How to detach small probe skycrane using only action groups?

[Xobotun]

This time I thought to land on Duna using thing that looks like skycrane. And for the sake of comfort I want to make a button that will eject it after landing. I thought that action groups will be best instrument, but I was wrong...

So, some screenshots with descriptions on Imgur:

Javascript is disabled. View full album

Can anyone explain me what did I do wrong, except using highly modded KSP? Honestly, I didn't check that on stock KSP, and I don't want to: too many things are installed.

Edited July 20, 2015 by Xobotun
Something wrong with Imgur embedding thing... x2 ---///--- Finally!

[Captain Sierra]

Javascript is disabled. View full album

Album embedded.

UPDATE:

The problem is a bug in which liquid engines do not fire when they're activated at the same time they're decoupled. Its an issue that can be reproduced stock as well. One solution would be to add two sepatrons to the skycrane not using symmetry, then tweak the thrust level of one down a bit (you don't want it falling back on top of you now).

ALternatively, since you presumably have the engines active from landing, you could slowly throttle up until you begin to lift off the ground, then quickly stage the decoupler.

Edited July 20, 2015 by Captain Sierra

[Xobotun]

Thanks, I've already found the according post in FAQ.

- - - Updated - - -

Oh, now I understand what is the reason.

I've been thinking of the second solution, that uses only engines I have, without needing any other sepatrons. The still have weight.

Well, thank you for quick reply!

[Michael R]

I just decouple right before or right as the landing legs touch ground. The lightened sky crane then is firing enough thrust to take off and fly away.

I've never tried this, but I suppose if you put a probe core on the crane and switched to it after decoupling, you could fly it to a controlled landing.