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This document goes into detail about the steps in CADing a drivetrain. I also explain the logic behind each tool and describe some special quirks and cases, which is why it's long. When going through it, make sure you understand what and why I'm doing. Make sure you have added all MKCad parts before starting. See MKCad to add the parts.
Original doc by Parth here. It's a whopping 93 pages, and talks about every single detail. Though if you have the time or willpower, it's an interesting read.
For the design decisions or any specific measurements, look below. For this guide, the robot is 28" x 28" and has a 12" wide cutout.
Table of Contents
Start by making a document for your drivetrain. Make a folder for the drivetrain. (We would usually make folders for each subsystem, but we only have the drivetrain here.) Put a Part Studio and Assembly in there, named "Drivetrain Parts" and "Drivetrain Assembly."
Start off with a sketch on the right plane, where we'll define what the front and back rail will look like.
The center of the tubes will be 3" off of the ground, since the wheels are 6". Since we know where the center will be, draw a center-point rectangle (R) and make it 2" x 1". Dimension (D) the center to be 3" off of the top plane, and make the front side 14" inches from the center (for a 28" robot).
The back rail is also 2x1 tubing, so we can make it the same. Use the mirror tool to mirror the rectangle over, using the Front plane (it looks like a line) as the mirror line.
First sketch done! It should look something like this now. Rename the sketch something like "front, back rail" and confirm the sketch.
Extrude the sketch. For the regions to extrude, click the name of your sketch on the sidebar to choose both of them at once.