I’m not sure where this project is going but it started out by me thinking about what I would consider useful parameters in designing a walking bipedal robot. Below is what sprung to mind and so inspired me to have a stab at the mechanical end of the problem and hence the running legs design (and as I have said I have done a more perambulatory walking design to ensure stability).
These are some of my driving thoughts, most of which are to do with weight saving, momentum and inertia:-
Minimise the mass of the legs. Strong enough to hold the robot and move it but no extra for actuators if possible. When the actuators are in the legs, the legs get heavier to deal with having to move the legs and their servos. As the legs get heavier the servos get bigger and so on. Keep the masses nearer to the hips and further from the feet.
Lower mass legs will swing more easily with lower momentum and inertia changes to deal with. Consequently the robot will suffer less from these mass/velocity changes as it moves, especially if the mass can be moved into the body area. I also have a swinging body/arm linked to the main driving motor to assist in countering the leg swing and stabilise linear momentum changes of the robot as a whole.
Continuously running motive force - compare running motor with stop/start/reverse servos. This can reduce the loading on some of the ‘joints’ and hence make for weight saving. It still requires speed changes but these are of the same order as the speed change of the entire robot and not of the stop/start/new direction of the legs which is pretty rapid.
Gait changes are the difficult thing to achieve with minimal actuators and my latest model allows changing the internal leverages... but the robot currently doesn’t walk as nicely as it runs :(.
Also it will have to deal with variations required by left and right legs in dealing with lumps and bumps and other external forces as well as its own balancing (to be done with body orientation changes as well as roll gait changes) but in the main these are synchronised for most activities.
Stall protection (such as a locked leg when falling over or excessive loading) can be provided by a clutch device on the main motor drive. Stall protection can mean the robot doesn't have to be strong enough to stop its own actuators from breaking itself apart.
Servos are used to control the leverage ratios of the linkages thereby meaning they have lower force requirements and are therefore smaller/lighter.
This comes mostly from an automaton/animatronics perspective which would add a control system (mechanics and software) on top of it.
And so on and so on...
This is a shed load of work but I may try to build a physical model depending on what else I’m working on, my energy and enthusiasm but I will refine the software model (as this can be done easily during tea in the kitchen!).
The modelling work is basically more of an art than a science as predicting the detail changes that happen are impossible even with small changes but there are some pretty impressive automatons (created by people a lot smarter and more persistent than me) - look at this one!!! The Silver Swan. I have seen it and it is mind blowing. http://www.thebowesmuseum.org.uk/collections/the-silver-swan/history/