Pendulum-in-Visual-Python/simple_fixed_visual.py at master · jhooft/Pendulum-in-Visual-Python · GitHub

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#visualization of the simple pendulum with fixed pivot

import vpython as vp
from vpython import vec, color
import time
import numpy as np
from math import sin, cos
#from decimal import Decimal

#GlowScript bits
scene = vp.canvas()
scene.width =1000
scene.height = 650
scene.range = 1.8
scene.title = "Moveable Pendulum"
#scene.visible = True
t0=time.time()
duration = 20.0 #seconds to run simulation

##############  initial conditions  ##############
theta0=0.2#initial angle         theta=0 is straight up, theta increases clockwise
thetadot0 = 0.3 #initial angular velocity of pend
atheta0 = 0. #initial angular accel0
p0 = 0. #initial position of slider
pdot0 = 0. #initial velocity of slider
ap0 = 0. #initial accel of slider
dtheta0 = 0.  #an incremental change of angle
###################################################

#################  Constants  #####################
m=1 #mass of pendulum
alpha=5 #ratio of pivot mass to pendulum mass
g=9.8 #gravitational accel
r=1 #length of pendulum arm
###################################################

################  Limitations  ####################
p_min = -1.7   #leftmost slider position      ####are these values compatible between graphics, ODE's??????
p_max = 1.7    #rightmost slider position
ap_max=3. #maximum acceleration of slider         #####i picked this number at random
pdot_max = 5.  #picked at random
###################################################


p = p0 #p is x-coordinate of the slider/pivot
pdot = pdot0
ap=ap0
theta = theta0 #theta is measured from 0 radians when pend is straight up and is positive to the left
thetadot = thetadot0
atheta= atheta0
dtheta = dtheta0
ap_adjust = 0


#####################the build assembly##############################
rod = vp.cylinder( pos=vec(-2.7,-.2,0), axis=vec(5.4,0,0), color = color.green, radius=0.02 )
rodlimitmarkleft = vp.cylinder( pos=vec(-1.7,-.2,0), axis=vec(.1,0,0), color = color.yellow, radius=0.02 )
rodlimitmarkright = vp.cylinder( pos=vec(1.7,-.2,0), axis=vec(.1,0,0), color = color.yellow, radius=0.02 )
supportleft = vp.box( pos=vec(-2.7,-1.3,0), color = color.red, size=vec(.1,2.2,.1) )
supportright = vp.box( pos=vec(2.7,-1.3,0), color = color.red, size=vec(.1,2.2,.1) )
slider = vp.box(pos=vec(p,rod.pos.y,0),color = color.red, size=vec(.1,.1,.1))
axlepin = vp.cylinder( pos=vec(slider.pos.x,slider.pos.y,slider.pos.z+0.1), axis=vec(0,0,.2), color = color.yellow, radius=0.02 )
pendulumarm = vp.cylinder(pos=vec(axlepin.pos.x,axlepin.pos.y,axlepin.pos.z+0.2), axis=vec(float(r)*cos(np.pi/2-float(theta)),float(r)*sin(np.pi/2-float(theta)),0), color = color.green, radius=0.02 )
pendulummass = vp.sphere(radius=.1,pos=vec(axlepin.pos.x+float(r)*cos(np.pi/2-float(theta)),axlepin.pos.y+float(r)*sin(np.pi/2-float(theta)),.3))
#pend = vp.compound([pendulumarm,pendulummass])       #????????
pivot = vec(axlepin.pos.x,axlepin.pos.y,axlepin.pos.z+.2)
######################################################################

#EQUATIONS OF MOTION
atheta = (g/r)*sin(theta)
#########################


dt = .05
count = 0
time.sleep(3)
while time.time() < (t0 + duration):
    vp.rate(10)
    theta = theta%(2*np.pi)

    atheta = (g/r)*np.sin(theta)

    thetadot +=  atheta*dt
    theta += thetadot*dt
    dtheta = -thetadot*dt

    pendulumarm.rotate(angle = dtheta, axis=vec(0,0,1), origin=pivot)
    pendulummass.pos.x = axlepin.pos.x+float(r)*cos(np.pi/2-float(theta))
    pendulummass.pos.y = axlepin.pos.y+float(r)*sin(np.pi/2-float(theta))