Bullet Collision Detection & Physics Library
btMultiBodyLink.h
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1 /*
2 Bullet Continuous Collision Detection and Physics Library
3 Copyright (c) 2013 Erwin Coumans http://bulletphysics.org
4 
5 This software is provided 'as-is', without any express or implied warranty.
6 In no event will the authors be held liable for any damages arising from the use of this software.
7 Permission is granted to anyone to use this software for any purpose,
8 including commercial applications, and to alter it and redistribute it freely,
9 subject to the following restrictions:
10 
11 1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.
12 2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
13 3. This notice may not be removed or altered from any source distribution.
14 */
15 
16 #ifndef BT_MULTIBODY_LINK_H
17 #define BT_MULTIBODY_LINK_H
18 
20 #include "LinearMath/btVector3.h"
22 
24 {
27 };
28 
29 //both defines are now permanently enabled
30 #define BT_MULTIBODYLINK_INCLUDE_PLANAR_JOINTS
31 #define TEST_SPATIAL_ALGEBRA_LAYER
32 
33 //
34 // Various spatial helper functions
35 //
36 
37 //namespace {
38 
40 
41 //}
42 
43 //
44 // Link struct
45 //
46 
48 {
50 
51  btScalar m_mass; // mass of link
52  btVector3 m_inertiaLocal; // inertia of link (local frame; diagonal)
53 
54  int m_parent; // index of the parent link (assumed to be < index of this link), or -1 if parent is the base link.
55 
56  btQuaternion m_zeroRotParentToThis; // rotates vectors in parent-frame to vectors in local-frame (when q=0). constant.
57 
58  btVector3 m_dVector; // vector from the inboard joint pos to this link's COM. (local frame.) constant.
59  //this is set to zero for planar joint (see also m_eVector comment)
60 
61  // m_eVector is constant, but depends on the joint type:
62  // revolute, fixed, prismatic, spherical: vector from parent's COM to the pivot point, in PARENT's frame.
63  // planar: vector from COM of parent to COM of this link, WHEN Q = 0. (local frame.)
64  // todo: fix the planar so it is consistent with the other joints
65 
67 
69 
71  {
72  eRevolute = 0,
75  ePlanar = 3,
76  eFixed = 4,
78  };
79 
80  // "axis" = spatial joint axis (Mirtich Defn 9 p104). (expressed in local frame.) constant.
81  // for prismatic: m_axesTop[0] = zero;
82  // m_axesBottom[0] = unit vector along the joint axis.
83  // for revolute: m_axesTop[0] = unit vector along the rotation axis (u);
84  // m_axesBottom[0] = u cross m_dVector (i.e. COM linear motion due to the rotation at the joint)
85  //
86  // for spherical: m_axesTop[0][1][2] (u1,u2,u3) form a 3x3 identity matrix (3 rotation axes)
87  // m_axesBottom[0][1][2] cross u1,u2,u3 (i.e. COM linear motion due to the rotation at the joint)
88  //
89  // for planar: m_axesTop[0] = unit vector along the rotation axis (u); defines the plane of motion
90  // m_axesTop[1][2] = zero
91  // m_axesBottom[0] = zero
92  // m_axesBottom[1][2] = unit vectors along the translational axes on that plane
94  void setAxisTop(int dof, const btVector3 &axis) { m_axes[dof].m_topVec = axis; }
95  void setAxisBottom(int dof, const btVector3 &axis)
96  {
97  m_axes[dof].m_bottomVec = axis;
98  }
99  void setAxisTop(int dof, const btScalar &x, const btScalar &y, const btScalar &z)
100  {
101  m_axes[dof].m_topVec.setValue(x, y, z);
102  }
103  void setAxisBottom(int dof, const btScalar &x, const btScalar &y, const btScalar &z)
104  {
105  m_axes[dof].m_bottomVec.setValue(x, y, z);
106  }
107  const btVector3 &getAxisTop(int dof) const { return m_axes[dof].m_topVec; }
108  const btVector3 &getAxisBottom(int dof) const { return m_axes[dof].m_bottomVec; }
109 
111 
112  btQuaternion m_cachedRotParentToThis; // rotates vectors in parent frame to vectors in local frame
113  btVector3 m_cachedRVector; // vector from COM of parent to COM of this link, in local frame.
114 
115  btVector3 m_appliedForce; // In WORLD frame
116  btVector3 m_appliedTorque; // In WORLD frame
117 
120 
122 
123  //m_jointTorque is the joint torque applied by the user using 'addJointTorque'.
