﻿ MotionDesigner Reference & User Interface > Motion Laws > Flexible-Polynomial Motion-Law > Throw - Quick-Return: 1: Finite Jerk @ Start/End Motion-Law

# Throw - Quick-Return: 1: Finite Jerk @ Start/End Motion-Law

### Throw: Quick-Return 1: Finite Jerk

Quick-Return=1

is not in the Motion-Law Selector.0

Quick-Return-1 motion-law is a Rise & Return motion-law.

It is continuous in Position, Velocity and Acceleration.

Construct the 'Quick-Return 1' motion with two Flexible Polynomial Segments.

The first segment is the Rise, and the second segment is the Return. Each segment is a 'mirror' of each other.

Usually, the segments have an equal duration, but this is not necessary.

Continuity at the Mid-Point Blend-Point

At the mid-point, the Position is at a maximum value [in the image, max P=1], and the Velocity is zero.

At the mid-point the segments both have a finite, negative acceleration.

The acceleration is continuous. The Jerk is also continuous and zero at the mid-point.

We can call this a Quick-Return Motion because at the point where the Rise becomes the Return, there is a negative, but continuous acceleration. 'Quick-Return Motion 1' is designed with two Flexible-Polynomial Segments - usually of equal duration, but not necessarily. Two Segments with Acceleration Continuity Start: Rise Segment 1 @ Start •Position = 0•Zero Velocity•Zero Acceleration•Unspecified Jerk [Actual = 320mm/s3]Mid-Point: Segment 1 @ End = Segment 2 @ Start •Position = 1•Zero Velocity•Match, but Unspecified Acceleration =Actual = –26.666mm/s2•Zero Jerk [End: Segment 2 @ End •Position 2 = 0•Zero Velocity •Zero Acceleration•Unspecified Jerk  [Actual = –320mm/s3]Note, the Jerk is near to its maximum acceleration crossover [at about 75 and 255] and velocity. Thus if there is backlash in the following mechanical system, crossover will have a relative high -impact value. It is designed with one Flexible-Polynomial Segment: Start: •Position = 0•Zero Velocity•Zero Acceleration•Unspecified Jerk [Actual = 40mm/s3]End: •Position = 1•Zero Velocity •Unspecified Acceleration•Zero JerkCv = 1.733 Ca = 4.583 Cd = –6.666 Cj max = 40 Cj min  = –22.5 Jerk at Crossover = -21.5