Hey guys,
My son bought me a couple of those key chain cams to strap-on to my rockets so I can get in-flight video. I was wondering, how do you guys who have used one secure it to your rocket, what have you found to be the minimum engine to have enough thrust to lift this safely, where do you position it, towards the front of the airframe or in the center? I'm really excited about getting out in some nice weather and trying one out. I always admire the in-flight video and have wondered what mine looked like from the same point of view.
Thanks for your time!
Steve
Most folks just use electrical tape to tape it to the side of the rocket. Usually you want any cargo (like this) to go as far forward as possible, because that moves the center of gravity (CG) forward and thus increases stability. BUT, if the rocket is already "overstable" (IE four big fins, fins swept sharply back, which pushes the center of pressure (CP) far back on the rocket, giving it a wide stability margin, or if it's already rather nose-heavy rocket even with the largest motor it will take installed, which means the CG is far forward to start with) putting the camera on the front end of the tube will INCREASE the stability margin and make the rocket VERY prone to weathercocking in any kind of wind. This isn't a good thing, because the rocket will turn sharply into the wind at liftoff once it clears the rod. For a rocket like this, put the camera closer to the center, but don't go BEHIND the LOADED center of gravity (IE with the motor and wadding and recovery device installed, as it if were ready for flight (minus ignitor).
Putting the camera on the BACK of the rocket will move the CG AFT, which is destabilizing. So don't mount it behind the loaded CG unless you're CERTAIN the rocket will remain stable, or you add noseweight to the front of the rocket to keep the loaded CG location at the same place as without the camera.
As for power, it depends on the rocket. I've heard of folks flying these things on A or B motors, but from the vids I've seen of the flights, it's only a few seconds of very shaky footage... the rocket lifts off, as soon as it starts to stabilize where you can actually see something, the rocket is keeling over at apogee, then the chute comes out and the thing gyrates wildly during deployment and as soon as it stabilizes it's nearly back on the ground. IMHO the smallest motor you should bother with flying these on is a "C" motor...
I wouldn't go with a very small airframe rocket either (less than about BT-55) because the camera and tape will screw up the airflow over the rocket if you use a rocket with a BT-50 or 20 airframe and tends to make it fly rather squirrelly. The larger tube makes the camera proportionally smaller than the rocket and means it sits tighter against the tube, which means less airflow disturbance from the camera at the fins, which means better stability. Plus, a bigger rocket is proportionally longer too, giving greater moments of inertia and slower pitch and yaw rates when perturbed in flight, meaning a more stable picture in the video. (longer, larger, heavier rockets turn slower and take longer to "damp out" oscillations than smaller rockets, which can be quite "twitchy" in flight, which makes for poor video).
Hope this helps and good luck with your project! OL JR
