constraint_specs.h

#pragma once

/// @file
/// This files contains simple structs used to store constraint specifications
/// defined by the user through MultibodyPlant API calls. These specifications
/// are later on used by our discrete solvers to build a model.

#include "drake/multibody/tree/multibody_tree_indexes.h"

namespace drake {
namespace multibody {
namespace internal {

// Struct to store coupler constraint parameters.
// Coupler constraints are modeled as a holonomic constraint of the form q₀ =
// ρ⋅q₁ + Δq, where q₀ and q₁ are the positions of two one-DOF joints, ρ the
// gear ratio and Δq a fixed offset.
template <typename T>
struct CouplerConstraintSpecs {
  // First joint with position q₀.
  JointIndex joint0_index;
  // Second joint with position q₁.
  JointIndex joint1_index;
  // Gear ratio ρ.
  T gear_ratio{1.0};
  // Offset Δq.
  T offset{0.0};
};

}  // namespace internal
}  // namespace multibody
}  // namespace drake