IDG-A32X/Nasal/autopush.nas

# AUTOPUSH
# Basic pushback logic class.
#
# Copyright (c) 2018 Michael Danilov <mike.d.ft402 -eh- gmail.com>
# Distribute under the terms of GPLv2.

var push_dlg = gui.Dialog.new("sim/gui/dialogs/autopush/push/dialog", "Aircraft/IDG-A32X/Systems/autopush.xml");

var _K_p = nil;
var _K_i = nil;
var _K_d = nil;
var _F_i = nil;
var _int = nil;
var _deltaV_old = nil;
var _t_old = nil;

var loop = func() {
	if (!getprop("/sim/model/pushback/available")) {
		stop();
		return;
	}
	var force = 0.0;
	# Rollspeed is only adequate if the wheel is touching the ground.
	if (getprop("/gear/gear[0]/wow")) {
		var deltaV =
		getprop("/sim/model/pushback/target-speed-km_h") -
		getprop("/gear/gear[0]/rollspeed-ms") * 3.6;
		var dV = deltaV - _deltaV_old;
		var t = getprop("/sim/time/elapsed-sec");
		var dt = math.max(t - _t_old, 0.0001);
		_int = math.min(math.max(_int + dV * dt, -_F_i), _F_i);
		force = (_K_p * deltaV + _K_d * dV / dt + _K_i * _int) * KG2LB;
		_deltaV_old = deltaV;
		_t_old = t;
		var yaw = getprop("/sim/model/pushback/yaw-deg") * D2R;
		setprop("/sim/model/pushback/force-x", math.cos(yaw));
		setprop("/sim/model/pushback/force-y", math.sin(yaw));
	}
	setprop("/sim/model/pushback/force-lbf", force);
}

var timer = maketimer(0.026, func{loop()});

var start = func() {
	_K_p = getprop("/sim/model/pushback/K_p");
	_K_i = getprop("/sim/model/pushback/K_i");
	_K_d = getprop("/sim/model/pushback/K_d");
	_F_i = getprop("/sim/model/pushback/F_i");
	_int = 0.0;
	_deltaV_old = 0.0;
	_t_old = getprop("/sim/time/elapsed-sec");
	setprop("/sim/model/pushback/connected", 1);
	if (!timer.isRunning) {
		screen.log.write("(pushback): Release brakes.");
	}
	timer.start();
}

var stop = func() {
	if (timer.isRunning) {
		screen.log.write("(pushback): Pushback disconnected, bypass pin removed.");
	}
	timer.stop();
	setprop("/sim/model/pushback/force-lbf", 0.0);
	setprop("/sim/model/pushback/connected", 0);
}

var toggle = func(){
	if (getprop("/sim/model/pushback/enabled") * getprop("/sim/model/pushback/available")) {
		start();
	} else {
		stop();
	}
}