luokai0 Robot Dynamics Expert
Before Starting
- Forward or inverse dynamics?
- Serial or parallel manipulator?
- Rigid body or flexible link assumption?
Core Expertise Areas
Lagrangian Dynamics
Lagrangian: L = T minus V, kinetic energy minus potential energy. Euler-Lagrange equations: d/dt of partial L over partial q-dot minus partial L over partial q = tau. Manipulator equation: M times q-double-dot plus C times q-dot plus G = tau. Inertia matrix M: symmetric positive definite, depends on configuration. Coriolis matrix C: centripetal and Coriolis terms, depends on config and velocity.
Newton-Euler Formulation
Recursive algorithm: outward pass computes velocities and accelerations, inward pass computes forces. Computational efficiency: O(n) for n-joint robot, preferred for real-time control. Free body diagram: each link has forces and moments from adjacent links. Inertia tensor: 3x3 matrix, depends on mass distribution and reference frame.
Inertia Parameters
Ten parameters per link: mass, center of mass position 3 values, inertia tensor 6 values. Parameter identification: excitation trajectories, least squares estimation. Minimum inertia parameters: subset that fully determines dynamics, reduces to base parameters.
Friction and Disturbances
Coulomb friction: constant opposing velocity, discontinuous at zero velocity. Viscous friction: proportional to velocity, easy to compensate. Stribeck effect: friction dip near zero velocity, causes stick-slip. Gravity compensation: subtract G from control torque to cancel gravity effects.
Best Practices
- Validate dynamics model against experimental measurements
- Use recursive Newton-Euler for real-time control implementations
- Identify inertia parameters in actual hardware for accurate model
- Include friction compensation for precision positioning tasks
Common Pitfalls
| Pitfall | Fix |
|---|---|
| Ignoring coupling in multi-joint control | Use full dynamics model not independent joints |
| Wrong inertia reference frame | Always specify frame for inertia tensor |
| Neglecting friction in high-precision tasks | Model and compensate Coulomb and viscous friction |
| Using nominal parameters without identification | Real hardware deviates from CAD model |
Related Skills
- robot-kinematics-expert
- control-theory-expert
- classical-mechanics-expert