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I am trying to move two lines joint to a fixed position sprite in a way similar to that of a pendulum. I would like the lines to swing from end to end each time. The image below shows what I want to achieve:

enter image description here

I'm moving the lines using angular velocity, but I'm not getting the pendulum/swinging effect (a cycle of the lines generally swinging faster as they move to the center and slowing down a bit when they change from one direction to another). I rather get some brisk movement then it slows down till the movement stops. Please see my SpriteKit code below:

extension Int {
  var degreesToRadians: Double { return Double(self) * .pi / 180 }
}
extension FloatingPoint {
  var degreesToRadians: Self { return self * .pi / 180 }
  var radiansToDegrees: Self { return self * 180 / .pi }
}

class GameScene: SKScene, SKPhysicsContactDelegate {

var anchorSprite = SKSpriteNode(imageNamed: "swingPin")
var armLeft = SKSpriteNode(imageNamed: "swingArm")
var armRight = SKSpriteNode(imageNamed: "swingArm")

override func didMove(to view: SKView) {


self.physicsWorld.gravity = CGVector(dx: 0, dy: -1.8)
self.physicsWorld.contactDelegate = self

var tealBg = SKSpriteNode(imageNamed: "tealBg")
tealBg.position = CGPoint(x: frame.midX, y: frame.midY)
tealBg.zPosition = 10
addChild(tealBg)

anchorSprite.position = CGPoint(x: frame.midX, y: frame.midY + frame.midY/2)
anchorSprite.zPosition = 20

anchorSprite.physicsBody = SKPhysicsBody(rectangleOf: anchorSprite.frame.size)
anchorSprite.physicsBody?.categoryBitMask = pinCategory
anchorSprite.physicsBody?.isDynamic = false
addChild(anchorSprite)

armRight.anchorPoint = CGPoint(x: 0.5, y: 1)
armRight.position = anchorSprite.position
armRight.zPosition = 20
armRight.physicsBody = SKPhysicsBody(rectangleOf: armRight.frame.size)
armRight.zRotation = CGFloat(Double(15).degreesToRadians)//CGFloat(Double.pi/6)
armRight.physicsBody!.isDynamic = true

addChild(armRight)

armLeft.anchorPoint = CGPoint(x: 0.5, y: 1)
armLeft.position = anchorSprite.position
armLeft.zPosition = 20
armLeft.physicsBody = SKPhysicsBody(rectangleOf: armRight.frame.size)
armLeft.zRotation = CGFloat(Double(-15).degreesToRadians)//CGFloat(-Double.pi/6)
armLeft.physicsBody!.isDynamic = true
addChild(armLeft)

// Create joint between two objects
//Pin joint
var pinAndRightArmJoint = SKPhysicsJointPin.joint(withBodyA: anchorSprite.physicsBody!, bodyB: armRight.physicsBody!, anchor: CGPoint(x: anchorSprite.position.x, y: self.armRight.frame.maxY))
self.physicsWorld.add(pinAndRightArmJoint)

var pinAndLeftArmJoint = SKPhysicsJointPin.joint(withBodyA: anchorSprite.physicsBody!, bodyB: armLeft.physicsBody!, anchor: CGPoint(x: anchorSprite.position.x, y: self.armLeft.frame.maxY))
self.physicsWorld.add(pinAndLeftArmJoint)

var fixArms = SKPhysicsJointFixed.joint(withBodyA: armLeft.physicsBody!, bodyB: armRight.physicsBody!, anchor: CGPoint.zero)
self.physicsWorld.add(fixArms)

pinAndRightArmJoint.shouldEnableLimits = true
pinAndRightArmJoint.lowerAngleLimit = CGFloat(Double(-60).degreesToRadians)
pinAndRightArmJoint.upperAngleLimit = CGFloat(Double(60).degreesToRadians)

}


override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
armRight.physicsBody?.angularVelocity = -100.0

}

Please note that though I believe this is the most appropriate approach to my problem, I'm open to another approach that would help me achieve the same result.

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0
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Use a sine wave:

angle = 45 * sin(time)
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