observation.md

1. ball_pos: ball position in base frame (ObjectSensor) d = 3

   v = (R_base^-1 @ (p_ball - p_base)) * [1, 1, 0]
   

   scale = 1.0
2. projected_gravity (OrientationSensor) d = 3

   v = R_base^-1 @ [0, 0, -1]
   

   scale = N/A # 1.0
3. commands (RCSensor) d = 15

   v = [
       0: x_vel = lin_vel[0],
       1: y_vel = lin_vel[1],
       2: yaw_vel = 0, # train = 0
       3: body_height = 0, # train in [-0.05, 0.05]
       4: step_frequency = 3, # train = 3
       5..8: gait = [phase, offset, bound] = trotting = [0.5, 0, 0], # train = [0.5, 0, 0]
       8: duration = 0.5, # train = 0.5 # duration = stance / (stance + swing)
       9: footswing_height = 0.09, # train = 0.09
       10: pitch = 0, # train = 0
       11: roll = 0, # train = 0
       12: stance_width = 0, # train in [0, 0.1]
       13: stance_length = uniform(0, 0.1), # train in [0, 0.1]
       14: unknown (aux_reward_coef) = uniform(0, 0.01), # train in  [0, 0.01]
   ]
   

   scale = [
       lin_vel = 2, lin_vel, ang_vel = 0.25,
       body_height_cmd = 2, gait_freq_cmd = 1,
       gait_phase = 1, gait_phase, gait_phase, gait_phase,
       footswing_height = 0.15, pitch = 0.3, roll = 0.3,
       stance_width = 1, stance_length = 1,
       aux_reward = 1,
   ]
   

4. dof_pos (JointPositionSensor) d = 12 dof_pos is relative to default pos, i.e. motorState.q - q0.

   q0 = {
       'FL_hip_joint': 0.1,
       'RL_hip_joint': 0.1,
       'FR_hip_joint': -0.1,
       'RR_hip_joint': -0.1,
       'FL_thigh_joint': 0.8,
       'RL_thigh_joint': 1.0,
       'FR_thigh_joint': 0.8,
       'RR_thigh_joint': 1.0,
       'FL_calf_joint': -1.5,
       'RL_calf_joint': -1.5,
       'FR_calf_joint': -1.5,
       'RR_calf_joint': -1.5,
   }
   

   print(env.dof_names) output

   ['FL_hip_joint', 'FL_thigh_joint', 'FL_calf_joint', 'FR_hip_joint', 'FR_thigh_joint', 'FR_calf_joint', 'RL_hip_joint', 'RL_thigh_joint', 'RL_calf_joint', 'RR_hip_joint', 'RR_thigh_joint', 'RR_calf_joint']
   

   This index-name mapping is used to computed default pos. dof_pos should be consistent with it. scale = 1
5. dof_vel (JointVelocitySensor) d = 12 scale = 0.05
6. action: a_{t-1} (ActionSensor) d = 12 scale = N/A # 1.0 Note: 0 init
7. last_action: a_{t-2} (ActionSensor(delay=1) / LastActionSensor(delay=1)) d = 12 scale = N/A # 1.0 Note: 0 init
8. clock (ClockSensor) d = 4

   dt = control.decimation * sim.dt = 4 * 0.005 = 0.02 # 50Hz
   per step: gait_index = (gait_index + dt * step_frequency) % 1 # scalar
   foot_indices = (gait_index + [phase + offset + bound, offset, bound, phase]) # pacing_offset = False
   v = sin(2π foot_indices)
   

   scale = N/A # 1.0
9. yaw (YawSensor) d = 1

   f = R_base @ [1, 0, 0]
   v = atan2(f[1], f[0]) # wrap to [-π, π]
   

   scale = N/A # 1.0
10. timing (TimingSensor) d = 1

    v = gait_index # see clock
    

    scale = N/A # 1.0