Amplitude and Frequency

This topic is 'How to use Gearing-Ratio parameter in the Gearing FB'.

The Gearing FB applies a linear mathematical function to transform motion-values at its input-connector to motion-values at its output-connector.

There are three Parameters in the Gearing FB dialog-box. The parameters make it similar to a 'Belt and Pulley'.

See also: Add Gearing FB.

Crank speed: different to the MMA








To drive a 'crank' at different speeds, counter clock-wise [default] or clock-wise, connect a Gearing FB, between the Linear-Motion FB and the Motion-Dimension FB.


There are two 'Cranks' in the image to the left.

left Crank: The input to the Motion-Dimension FB is directly from the motion-values at output-connector of the Linear-Motion FB. This increases linearly from 0 to 360, and repeats. Thus, the Crank will rotate Counter-Clockwise at a constant speed.


right Crank: Its motion is  the same as the output from the Gearing FB. The input to the Gearing FB1s-red is directly from the Linear-Motion FB. If we edit the Gearing Ratio in the Gearing FB dialog-box  to be '–1', its output will be 0 to -360, and repeat. Thus, the Crank will rotate Clockwise. If we edit the Gearing FB to '3', [as a different example], its output will be 0 to 1080.

'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

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 = 0–360º
Motion FB range = 0–100mm
Gearing Ratio = '3'...

The Gearing FB increases the AMPLITUDE of the Slider by 3x



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 – 100mm every 360.

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 360 to 0, thus the Motion becomes reversed.



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

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