Introduction
This catapult is ugly but it works.   While most maps won't include a catapult, the point of this tutorial is to show the versatility of the func_ut_train and to encourage mappers NOT to be intimidated from using it. This particular catapult is operated simpy by stepping on the catapult plate - it returns automatically. To make things a lot easier on you here is the mapfile for this tutorial (including a complied .bsp).  If you do not know where these go, well...

Step 1 - do the brushwork (origin brush too!)

• make your catapult - do a better job than I have.  Below is the catapult in the attached mapfile (see figure 1)
• make sure you provide an origin for the object - you can do this manually as a key/value pair but it is more intuitive to use a brush - in figure 1 below the orange box on the left end of the catapult is the origin (flush with the bottom and outside end of the catapult) - it is a 16x16x16 brush covered with common/origin texture (you could make the origin brush smaller for more precise hinging)
• once you have it looking the way you want select every brush that will make the catapult...

Step 2 - make it a func_ut_train and set the key/value pairs

• with all the brushes selected bring down the entities menu (right click in Radiant) and select func_ut_train.
• set the keys/value pairs for the train as per the diagram above (figure 1)
• note: that the func_ut_train targets one of the path_ut_stops in step 3 - allowing you to actually draw the catapult where ever you like - this is useful when you include complicated texturing which (if I remember correctly), like rotating doors, aligns with the world origin (x-0; y-0; z-0) - in such cases it is a good idea to do the final texturing with your catapult's origin exactly overlapping the world origin

• insert two path_ut_stops - these are the brown boxes in figure 1
• in gtkradiant for example right click anywhere on the worksurface window and select path_ut_stop
• remember that the origin brush is what aligns with these path_ut_stop entities when it moves
• set the key/value pairs as per figure 1
• in this case the rotationTime (in milliseconds) and rollSpeed (actually an angle not a speed, but the final angle is determined by the formula: rotationTime * rollSpeed - e.g.s 1 second * 90 degrees = 90 degrees; 2 seconds * 45 degrees = 90 degrees) keys are used to get the catapult rotate - thus the catapult actually moves from one path_ut_stop to the other and at the same time it rotates
• note: that the path_ut_stops are not in the exact same spot, allowing just rotation - the func_ut_train seems to require some lateral movement - not just roll
• note: the path_ut_stop that causes the reverse or return rotation (targetname bottom)  has a negative angle (-90)

• the func_keyboard_interface is what connects everything up - the source of many errors in making func_ut_trains
• make a brush, cover it with common/nodraw texture (purple) on all sides (see figure 1)
• set the keys as in the figure 1
• note: the display is set to 0 so you do not actually see the interface

• unfortunatley the func_ut_train will not actually fling you, you need to add a target_push to do that
• a target_push is unique in that it has to be triggered (unlike a regular jumppad trigger_push which is automatic)
• in radiant right click and add a target_push (grey box) with the keys as listed in figure 1
• the target_push has to target either an info_notnull, or as in this case, a target_position which represents the apex of flight (not drawn, in figure 1)

• the target_push will be triggered by an invisible trigger_multiple (a brush covered on all 6 sides with the pale brown common/trigger texture) as shown in figure 1
• noting where the catapult will be drawn in game (see note in Step 2) place the trigger_multiple over your fling platform, or basket (help me out here I didn't grow up in medieval times so the terminology escapes me)
• upward fling: have the trigger_multiple target the path_ut_stop that causes the positive 90 degree rotation, in this case the one with targetname top - of course to complicate things I have had problems with direct triggering of path_ut_stops so we do this through a target_relay
• catapult return: to return the catapult to the start position include a target_delay with a wait key set to 2 seconds - thus after flinging the player, the catapult returns to the bottom in 2 seconds
• note: the trigger_multiple and the target_delay have the same wait keys (2 seconds) - why? because the trigger_multiple stays on the ground and does not move with the catapult arm - thus, you don't want players being flung about when the arm is still in the up position

NOTES

• to use the catapult simply jump on the fat end - uh err, /god helps when testing the catapult
• if you want to encourage teamplay with the catapult make it triggered by a button - thus you atually need a teammate to launch you (i.e push the button while you stand on the catapult)
• a func_ut_train can be transformed into various interesting in-game moving objects - hopfully this simple use gives you ideas - for tutorials on other uses of func_ut_trains (e.g. the object rotates as it moves) see the tutorials on making a helicopter and an elevator that stops at several floors at the 6th Floor.  A tutorial for a simple 2 floor elevator is located here.
• for further help with func_ut_trains please visit the UT level design forum