to get a good look at the mesh points to confirm.
- The belt tensioning system was usable but didn’t work great. The slots weren’t made low enough to get good tension on the idler bearing. I did change the CAD later to make the slot longer, but didn’t print it. I’d change the design to have a fixed axle position roughly where the bottom of the slot is in the CAD, and 3D print sleeves of varying thickness to go around the bearing to adjust its effective diameter and get proper tension that way. The head of the setscrew holding the axle in place would also interfere with coral in the claw (they could’ve been cut down or replaced with a shorter bolt… but that’s a workaround for a bad design IMO)
- I completely eyeballed the roller wheel placement, and there’s no way to adjust their positions. I’d definitely want some way of doing that, since it takes 8 hours and 250g of material for every print.
The total BOM was about $175 USD from thriftybot and mcmaster-carr, not including taxes and shipping or the cost of the filament
| Part | Count | Total Cost | Supplier |
|---|---|---|---|
| 105 Tooth Single Sided 9mm Wide HTD Timing Belts | 2 | $15.98 | Single Sided 9mm Wide HTD Timing Belts |
| QTY 4 - 3 Inch Thrifty Squish Wheels | 1 | $30.00 | QTY 4 - 3 Inch Thrifty Squish Wheels |
| QTY 10 - Flanged 1/2 Inch Hex Ball Bearings | 2 | $60.00 | QTY 10 - Flanged 1/2 Inch Hex Ball Bearings |
| QTY 25 - 10-32 Brass Flanged Screw-to-Expand Inserts for Plastic | 2 | $15.98 | QTY 25 - 10-32 Brass Flanged Screw-to-Expand Inserts for Plastic |
| QTY 1 - 36 Inch Long 1/2" Rounded Hex Shaft - 7075 Aluminum | 1 | $24.99 | QTY 1 - 36 Inch Long 1/2" Rounded Hex Shaft - 7075 Aluminum |
| 3" OD x 2.5" ID x .25" X-Contact Bearing | 1 | $29.99 | 3" OD x 2.5" ID x .25" X-Contact Bearing |
| Torx Alloy Steel Socket Head Screws, 10-32 Thread Size, 1" Long (Pack of 50) | 1 | $14.57 | McMaster-Carr |
| 18-8 Stainless Steel Button Head Torx Screws 10-32 Thread, 1/2" Long (Pack of 50) | 1 | $9.22 | McMaster-Carr |