Stéphane on Locomotion - Comments: Humanoid and wheeled-legged controllers in C++ and Python: balancing at different frequencies

Posted by: Yuki Onishi

2022-11-28T10:47:00+01:00

That's good to hear! I contribute to OpenRR, the Open Rust Robotics platform. You should check it out.

Posted by: Yuki Onishi

2022-11-28T10:46:00+01:00

You mentioned Rust and Julia. Do you have plans to extend Vulp to these languages?

Posted by: Stéphane

2022-11-28T10:44:00+01:00

Indeed, this analysis does not consider the distance to the edge of the support area.

I agree with you that the maximum sampling period should be affected by the position of the ZMP within its support area.

Posted by: Yuichi Tazaki

2022-11-28T10:44:00+01:00

I have a follow-up question: does this work consider the distance from the ZMP to the edge of its support area?

It seems the maximum sampling period would become smaller as this distance shrinks.

Posted by: Stéphane

2022-11-28T10:42:00+01:00

Vulp being a protocol, it is open to implementation in either Rust or Julia. Rust has proper safety guarantees compared to C++, and Julia performs faster than Python with roughly the same level of abstraction—although, regarding this last point, we saw in this presentation that the current performance of Python is already sufficient for many balancing use cases. Personally I'm interested in Rust's guarantees and type system.

Posted by: Stéphane

2022-11-28T10:42:00+01:00

We indeed need to specify what is discretized exactly. In this analysis, the continuous-time DCM dynamics are discretized with sampling time $\def\bfA{\boldsymbol{A}} \def\bfB{\boldsymbol{B}} \def\bfC{\boldsymbol{C}} \def\bfD{\boldsymbol{D}} \def\bfE{\boldsymbol{E}} \def\bfF{\boldsymbol{F}} \def\bfG{\boldsymbol{G}} \def\bfH{\boldsymbol{H}} \def\bfI{\boldsymbol{I}} \def\bfJ{\boldsymbol{J}} \def\bfK{\boldsymbol{K}} \def\bfL{\boldsymbol{L}} \def\bfM{\boldsymbol{M}} \def\bfN{\boldsymbol{N}} \def\bfO{\boldsymbol{O}} \def\bfP{\boldsymbol{P}} \def\bfQ{\boldsymbol{Q}} \def\bfR{\boldsymbol{R}} \def\bfS{\boldsymbol{S}} \def\bfT{\boldsymbol{T}} \def\bfU{\boldsymbol{U}} \def\bfV{\boldsymbol{V}} \def\bfW{\boldsymbol{W}} \def\bfX{\boldsymbol{X}} \def\bfY{\boldsymbol{Y}} \def\bfZ{\boldsymbol{Z}} \def\bfalpha{\boldsymbol{\alpha}} \def\bfa{\boldsymbol{a}} \def\bfbeta{\boldsymbol{\beta}} \def\bfb{\boldsymbol{b}} \def\bfcd{\dot{\bfc}} \def\bfchi{\boldsymbol{\chi}} \def\bfc{\boldsymbol{c}} \def\bfd{\boldsymbol{d}} \def\bfe{\boldsymbol{e}} \def\bff{\boldsymbol{f}} \def\bfgamma{\boldsymbol{\gamma}} \def\bfg{\boldsymbol{g}} \def\bfh{\boldsymbol{h}} \def\bfi{\boldsymbol{i}} \def\bfj{\boldsymbol{j}} \def\bfk{\boldsymbol{k}} \def\bflambda{\boldsymbol{\lambda}} \def\bfl{\boldsymbol{l}} \def\bfm{\boldsymbol{m}} \def\bfn{\boldsymbol{n}} \def\bfomega{\boldsymbol{\omega}} \def\bfone{\boldsymbol{1}} \def\bfo{\boldsymbol{o}} \def\bfpdd{\ddot{\bfp}} \def\bfpd{\dot{\bfp}} \def\bfphi{\boldsymbol{\phi}} \def\bfp{\boldsymbol{p}} \def\bfq{\boldsymbol{q}} \def\bfr{\boldsymbol{r}} \def\bfsigma{\boldsymbol{\sigma}} \def\bfs{\boldsymbol{s}} \def\bftau{\boldsymbol{\tau}} \def\bftheta{\boldsymbol{\theta}} \def\bft{\boldsymbol{t}} \def\bfu{\boldsymbol{u}} \def\bfv{\boldsymbol{v}} \def\bfw{\boldsymbol{w}} \def\bfxi{\boldsymbol{\xi}} \def\bfx{\boldsymbol{x}} \def\bfy{\boldsymbol{y}} \def\bfzero{\boldsymbol{0}} \def\bfz{\boldsymbol{z}} \def\defeq{\stackrel{\mathrm{def}}{=}} \def\p{\boldsymbol{p}} \def\qdd{\ddot{\bfq}} \def\qd{\dot{\bfq}} \def\q{\boldsymbol{q}} \def\xd{\dot{x}} \def\yd{\dot{y}} \def\zd{\dot{z}} \delta t$ . Meanwhile, force control is assumed to run in an underlying continuous process, but its outcome (e.g. delay) is lumped in a ZMP tracking error at the next sampling time.

Posted by: Stéphane

2022-11-28T10:42:00+01:00

👍

Posted by: Takumi Kamioka

2022-11-28T10:42:00+01:00

This question is about balancing as a low-frequency task (slide 26 about this work). Isn't this result assuming continuous-time control at some stage?

Posted by: Stéphane

2022-11-28T10:40:00+01:00

Currently Vulp only supports Linux for x86 and ARM architectures, which is Upkie's use case. We can add Windows support to the roadmap: #3.

Note however that Vulp targets mostly researchers, research engineers, or PhD students. It may have some rough edges for students earlier in the learning curve.

Posted by: Yuichi Tazaki

2022-11-28T10:40:00+01:00

Does Vulp run on Windows? This would be helpful when setting up a teaching environment for students.