When I designed AYUCR II I decided to use the oppurtunity to make some changes and improvements to the original design. Certain things about the original design didn't meet my expectations or simply didn't work that well. I also wanted to cut out some of the "fat" in the original design to make the new rocket lighter and smaller. Here is an overview of what has changed.
The booster remains largely unchanged. I did add a 54mm motor mount and boattail. The 54mm mount gives me the oppurtunity to use some more interesting motors like the J90 or J180. I hope to fly those at LDRS and get some really high flights as well as some cool looking boost shots. The boattail was added mostly because I like the way it looks.
I describe the midsection separately because it had changed a little. AYUCR II used the same method of packing the chutes in the same tube (remember the booster and payload come down under separate chutes). I had some trouble with this arrangement in AYUCR I but only ever had one somewhat serious problem with it. The maiden flight of AYUCR I was almost a disaster because the two chutes tangled. I thought I had solved this with more careful packing in subsequent flights. The maiden flight of AYUCR II suffered a more serious failure. On many flights AYUCR was set to fire the deployment charge downward into the chutes. I was worried that this might someday force the chutes into the booster and cause a failure. I decided to run a long wire from the altimeter past the chutes to a charge below the chutes to push them out. Even this wasn't enought. Although the two halves separated cleanly at apogee the booster chute never came out. It was still packed in the top half of the booster. The booster alone is unstable according to normal stability tests but the booster still streamlined in and cored. Luckily the tubing for the booster is in two pieces. The top piece absorbed the impact and was destroyed with only minor damage to the fin can. I needed a better, more reliable way to deploy the chutes.
I am pretty convinced that deploying chutes has nothing to do with the ejection charge pushing the chutes out of the tube. The momentum of the two halves separating pulls the shock cord out and that pulls out the chute in most rockets. Relying on the ejection charge to spit out the booster chute can and will eventually cause failure. My solution was fairly simple. In the new section of tubing I placed a bulkhead with an eyebolt facing downward. This separates the midsection into two compartments. Instead of screwing this new section of tubing to the fincan as I had in the past I left it to slide freely. The rocket separates in two places. I now attached the booster shock cord to both the midsection and the fin can and rely on motor ejection to deploy the booster chute. I feel that motor ejection is more reliable than my old scheme. The payload still deploys its own chute, packed into the upper compartment of the midsection, via an altimeter. This has worked flawlessly on two flights. I suppose this makes it really AYUCR IIa.
The payload section with the camera has the most changes from the first design. I am using a new camera, programmable timer, different altimeter, different mirror, and a different rigging for the chute. The programmable timer is described on its own page the rest I'll describe here:
The camera I am using now is the Olympus Stylus. The Olympus HiLite was no longer available when I went shopping for a replacement to the one I smashed on the salt at Bonneville. The Stylus is about the same size but subjectively it seems to take better pictures. It is more expensive, about $79 online. It was much easier to modify for external shutter than the HiLite. There is a separate board under the shutter button with wires leading to the main board. This provided easily accessable solder points for soldering my own leads to. I left off the sliding lense cover to save a little weight and to make it a better fit in the coupler tube that houses the camera. Opening and closing the cover normally turns the camera on and off. Removing this cover exposes a little lever below the lens that was articulated by the sliding cover. This turns out to be a benefit because using a screwdriver I can now flip this lever from outside the rocket incase I get to the pad and can't remember if I turned the camera on or not. I highly recommend the Stylus for rocket projects. The Stylus Epic, also by Olympus, is slightly smaller and more expensive but might be an even better choice. It should even fit in a 2.56 tube. If there is an AYUCR III That is the camera I will use.
For the altimeter I chose the AltAcc by BlackSky research. I am a big fan of these for their reliability, small size and recording capability. I have also written Palm Pilot software for the AltAcc to capture and display the data in the field without needing a laptop. The data from the AltAcc proves useful in this case. Coupled with the programmable camera timer which provides accurate timing of shots I can deduce the approximate altitude of each shot. I redisigned the altimeter bay to be more easily accessable. This saves on prep time in the field, one of my big complaints about the old design.
Rather that rigging the chute to a eyebolt on the lower end of the altimeter bay as in the old design I put a small hole in the side of the rocket just above the break point of the payload section. I tied a knot in the plumb line and fed it through a washer and out through the hole. The washer helps keep the knot from ripping out of the hole (the tubes are cardboard) under stress. the other end is still attached to the nose cone as before.
The mirror is similar in shape to the old one but it differs in construction. I made the new one out of a block of balsa and fiberglassed over it. This makes it much lighter and just as strong as the old, cst epoxy one. I have recently devised a way to make a retractable mirror. I like the shots with the mirror under boost but the mirror doesn't take as nice pictures on descent as simply shooting straight out the side of the rocket. The restractable mirror is curved on the surface that attaches to the rocket to conform to the airframe. There is a panhead screw on this mating surface that sticks out and slides anong a groove in the payload section. A piece of Kevlar thread holds it in place during boost and a rubber band pulls it up out of the way at ejection. I have yet to fly this so I don't know how well it will work.