Control of Running and Walking

Paper One

Marc H. Raibert and Jessica K. Hodgins. Animation of dynamic legged locomotion. In SIGGRAPH ’91: Proceedings of the 18th annual conference on Computer graphics and interactive techniques, pages 349–358, New York, NY, USA, 1991. ACM Press.

This is an example response. To add your own response, click on 'Edit' above. Paragraphs are separated with just a blank line. This paper is interesting because... It is flawed because ... I didn't understand the following bits... Open problems are ... -- Michiel van de Panne

Similar to my comments from last class, I enjoyed this "older" SIGGRAPH paper because it reads like a good textbook as opposed to a research paper. Anyways, the main issue I've always had with control based techniques is that while they ensure physical correctness, they do not necessarily look real (that is, like an actual human). The paper sort of steals my thunder on this by saying "... animals move with a smoothness and coordination that is not required by physical realism alone". Nevertheless, this paper is good in that it provides a good initial exploration into the successful use of applying control algorithms to generate balanced walking and running motions. I'm not quite sure I understand their allometric derivations of the scale factors in Table 1. Clearly, the dimension (not units!) of velocity are LT^{-1}, but why is its scale factor L^{1/2}? -- KenRose

(Animation of Dynamic Legged Locomotion) I strongly agree with the words that the control inputs are more like “suggestions” that must be reconciled with the dynamic state and structure of the system than “commands” since that might make the locomotion more realistic. I also feel very comfortable reading this paper since it provides the basic background of control system in which I don’t have much experience. FSM is very popular in NPC motion control in games, and is simple to implement. While on the other hand, sometimes it will make the NPC act stupidly as the opponent of human player. So nowadays researchers and practitioners are trying to endow the NPCs with more intelligence so as to make the games more interesting.--Zhangbo Liu

The results seem interesting, I hope that we'll be treated to a video during the presentation today. I share Ken's confusion about the scaling factors (wrt to velocity and time). That table is neat in showing that it's not straightforward to scale a dynamic creature as one would maybe expect. On page 355 they note that they're assuming an infinited coefficient of friction to prevent slipping, but that in actuality, their models need a relatively small (?) coefficient to accomplish this. I can't remember much about the magnitudes of realistic coefficients of friction, so are the figures they quote indeed "realistic"? -- Main.Daniel Eaton

(Animation of Dynamic Legged Locomotion) The authors state that the motions described in the paper are physically realistic. It is hard to tell without seeing a animation, but I am guessing that control methods as well as any other method could generate a non-realistic motion, and it is up to the implementation to dictate the motion “quality”. It would be interesting for me to discuss/analyze that point. Another question is whether physicaly based motion is a realistic one and vice versa. – Hagit Schechter

Paper Two

Joseph Laszlo, Michiel van de Panne, and Eugene Fiume. Limit cycle control and its application to the animation of balancing and walking. In SIGGRAPH ’96: Proceedings of the 23rd annual conference on Computer graphics and interactive techniques, pages 155–162, New York, NY, USA, 1996. ACM Press.

Another paper. Please add your comments below.

This set of papers is significantly different from what I have seen in our class so far, it introduces quite a few new concepts which I expect more elaborations on, such as what does it mean by unstable motion? Linear predictive model (section 5.2), and proportional derivative controller (PD). The idea presented in the paper is very neat, using FSM to determine next state and PD controller to compute the required force and torques which can lead the articulated figure to the desired pose. However, control perturbation is used to solve this control problem and perturbation is like trial-and-error therefore, it would still be an issue of the efficiency. -- Steven Chang

I liked the result of this paper in that it was able to apply control techniques to an articulated figure with a higher number of DOF (19). The previous paper only applied the control algorithms to models with a few DOF, which further limited their realism. I would like to know more about the selection of the regulation variables. Specifically, is this something that is done once for one class of closed-loop motion (e.g., I'll use swing COM for running) or does it have to be done for every motion? Also, the paper mentions that "the evidence for the above linear approximation is empirical". Are there closed loop motions for which perturbations result in non-linear effects? Finally, are there videos of the final animations? The paper mentions that the results still do have a robotic feel to them for the case of the 4 pose FSM. -- KenRose

(Limit cycle control) I am interested to learn if there have been significant results in controlling complex / less stable types of motion such as running. Also, I assume that control techniques are used in robotics research as well, and am interested to compare the different challenges and results in the two areas. -- Hagit Schechter