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Summary of Changes Made to ezgripper.xml

Key Changes That Could Affect Spring Behavior

1. Joint Range Changes

BEFORE (HEAD~1):

  • F1_palm_knuckle: range="-1.57 0.35" (-90° to +20°)
  • F2_palm_knuckle: range="-1.57 0.35" (-90° to +20°)

AFTER (current):

  • F1_palm_knuckle: range="-1.57 0.436" (-90° to +25°)
  • F2_palm_knuckle: range="-1.57 0.436" (-90° to +25°)

2. Spring Parameter Changes

BEFORE (HEAD~1):

  • F1_palm_knuckle: stiffness="1.0" springref="-2.0" damping="0.1"
  • F1_knuckle_tip: stiffness="1.0" springref="-0.33" damping="0.1"
  • F2_palm_knuckle: stiffness="1.0" springref="-2.0" damping="0.1"
  • F2_knuckle_tip: stiffness="1.0" springref="-0.33" damping="0.1"

AFTER (current):

  • F1_palm_knuckle: stiffness="0.02459949416" springref="-3.14" damping="1.0"
  • F1_knuckle_tip: stiffness="0.05114105365" springref="-4.71" damping="1.0"
  • F2_palm_knuckle: stiffness="0.02459949416" springref="-3.14" damping="1.0"
  • F2_knuckle_tip: stiffness="0.05114105365" springref="-4.71" damping="1.0"

3. Collision Changes

BEFORE (HEAD~1):

  • Palm mesh: contype="3" conaffinity="3" (enabled)
  • Finger meshes: contype="3" conaffinity="3" (enabled)
  • No mechanical stops

AFTER (current):

  • Palm mesh: contype="0" conaffinity="0" (disabled)
  • Finger meshes: contype="0" conaffinity="0" (disabled)
  • Added mechanical stops with contype=4,5,6

4. Position Changes

BEFORE (HEAD~1):

  • F1_L1 pos="0.0755 0.03 0"
  • F2_L1 pos="0.0755 -0.03 0"
  • Palm pulleys at pos="0.0755 0.010 0" and pos="0.0755 -.010 0"

AFTER (current):

  • F1_L1 pos="0.07255 0.03 0"
  • F2_L1 pos="0.07255 -0.03 0"
  • Palm pulleys at pos="0.07255 0 0"

5. Tendon and Actuator Changes

BEFORE (HEAD~1):

  • Tendons enabled with L2 pulleys
  • Actuators enabled

AFTER (current):

  • Tendons commented out (disabled)
  • Actuators commented out (disabled)

Critical Issue Analysis

Spring Torque = 0.000000 N·m

The debug showed that spring torque is 0 at all angles, which suggests one of these issues:

  1. Springref outside joint range: -3.14 rad (-180°) is outside -1.57 to 0.436 range
  2. Stiffness too low: Changed from 1.0 to 0.0246 (40x reduction)
  3. Damping too high: Changed from 0.1 to 1.0 (10x increase)
  4. MuJoCo version/compatibility: Spring definition format might have changed
  5. Joint type change: Joint configuration might affect spring calculation

Most Likely Causes

  1. Springref outside range: -3.14 rad is far outside the -1.57 to 0.436 range
  2. Stiffness reduction: 1.0 → 0.0246 is a 40x reduction
  3. Damping increase: 0.1 → 1.0 might overdamp the system

Recommendations

  1. Fix springref: Change to within joint range (e.g., -1.4 rad for -80°)
  2. Check stiffness: Verify if 0.0246 is correct value
  3. Reduce damping: Try 0.1 instead of 1.0
  4. Test with original values: Revert to HEAD~1 spring parameters to verify