﻿ Getting Started Tutorials - MechDesigner > Tutorial 15: Patterns - Indexing-Chain example > Step 15.1: Piggyback Sliders and the Belt Motion

# Step 15.1: Piggyback Sliders and the Belt Motion

NOTE:

Tutorial 15 was written before the Motion-Path FB was available.

Piggyback Sliders are included, below. They remain an important modeling technique.

What is a Piggyback? I am not sure if it is only an English term?

When someone is off the ground and on the back of a standing person, and their hands are around the standing person's neck (to hold, not to strangle!) and their legs around each side and held by the standing person's arms, then the person that is off the ground is being given a Piggyback.

The person on the back (imagine he can climb a ladder that is also held by the person on the ground!) has a motion that is combination of their own motion and the motion of the person on the ground.

Why Piggyback Sliders?

We can design Parametric Motions - that is, a motion for the person moving on the ground, (parallel to the X-axis,)  and a motion for the person being given the Piggyback, (parallel to the Y-axis). The result is a X-Y Planar motion that we can easily design.

Why not Piggyback Rockers?

Yes, we can have Piggyback Rockers also - exactly like a SCARA robot.

However, it is almost impossible to design the motions for Piggyback Rockers and predict the planar motion of the Point at the end of the SCARA robot.

### Piggyback Sliders and a Belt.

We add two Motion-Parts - Sliders - and assemble them as Piggyback Sliders.

We will name the Sliders : Slider-X and Slider-Y

In this tutorial, we design motions for the Slider-X and Slider-Y such that a Point on the Slider-Y follows the path of a Point on a belt. We motions for Slider-X and Slider-Y are designed here.

#### Quick Instructions: Add Piggyback Sliders

Quick Instructions:

 1.Add a Line to the Base-Part that is parallel to the X-axis of the Mechanism-Plane 2.Add the Slider to the Line in the Base-Part - Slider-X 3.Edit the Slider-X to add a Line that is parallel to its Y-axis 4.Add aSlider to the Line in Slider-X - this is Slider-Y 5.Design the motions for each Slider. 6.Add a Trace-Point to a Point on Slider-Y - this is Point-XY. 7.Run menu  > Cycle to watch the Piggyback Sliders.

#### More Detailed Instructions: Add Piggyback Sliders

 1.Edit the Base-Part 2.Part-Editor: Geometry toolbar > Add Line , Constraints toolbar > Add Horizontal : Click the Line; Close the Part-Editor 3.Mechanism-Editor: Add a Part; Add a Slide-Joint between the Part and the Line in the Base-Part 4.Mechanism-Editor: Add a Motion-Dimension FB to identify the X Slider 5.Mechanism-Editor: Add a Linear-Motion FB and a Motion FB to the graphic-area Connect the FBs with wires. 6.Rename the Slider to X SLIDER

Edit the X-Slider, Add a Vertical Line

 1.Mechanism-Editor: Edit X-Slider Part : Part-Editor:  Edit length to 100mm. 2.Part-Editor: Geometry toolbar > Add Line , Drag UPWARDS to add the Line : Constraints toolbar > Add Vertical - Click the Line; 3.Part-Editor: Geometry toolbar > Add Dimension  - Line = 100mm 4.Part-Editor: Constraints toolbar > Coincident , Click start-Point of the two Lines. 5.Close the Part-Editor

 1.Mechanism-Editor: Add a Part 2.Mechanism-Editor: Add Slide-Joint : Click CAD-Line in new Part and vertical Line in the X-Slider 3.Mechanism-Editor: Add a Motion-Dimension FB to specify the Position of the Y-Slider. 4.Mechanism-Editor: Add a Linear-Motion FB and a Motion FB to the graphic-area 5.Mechanism-Editor: Connect the FBs 6.Rename the new Slider to Y-SLIDER

Get Motions for the Sliders - Example Motions

 1.Mechanism-Editor: Edit the Motion FB connected to the X-Slider to open the Motion FB dialog-box 2.Mechanism-Editor: Select X-Motion in the drop-down box. 3.Close the Motion FB dialog-box 4.Mechanism-Editor: Edit the Motion FB connected to the Y-Slider to open the Motion FB dialog-box 5.Mechanism-Editor: Select the Y-Motion in the drop-down box for the Y-Slider 6.Close the Motion FB dialog-box Show the Trace-Path: 7.Mechanism-Editor: Do Kinematic-element > Add Trace-Point , click a Point on the Y-Slider

Run menu > Cycle (or ALT+C)

X Motion

This is a motion for the X-axis.

Use a Motion FB to link this motion to the Motion-Dimension FB to move the X-Slider.

Y Motion

This is a motion for the Y-axis.

Use a different Motion FB to link to the Motion-Dimension FB to move the Y-Slider.

These two example motions define the motion along the XY-path on the Mechanism-Plane

We show the  XY-path in the graphic-area with a Trace-Point.

Design the Motion for the Belt.

We need to design the motions an imaginary point on a Belt as it moves around two Pulleys.

The Point moves in along an arc as it moves around the pulleys.

The Point moves in a straight line as it moves between the pulleys.

Design decisions we have made for the Belt:

The belt has twelve (12) pockets

Each pocket and tool has a pitch of 100mm

Each Pulley has five teeth

oThe belt-length is exactly 12 × 100mm = 1200mm.

oCircumference of each Pulley = 5 × 100 = 500mm,

oRadius of each Pulley = 500/2π = 79.577mm

oDistance between Pulleys = (1200 – 500) ÷ 2 = 350mm

 Motion Design Preparation and Calculations for the Piggyback Sliders
 How to Find the Phase Parameter for the Sinusoid Segments
 Complete the Model in MechDesigner