How to Convert Lead Compensator Output to PWM for Hexacopter Height Control?

[huntflex]

Homework Statement

Hello, I'm not looking for an answer to my problem, just some hints. Any help would be greatly appreciated.
I am required to control a hexacopter, so I'm designing a lead compensator to control the height, it should be able to counteract the pull of gravity. So far I have designed it, but my problem is that I need its output to be in PWM form.
I already have a scaling which is a= 0.1956 N/PWM, it is also given that a value of 143 PWM will generate hover thrust.(These constants are found from tests on the motor, and are for all 6 motors).

Homework Equations

I realize that the feedfwd (see block diagram) should be some value, but I don't know what.

The Attempt at a Solution

Attached is a snapshot of the block diagram.

Thanks for any help :)

 

[CWatters]

I've long since forgotten my control theory but what does 143PWM mean? What are your units for PWM in a= 0.1956 N/PWM ?

Is it a = 0.1956 Newtons/percent ?

If the pulse width modulation can vary from 0% to 100% how can you have 143%

 

[huntflex]

That is actually a very good question, what I can see from the data that was given to me is that the transfer function for the motor was derived by subjecting it to steps from 150 PWM to 170 PWM, from there a linear regression could be made, and from there it is derived that the slope is a = 0.1956 Newton/PWM. Which means for every PWM sent in, 0.1956 Newton is added to the system.

 

[huntflex]

I just found out, that it's how the Arduino board works, you write 0-255, where 0 is 0% duty cycle, and 255 is 100 % duty cycle

 

[rezeew]

Hello, it sounds like you are on the right track with your lead compensator design. To convert the output of your lead compensator into PWM form, you will need to use the scaling factor you have already calculated (a = 0.1956 N/PWM). This will allow you to convert the desired thrust output (in Newtons) into the corresponding PWM value.

As for the feedforward value, this will depend on your specific system and the requirements for your hexacopter's height control. It will likely involve some trial and error to find the optimal feedforward value, as it will need to be adjusted based on the weight and other characteristics of your hexacopter.

I suggest starting with a conservative estimate for the feedforward value and then fine-tuning it through testing and experimentation. Additionally, you may want to consider implementing a closed-loop control system to further improve the accuracy and stability of your hexacopter's height control. Good luck with your project!