Differential Planetary Gears

These are more complex to model because they have two degrees-of-freedom.

Differential Gears use two independent input drives to rotate a single output shaft.

There are two standard variations:

If you take one as the input and one as the output, the effective gear ratio between them depends on the speed of the third gear.

Differential Gears are frequently used:

For information: this is the model after completion of this step.

Profile Elements also added.

STEP 1:

Add two Parts

STEP 2:

Join Part with a Pin-Joint to a Point at the end of Line in the Base-Part

Steps 1 and 2 are complete.

Both Gear-Pairs use the CAD-Line along the centre of Part as the Line-of-centres.

STEP 3:

Join Part with a Pin-Joint to the Point in Part

Step 3 is not complete...

The Point at the end of Part is selected (it is red) and

The Pin-Joint, with two Points, is about to be clicked.

The Select Element dialog-box opens.

This is why we select a 'Free' Point first. Point is not ambiguous.

•	The second Point in the Pin-Joint is ambiguous.

Which Point do we select in the Select Elements dialog-box to complete Add Pin-Joint?

We must select the Point7 in Part because Line is in Part and is the Line-of-centres.

To select the elements in the Select Elements dialog-box:

1.

down

Step 3 is complete

•	A Rocker Motion-Dimension FB between the CAD-Line in Part and the Line in the Base-Part.

•	See Motion-Dimension (Remember: A Rocker Motion-Dimension needs a Kinematically Defined Line and a 'Free' Line. Only, the Pin-Joint1 satisfies this requirement.)

•	The Second Motion-Dimension FB is between the CAD-Line in Part and the CAD-Line in Part.

•	See Motion-Dimension (Remember: Only, the Pin-Joint2 is available for the Rocker as Pin-Joint 1 is used.)

Step 4 is complete

STEP 5:

Add a new Part to the end of the Part

Select the Cad-Lines in Parts. Note: New Numbers in the image for Elements

Step 5 complete.

Step 6 not complete.

Step 6 complete.

Edit: Number-of-Teeth and Module:

•	Gear 1 = 60

•	Gear 2 = 30

We must now add a second Gear-Pair.

STEP 8:

Add a new Part

Step 9 is not complete...

Point at the end of Part is selected (it is red) and the Point at the Pin-Joint is clicked.

The Select Element dialog-box opens.

This is why we select a 'Free' Point first. Point is not ambiguous.

•	The second Point in the Pin-Joint is ambiguous.

Which Point do we select in the Select Elements dialog-box to complete Add Pin-Joint?

We must select the Point7 in Part (again) because it is the Line-of-centres.

To select the elements in the Select Elements dialog-box:

1.

down

Step 9 is complete.

With reference to the image:

•	Select the CAD-Lines in Parts

Step 10 is complete.

Remember: Double-click the Gear in the graphic-area.

Edit: Number-of-Teeth Module and Mesh

•	Gear 1 = 30 (the planet gear) same as Gear 2 in the Gear-Pair 1

•	Gear 2 = 120

Step 11 is complete.

Steps 11,12,13 are complete

Edit the Gear Ratio on the Gearing FBs

Motion-Dimension 1 controls the speed of the Carrier

Motion-Dimension 2 controls the speed of the Sun - see note

(Note: Motion-Dimension 2 is relative to Motion-Dimension 1. Hence, a Gear Ratio of 0 given to Motion-Dimension 2 means the Sun rotates at the same speed as Motion-Dimension 1 not necessarily 0.

To stop the rotation of the Sun, you must apply the negative Gear Ratio in the Gearing FBs.

For example,1 and -1 in the Gearing FBs will make the Sun stationary.