| |
| """ |
| Example how substep_callback can be used to detect contacts/penetrations that |
| are not visible in between steps. |
| |
| In this example a sphere pushes a cylinder, which then slides away. |
| The entirety of the contact and separation happens in substeps. |
| |
| In between steps there is always zero contacts, so the push is not observed. |
| |
| We use a substep_callback to get a sum of the external forces on the cylinder. |
| """ |
| from mujoco_py import load_model_from_xml, MjSim |
|
|
| MODEL_XML = """ |
| <mujoco> |
| <size nuserdata="1"/> |
| <worldbody> |
| <body name="robot" pos="0 0 0"> |
| <geom rgba="1 0 0 1" size="0.15" type="sphere"/> |
| <joint axis="1 0 0" damping="1" name="j" type="slide"/> |
| </body> |
| <body name="cylinder" pos=".5 0 0"> |
| <geom size="0.15 0.15" type="cylinder"/> |
| <joint axis="1 0 0" damping="10" type="slide"/> |
| </body> |
| </worldbody> |
| <actuator> |
| <position joint="j" kp="2000"/> |
| </actuator> |
| </mujoco> |
| """ |
|
|
| fn = ''' |
| #define SQUARE(a) (a * a) |
| void fun(const mjModel* m, mjData* d) { |
| for (int i = d->ne; i < d->nefc; i++) { |
| pos_sum += SQUARE(d->efc_pos[i]); |
| } |
| } |
| ''' |
|
|
| sim = MjSim(load_model_from_xml(MODEL_XML), nsubsteps=50, |
| substep_callback=fn, userdata_names=['pos_sum']) |
| t = 0 |
| while t < 10: |
| t += 1 |
| sim.data.ctrl[0] = .2 |
| print('t', t) |
| sim.step() |
| |
| assert sim.data.ncon == 0, 'No contacts should be detected here' |
| |
| if t > 1: |
| assert sim.data.get_userdata('pos_sum') > 0 |
|
|
