Here is probably the simplest robot leg that allows forward and backward and up and down movement. It only requires a toy geared motor and some other miscellaneous stuff to build. I didn't have to buy anything to build this project.
The problem with leg movement is that as the leg moves forward or backward it also needs to go up to prevent dragging it's foot on the floor. The wheel has all the correct motions built in and it is just a matter of attaching the leg to the wheel in such a way as to take advantage of that range of motion (using crank/slider mechanism).
The build log is just a generalized discussion of photos of my build as everyone's use of materials would probably be very different.
1. I plan to add a knee joint to the leg that will lift the foreleg or bottom of the leg up as the thigh moves forward or back thereby making it easier to step over obstacles..
2. It would be really cool to add a solenoid to lower and raise the pivot point of the leg. This would reduce and enlarge the leg stride on the fly making a way to increase and decrease the efficiency of the robot leg while it is moving.
3. It would also be interesting to put 6 of these legs together and see how a robot can move without using computer control to coordinate the legs movements.
4. Put a shoe on the leg - noticed it is slipping a bit on the carpet.
Step 1: Mount Motor on Tether
The motorized wheel comes from a toy construction truck. I mounted the motor on an acrylic ruler by drilling two holes through the ruler and into the motor gear box. Be careful that you do not drill into the gears. Then use self tapping or wood screws to attach the ruler, which serves as the tether, to the gear box. Note I hotglued and zip tied the motor wires to the gear box so that they don't get pulled out.
After that I drilled and bolted a spacer which is the plastic box (gotten from half of a power supply box) to the bottom of the ruler or tether.
Onto the spacer I bolted another short piece of acrylic ruler which will serve as the mount for the leg pivot point.