Step 5.6: Gearing, Amplitude and Frequency

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Step 5.6: Gearing, Amplitude and Frequency

Amplitude and Frequency

This topic is: How to use the Gearing-Ratio parameter in the Gearing FB to edit the Amplitude and Frequency of motion-values.

We will use the Gearing-Ratio parameter. The motion-values in this tutorial are given to a rotating part we call a Rocker or Crank.

Note:  We use the term Crank when the kinematic-element Rocker rotates continuously.

Crank speed: Rotate a Crank at a speed that is different to the MMA

This is the most basic application. A crank rotates continuously, and we want it to rotate at a different speed or direction.

We use a Gearing FB to change the angular velocity of a Crank.

Connect a Linear Motion FB to a Gearing FB to a Motion-Dimension FB








There are two 'Cranks' in the image.

The right-crank has a Gearing FB.

Left Crank:

The Linear-Motion FB increases linearly from 0 to 360, and repeats.

Thus, the Crank rotates Counter-Clockwise at a constant speed, equal to the MMA.

Note: Counter-Clockwise is the standard positive direction.

Right Crank:

Edit the Gearing FB to edit the Gearing Ratio parameter.

Gearing Ratio: = -1 :

The output = 0 to –360. The Crank rotates Clockwise each machine-cycle.  

Gearing Ratio: = 3 - the output is now 0 to 1080. The crank rotates 3x for each machine-cycle.

Crank on Crank







We can add a crank to a crank.


Shown to the left is an Epicycloid Curve. To do this:

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

2.Join a new Part to the end of the first Part with Pin-Joints

3.Use Motion-Dimension FBs fix the start angle of the two Parts.

4.Drive the Part joined to the Base-Part with a Linear-Motion FB – it is a Crank.

5.Drive the second Part, with a Gearing FB, and edit its Gearing Ratio to -3.

6.Use a Trace-Point to trace the path of the Point at the end of the second Part

Note: You can easily replicate this motion with a Gear-Pair.

Gearing FB : Motion Amplitude AND Frequency

There are three ways to use a Gearing FB. We can connect Gearing FBs to the input or the the output of a Motion FB.

A Gearing FB joined to the:

input a Motion FB will change the frequency of the Motion

output a Motion FB will change the amplitude of the Motion

input and output will change the magnitude and frequency of a motion.

Also, we can use a Gearing FB to change the direction of a motion.



Here, we connect a Motion FB to the input of the Gearing FB.

For example:

Linear-Motion FB range = 0 to 360º

Motion FB range = 0 to 90mm

Gearing Ratio = '3'...

The Gearing FB changes the AMPLITUDE of the Slider 0 to 270mm



Here, we connect the Gearing FB to the input of the Motion FB.

For example:

Linear-Motion FB range = 0 – 360º

Gearing Ratio = '3',

Input to Motion FB: range 0 – 1080º

Output from Motion FB range = 0 – 90mm 3 times in one machine-cycle.

The Gearing FB increases the FREQUENCY of the Sliders motion by 3x

Note - if the Gearing FB is '–ve', the input to the Motion FB is 0 to -360 thus the Motion is 'played' in reverse.



To change the amplitude and frequency of a motion, connect a Gearing FB before and after a Motion FB.

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