CRRCSim comes with a number of controllers which can be used to alter a model's behaviour. They can be controllers (in the meaning of closed loop control) or simply save flight data to files or modify input variables (the user's stick input) or something else. Controllers can receive keyboard input and write to the logging console window as well.
They are activated and adjusted by tweaking either the xml file which describes the model (currently only for multicopter models) or CRRCSims global configuration file. There is no GUI.
As far as controllers are concerned, you become a "model creator" once you edit one, but in contrast to general "model creating" this is easy and might therefore be done by a user, too. For example, if you don't like the quadrocopter qc01 to limit throttle in flips automatically, simply remove the corresponding line from qc01.xml.
Some controllers can be used together with other controllers, some can not.
This is not a real controller. The user's throttle input is in the range 0 .. 1. This controller alters throttle in the following way:
If throttle_in < off, throttle_out = 0.
Otherwise, throttle_out = min + (throttle_in - off) * mul
It is defined like that:
<ScaleThrottle off="0.06" min="0.178" mul="0.54" />
It can be combined with controllers not altering throttle and with LimitFlipThrottle.
Again, this is no real controller. It only limits throttle, which is interesting for multicopters while flying loopings or flips.
If attitude is less than 60° from horizontal, throttle is not limited. At 90° it is limited to max90, at 180° (upside down) it is limited to max180.
It is defined like that:
<LimitFlipThrottle max90="0.618" max180="0.3" />
It can be combined with controllers not altering throttle and with ScaleThrottle.
To be used with multicopters, results in a rate controlled setup, so the sticks command how fast the copter rotates around roll/nick/yaw axis.
This controller is explained in "How to adjust multicopter parameters, multicopter model version 1" (qc01.tex), which is available online as pdf.
This one can not be combined with MCopter01.
To be used with multicopters, results in an attitude controlled setup for roll/nick and rate controlled for yaw axis.
<MCopter01>
<roll scale="1.8" kp="7" kd="0.246" />
<pitch scale="1.8" kp="7" kd="0.246" />
<yaw scale="-9.93" kp="0.352" ki="0.835" />
</MCopter01>
The yaw controller is just like the Omega type (see above). For roll and pitch, the setpoint is stick_input * scale (in radians). Remember, stick input is -0.5 ... 0.5. kp is multiplied with the difference in attitude and gives the setpoint for the underlying rate controller. The difference in rotation rate is multiplied with kd. The result is the controllers output. Therefore, kd here is equivalent to kp of the Omega controller.
This one can not be combined with Omega.
<?xml version="1.0" ?>
<crrcsimConfig version="2">
<controllers>
<ScaleThrottle off="0.06" min="0.178" mul="0.54" />
<LimitFlipThrottle max90="0.618" max180="0.3" />
</controllers>
...
The examples show the file's first two lines, too, to make clear that
the controller-section has to be a child of crrcsimConfig.
Every controller inherits its interface from Controller, which is defined in src/mod_cntrl/controller.h and .cpp.
They are instantiated via Controller::LoadList() in the same files. It is up to the FDM to execute the controllers, even the global ones.
To see how everything is done, it may be best to take a look at the class CRRC_AirplaneSim_MCopter01 in src/mod_fdm/fdm_mcopter01/ and Cntrl_MCopter01 as an example. If you are new to CRRCSim, you surely don't know SimpleXMLTransfer, which is the class used to read/write XML. This controller shows its basic usage and makes use of keyboard input and log output, too.
The current controller implementation is not perfect; for example a serial connection of controllers is not possible (while a parallel connection is). However I felt it to be powerful enough while being simple...
Before this controller framework was implemented, an interface to the "MNav" autopilot was implemented into CRRCSim. It was build as an input method (similar to joystick, transmitter or whatever).
Doing it like this has several drawbacks:
This subsection is not here to blame MNav but to explain why it is different from other controllers and why better not doing it like this. When it was implemented I, JWW, have not been interested and/or clever enough to say 'hey, don't do it like that'.
Das Thermikbuch fuer Modellflieger written by Markus Lisken and Ulf Gerber, Verlag fuer Technik und Handwerk, Baden-Baden.
With a helicopter, a controller could take care of pitch, throttle and yaw while the pilot practises nick and roll. Note: the heli01-FDM doesn't execute local controllers yet, only global ones.