Best Camera location On A Rocket??

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Pyropetepete

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So I bought a Landru13 Mobius HD Camera Shroud for Rockets - 3D Printed and a normal lens Mobius HD Camera.

Now where is the best place to mount it on the rocket for the show? Haven't seen much said about this
 
What do you want to see? Lots of the rocket? A little bit of the rocket? No rocket and just the ground falling away?
Those views are what you'd get if you put the camera at various points along the rocket from nose to tail.

By normal lens, I'm guessing not wide angle. That also will affect how much you see on either side of the rocket if you go with a forward mount.

kj
 
Mount above the separation point to get a nice apogee deployment shot. You can invert the image during descent with editing tools if you want that view. I also like to tilt the camera away from the rocket body by 10 degrees or so to get less rocket in the view. Would be nice if the Möbius HD shroud could do that, by the way, since it sticks out so far from the body already.
 
Put the camera in the shroud and turn it on. Place it on the rocket and move it up and down calling out how far it is from the nose. Download the video and see what looks best to you.
 
What's not really being discussed, are issues relating to drag/stability. Now obviously, every rocket will be affected differently depending on it's particular length/stability/etc., but I think that a general discussion here would be helpful. The Mobius shroud DOES stick out quite a bit, even without any sort of tilting/angling. I know myself that even on a 7'x3" rocket I was thinking, "dang that thing has got to have a huge influence on drag/stability". I ended up mounting it on the payload airframe, just above the separation point. But honestly, I only trusted this because I've seen it done on other's rockets. But it did give me pause.

Any feedback/experience/advice folks may have regarding this (as opposed to choices made for the actual video framing) would be interesting.

thanks, s6
 
For my rockets, I place the camera on the booster section of the rocket. Doing this essentially guarantees that you'll be looking at the ground for the duration of the descent. If you place it on the upper section, you will be looking at horizon and sky, often in a vomit inducing manner, after apogee deployment.

ImageUploadedByRocketry Forum1416342550.255057.jpg

This video was shot in the position shown and described above:
[video=youtube_share;tL1kdGE1O1g]https://youtu.be/tL1kdGE1O1g[/video]
 
What's not really being discussed, are issues relating to drag/stability. Now obviously, every rocket will be affected differently depending on it's particular length/stability/etc., but I think that a general discussion here would be helpful. The Mobius shroud DOES stick out quite a bit, even without any sort of tilting/angling. I know myself that even on a 7'x3" rocket I was thinking, "dang that thing has got to have a huge influence on drag/stability". I ended up mounting it on the payload airframe, just above the separation point. But honestly, I only trusted this because I've seen it done on other's rockets. But it did give me pause.

Any feedback/experience/advice folks may have regarding this (as opposed to choices made for the actual video framing) would be interesting.

thanks, s6

This topic has been covered before in-depth on several occasions, but since the question was asked and it is a good one, here goes (again).

The first thing everyone seems to worry about is the effects of drag and off-center, non-axisymmetric aerodynamic effects (having something sticking out into the airflow on one side of the rocket that's not on the other). Well, this is negligible in most cases... We've been flying these sorts of things in the regular configurations (cameras and mirror hoods sticking out of one side of the rocket and not the other, or gliders, or shuttle models, etc) for decades and so long as the rocket isn't so tiny that the aero-effects completely overwhelm the corrective power of the fins or double the normal airframe drag, it's really not much of a concern. (IOW, taping a camera onto the side of an Estes Wizard might give problems, due to the small size of the rocket and the relatively large size of the camera by comparison). So long as the rocket is "large enough" (so that the aero effects don't overwhelm it) and the stability margins are maintained, it's not a problem.

The most important thing is maintaining the correct CG/CP relationship. This is, primarily, affected by where the mass of the camera is placed. If the camera is located near the nose or upper end of the main body tube, the additional mass of the camera will tend to move the CG forward, which increases the "calibers of stability" (distance between the CG and CP). This tends to make the rocket MORE stable, since it gives a longer moment arm of inertia between the fins corrective forces and the point the rocket rotates around in three dimensions (the center of gravity). Placing the mass of the camera lower on the rocket body, but above the present CG, will move the CG proportionally slightly forward, until the camera's mass is placed at the present CG location, at which point it will not move the CG location at all. If we put the camera's mass BEHIND the present CG location, it will move the CG aft as well. The further aft the camera's mass is placed, the further aft the CG location will shift. Generally speaking, this is DESTABILIZING, as it reduces the calibers of stability by shifting the CG aft towards the CP point. How much the CG shifts aft is also proportional to the ratio of the mass of the camera compared to the mass of the rocket. Putting the camera at the aft end of the body tube, or as some folks have done, BEHIND the rocket on a "boom" or stick so its filming the entire rocket from below and behind (an interesting view to be sure, but it requires a lot of careful work to carry off successfully) is the MOST destabilizing-- the further aft the camera is mounted, or the longer the boom the camera is mounted on out the back, the further aft the CG will shift, moving it closer to, or even worse, BEHIND the center of pressure. If this happens, the rocket WILL be unstable. The closer together the CG and CP are, the more aero-effect the camera will have on the rocket as well, because the fins won't be able to generate enough corrective force through the shortened moment arm of inertia to overpower whatever aero effects the camera induces on the airframe. (the fins have less "leverage" to keep the rocket flying straight, thus allowing the small aero effects to have more influence on the flight path... and in the case of mounting the camera on a boom behind the rocket, at the same time giving those aero effects a longer moment of inertia-- more leverage!)

