Rambots generally are considered 'boring' by the producers. There isn't a 'wow' factor when they come onto the arena with an active weapon spinning, hitting, etc. Storm 2 was rather infamously hit with a bit of controversy from producers after perceived bias against it due to this. An article about that is written here; http://robotwars.wikia.com/wiki/Storm_2/Controversy - it's a rather good read, but i just love reading up on everything...

Don't let that put you off though, if you look the part, even with just an amazingly artistic paintjob or something, that'll improve your chances. It's probably a case of, they won't put more than 1 or 2 of that specific type in a series on TV, and give more to the more 'impressive' flippers & spinners, but if you can make a name for yourself or even just look the part, you'll probably have just as much chance as any other to get on there.