Two-Wheel Drive Base

Step 1 of 10. Lay a 2x12 beam down flat. This is one side of the chassis.

Step 2 of 10. Push a shaft through hole 1 and hole 10 of the front row. Count from the end: hole 1 is the second hole along.

Step 3 of 10. Push a wheel onto the end of each shaft. The flat of the shaft has to line up with the square hole in the wheel - turn the wheel until it drops on.

Step 4 of 10. Lock a collar on the outside of each wheel. Press it right up to the wheel. A gap here is what makes a wheel fall off later.

Step 5 of 10. Build a second side frame exactly like the first, and set it down mirrored - wheels facing out. Hold them side by side. They should look like a pair of hands, not like two left hands.

Step 6 of 10. Lay a 1x8 beam across both rails, near the front. Turn it a quarter turn so it runs across the rails, not along them.

Step 7 of 10. Push four connector pins down through the cross beam into the rails underneath. Two pins into each rail. One pin per rail would let the frame pivot - the second pin is what stops it.

Step 8 of 10. Repeat at the back: one cross beam, four more pins.

Step 9 of 10. Sit the brain on the two cross beams, ports facing the back. It should sit flat. If it rocks, a pin underneath is not pushed all the way home.

Step 10 of 10. Check it. Push the base along the floor - both wheels should turn freely. Then hold two opposite corners and twist. Nothing should move. If it racks, press each pin home until it clicks.