Five hours after starting my 24 hour design of a Tiny Mobile Robot (tiny24hourmobot) I have managed to 3D print a rectangular band that will hold two continuous rotation servo motors. I did think of using the DC motors from inside two broken micro servo motors but I thought they would be rotating too fast, plus I would have had to include a dual H bridge DC motor drive as well. I do have one but it seemed an unnecessary complication when I could just use two continuous rotation servo motors. I did check that the two servos would fit inside the red spray can top I intended to use before printing the rectangular holder. Unfortunately I forgot to include the diameter of the wheels. The micro servo motors come with 24 mm diameter circular fixings which I thought would make great wheels and save me 3D printing them. Unfortunately this makes the motor - wheel combination 51.5 mm wide at its widest point, whereas the inside diameter of the spray can top is only 50.0 mm wide. I could try reducing the diameter of the wheels by a couple of mm but then there might not be enough clearance between the bottom of the servo motor and the ground.
Hay oh. Nothing much to be done there so I've now changed to 3D printing the equivalent of the spray can top.It does mean that I will be able to design it so that the motor unit fits into it nicely fixes together. I may not be using the exact spray can top I wanted but it is pretty close and I can probably find a slightly larger spray can sometime in the future if I still want to use recycles can tops.