124  //It gets set to zero after each internal stepSimulation call
126 
128  int m_flags;
129 
130  int m_dofCount, m_posVarCount; //redundant but handy
131 
133 
135 
136  btTransform m_cachedWorldTransform; //this cache is updated when calling btMultiBody::forwardKinematics
137 
138  const char *m_linkName; //m_linkName memory needs to be managed by the developer/user!
139  const char *m_jointName; //m_jointName memory needs to be managed by the developer/user!
140  const void *m_userPtr; //m_userPtr ptr needs to be managed by the developer/user!
141 
142  btScalar m_jointDamping; //todo: implement this internally. It is unused for now, it is set by a URDF loader. User can apply manual damping.
143  btScalar m_jointFriction; //todo: implement this internally. It is unused for now, it is set by a URDF loader. User can apply manual friction using a velocity motor.
144  btScalar m_jointLowerLimit; //todo: implement this internally. It is unused for now, it is set by a URDF loader.
145  btScalar m_jointUpperLimit; //todo: implement this internally. It is unused for now, it is set by a URDF loader.
146  btScalar m_jointMaxForce; //todo: implement this internally. It is unused for now, it is set by a URDF loader.
147  btScalar m_jointMaxVelocity; //todo: implement this internally. It is unused for now, it is set by a URDF loader.
148 
149  // ctor: set some sensible defaults
151  : m_mass(1),
152  m_parent(-1),
153  m_zeroRotParentToThis(0, 0, 0, 1),
154  m_cachedRotParentToThis(0, 0, 0, 1),
155  m_collider(0),
156  m_flags(0),
157  m_dofCount(0),
158  m_posVarCount(0),
160  m_jointFeedback(0),
161  m_linkName(0),
162  m_jointName(0),
163  m_userPtr(0),
164  m_jointDamping(0),
165  m_jointFriction(0),
168  m_jointMaxForce(0),
170  {
171  m_inertiaLocal.setValue(1, 1, 1);
172  setAxisTop(0, 0., 0., 0.);
173  setAxisBottom(0, 1., 0., 0.);
174  m_dVector.setValue(0, 0, 0);
175  m_eVector.setValue(0, 0, 0);
176  m_cachedRVector.setValue(0, 0, 0);
177  m_appliedForce.setValue(0, 0, 0);
178  m_appliedTorque.setValue(0, 0, 0);
181  //
182  m_jointPos[0] = m_jointPos[1] = m_jointPos[2] = m_jointPos[4] = m_jointPos[5] = m_jointPos[6] = 0.f;
183  m_jointPos[3] = 1.f; //"quat.w"
186  }
187 
188  // routine to update m_cachedRotParentToThis and m_cachedRVector
190  {
191  btScalar *pJointPos = (pq ? pq : &m_jointPos[0]);
192 
193  switch (m_jointType)
194  {
195  case eRevolute:
196  {
199 
200  break;
201  }
202  case ePrismatic:
203  {
204  // m_cachedRotParentToThis never changes, so no need to update
206 
207  break;
208  }
209  case eSpherical:
210  {
211  m_cachedRotParentToThis = btQuaternion(pJointPos[0], pJointPos[1], pJointPos[2], -pJointPos[3]) * m_zeroRotParentToThis;
213 
214  break;
215  }
216  case ePlanar:
217  {
219  m_cachedRVector = quatRotate(btQuaternion(getAxisTop(0), -pJointPos[0]), pJointPos[1] * getAxisBottom(1) + pJointPos[2] * getAxisBottom(2)) + quatRotate(m_cachedRotParentToThis, m_eVector);
220 
221  break;
222  }
223  case eFixed:
224  {
227 
228  break;
229  }
230  default:
231  {
232  //invalid type
233  btAssert(0);
234  }
235  }
236  }
237 };
238 
239 #endif //BT_MULTIBODY_LINK_H
void setValue(const btScalar &_x, const btScalar &_y, const btScalar &_z)
Definition: btVector3.h:640
void setIdentity()
Set this transformation to the identity.
Definition: btTransform.h:166
#define btAssert(x)
Definition: btScalar.h:133
btVector3 quatRotate(const btQuaternion &rotation, const btVector3 &v)
Definition: btQuaternion.h:926
btVector3 can be used to represent 3D points and vectors.
Definition: btVector3.h:80
The btTransform class supports rigid transforms with only translation and rotation and no scaling/she...
Definition: btTransform.h:28
The btQuaternion implements quaternion to perform linear algebra rotations in combination with btMatr...
Definition: btQuaternion.h:49
float btScalar
The btScalar type abstracts floating point numbers, to easily switch between double and single floati...
Definition: btScalar.h:294