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 
39 
41 
42 //}
43 
44 //
45 // Link struct
46 //
47 
49 {
50 
52 
53  btScalar m_mass; // mass of link
54  btVector3 m_inertiaLocal; // inertia of link (local frame; diagonal)
55 
56  int m_parent; // index of the parent link (assumed to be < index of this link), or -1 if parent is the base link.
57 
58  btQuaternion m_zeroRotParentToThis; // rotates vectors in parent-frame to vectors in local-frame (when q=0). constant.
59 
60  btVector3 m_dVector; // vector from the inboard joint pos to this link's COM. (local frame.) constant.
61  //this is set to zero for planar joint (see also m_eVector comment)
62 
63  // m_eVector is constant, but depends on the joint type:
64  // revolute, fixed, prismatic, spherical: vector from parent's COM to the pivot point, in PARENT's frame.
65  // planar: vector from COM of parent to COM of this link, WHEN Q = 0. (local frame.)
66  // todo: fix the planar so it is consistent with the other joints
67 
69 
71 
73  {
74  eRevolute = 0,
77  ePlanar = 3,
78  eFixed = 4,
80  };
81 
82 
83 
84  // "axis" = spatial joint axis (Mirtich Defn 9 p104). (expressed in local frame.) constant.
85  // for prismatic: m_axesTop[0] = zero;
86  // m_axesBottom[0] = unit vector along the joint axis.
87  // for revolute: m_axesTop[0] = unit vector along the rotation axis (u);
88  // m_axesBottom[0] = u cross m_dVector (i.e. COM linear motion due to the rotation at the joint)
89  //
90  // for spherical: m_axesTop[0][1][2] (u1,u2,u3) form a 3x3 identity matrix (3 rotation axes)
91  // m_axesBottom[0][1][2] cross u1,u2,u3 (i.e. COM linear motion due to the rotation at the joint)
92  //
93  // for planar: m_axesTop[0] = unit vector along the rotation axis (u); defines the plane of motion
94  // m_axesTop[1][2] = zero
95  // m_axesBottom[0] = zero
96  // m_axesBottom[1][2] = unit vectors along the translational axes on that plane
98  void setAxisTop(int dof, const btVector3 &axis) { m_axes[dof].m_topVec = axis; }
99  void setAxisBottom(int dof, const btVector3 &axis)
100  {
101  m_axes[dof].m_bottomVec = axis;
102  }
103  void setAxisTop(int dof, const btScalar &x, const btScalar &y, const btScalar &z)
104  {
105  m_axes[dof].m_topVec.setValue(x, y, z);
106  }
107  void setAxisBottom(int dof, const btScalar &x, const btScalar &y, const btScalar &z)
108  {
109  m_axes[dof].m_bottomVec.setValue(x, y, z);
110  }
111  const btVector3 & getAxisTop(int dof) const { return m_axes[dof].m_topVec; }
112  const btVector3 & getAxisBottom(int dof) const { return m_axes[dof].m_bottomVec; }
113 
115 
116  btQuaternion m_cachedRotParentToThis; // rotates vectors in parent frame to vectors in local frame
117  btVector3 m_cachedRVector; // vector from COM of parent to COM of this link, in local frame.
118 
119  btVector3 m_appliedForce; // In WORLD frame
120  btVector3 m_appliedTorque; // In WORLD frame
121 
124 
126 
127  //m_jointTorque is the joint torque applied by the user using 'addJointTorque'.
128  //It gets set to zero after each internal stepSimulation call
130 
132  int m_flags;
133 
134 
135  int m_dofCount, m_posVarCount; //redundant but handy
136 
138 
140 
141  btTransform m_cachedWorldTransform;//this cache is updated when calling btMultiBody::forwardKinematics
142 
143  const char* m_linkName;//m_linkName memory needs to be managed by the developer/user!
144  const char* m_jointName;//m_jointName memory needs to be managed by the developer/user!
145  const void* m_userPtr;//m_userPtr ptr needs to be managed by the developer/user!
146 
147  btScalar m_jointDamping; //todo: implement this internally. It is unused for now, it is set by a URDF loader. User can apply manual damping.
148  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.
149  btScalar m_jointLowerLimit; //todo: implement this internally. It is unused for now, it is set by a URDF loader.
150  btScalar m_jointUpperLimit; //todo: implement this internally. It is unused for now, it is set by a URDF loader.
151  btScalar m_jointMaxForce; //todo: implement this internally. It is unused for now, it is set by a URDF loader.
152  btScalar m_jointMaxVelocity;//todo: implement this internally. It is unused for now, it is set by a URDF loader.
