I want to be able to have a weighted cube sitting in a trigger_catapult that is disabled. I then want to fire the cube by enabling the catapult. This does not happen (although, curiously, the cube does twitch a bit!).

The problem is that the catapult does not appear to like an object with zero velocity. If I change the catapult parameters to:

Use Threshold check - Yes
Lower Threshold - 1

it still does not work. When the catapult is enabled the following is displayed in the console:

Catapult "catapult5-trigger" ignoring object "prop_weighted_cube" because its velocity is outside of the threshold. (Object Velocity: 0.0 -- Object needed to be between 0.0 and 684.3)

Anybody got any ideas of how to catapult a stationary object?

Sorry, false alarm. Just did some more searching and it looks like there's a solution posted here:

http://forums.thinking.withportals.com/mapping-help/button-activated-aerial-faith-plate-sort-of-works-t2757.html

Although I haven't quite sussed out how it works. I may have some more questions later!

you can put a small minimal height trigger push on the catapult too and when the catapult activated 0.01 later, the push probably move the cube just enough to activate the catapult a milisecond later.
or put a thin func_brush above the catapult that barely noticable (invisible) 1-2 pixel above, enabled, and when the catapult enabled then disable it and the cube will fall 1-2 inc (pixel) and will be in motion for the catapult. No other idea to barely move the cube to be in motion.