This demo is about the simulation of a crawling spider robot with six legs, where we control the motion of the legs with 18 actuators.

In deail, one performs the following steps:

Use SolidWorks to make a 3D CAD model of the crawling robot,
export it as a .pyfile using the Chrono::SolidWorks add-in; ex. use the name spider_robot.py
create a Python program, ex. use the name demo_spider.py, using the functions of PyChrono to load and simulate spider_robot.py.

For your convenience, the CAD model, the converted spider_robot.py model, and the demo_spider.py program are all available in the following archive:

spider_robot.zip.

The following is the complete listing of demo_spider.py (it must stay in the same directory where you exported your CAD model with the name spider_robot.py)

Note how we used mybody = mysystem.SearchBody('...'); and mymarker = mybody.SearchMarker('...'); to retrieve object pointers from their names in the 3D CAD model. Also note that a part that shows as M-410iB-300 -1/ArmBase<1> in the GUI of SolidWorks, becomes M-410iB-300 -1/ArmBase-1 for the Python side; i.e. the <N> suffix becomes -N.

Finally, note how we used ChFunction objects to build some basic loop motions for the actuators, in prescribed rotation mode.

ATTENTION! The source code listed below may not be compatible with your current version of PyChrono and may need to be slightly adjusted to reflect any recent API changes.

import os
import math
import pychrono as chrono
import pychrono.postprocess as postprocess
import pychrono.irrlicht as chronoirr
 
# class to use ChLinkMotorRotationAngle given the markers from the CAD
class SpiderRobotMotor(chrono.ChLinkMotorRotationAngle):
    def __init__(self):
        super().__init__()
        self.bodylist = []
    def Initialize(self, mark1, mark2):
        body1 = mark1.GetBody()
        body2 = mark2.GetBody()
        self.bodylist.append([body1, body2])
        frame = mark1.GetAbsFrame()
        super().Initialize(body1, body2, frame)
    def Set_rot_funct(self, rotfun):
        super().SetAngleFunction(rotfun)
 
print ("Load a model exported by SolidWorks")
 
 
 
# ---------------------------------------------------------------------
#
#  Create the simulation system and add items
#
 
mysystem      = chrono.ChSystemNSC()
chrono.ChCollisionModel.SetDefaultSuggestedEnvelope(0.05)
chrono.ChCollisionModel.SetDefaultSuggestedMargin(0.05)
 
parts = chrono.ImportSolidWorksSystem('./spider_robot')
 
for ib in parts:
    mysystem.Add(ib)
 
# Retrieve objects from their name as saved from the SolidWorks interface
# (look the spider_robot.py file to guess them, or look their name in SW)
 
