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.

The MMA increases at a steady rate from 0 to 360 whenever we cycle the model.

Put a Gearing FB between the Linear-Motion FB and the Motion-Dimension FB.

[>> = wire]

Before: Linear-Motion FB] >> Motion-Dimension FB
After: Linear-Motion FB] >> Gearing FB >> 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.

Note: Counter-Clockwise is the standard positive direction.

Right Crank:

Edit the Gearing FB to edit the 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 called a Deltoid – it has a shape like a delta. To do this:

1.Connect two Parts end-to-end with Pin-Joints, the first Part to the Base-Part
2.Use Motion-Dimension FBs fix the initial angle of the two Parts.
3.Drive the 'first' Part joined to the Base-Part with a Linear-Motion FB – it is a 'Crank'.
4.Make the second Part half the length of the first Part
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 to show the Deltoid - the deltoid curve is the trace of the point at 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 'before' and 'after' a Motion FB.

A Gearing FB x

before a Motion FB will change the frequency of the Motion
after a Motion FB will change the amplitude of the Motion
before and after 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.

tog_minusVIDEOS :







Tutorial and Reference Help Files for MechDesigner and MotionDesigner 13.2 + © Machine, Mechanism, Motion and Cam Design Software by PSMotion Ltd