I'm working on my first dual deploy rocket. Im wondering why, in most of the altimeter bay "kits" for sale, the sleds are so much shorter than the available space? Why not make the sled go from bulkhead to bulkhead? Is there a reason?
No reason I can think of that hasn't already been stated. My sleds tend to be made about 2 or so inches short, because I like to route wires between and around the all-threads, and it allows me to adjust the position of my Av-Bay switches which are mounted on the sled, if I happen to be a bit off on the switches location.
I always begin my sled at the lower bulkhead which is fixed in position...
I stop an inch or so short of the forward bulkhead so that when I'm assembling
the av bay for a flight I don't run the risk of pinching wire between the sled and forward bulkhead...
There's also plugs there for the main charges,, you need a bit of room to close up the bay...
I know exactly what you're talking about. I got a cardboard Madcow DX3 for a MPR test bed along with their AV bay kit, the coupler was about 7" but their nice pre-fab sled was only about 4". I ended up making my own. I don't know why they didn't make the sled as long as the coupler... it makes no sense. Most DD bays only come with the coupler and the bulkplates, so you're gonna have to make your own sled anyway (and in most cases, come up with the hardware too). I routinely order longer couplers than what the manufacturers ship... my GL Escape Velocity has a 12" AV bay, since I use it for testing electronics and I'm always taking it apart.
For the average flyer, how much real estate do you really need? Computer, switch, and battery? Sometimes double that, and really, how often are you really doing dual redundant dual deploy where you invest in 2 sets of computers and batteries for 1 rocket? If you are, chances are that it's because the rocket is either unique or expensive enough to warrant it, and you go into the project knowing the technical hurdles.
The only issue that I have with conventional av bays is that if you put the sled on the all thread is that you lose SO MUCH space in smaller bays. 4" and greater it's not much of an issue, but get into 2.56 and smaller tubes and it takes some serious planning to get 2 computers in there, or one computer on the conventional stand offs. Pain in the butt.
I find it much easier to just cut a piece of ply that's the full diameter and full length of bay. The bulkheads will keep it from moving, and I've not had to worry about it spinning at all..