1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
|
/*************************************************************************
* *
* Open Dynamics Engine, Copyright (C) 2001,2002 Russell L. Smith. *
* All rights reserved. Email: russ@q12.org Web: www.q12.org *
* *
* This library is free software; you can redistribute it and/or *
* modify it under the terms of EITHER: *
* (1) The GNU Lesser General Public License as published by the Free *
* Software Foundation; either version 2.1 of the License, or (at *
* your option) any later version. The text of the GNU Lesser *
* General Public License is included with this library in the *
* file LICENSE.TXT. *
* (2) The BSD-style license that is included with this library in *
* the file LICENSE-BSD.TXT. *
* *
* This library is distributed in the hope that it will be useful, *
* but WITHOUT ANY WARRANTY; without even the implied warranty of *
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the files *
* LICENSE.TXT and LICENSE-BSD.TXT for more details. *
* *
*************************************************************************/
/*
test the Coulomb friction approximation.
a 10x10 array of boxes is made, each of which rests on the ground.
a horizantal force is applied to each box to try and get it to slide.
box[i][j] has a mass (i+1)*MASS and a force (j+1)*FORCE. by the Coloumb
friction model, the box should only slide if the force is greater than MU
times the contact normal force, i.e.
f > MU * body_mass * GRAVITY
(j+1)*FORCE > MU * (i+1)*MASS * GRAVITY
(j+1) > (i+1) * (MU*MASS*GRAVITY/FORCE)
(j+1) > (i+1) * k
this should be independent of the number of contact points, as N contact
points will each have 1/N'th the normal force but the pushing force will
have to overcome N contacts. the constants are chosen so that k=1.
thus you should see a triangle made of half the bodies in the array start to
slide.
*/
#include <ode/ode.h>
#include <drawstuff/drawstuff.h>
#ifdef _MSC_VER
#pragma warning(disable:4244 4305) // for VC++, no precision loss complaints
#endif
// select correct drawing functions
#ifdef dDOUBLE
#define dsDrawBox dsDrawBoxD
#define dsDrawSphere dsDrawSphereD
#define dsDrawCylinder dsDrawCylinderD
#define dsDrawCapsule dsDrawCapsuleD
#endif
// some constants
#define LENGTH 0.2 // box length & width
#define HEIGHT 0.05 // box height
#define MASS 0.2 // mass of box[i][j] = (i+1) * MASS
#define FORCE 0.05 // force applied to box[i][j] = (j+1) * FORCE
#define MU 0.5 // the global mu to use
#define GRAVITY 0.5 // the global gravity to use
#define N1 10 // number of different forces to try
#define N2 10 // number of different masses to try
// dynamics and collision objects
static dWorldID world;
static dSpaceID space;
static dBodyID body[N1][N2];
static dJointGroupID contactgroup;
static dGeomID ground;
static dGeomID box[N1][N2];
// this is called by dSpaceCollide when two objects in space are
// potentially colliding.
static void nearCallback (void *data, dGeomID o1, dGeomID o2)
{
int i;
// only collide things with the ground
int g1 = (o1 == ground);
int g2 = (o2 == ground);
if (!(g1 ^ g2)) return;
dBodyID b1 = dGeomGetBody(o1);
dBodyID b2 = dGeomGetBody(o2);
dContact contact[3]; // up to 3 contacts per box
for (i=0; i<3; i++) {
contact[i].surface.mode = dContactSoftCFM | dContactApprox1;
contact[i].surface.mu = MU;
contact[i].surface.soft_cfm = 0.01;
}
if (int numc = dCollide (o1,o2,3,&contact[0].geom,sizeof(dContact))) {
for (i=0; i<numc; i++) {
dJointID c = dJointCreateContact (world,contactgroup,contact+i);
dJointAttach (c,b1,b2);
}
}
}
// start simulation - set viewpoint
static void start()
{
static float xyz[3] = {1.7772,-0.7924,2.7600};
static float hpr[3] = {90.0000,-54.0000,0.0000};
dsSetViewpoint (xyz,hpr);
}
// simulation loop
static void simLoop (int pause)
{
int i;
if (!pause) {
// apply forces to all bodies
for (i=0; i<N1; i++) {
for (int j=0; j<N2; j++) {
dBodyAddForce (body[i][j],FORCE*(i+1),0,0);
}
}
dSpaceCollide (space,0,&nearCallback);
dWorldStep (world,0.05);
// remove all contact joints
dJointGroupEmpty (contactgroup);
}
dsSetColor (1,0,1);
dReal sides[3] = {LENGTH,LENGTH,HEIGHT};
for (i=0; i<N1; i++) {
for (int j=0; j<N2; j++) {
dsDrawBox (dGeomGetPosition(box[i][j]),dGeomGetRotation(box[i][j]),
sides);
}
}
}
int main (int argc, char **argv)
{
int i,j;
dMass m;
// setup pointers to drawstuff callback functions
dsFunctions fn;
fn.version = DS_VERSION;
fn.start = &start;
fn.step = &simLoop;
fn.command = 0;
fn.stop = 0;
fn.path_to_textures = "../../drawstuff/textures";
if(argc==2)
{
fn.path_to_textures = argv[1];
}
// create world
dInitODE();
world = dWorldCreate();
space = dHashSpaceCreate (0);
contactgroup = dJointGroupCreate (0);
dWorldSetGravity (world,0,0,-GRAVITY);
ground = dCreatePlane (space,0,0,1,0);
// bodies
for (i=0; i<N1; i++) {
for (j=0; j<N2; j++) {
body[i][j] = dBodyCreate (world);
dMassSetBox (&m,1,LENGTH,LENGTH,HEIGHT);
dMassAdjust (&m,MASS*(j+1));
dBodySetMass (body[i][j],&m);
dBodySetPosition (body[i][j],i*2*LENGTH,j*2*LENGTH,HEIGHT*0.5);
box[i][j] = dCreateBox (space,LENGTH,LENGTH,HEIGHT);
dGeomSetBody (box[i][j],body[i][j]);
}
}
// run simulation
dsSimulationLoop (argc,argv,352,288,&fn);
dJointGroupDestroy (contactgroup);
dSpaceDestroy (space);
dWorldDestroy (world);
dCloseODE();
return 0;
}
|
