Add conveyor belts example (#3705)

Author: jvonmuralt

CHANGELOG.md

@@ -35,6 +35,7 @@
 - Add opt-in `body_frame_origin="com"` to `ModelBuilder.add_rod()` and `ModelBuilder.add_rod_graph()` for COM-centered cable capsule body frames.
 - Add `sign_method` argument to `Mesh.build_sdf` and `SDF.create_from_mesh` support for a `"normal"` (angle-weighted pseudo-normal) sign strategy, for selecting the inside/outside sign of the baked SDF (`"auto"`, `"parity"`, `"winding"`, or `"normal"`).
 - Add `forward_depth_image` output support to `SensorTiledCamera.update()` and `SensorTiledCamera.utils.create_forward_depth_image_output()` for native forward-depth rendering without post-processing `depth_image`.
+- Add the `basic_conveyor_forces` example: a multi-belt conveyor circuit that transports rigid boxes with per-belt velocity fields, applying Coulomb-limited tangential body forces from reported per-contact normal forces across `SolverXPBD`, `SolverVBD`, and `SolverMuJoCo`.
 - Add optional `shear_stiffness`/`shear_damping` and `twist_stiffness`/`twist_damping` controls to `ModelBuilder.add_joint_cable()`, `ModelBuilder.add_rod()`, and `ModelBuilder.add_rod_graph()`; omitted shear defaults to stretch and omitted twist defaults to bend for compatibility.
 - Add `newton.utils.CableStiffness` and extend `newton.utils.create_cable_stiffness_from_elastic_moduli()` with `poissons_ratio`/`shear_modulus` inputs that include torsional `GJ/L` stiffness.
 - Add VBD cable validation examples covering bend stiffness, analytical bend/twist response, torsion material mapping, routed twist transfer, twist-buckling link verification, Michell/Zajac threshold behavior, and Dahl hysteresis.

README.md

@@ -142,7 +142,11 @@ If you run the examples from a source checkout with uv, use
         <img width="320" src="https://raw.githubusercontent.com/newton-physics/newton/main/docs/images/examples/example_basic_dzhanibekov.jpg" alt="Dzhanibekov">
       </a>
     </td>
-    <td></td>
+    <td align="center" width="33%">
+      <a href="https://github.com/newton-physics/newton/blob/main/newton/examples/basic/example_basic_conveyor_forces.py">
+        <img width="320" src="https://raw.githubusercontent.com/newton-physics/newton/main/docs/images/examples/example_basic_conveyor_forces.jpg" alt="Conveyor Forces">
+      </a>
+    </td>
   </tr>
   <tr>
     <td align="center" width="33%">
@@ -151,7 +155,9 @@ If you run the examples from a source checkout with uv, use
     <td align="center" width="33%">
       <code>python -m newton.examples basic_dzhanibekov</code>
     </td>
-    <td></td>
+    <td align="center" width="33%">
+      <code>python -m newton.examples basic_conveyor_forces</code>
+    </td>
   </tr>
   <tr>
     <td colspan="3"><h3>Robot Examples</h3></td>