CAD Model

To construct the final system we originally planned to 3d print much of our frame an use a waterjet cutter to cut our links from a sheet of FR4. A CAD model of the final system is shown below(links and springs omitted for clarity).

In this system we planned for every leg to have a variable stroke mechanism and to distribute power to each leg with belts from a centrally located motor. We also planned to use a servo hooked up to bevel gears to drive belts on opposite sides of the robot to turn the amplitude control links. However, when it came time to print our parts, we ran into manufacturing problems. First, the 3D printer we were using did not have enough resolution to print our belt pulleys, second, the frame required too much time to print. So we decided to redesign.

Redesign

We decided that making the system above with variable stroke mechanisms on every leg would be too difficult to redesign without pulleys, so we took a look back at some of earlier designs.  Our early simulation work using a Klann linkage demonstrated that we could get stable, but very bumpy walking behavior with a klann linkage, however we could not turn. One way we could turn is if we were to rotate the front legs with respect to the body, however, this would necessitate a CV joint to transmit power to the back legs. To simplify things and make the system more stable, we got rid of the back legs. We made the links out of hand-cut lexan plastic and the joints out of 1/8" steel shaft with washers and retaining rings. To make our links, we printed out drawings of the link shapes we want from our CAD tools, cut the drawing out of paper and used it as a template to mark cut locations and center punch hole locations into the material. We used a faulhaber 2224 motor with a 14:1 gearbox to actuate the legs and used a standard hobby servo for steering.

Videos:

https://drive.google.com/folderview?id=0Bzkdz1bVRM_8b2VMM202NHo4ZE0&usp=sharing

Recommendations for future teams building walking robots

• Get the linkage synthesized as soon as possible
• Make it small and light, the lighter the robot is, the less chance your links will bind.
• Use self locking retaining rings instead of e-clips, e-clips require grooves that are tedious to machine
• We found that precision steel shaft, oiled brass washers, and an adequately sized hole worked very well for joints
• We were able to make complicated and surprisingly precise link shapes by using a 1:1 scale engineering drawing as a template to cut and drill holes
• Don't count on the 3d printer for everything.