aka Drivetrain CAD in 20 Seconds
Some teams feel that West-Coast style drives are out of their reach and feel forced to use the kitbot year after year, so we on Team 449 - The Blair Robot Project put together a spreadsheet-driven CAD where anyone can quickly type in parameters into a spreadsheet and the CAD will be updated appropriately. This CAD matches the style which Team 449 has been using, with 6 MiniCIMs in two VexPro ball shifter gearboxes placed in the back of the robot. Wheels can either be 4 or 6 inches in diameter, and can either have all six wheels be Colson Performa wheels, or they can be set as 2+4 with Colson wheels in the center and VexPro omni wheels on the edges. The frame is made of four lengths of aluminum 1/8" thick 2x1 tube and can be heavily customized through the spreadsheet. While this tool is focused on belts (specifically 15mm wide HTD belts), and includes a c-c distance chart for 5mm HTD, this could also be used for chain drive with a bit of effort.
This tool requires Autodesk Inventor 2018 and Microsoft Excel (free alternatives don’t work).
Features:
- Customizable 2x1x1/8" aluminum tube drive.
- Supports standard 6-Colson WCD and 2+4, with both 6" and 4" wheel diameter.
- Easy to adjust dimensions, wheel types, etc.
- Fully constrained VexPro Ball Shifter Gearbox CAD.
- 5mm HTD belt C-C distance chart included.
- Hardware, belts, etc. are included in the CAD (with text on the belts!)
How to use:
- Download the files from https://grabcad.com/library/spreadsheet-deriven-back-driven-vexpro-ball-shifter-wcd-1
- Extract the contents of the .zip to the desired location.
- Double click “Spreadsheet Deriven VexPro Ball Shifter WCD.ipj” at root
- In Windows Explorer Go to Workspaces\Workspace\Base Frame
- Open “Base Frame Sheet.xlsx” and “Base Frame With Gearboxes.iam”
- Set your settings in the spreadsheet. Remember, bad inputs make bad results.
- Go to “Base Frame With Gearboxes.iam” in Inventor.
- Go to the Manage tab and click on the iTrigger button. This updates wheels.
- Then, click the update button (the lightning bolt) at the top. This updates dimensions and constraints.
- Preview the generated results, and repeat steps 4-7 as needed.
Helpful 449 WCD/2+4 Tips:
- Make a test piece to test c-c distance, belt tension, and wheel-ground contact before finalizing exact specs.
- We found that 6" Colsons are slightly smaller than 6" omnis. This reduces how good they are at providing traction to a 2+4 drive, since they aren’t touching the ground. This is one of the things to check for and adjust in tip 1. We found a .007" center drop works well enough for a 6" wheel 2+4.
- 3D print gearbox shields for the third stage of the gearboxes to keep them clean.
- After this past year we’ve come to like 2+4 (with no center drop, obviously) quite a lot. If you’ve never tried making and using a 2+4 drive, I would strongly recommend doing so.
If you come across any problems or have any questions about the design, feel free to ask!