How to control cable length in cable-driven manipulator

Hello @aryakarani

Thank you so much for your answer!! This is my current code:

# -*- coding: utf-8 -*-
from stlib.physics.deformable import ElasticMaterialObject
from stlib.physics.constraints import FixedBox
from stlib.scene import Node
from softrobots.actuators import PullingCable
from splib.loaders import loadPointListFromFile
import Sofa
import os

#Opening the file
file1 = open("myfile.txt","w")

#Defining the python controller
class CilinderController(Sofa.PythonScriptController):
    def __init__(self, node, cable1, cable2, cable3):
        self.node=node
        self.cableconstraintvalue1 = cable1.getObject("CableConstraint").findData('value')
        self.cableconstraintvalue2 = cable2.getObject("CableConstraint").findData('value')
        self.cableconstraintvalue3 = cable3.getObject("CableConstraint").findData('value')
        self.cableconstraintdisp1 = cable1.getObject("CableConstraint").findData('displacement')
        self.cableconstraintdisp2 = cable2.getObject("CableConstraint").findData('displacement')
        self.cableconstraintdisp3 = cable3.getObject("CableConstraint").findData('displacement')
        self.name = "CilinderController"
        self.n=1
        self.deformableObject = self.node.ElasticMaterialObject
        
      
    #Control actions for each cable (extend and retract)    
    def onKeyPressed(self,c):
        if (c == "4"):
            self.cableconstraintvalue1.value =  self.cableconstraintvalue1.value[0][0] + 1.
        if (c == "1"):
            self.cableconstraintvalue1.value =  self.cableconstraintvalue1.value[0][0] - 1.
        if (c == "5"):
            self.cableconstraintvalue2.value =  self.cableconstraintvalue2.value[0][0] + 1.
        if (c == "2"):
            self.cableconstraintvalue2.value =  self.cableconstraintvalue2.value[0][0] - 1.
        if (c == "6"):
            self.cableconstraintvalue3.value =  self.cableconstraintvalue3.value[0][0] + 1.
        if (c == "3"):
            self.cableconstraintvalue3.value =  self.cableconstraintvalue3.value[0][0] - 1.    
        if (c == "9"):
            #file1.write(str(Output1))
            self.node.getRootContext().animate = False
            file1.close() 

    #Writing the displacements and point position to a file        
    def onEndAnimationStep(self,dt):
        # displacement1  = self.cableconstraintdisp1.value
        # displacement2  = self.cableconstraintdisp2.value
        # displacement3  = self.cableconstraintdisp3.value
        displacement1  = self.cableconstraintvalue1.value
        displacement2  = self.cableconstraintvalue2.value
        displacement3  = self.cableconstraintvalue3.value
        # dispform1 = "{:.2f}".format(displacement1)
        # dispform2 = "{:.2f}".format(displacement2)
        # dispform3 = "{:.2f}".format(displacement3)
        dispform1 = displacement1
        dispform2 = displacement2
        dispform3 = displacement3
        position=self.deformableObject.dofs.getData("position").value
        positionform1="{:.2f}".format(float(position[493][0]))
        positionform2="{:.2f}".format(float(position[493][1]))
        positionform3="{:.2f}".format(float(position[493][2]))
        file1.write(str(self.n) + ',' + str(dispform1) + ","+ str(dispform2) + "," + str(dispform3) + ", ["+ str(positionform1) + ";" + str(positionform2) + ";" + str(positionform3)+"]"+'\n')
        self.n +=1         
            

def Cilinder(parentNode=None, name="Cilinder",
           rotation=[0.0, 0.0, 0.0], translation=[0.0, 0.0, 0.0],
           fixingBox=[0.0,0.0,0.0], pullPointLocation=[0.0,0.0,0.0]):

    #Defining the elastic material
    cilinder = Node(parentNode, "Cilinder")
    eobject = ElasticMaterialObject(cilinder,
                                   volumeMeshFileName="data/mesh/Elo3D.vtk",
                                   poissonRatio=0.49,
                                   youngModulus=48000000,
                                   totalMass=1.5,
                                   surfaceColor=[0.0, 0.8, 0.7],
                                   surfaceMeshFileName="data/mesh/EloSurface.stl")
    FixedBox(eobject,
             doVisualization=True,
             atPositions=[-30, 0 ,-30 ,30 ,5,30])

    #Creating the cables
    cable1 = PullingCable(eobject, cableGeometry=loadPointListFromFile("data/mesh/cable1S.json"))
    cable2 = PullingCable(eobject, cableGeometry=loadPointListFromFile("data/mesh/cable2S.json"))
    cable3 = PullingCable(eobject, cableGeometry=loadPointListFromFile("data/mesh/cable3S.json"))
    
    #Calling the controller
    CilinderController(cilinder,cable1,cable2,cable3) 

This is the relevant part, the rest is just defining the scene. As you can see, my goal is to get the cable lengths and the position of a point to a file. What happens right now is that the displacements show up as zero when the robot is at rest (the cable length at rest is meant to be 84.63 cm) and when I give inputs, it changes to “1” or “-1” etc, according to the given input.

There are other ways to define the cables, maybe that’s the issue? The cable geometry files are just a list of points through where the cables pass in the channels inside the robot

Hi @hugo

I had to put the work on hold because of exams, but I’ve now returned and I’m still trying to figure things. I think me and @aryakarani have different implementations of the CableConstraint, since I think I used an old one that came with an older version of the SoftRobots plugin that is not the same as newer documentation shows, so I’m working around that, but thank you for checking in! I will update the thread if I am sucessful in order to help other people with the same problem

Best wishes,

Diogo