153 
154  // ctor: set some sensible defaults
156  : m_mass(1),
157  m_parent(-1),
158  m_zeroRotParentToThis(0, 0, 0, 1),
159  m_cachedRotParentToThis(0, 0, 0, 1),
160  m_collider(0),
161  m_flags(0),
162  m_dofCount(0),
163  m_posVarCount(0),
164  m_jointType(btMultibodyLink::eInvalid),
165  m_jointFeedback(0),
166  m_linkName(0),
167  m_jointName(0),
168  m_userPtr(0),
169  m_jointDamping(0),
170  m_jointFriction(0),
171  m_jointLowerLimit(0),
172  m_jointUpperLimit(0),
173  m_jointMaxForce(0),
174  m_jointMaxVelocity(0)
175  {
176 
177  m_inertiaLocal.setValue(1, 1, 1);
178  setAxisTop(0, 0., 0., 0.);
179  setAxisBottom(0, 1., 0., 0.);
180  m_dVector.setValue(0, 0, 0);
181  m_eVector.setValue(0, 0, 0);
182  m_cachedRVector.setValue(0, 0, 0);
183  m_appliedForce.setValue( 0, 0, 0);
184  m_appliedTorque.setValue(0, 0, 0);
185  //
186  m_jointPos[0] = m_jointPos[1] = m_jointPos[2] = m_jointPos[4] = m_jointPos[5] = m_jointPos[6] = 0.f;
187  m_jointPos[3] = 1.f; //"quat.w"
188  m_jointTorque[0] = m_jointTorque[1] = m_jointTorque[2] = m_jointTorque[3] = m_jointTorque[4] = m_jointTorque[5] = 0.f;
189  m_cachedWorldTransform.setIdentity();
190  }
191 
192  // routine to update m_cachedRotParentToThis and m_cachedRVector
194  {
195  btScalar *pJointPos = (pq ? pq : &m_jointPos[0]);
196 
197  switch(m_jointType)
198  {
199  case eRevolute:
200  {
201  m_cachedRotParentToThis = btQuaternion(getAxisTop(0),-pJointPos[0]) * m_zeroRotParentToThis;
202  m_cachedRVector = m_dVector + quatRotate(m_cachedRotParentToThis,m_eVector);
203 
204  break;
205  }
206  case ePrismatic:
207  {
208  // m_cachedRotParentToThis never changes, so no need to update
209  m_cachedRVector = m_dVector + quatRotate(m_cachedRotParentToThis,m_eVector) + pJointPos[0] * getAxisBottom(0);
210 
211  break;
212  }
213  case eSpherical:
214  {
215  m_cachedRotParentToThis = btQuaternion(pJointPos[0], pJointPos[1], pJointPos[2], -pJointPos[3]) * m_zeroRotParentToThis;
216  m_cachedRVector = m_dVector + quatRotate(m_cachedRotParentToThis,m_eVector);
217 
218  break;
219  }
220  case ePlanar:
221  {
222  m_cachedRotParentToThis = btQuaternion(getAxisTop(0),-pJointPos[0]) * m_zeroRotParentToThis;
223  m_cachedRVector = quatRotate(btQuaternion(getAxisTop(0),-pJointPos[0]), pJointPos[1] * getAxisBottom(1) + pJointPos[2] * getAxisBottom(2)) + quatRotate(m_cachedRotParentToThis,m_eVector);
224 
225  break;
226  }
227  case eFixed:
228  {
229  m_cachedRotParentToThis = m_zeroRotParentToThis;
230  m_cachedRVector = m_dVector + quatRotate(m_cachedRotParentToThis,m_eVector);
231 
232  break;
233  }
234  default:
235  {
236  //invalid type
237  btAssert(0);
238  }
239  }
240  }
241 };
242 
243 
244 #endif //BT_MULTIBODY_LINK_H
void setValue(const btScalar &_x, const btScalar &_y, const btScalar &_z)
Definition: btVector3.h:652
void setIdentity()
Set this transformation to the identity.
Definition: btTransform.h:172
#define btAssert(x)
Definition: btScalar.h:131
btVector3 quatRotate(const btQuaternion &rotation, const btVector3 &v)
Definition: btQuaternion.h:917
btVector3 can be used to represent 3D points and vectors.
Definition: btVector3.h:83
The btTransform class supports rigid transforms with only translation and rotation and no scaling/she...
Definition: btTransform.h:34
The btQuaternion implements quaternion to perform linear algebra rotations in combination with btMatr...
Definition: btQuaternion.h:55
float btScalar
The btScalar type abstracts floating point numbers, to easily switch between double and single floati...
Definition: btScalar.h:292