Why does the Gear Box in Simscape Onramp Task use a positive gear ratio (0.01) if it reverses the direction of rotation?

I’ve attached screenshots showing:

• Task description
• Gear Box block parameters
• Circuit diagram setup

I'm working on Task 1 of Simscape Onramp's 'Feedback Control (Practice)' module. The Gear Box block is supposed to reverse rotation direction, but the gear ratio is set to a positive value (0.01). Shouldn't it be negative (-0.01) to reflect the reversal? The task description seems to contradict the gear ratio setting.

I look forward to getting better insights on this! Thank you.

Answer 1

[Vibha]

Thank you for helping, @Adarsh.

But according to the gearbox documentation, if the output shaft of the gearbox rotates in the opposite direction to that of the input shaft, shouldn't we provide a negative value of gear ratio in the block parameters dialog?

[Adarsh]

Yes, it must be negative, the description is inconsistent. In the model the negative sign is for Rotational Electro Mechanical converter that is the reason it is connected in reverse.

Answer 2

[Adarsh]

Hi @Vibha,

I understand that the description mentioning “The Gear Box reverses the rotation direction” is ambiguous with the positive “Gear ratio”.

A positive “Gear ratio” implies that the angular velocity of the input shaft and the output shaft are in the same direction.

The output of the “Rotational Mechanical Converter (IL)” is in the negative direction and for the “Rotational Electromechanical Converter” if the current flowing from the “+” to “-“ port is positive then the torque is positive acting from port C to port R.

So, to ensure generating the positive current the output of “Gear Box” is connected to the R port of the “Rotational Electromechanical Converter”.

Based on my understanding, by reversal they mean the final output of “Gear Box” is in negative direction and hence “Inertia” and “Rotational Electromechanical Converter” are in the opposite signs.

For more information on “Gear Box” and “Rotational Electromechanical Converter” you can refer to the following documentation links:

1. https://www.mathworks.com/help/releases/R2023b/simscape/ref/rotationalelectromechanicalconverter.html
2. https://www.mathworks.com/help/releases/R2023b/simscape/ref/gearbox.html

In case you need any further clarification, you can reach out to MathWorks Technical team from the link below:

https://www.mathworks.com/support/contact_us.html