my question revolves around 4 limbs robot ( but maybe even 2 limbs ) walking. As i see in many videos robots start "walking on the spot" in order to balance before actually moving somewhere. Why is that ? Has someone managed to start walking immediately skipping the "walking on the spot" phase?

Thanks in advance for the time spent answering this!

EDIT: Just to clarify, this is the behaviour that i'm talking about


at 11 sec

  • $\begingroup$ humans do something similar (not a couple of steps in one spot though) .... we lift one foot so that our body starts to fall forward $\endgroup$
    – jsotola
    Mar 4 '19 at 21:55

The behavior of going on the spot is the consequence of a hierarchical control system. The motion controller on the lower level can balance the robot, while the controller on the task level is able to execute a longer trajectory. The programming of such hierarchical control architecture is done independent from each other. The biped robot is in reality a combination of a car-like motion model which can drive forward and backward plus a walking controller which is able to maintain the center of gravity.

It is surprisingly easy to overcome this phenomena. All what the programmer has to do is to modify the animation script. If the high-level planner has a goal from the beginning at timecode 0, the robot will not wait but it will move as fast as possible into the direction. The robots behavior at a certain point in time are determined by the script, very similar to animating a virtual human.

An animation script is a notation for writing down a time-schedule. It defines, at which point in time the robot is doing which action. It can be visualized as a gantt-chart in which behaviors can overlapping at the same time.


  • $\begingroup$ That sounds like a wild guess (which is probably correct for the robot you are working on) and is for sure not correct for all robots. What do you mean by "animation script"? $\endgroup$
    – FooTheBar
    Mar 4 '19 at 9:48
  • $\begingroup$ Do you have an example of a system with this implementation? If "maintaining balance" and "walk to waypoint" send commands to the motors, which command is executed? $\endgroup$
    – FooTheBar
    Mar 4 '19 at 12:58
  • $\begingroup$ If i understand the comment right, the explanation with the gantt chart is too abstract and it remains unclear how the high-level actions are converted into lowlevel servo actions. $\endgroup$ Mar 4 '19 at 18:48

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