I created these for my Makeblock Constructor, but they're Lego Technic compatible so you can use them to support your next robot.
Basically you're sandwiching a 1/4" nut inside four layers of 1/8" plywood. The center two layers have hex cutouts and that's where the nut goes. The layers above and below have smaller, circular holes.
Glue those layers together with wood glue, making sure to put the nut inside before the glue sets. Put #4 x 0.75" screws in the two smaller holes to clamp the assembly. You can either remove the screws afterwards (as I did) or leave them in for extra strength.
Next, glue the brace (the triangular part) into the back. Note that I only use one back piece in the photos, but I'm suggesting two. Glue them together and clamp them until they're solid, then glue in the brace.
The next step is to pop the bottom into the back. It's not too tricky; just don't use too much force. Squirt some glue in all the cracks. Once the glue is dry, feel free to paint the legs with ordinary spray paint.
The final step is to screw in the furniture pads. They were $4 at Home Depot and have 1/4" threaded connectors. Perfect!