Corona SDK Pulley Joint Example

require "physics"
physics.start()
physics.setGravity(0, 9.8)
physics.setDrawMode("hybrid")

function getBall(x, y, radius, type, props)
    if props == nil then
        props = {density=0.3, friction=0.3, bounce=0.3}
    end
    local ball = display.newCircle(x, y, radius)
    ball:setFillColor(0, 255, 0)
    physics.addBody(ball, props)
    return ball
end

function getWall(x, y, width, height)
    local wall = display.newRect( x, y, width, height)
    wall:setFillColor( 255, 0, 0, 100)
    physics.addBody(wall, "static", { friction=0.5, bounce=0.0, density=2 } )
    return wall
end

floor = getWall(0, 460, 320, 20)
leftWall = getWall(0, 0, 20, 500)
rightWall = getWall(320, 0, 20, 500)
roof = getWall(0, 0, 460, 20)

ball1 = getBall(100, 100, 10)
ball2 = getBall(100, 200, 10, {density=2, friction=0.3, bounce=2})

length1Text = display.newText("Hello World!", 0, 0, native.systemFont, 16)
length2Text = display.newText("Hello World!", 0, 0, native.systemFont, 16)

length1Text.x = 200
length1Text.y = 300
length2Text.x = length1Text.x
length2Text.y = length1Text.y + 22

dragging = false
lastClicked = nil

function touch(event)
    length1Text.text = tostring(pulleyJoint.length1)
    length2Text.text = tostring(pulleyJoint.length2)

    if pulleyJoint.length2 > 170 or pulleyJoint.length1 > 170 then
        dragging = false
        if lastClicked then
            lastClicked.bodyType = "dynamic"
            lastClicked = nil
        end
    end

    local phase = event.phase
    if phase == "began" then
        dragging = true
        lastClicked = event.target
        lastClicked.bodyType = "kinematic"
        -- Stop current motion, if any
        lastClicked:setLinearVelocity( 0, 0 )
        lastClicked.angularVelocity = 0
        return true
    elseif phase == "moved" then
        if dragging == false then return false end
        lastClicked.x = event.x
        lastClicked.y = event.y
        return true
    elseif phase == "ended" or phase == "cancelled" then
        if dragging == true then
            dragging = false
            lastClicked.bodyType = "dynamic"
            lastClicked = nil
            return true
        else
            return false
        end
    end
end

ball1:addEventListener("touch", touch)
ball2:addEventListener("touch", touch)

pulleyJoint = physics.newJoint( "pulley", ball1, ball2, 150, 50, 170,50, ball1.x,ball1.y, ball2.x,ball2.y, 1.0 )