Just to follow this up (as it's always nice when someone does) - I finally got round to making a reasonably priced working DMX release mechanism. I tried servos with hooks on, servos withdrawing pins from shackles (all the servos required Servo Control boxes from Milford) , energise to release holding magnets (which worked but proved too expensive), energise to hold magnets (which worked and were cheap, but dropped the load if power was lost) and finally settled on this:
Which is a 24V 0.6A solenoid, withdrawing the pin from a snap shackle. We have a Milford DMX relay box and a 24V bench power supply, which should work to give us eight DMX channels of release.
The solenoids are Xerox (so I assume from photocopiers) and are just over £2 a piece in bulk, the release device is a '52mm fixed snap shackle' for marine use (quick release of ropes) and should be around £2.50 a piece in bulk. They were originally mounted on folded steel but this a piece of 6mm Perspex (or whatever it is) cut on a CNC machine (to avoid the work of measuring and machining them in bulk) and folded. The mounting for the shackle is exactly what it looks like.
Thing should run from a car battery, or two car batteries in series. It does operate on 12V if you use a smaller snap with a weaker spring.
Only thing I'm not sure about now is what to do with the power supply - whether to mount some kind of connector on it, or just use inline crimps or connector.
This post has been edited by TomHoward: 21 September 2010 - 12:48 PM