Um... you can't walk on two legs without friction.
My bad. I chose a bad term because there is not, to my knowledge, a word that quite captures what I have in mind.
I meant that the object producing the forcefield cannot use friction from inside the field to rotate the exterior of the field.
The forcefield's exterior
is sort of 'grippy.' If a globe had a forcefield, and its axis was pointed directly upward, and you dropped a pancake on the top of the axis, it would sit there (and slowly cook), not slide off.
The thing is, the orientation of the object inside the forcefield doesn't rotate the forcefield itself. If you tilted the globe so its axis pointed horizontally, the forcefield doesn't move. The pancake stays on top.
Similarly, if you had a wheel with a forcefield, spinning the wheel would not cause it to move along the ground. It would just be spinning inside the forcefield, never quite contacting the surface below it, even while the forcefield itself
is keeping the object in place with some friction.
Now, the forcefield keeps matter from coming in, but will let matter out, so if the globe with a pancake on top had, like, a thruster, it could shoot and push itself. And if the globe moved fast enough, inertia could cause the pancake to be dislodged as the globe sped away.
Imagine the object was not radially symmetrical, but say it was T-shaped, with a thruster pointing out from the bottom and from each end of the the T, and with a gyroscope to stabilize it. If you had the T standing upright and it fired the bottom thruster, it could hop up, then fall back down, and could use its gyroscope to ensure it landed upright again. If it while standing on a surface it fired the left thruster, it would just teeter, and then gravity would cause it to fall over. But if it launched up, then fired a lateral thruster, it would start to fall, but could then fire its bottom thruster, then use the right thruster to turn it facing back upright, letting it land on its foot.
So it's possible to maneuver with reaction thrust. But you only have finite fuel for that (and thrusters produce a lot of heat). It's not efficient for a ground vehicle.
But if you have a biped, what it can do is lift a leg, extend the leg, and let gravity cause it to teeter. Then it catches itself on the leg, and lets momentum carry it forward so it can repeat the process with the other leg. The grippiness of the forcefield lets the mech step on the ground and keep its balance. And using gears and gyros inside the object to shift its center of gravity and to push off from the ground is more reusable than thrusters.
