Alright, first post marked as spam automatically? Could a moderator look into it please.
A quick rundown, because that was a long post I made. I like to make a Disabled Flagship drift mechanic into the game using behaviour with periodic effect issuing move command to unit so it's drifts forward and turning slightly in one or another direction.
The way I would do this is with a persistent effect and an issue order effect.
First create an issue order effect, then set the effect "Effect: Ability" field to Move, set "Effect: Player" to source, set "Effect: Unit" to source and finally set "Target: Target" to "(None)Target Point".
After that create a persistent effect, this effect will handle the location of the target point where move command is given. In the persisten effect set the "Period: Count" to 1. Then add three durations of 0.0 seconds in the "Effect Period: Duration" field. Then in the "Effect: Period Effects" add the issue order effect you created previously. After that go to the "Effects: Periodic Offsets" and add three offsets, this will be used to set the direction in which the move command is given. The offsets have three parameters (X, Y, Z), in one of the offsets put (X: 0.2, Y: -1.0, Z: 0.0), in another put (X: -0.2, Y: -1.0, Z: 0.0) and in the final one put (X: 0.0, Y: -1.0, Z: 0.0). After that go to the "Effect: Random Offset" and "Effect: Random Period" fields and set both to enabled. Finally go the "Target: Location Offset - Start" field and set it to "(None)Origin Point". Then add the persistent effect as periodic effect to the behaviour that makes the ship drift.
The persistent with these parameters will choose at random one of the three offsets once and execute the move command, taking the original position of the unit with the behaviour and issue that unit the move command to the target point with one of the offsets. The -1 in Y parameter of the offsets, sets the target point for issue order effect, to be to a distance of 1 ahead of the initial position of the unit with the behaviour, the -0.2 or 0.2 in the X parameter of the offsets, will move the point set the by the Y parameter value slightly to the left or the right of the unit with the behaviour and the offset with a parameter of X = 0 and Y = -1 will order the unit the unit to go forward by a distance of 1.
I hope you find this helpful, tweak the values of the offsets in the persistent to achieve the desired effect.
Can you use this same set up to create a circular "holding pattern" for air units? Say you have a Wraith that doesn't have any active commands or ques. If it was to sit stationary, can you use periodic movements to have that unit perform a closed loop circle?
Also, could you use this same effect to force all air units (with no given commands) to move in a straight path until you give them a command? Like, when they are created they just fly straight. You tell it to move a different direction. That air unit will face that direction and then continuously move in that direction, *including* flying over the point you clicked on?
I don't see why not, mine works as such actually, though not a perfect circle due other factors, but it does make the ship turn in one specific direction. So can make a circle so long the unit is not disrupted.