bbody    = mysystem.SearchBody('Part3^SPIDER_ROBOT-1')
bbody.SetBodyFixed(False)
b1base    = mysystem.SearchBody('M-410iB-300 -1/ArmBase-1')
b1turret  = mysystem.SearchBody('M-410iB-300 -1/M-410iB-300-02-1')
b1bicept  = mysystem.SearchBody('M-410iB-300 -1/M-410iB-300-03-1')
b1forearm = mysystem.SearchBody('M-410iB-300 -1/M-410iB-300-06-1')
m1_1B = b1base.   SearchMarker('marker_M1_B')
m1_1A = b1turret. SearchMarker('marker_M1_A')
m1_2B = b1turret. SearchMarker('marker_M2_B')
m1_2A = b1bicept. SearchMarker('marker_M2_A')
m1_3B = b1bicept. SearchMarker('marker_M3_B')
m1_3A = b1forearm.SearchMarker('marker_M3_A')
b2base    = mysystem.SearchBody('M-410iB-300 -2/ArmBase-1')
b2turret  = mysystem.SearchBody('M-410iB-300 -2/M-410iB-300-02-1')
b2bicept  = mysystem.SearchBody('M-410iB-300 -2/M-410iB-300-03-1')
b2forearm = mysystem.SearchBody('M-410iB-300 -2/M-410iB-300-06-1')
m2_1B = b2base.   SearchMarker('marker_M1_B')
m2_1A = b2turret. SearchMarker('marker_M1_A')
m2_2B = b2turret. SearchMarker('marker_M2_B')
m2_2A = b2bicept. SearchMarker('marker_M2_A')
m2_3B = b2bicept. SearchMarker('marker_M3_B')
m2_3A = b2forearm.SearchMarker('marker_M3_A')
b3base    = mysystem.SearchBody('M-410iB-300 -3/ArmBase-1')
b3turret  = mysystem.SearchBody('M-410iB-300 -3/M-410iB-300-02-1')
b3bicept  = mysystem.SearchBody('M-410iB-300 -3/M-410iB-300-03-1')
b3forearm = mysystem.SearchBody('M-410iB-300 -3/M-410iB-300-06-1')
m3_1B = b3base.   SearchMarker('marker_M1_B')
m3_1A = b3turret. SearchMarker('marker_M1_A')
m3_2B = b3turret. SearchMarker('marker_M2_B')
m3_2A = b3bicept. SearchMarker('marker_M2_A')
m3_3B = b3bicept. SearchMarker('marker_M3_B')
m3_3A = b3forearm.SearchMarker('marker_M3_A')
b7base    = mysystem.SearchBody('M-410iB-300 -7/ArmBase-1')
b7turret  = mysystem.SearchBody('M-410iB-300 -7/M-410iB-300-02-1')
b7bicept  = mysystem.SearchBody('M-410iB-300 -7/M-410iB-300-03-1')
b7forearm = mysystem.SearchBody('M-410iB-300 -7/M-410iB-300-06-1')
m7_1B = b7base.   SearchMarker('marker_M1_B')
m7_1A = b7turret. SearchMarker('marker_M1_A')
m7_2B = b7turret. SearchMarker('marker_M2_B')
m7_2A = b7bicept. SearchMarker('marker_M2_A')
m7_3B = b7bicept. SearchMarker('marker_M3_B')
m7_3A = b7forearm.SearchMarker('marker_M3_A')
b8base    = mysystem.SearchBody('M-410iB-300 -8/ArmBase-1')
b8turret  = mysystem.SearchBody('M-410iB-300 -8/M-410iB-300-02-1')
b8bicept  = mysystem.SearchBody('M-410iB-300 -8/M-410iB-300-03-1')
b8forearm = mysystem.SearchBody('M-410iB-300 -8/M-410iB-300-06-1')
m8_1B = b8base.   SearchMarker('marker_M1_B')
m8_1A = b8turret. SearchMarker('marker_M1_A')
m8_2B = b8turret. SearchMarker('marker_M2_B')
m8_2A = b8bicept. SearchMarker('marker_M2_A')
m8_3B = b8bicept. SearchMarker('marker_M3_B')
m8_3A = b8forearm.SearchMarker('marker_M3_A')
b9base    = mysystem.SearchBody('M-410iB-300 -9/ArmBase-1')
b9turret  = mysystem.SearchBody('M-410iB-300 -9/M-410iB-300-02-1')
b9bicept  = mysystem.SearchBody('M-410iB-300 -9/M-410iB-300-03-1')
b9forearm = mysystem.SearchBody('M-410iB-300 -9/M-410iB-300-06-1')
m9_1B = b9base.   SearchMarker('marker_M1_B')
m9_1A = b9turret. SearchMarker('marker_M1_A')
m9_2B = b9turret. SearchMarker('marker_M2_B')
m9_2A = b9bicept. SearchMarker('marker_M2_A')
m9_3B = b9bicept. SearchMarker('marker_M3_B')
m9_3A = b9forearm.SearchMarker('marker_M3_A')
 
 
 
period = 2
mfunc_sineS   = chrono.ChFunction_Sine(0, 1.0/period,  0.2)  # phase, frequency, amplitude
mfunc_swingSa = chrono.ChFunction_Repeat()
mfunc_swingSa.Set_fa(mfunc_sineS)
mfunc_swingSa.Set_window_length(period)
mfunc_swingSa.Set_window_start(0)
mfunc_swingSb = chrono.ChFunction_Repeat()
mfunc_swingSb.Set_fa(mfunc_sineS)
mfunc_swingSb.Set_window_length(period)
mfunc_swingSb.Set_window_start(period/2.0)
mfunc_sineD   = chrono.ChFunction_Sine(0, 1.0/period, -0.2)  # phase, frequency, amplitude
mfunc_swingDb = chrono.ChFunction_Repeat()
mfunc_swingDb.Set_fa(mfunc_sineD)
mfunc_swingDb.Set_window_length(period)
mfunc_swingDb.Set_window_start(period/2.0)
mfunc_swingDa = chrono.ChFunction_Repeat()
mfunc_swingDa.Set_fa(mfunc_sineD)
mfunc_swingDa.Set_window_length(period)
mfunc_swingDa.Set_window_start(0)
 
