Contact, wheel slip, and friction documentation #694

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scpeters wants to merge 38 commits into gz-physics8 from scpeters/wheel_slip_tutorial

Member

scpeters commented Sep 27, 2024

🎉 New feature

Summary

This adds the following documentation of the following topics:

Simulation of contact, slip, and friction in Gazebo
Special considerations for modeling wheel contact / slip / friction

I'm not sure if a gz-physics tutorial is the right place for this; I'm open to moving it elsewhere. It still needs a few figures, but it collects a lot of knowledge about contact simulation in general and specifically for wheel-terrain contact. It includes both Gazebo Classic and gz-sim.

Test it

Checklist

Signed all commits for DCO
Added tests
Added example and/or tutorial
Updated documentation (as needed)
Updated migration guide (as needed)
Consider updating Python bindings (if the library has them)
codecheck passed (See contributing)
All tests passed (See test coverage)
While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

scpeters added 30 commits

July 10, 2024 03:58


          Tutorial about contact, slip, and friction

124cfb4

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          Tutorial about wheel-terrain contact

cbcea78

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          fix whitespace

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          Try an svg illustration of contact

8a0b5fa

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          Use svg groups and define top objects last

ea45fc2

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          Add animation of contact without slip

21e89f5

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          Add animation of contact with slip

dc8fee2

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          Use one large box on bottom

0af01a1

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          Make box slide and wheel slip backwards

8a752c5

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          Use same smaller radius for top circles

bd5b118

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          Make contact figure look more like slip figures

69322c4

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          Add illustrations of contact without and with slip

c5df8b2

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          update wording

1db11c7

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          more friction write-up

1c4ad5b

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          discuss constraint relaxation, add ascii plot

9ae8f23

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          compare friction step to saturation plot

c02caa6

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          Merge branch 'scpeters/contact_slip_friction' into scpeters/wheel_sli…

7b58cfa

…p_tutorial


          re-order section, add references about non-dim slip

7b0e09c

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          incorporate feedback about friction

489396a

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          Expand description of slip compliance

75dc5a1

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          document mu, friction coefficient

5ca2408

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          Merge branch 'scpeters/contact_slip_friction' into scpeters/wheel_sli…

53e3dfb

…p_tutorial


          define wheel directions, nondimensional wheel slip

55f2b4b

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          Comment on accuracy, consistency of contact points

2f4e156

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          Merge branch 'scpeters/contact_slip_friction' into scpeters/wheel_sli…

9d86ebc

…p_tutorial


          add comment

6dc031b

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          define sat(x), relaxed friction function

93aa332

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          Merge branch 'scpeters/contact_slip_friction' into scpeters/wheel_sli…

d88128e

…p_tutorial


          define friction curve with slip differently

73b2a7a

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          Merge branch 'scpeters/contact_slip_friction' into scpeters/wheel_sli…

eed7b48

…p_tutorial

scpeters added 7 commits

September 25, 2024 18:24


          change V_C to v_t, V_W to v_W for consistency

847ca5e

match the variable names used in contact tutorial

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          document wheel slip plugin's nondimensional calcs

9944b2a

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          Add contact patch discussion, plowing figures

3f457dd

use markdown tables in wheel slip discussion

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          fix table syntax

a3d615d

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          clarify slip value definitions with s_a, s_b, S_a

57946c6

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          move wheel coordinates earlier, finish plowing

4e8f218

Signed-off-by: Steve Peters <scpeters@openrobotics.org>


          document nonlinear friction model

b7eb227

Signed-off-by: Steve Peters <scpeters@openrobotics.org>

github-actions bot added the 🏛️ ionic label


          Merge branch 'gz-physics8' into scpeters/wheel_slip_tutorial

6c768ff

azeey added this to the Jetty Release milestone

iche033 reviewed

View reviewed changes

Contributor

iche033 left a comment

This tutorial has really great info and I think we should try to get this in!

One thing I noticed is that it refers to ODE and Gazebo-classic's code / unmerged PRs in many places to describe in detail how some features are implemented there. I am guessing some of these features are not available in the modern gazebo yet. I think it's fine to point to classic if it helps to illustrate various concepts presented but it would good to clarify whether which of these features are available in the modern Gazebo yet. Focusing more on the modern gazebo would be nice so that the tutorial does not seem like it's written for classic.

tutorials/11_wheel_contact.md

+              pressure and an equivalent normal force vector that is inclined relative to the
+              undisturbed surface normal.
+              In the right portion of the illustration below, the equivalent normal force
+              opposes the motion of the wheel, requiring travtive torque to be applied in

Contributor

iche033 Aug 7, 2025

tractive?

Suggested change

      
            opposes the motion of the wheel, requiring travtive torque to be applied in
          
            opposes the motion of the wheel, requiring tractive torque to be applied in

tutorials/11_wheel_contact.md


		![Illustration of a rigid wheel in contact with a deformable surface at rest and while rolling with a plowing effect.](img/deformable_terrain.png)

		This longitudinal plowing effect has been approximated in Gazebo Classic by

Contributor

iche033 Aug 7, 2025

is plowing effect supported in gz-physics / gz-sim? If not, we probably want to it clear that those tags are not currently supported yet.

tutorials/10_contact_slip_friction.md

+                    with units of `m/s`.
+              - Torsional slip `ω_n` is computed at each contact point as follows:
+                  - Compute the angular velocity of each shape.
+                  - Compute the diference between these velocities to yield the

Contributor

iche033 Aug 7, 2025

Suggested change

      
                - Compute the diference between these velocities to yield the
          
                - Compute the difference between these velocities to yield the

Contributor

azeey commented Aug 7, 2025

I'm not sure if a gz-physics tutorial is the right place for this; I'm open to moving it elsewhere.

We don't have clear policy about this, but the way I'm thinking about it right now is that if the tutorial describes how to use the API in the package or is written to show how to use a specific feature/plugin in the package, it should be kept with the package. Otherwise, it should go to https://github.com/gazebosim/docs. In this case, since most of the content is conceptual, I'd vote for moving it to gazebosim/docs. Thoughts?

azeey removed this from the Jetty Release milestone

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