Hmm... a short mecha series, you say? With lots of comedy? Hmm...
How long can you go?
Gundam 08th MS Team is a fantastic mecha series with a few elements of comedy, but it's 13 episodes long.
Gundam 0080 is a 5-episode OVA series, but it doesn't really have a whole lot of comedy elements in it
You could also check out
Giant Robo, clocking in at 7 OVA episodes.
I wish I could help you more, but there aren't really a whole lot of short mecha series