In order to keep the micro-controller from bogging down, I was thinking I could run each leg off its own controller, and link them all to a mother board to facilitate faster movement.
I'm very much in favor of distributed processing(/"controlling") - Divide and conquer
However... the speed of movement alone is a poor excuse for doing so and I think that you suffer from the typical "underestimating speed of microcontroller syndrome" USOMS for short
6 legs, each 10-DoF (just to exaggerate) and a lowly 1MIPS controller gives a refresh rate of:
Or 16.667 round trips each second, assuming one instruction per DoF, which is probably too little. With 10 instructions for each DoF, you can still service them all 1'667 times each second and that's just with a 1MIPS controller. How fast do you need to go?
One for each leg vs. one for all legs (still having a master controller, either reading the sensors directly or through a "sensor controller"...
One for each:
Programming gets easier, as they all need the same software, so program one and clone the rest.
Wiring might get more complicated and there will be more to trouble shoot when it acts up (although swapping out controllers will help determining if it's a bad controller, bad software/wiring/whatever.
By all means, do it, but do it for the right reasons
I wouldn't use Arduinos for the "leg controllers" however - a through hole controller, a cap and not much else, on a bit of Vero board, is all it takes.
[...] link them via USB to a main/motherboard for instruction.
SPI or IIC will be cheaper and easier.
I could program each UNO with its own set of commands for standard movements,
They all need to be the same, unless you make each leg different from the next.
Programming just a single "step" into each - the timing of the steps should be determined by the master.
Any idea if my theory will work?
Of course it will work (distributed processing has worked for decades
Depending on your previous with controllers, it may be a huge project to take on. If the "leaf switch 'bots" you have built, didn't contain a controller, I'd advice taking a trial step up by doing something like the $50 robot from this site - just to get a feel for it...
But ultimately... You be the judge.