Getting Started Tutorials - MechDesigner > Tutorial 2A: Four-bar Kinematic-Chains > Step 2.8: Model a 'Pin in a Straight Slot'

A 'Pin-in-a-Slot' Mechanism

You may think a Pin-in-a-Slot is a special type of joint.

Three representations of a 'Pin-in-a-Slot'.

The mechanical-design of a Pin-in-a-Slot might be similar to Diagram A, in which we see two Parts :

•Part : a lever with a pin roller at its end

•Part : a part with a linear slot

However, the kinematic-design of a Pin-in-a-Slot is always three Parts.

Diagram B shows a different mechanical configuration, with three Parts:

•Part : a lever, with a Pin-Joint at its end

•Part : a part with a slot

•Part : a block (or a piston) that slides along the slot with a Slide-Joint, AND is also joined to the lever with a Pin-Joint

It helps me to imagine that Part is a Slide-Rail, and Part is a Sliding-Block that slides along the Slide-Rail.

Diagram C shows a system that is a similar construction to Diagram B.

Diagram C shows the Pin-Joint is offset to one side of the Slide-Joint.

All three designs use the same kinematic-construction - they use the R-R-P Dyad.

Video:

General: To model a Pin-in-a-Slot

One of eight kinematic options for a Pin in a Slot

Dyad ONLY -

Note: This shows

STEP 1: Draw a Line† in Part - in this case, it is a Line in the Base-Part

Add dimensions and constraints to the Line. It will be the Slide-Rail.

STEP 2: Add a

STEP 3: Join Part to Part with a Slide-Joint - E.g. Click the CAD-Line in Part then the new Line in Part

Part is now the Slide-Block.

STEP 4: If necessary, edit Part to add a Point. E.g. Point‡ to define the position of a Pin-Joint in Part

STEP 5: Join, with a Pin-Joint, the start-Point (origin) of Part to the Point in Part

Notes:

† You can add a CAD-Line in a Part or use the CAD-Line along the center of the Part.

‡ STEP 4 may not be necessary as you can use the start-Point or end-Point of the CAD-Line in Part when you do STEP 5.

Eight Possible Pin-in-a-Slot Kinematic-Chains

The Pin-in-a-Slot is actually two joints (of the three total joints) in a Dyad.

In the Dyads we describe below, the letters R-P represent the two joints.

•The R is a Pin-Joint - R for Revolute-Joint, which is the kinematic-term for Pin-Joint.

•The P is a Slide-Joint - P for Prismatic-Joint, which is the kinematic term for Slide-Joint.

When you add a third joint, which may be a Slide-Joint(P) or a Pin-Joint(R), the Dyad is complete.

You can also join the Dyad to a Rocker or a Slider. Thus, it is possible to build eight different kinematic-chains.

Configurations:

1 & 2: RP+R + Rocker OR RP+R + Slider. The Dyad is an RPR Dyad.

3 & 4: RP+P + Rocker OR RP+P + Slider. The Dyad is an RPP Dyad.

5 & 6: R+RP + Rocker OR R+RP + Slider. The Dyad is an R-R-P Dyad.

7 & 8: P+RP + Rocker OR P+RP + Slider. The Dyad is a PRP Dyad.

Remember also, it is possible for each Dyad to have a maximum of four different closures. See Change Dyad Closure.

Configuration 1 (See Step 2.7)

This is a Rocker and an R-P-R Dyad

Join Part to the Base-Part with a Pin-Joint

Join Part to Part with a Slide-Joint. The Joint uses the CAD-Line in the two Parts.

Join Part to Part with a Pin-Joint

Join Part to the Base-Part with a Pin-Joint.

(A Motion-Dimension FB identifies the Part we will move with a specified motion.

The motion-values at the input-connector to the Motion-Dimension give the rotation to the Part)

Configuration 2

This is a Rocker and an R-R-P Dyad (or P-R-R if you prefer to start from the Motion Driven Joint)

Part is joined to the Base-Part with a Pin-Joint

(A Motion-Dimension FB identifies Part as the Part we will move with a specified motion.

The motion-values at the input-connector to the Motion-Dimension give the rotation to the Part)

Part is joined to Part with a Slide-Joint. The Joint uses the CAD-Line in the two Parts.

Part is joined to Part with a Pin-Joint .

Part is joined to the Base-Part with a Pin-Joint.

Configuration 3 (See Step 2.6)

This is a Rocker and an R-P-P Dyad

Join Part to the Base-Part with a Slide-Joint

Add a Line to Part. Use the new Line to join Part to Part with a Slide-Joint.

Join Part to Part with a Pin-Joint

Join Part to Base-Part with a Pin-Joint.

(A Motion-Dimension FB identifies Part as the Part we will move with a specified motion.

The motion-values at the input-connector to the Motion-Dimension give the rotation to the Part)

Configuration 4

This is a Slider and an R-R-P Dyad (or a P-R-R if you prefer to start from the Driven Joint)

Join Part to the Base-Part with a Slide-Joint

(A Motion-Dimension FB identifies Part as the Part we will move with a specified motion.

The motion-values at the input-connector to the Motion-Dimension give the displacement to the Part)

Add a Line to Part. Use the new Line to join Part to Part with a Slide-Joint.

Join Part to Part with a Pin-Joint

Join Part to the Base-Part with a Pin-Joint.

Configuration 5

This is a Slider and an P-R-P Dyad

Join Part to the Base-Part with a Slide-Joint

(A Motion-Dimension FB identifies Part as the Part we will move with a specified motion.

The motion-values at the input-connector to the Motion-Dimension give the displacement to the Part)

Add a Line to Part. Use the new Line to join Part to Part with a Slide-Joint.

Join Part to Part with a Pin-Joint

Join Part to the Base-Part with a Slide-Joint. This Slide-Joint is at a fixed angle of approximately 60º

Configuration 6

This is a Rocker and an P-R-P Dyad

Join Part to the Base-Part with a Pin-Joint

(A Motion-Dimension FB identifies Part as the Part we will move with a specified motion.

The motion-values at the input-connector to the Motion-Dimension give the rotation to the Part)

Add a Line to Part. Use the new Line to join Part to Part with a Slide-Joint.

Join Part to Part with a Pin-Joint

Join Part to the Base-Part with a Slide-Joint. The Slide-Joint is at fixed angle of approximately 60º

Configuration 7

This is a Slider and an R-P-R Dyad

Join Part to the Base-Part with a Pin-Joint

Add a Line to Part. Use the new Line to join Part to Part with a Slide-Joint.

Join Part to Part with a Pin-Joint

Join Part to the Base-Part with a Slide-Joint. The Slide-Joint is at a fixed angle of approximately 60º

(A Motion-Dimension FB identifies Part as the Part we will move with a specified motion.

The motion-values at the input-connector to the Motion-Dimension give the displacement to the Part)

Configuration 8

This is a Slider and an R-P-P Dyad

Join Part to the Base-Part with a Slide-Joint

Add a Line to Part. Use the new Line to join Part to Part with a Slide-Joint.

Join Part to Part with a Pin-Joint

Join Part to the Base-Part with a Slide-Joint. The Slide-Joint is at a fixed angle of approximately 60º

(A Motion-Dimension FB identifies Part as the Part we will move with a specified motion.

The motion-values at the input-connector to the Motion-Dimension give the displacement to the Part)