 
mfunc_sigma  = chrono.ChFunction_Sigma()
mfunc_sigma.Set_amp(-0.2)
mfunc_sigma.Set_end(0.5)
mfunc_const  = chrono.ChFunction_Const()
mfunc_sigmb  = chrono.ChFunction_Sigma()
mfunc_sigmb.Set_amp(0.2)
mfunc_sigmb.Set_end(0.5)
mfunc_seq    = chrono.ChFunction_Sequence()
mfunc_seq.InsertFunct(mfunc_sigma, 0.5, 1, True) # fx, duration, weight, C0 continuity
mfunc_seq.InsertFunct(mfunc_const, 1.0, 1, True) # fx, duration, weight, C0 continuity
mfunc_seq.InsertFunct(mfunc_sigmb, 0.5, 1, True) # fx, duration, weight, C0 continuity
mfunc_updownA = chrono.ChFunction_Repeat()
mfunc_updownA.Set_fa(mfunc_seq)
mfunc_updownA.Set_window_length(period)
mfunc_updownB = chrono.ChFunction_Repeat()
mfunc_updownB.Set_fa(mfunc_seq)
mfunc_updownB.Set_window_length(period)
mfunc_updownB.Set_window_phase(period/2.0)
 
# Add actuators to Leg n.1
 
motor1_1 = SpiderRobotMotor()
motor1_1.Initialize(m1_1A, m1_1B)
motor1_1.Set_rot_funct(mfunc_swingSa)
mysystem.Add(motor1_1)
 
motor1_2 = SpiderRobotMotor()
motor1_2.Initialize(m1_2A, m1_2B)
motor1_2.Set_rot_funct(mfunc_updownA)
mysystem.Add(motor1_2)
 
motor1_3 = SpiderRobotMotor()
motor1_3.Initialize(m1_3A, m1_3B)
motor1_3.Set_rot_funct(mfunc_const)
mysystem.Add(motor1_3)
 
# Add actuators to Leg n.2
 
motor2_1 = SpiderRobotMotor()
motor2_1.Initialize(m2_1A, m2_1B)
motor2_1.Set_rot_funct(mfunc_swingSb)
mysystem.Add(motor2_1)
 
motor2_2 = SpiderRobotMotor()
motor2_2.Initialize(m2_2A, m2_2B)
motor2_2.Set_rot_funct(mfunc_updownB)
mysystem.Add(motor2_2)
 
motor2_3 = SpiderRobotMotor()
motor2_3.Initialize(m2_3A, m2_3B)
motor2_3.Set_rot_funct(mfunc_const)
mysystem.Add(motor2_3)
 
# Add actuators to Leg n.3
 
motor3_1 = SpiderRobotMotor()
motor3_1.Initialize(m3_1A, m3_1B)
motor3_1.Set_rot_funct(mfunc_swingSa)
mysystem.Add(motor3_1)
 
motor3_2 = SpiderRobotMotor()
motor3_2.Initialize(m3_2A, m3_2B)
motor3_2.Set_rot_funct(mfunc_updownA)
mysystem.Add(motor3_2)
 
motor3_3 = SpiderRobotMotor()
motor3_3.Initialize(m3_3A, m3_3B)
motor3_3.Set_rot_funct(mfunc_const)
mysystem.Add(motor3_3)
 
# Add actuators to Leg n.9
 
motor9_1 = SpiderRobotMotor()
motor9_1.Initialize(m9_1A, m9_1B)
motor9_1.Set_rot_funct(mfunc_swingDb)
mysystem.Add(motor9_1)
 
motor9_2 = SpiderRobotMotor()
motor9_2.Initialize(m9_2A, m9_2B)
motor9_2.Set_rot_funct(mfunc_updownB)
mysystem.Add(motor9_2)
 
motor9_3 = SpiderRobotMotor()
motor9_3.Initialize(m9_3A, m9_3B)
motor9_3.Set_rot_funct(mfunc_const)
mysystem.Add(motor9_3)
 
