I made it at TechShop.
Step 1: Go get stuff
(x1) An 11" x 6" laser cut bracket (file attached below)
(x2) 3D printed servo wheel
(x2) Parallax continuous rotation servos modified for direct drive
(x1) 3D printed wheel and pivots (printed at precisely 1/4 the model size)
(x1) 1/4" x 2" stainless Steel rod
(x1) 4 x AA battery holder
(x4) AA batteries
(x12) 4" zip ties
(x8) 12" zip ties
(x2) 4-40 x 1/2" nuts, bolts and washers
(x1) 220 Sandpaper (optional - not pictured)
(x1) Polycrylic stain (optional - not pictured)
Step 2: Sand and stain (optional)
Sand both sides of your wooden bracket and wipe them off.
Coat one side with wood stain. Wait for it to dry, sand it lightly, and then coat it again.
When the first side is dry, repeat on the opposite side.
Step 3: Drill
Repeat on the other servo.
Step 6: Attach the wheel
Slip the wheel into front fork of the laser cut bracket and zip tie the pivots firmly in place.
Step 7: Attach the servos
Make sure the servos are on the same side of the bracket as the pivots.
Step 8: Battery holder
Line up its mounting holes with holes in the bracket and fasten it in place with the 4-40 nuts, bolts and washers.
Step 9: Wire it up
Twist together the red wire from the servo on the left to the black wire of the servo on the right. Connect both of these to the red wire from the battery holder.
Twist together the black wire from the servo on the left to the red wire of the servo on the right. Connect both of these to the black wire from the battery holder.
Solder both pairs of wire together to make a more reliable electrical connection.