You might be able to use the the opposite foot to begin the rotation of your chassis, but it will be dependent on your chassis and foot geometry.
Using your photos for reference, the left foot would push up beginning the chassis rotation, while the right foot would rotate simultaneously. At some point the center-of-gravity (CoG) would shift enough so that the remainder of the chassis rotation could be done only on the right root.
I have a similar robot. It has an extra DoF, but if you ignore the knee joint, it is similar to your design. These pictures show the basic idea.
Exaggerated rotation of opposite foot only:
Rotation of both feet simultaneously:
Whether or not this will work for you is dependent on a few things:
- If your legs are too far apart (hip too wide), then this might not work because the opposite foot will never be able to help shift CoG enough that the primary foot can take over and keep balance.
- Your foot joint location and geometry must be such that it can initiate enough of the rotation.
- Consider that you can rotate the opposite foot in either direction to start the shift, and if the joint is not centered on the foot, then the direction you rotate the foot will change the amount of much leverage available to that foot.
- Your opposite foot servo must have enough power to begin the chassis rotation by lifting a portion of the machine.