# Add actuators to Leg n.8
 
motor8_1 = SpiderRobotMotor()
motor8_1.Initialize(m8_1A, m8_1B)
motor8_1.Set_rot_funct(mfunc_swingDa)
mysystem.Add(motor8_1)
 
motor8_2 = SpiderRobotMotor()
motor8_2.Initialize(m8_2A, m8_2B)
motor8_2.Set_rot_funct(mfunc_updownA)
mysystem.Add(motor8_2)
 
motor8_3 = SpiderRobotMotor()
motor8_3.Initialize(m8_3A, m8_3B)
motor8_3.Set_rot_funct(mfunc_const)
mysystem.Add(motor8_3)
 
# Add actuators to Leg n.7
 
motor7_1 = SpiderRobotMotor()
motor7_1.Initialize(m7_1A, m7_1B)
motor7_1.Set_rot_funct(mfunc_swingDb)
mysystem.Add(motor7_1)
 
motor7_2 = SpiderRobotMotor()
motor7_2.Initialize(m7_2A, m7_2B)
motor7_2.Set_rot_funct(mfunc_updownB)
mysystem.Add(motor7_2)
 
motor7_3 = SpiderRobotMotor()
motor7_3.Initialize(m7_3A, m7_3B)
motor7_3.Set_rot_funct(mfunc_const)
mysystem.Add(motor7_3)
 
#
# Create a floor
 
mfloor = chrono.ChBody()
mfloor.SetBodyFixed(True)
mfloor.GetCollisionModel().ClearModel()
mymat = chrono.ChMaterialSurfaceNSC()
mymat.SetRestitution(0.0)
mfloor.GetCollisionModel().AddBox(mymat, 10,0.5,10, chrono.ChVectorD(0,0.8,0))
mfloor.GetCollisionModel().BuildModel()
mfloor.SetCollide(True)
mysystem.Add(mfloor)
 
mfloorshape = chrono.ChBoxShape()
mfloorshape.GetBoxGeometry().Size = chrono.ChVectorD(10,0.5,10)
mfloorshape.GetBoxGeometry().Pos  = chrono.ChVectorD(0,0.8,0)
mfloor.AddAsset(mfloorshape)
 
mfloorcolor = chrono.ChColorAsset(0.2,0.2,0.2)
mfloor.AddAsset(mfloorcolor)
 
# ---------------------------------------------------------------------
#
#  Create an Irrlicht application to visualize the system
#
 
myapplication = chronoirr.ChIrrApp(mysystem, 'Test', chronoirr.dimension2du(1280,720))
 
myapplication.AddTypicalSky('./data/skybox/')
myapplication.AddTypicalCamera(chronoirr.vector3df(2.8,2.6,2.8),chronoirr.vector3df(0.0,2.6,0.0))
myapplication.AddTypicalLights()
myapplication.AddLightWithShadow(chronoirr.vector3df(10,20,10),chronoirr.vector3df(0,2.6,0), 10 ,10,40, 60, 512)
 
            # ==IMPORTANT!== Use this function for adding a ChIrrNodeAsset to all items
            # in the system. These ChIrrNodeAsset assets are 'proxies' to the Irrlicht meshes.
            # If you need a finer control on which item really needs a visualization proxy in
            # Irrlicht, just use application.AssetBind(myitem) on a per-item basis.
 
myapplication.AssetBindAll()
 
            # ==IMPORTANT!== Use this function for 'converting' into Irrlicht meshes the assets
            # that you added to the bodies into 3D shapes, they can be visualized by Irrlicht!
 
myapplication.AssetUpdateAll()
 
            # ==IMPORTANT!== Use this function for enabling cast soft shadows
 
myapplication.AddShadowAll()
 
# ---------------------------------------------------------------------
#
#  Run the simulation
#
solver = chrono.ChSolverBB()
solver.SetMaxIterations(200)
mysystem.SetSolver(solver)
myapplication.SetTimestep(0.001)
 
 
while(myapplication.GetDevice().run()):
    myapplication.BeginScene()
    myapplication.DrawAll()
    myapplication.DoStep()
    myapplication.EndScene()