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DRRT PID Tuner

DRRT PID Tuner is a simple mod that tunes some ship navigation parameters to make the AI rotate ships more quickly and more accurately.

This mod is made for the Debris Regional Reassembly Tournament series.

EXTREMELY SIMPLE MOD that changes three cvars:
This makes all ships turn much more aggressively; i.e. ships will use the maximum possible force from their thrusters for a longer period of time whenever they are commanded to rotate. These P and D gains end up significantly decreasing the steady state error and settling time for all ships when executing a rotation.

This mod also prevents the game for using Slider thrust calculations for ships that turn slowly: kNavCanRotateThreshold is the threshold rotation rate (in rad/sec^2) that controls whether a ship is considered a Slider or not. By default, this value is 1.0.

The gain values are used to control how aggressively ships will want to rotate to their target position.
Changing these cvars does NOT change the behavior of the AI; it only changes how well ships will execute the AI's commands.

Reassembly uses a PD controller; i.e., a PID controller, but without the Integrator. kNavRotKp is the Proportional gain, and kNavRotKd is the Derivative gain.

NOTE: This mod affects ALL ships, including your own ship in campaign mode. I personally enjoy the snappier control, but you might not! So, beware.

My understanding of a PID controller is as follows. I'm no controls engineer, so don't take this as 100% correct information!

A "controller" is a device or piece of software or something similar that directs things how to move or change. Controllers can correct errors and stuff and are everywhere. Robot arms need a type of controller to keep them accurate and consistent, thermostats need to hit a target temperature, et cetera.

A "feedback controller" takes information about the actual system its controlling and calculates how far it is off from the goal. It then attempts to correct itself using this error value. Robot arms will resist when you try to move them, and thermostats will try to make the building warmer if the temperature becomes too cold. This is because they use feedback controllers.

A PID controller is a type of simple but robust feedback controller. It doesn't require a bunch of fancy calculations, yet is still used widely for a variety of tasks.

In this context, the "system" we're controlling is your ship, and our PD controller only pays attention to the ship's orientation.
A PID controller comprises three functions. The value passed into these functions is the difference between the target orientation as declared by the ship's AI and the ship's current orientation. This value is called the error of the system.

• The Proportional controller (the "P" in PID) takes in the current error of the system and outputs thrust proportional to this value. That is, when your ship is very far away from its target orientation, the thrusters will push harder than if your ship is very close to your target orientation. This is a simple way to correct for error, and it works.
  
• The Integral controller (the "I" in PID) takes in the current error of the system and ADDS it to the sum of all previous error values passed into it. That is, it takes the "area under the curve" of the error; it integrates the error. This controller comes into play when the error of your system remains constant for a while; i.e. you're stuck on something and you're still trying to rotate. If this occurs, the Integral controller will slowly ramp up your ship's thrust until its sum gets back to zero. This causes your system to have zero or very little steady state error.
  
• The Derivative controller (the "D" in PID) takes the current error of the system and finds the difference between it and the previous error value passed into it; it takes the difference between the current and previous error, the derivative of the error. Unlike the other two controllers, the Derivative controller by itself will not try to correct the error of the system, as when error is constant, it will have no influence: the derivative of the error is zero when error is constant.
  This controller is useful when the other controllers' influence is small: If your ship is close to the target orientation (i.e. low P and I influence), but the error value is changing rapidly, your ship will likely overshoot the rotation and oscillate around the target. The Derivative controller minimizes this overshooting by increasing power when the rate of change of error is high.

The influence of each of these functions on your system depends on the gains assigned to them. When the gain is higher, the controller has more influence.

The "P gain" is for the Proportional controller, the "I gain" is for the Integral controller, and the "D gain" is for the Derivative controller.

These gains are the only thing that this mod changes. Note that the I gain in Reassembly cannot be set with a cvar and is likely 0; the I controller has no influence on ships.

I called this mod a "PID Tuner" because "PD" can be easily mistaken as an acronym for "Point Defense".

This mod was made to look more official than a "simple cvar mod" so that participants could more easily find it.

This mod was created to test the idea that increasing the gains of Reassembly's PD controller would make the process of designing and watching ships that need to aim themselves toward the enemy much less frustrating. I believe this is a good idea for the DRRT series.

Commonly, in the DRRT series, the Standardized Factions mod is required for ship design. This mod changes cvars that SF does not interact with. That is, this mod's position in Reassembly's mod list relative to Standardized Factions does not matter.

I will put this mod on github eventually. Sorry non-steam users!

Final image by MonsPubis

Ships in preview pictures from 2022 Winter DRRT. Other ships are my own.