Way back in 2016 we posted some ideas for how to make strong 120 degree cranks in LEGO here. We still get questions about 120 degree cranks, so here is another diagram to show how LEGO's Technic rotor part #44374 could be used to make cranks of length 2 LEGO holes to drive 3 legs 120 degrees out of phase.
The purpose here is not to limit you to only using LEGO's rotors when making 120 degree cranks, but instead to use the rotors to illustrate the geometry of a 120 degree crank/axle system - hope it helps to clarify things.
Notice that every crank connection is keyed such that every axle connected to them is forced to rotate along with the crank, which transfers the rotation to the adjacent crank.
Note: if you are building larger or heavier walkers you may want to support the axle between each leg with beams that connect the Center of Rotation to the robot's frame, as is done in the simple 180 degree crank/axle system below (of course, instead of using a single beam connection like below you should use two diagonals that connect the Center of Rotation to the front and back sides of the frame, creating a strong triangle that resists front/back forces)