Now, cameras HAVE been mounted on long booms out to the SIDE of the rocket, filming the rocket from an external "chase plane" perspective... BUT, generally speaking, the booms extend from the nosecone or forward end of the rocket body tube, and the camera is usually located at some point forward of the present CG, or in a plane close to it. Thus, the CG will either not move at all or slightly (proportionally) forward, depending on how far forward of the present CG the camera's mass is. As already said, this tends to increase the stability margin by increasing the distance between the CG and CP and giving the fins "more leverage" to correct the flight path, which usually is capable of overpowering any aero-effects from the camera and booms. One other important consideration is, that an equivalent "dead mass" is placed on the opposite side and location of the rocket (axi-symmetrically) to ensure that the off-center mass does not move the CG outside the diameter of the tube, wrecking the stability of the rocket. This usually also closely mimics the aero-effects of the camera being out in the slipstream on the end of the boom, helping to "cancel out" the aero effects as well (but doubling them overall, so care is still required).

Generally speaking, however, the placement of the camera's mass and its effect on the CG location has more to do with stability impacts than aero effects from the camera and any "opposing dead mass" used for balance. In short, the further forward, the better, generally speaking, just as with any other payload.

Remember to check the stability in both a "loaded for launch" configuration (motor installed full of propellant) and the "burnout" or "coast" configuration (basically, empty motor casing). (The CG is located the farthest aft at liftoff on model rockets powered by solid propellant motors, and moves forward as propellant burns off until all the propellant and delay grain are consumed and only the empty casing remains. (in a similar manner, CP is also at its most forward location when the rocket is sitting still, and tends to move aft as the fins generate the most corrective force as airspeed increases to maximum in flight, then shifts back forward again as the rocket decelerates during coast... IOW, CP location is also influenced by the airspeed of the rocket (as well as the angle of attack).

Hope this helps! OL JR :)
 
This topic has been covered before in-depth on several occasions, but since the question was asked and it is a good one, here goes (again).

The first thing everyone seems to worry about is the effects of drag and off-center, non-axisymmetric aerodynamic effects (having something sticking out into the airflow on one side of the rocket that's not on the other). Well, this is negligible in most cases... We've been flying these sorts of things in the regular configurations (cameras and mirror hoods sticking out of one side of the rocket and not the other, or gliders, or shuttle models, etc) for decades and so long as the rocket isn't so tiny that the aero-effects completely overwhelm the corrective power of the fins or double the normal airframe drag, it's really not much of a concern. (IOW, taping a camera onto the side of an Estes Wizard might give problems, due to the small size of the rocket and the relatively large size of the camera by comparison). So long as the rocket is "large enough" (so that the aero effects don't overwhelm it) and the stability margins are maintained, it's not a problem.

The most important thing is maintaining the correct CG/CP relationship. This is, primarily, affected by where the mass of the camera is placed. If the camera is located near the nose or upper end of the main body tube, the additional mass of the camera will tend to move the CG forward, which increases the "calibers of stability" (distance between the CG and CP). This tends to make the rocket MORE stable, since it gives a longer moment arm of inertia between the fins corrective forces and the point the rocket rotates around in three dimensions (the center of gravity). Placing the mass of the camera lower on the rocket body, but above the present CG, will move the CG proportionally slightly forward, until the camera's mass is placed at the present CG location, at which point it will not move the CG location at all. If we put the camera's mass BEHIND the present CG location, it will move the CG aft as well. The further aft the camera's mass is placed, the further aft the CG location will shift. Generally speaking, this is DESTABILIZING, as it reduces the calibers of stability by shifting the CG aft towards the CP point. How much the CG shifts aft is also proportional to the ratio of the mass of the camera compared to the mass of the rocket. Putting the camera at the aft end of the body tube, or as some folks have done, BEHIND the rocket on a "boom" or stick so its filming the entire rocket from below and behind (an interesting view to be sure, but it requires a lot of careful work to carry off successfully) is the MOST destabilizing-- the further aft the camera is mounted, or the longer the boom the camera is mounted on out the back, the further aft the CG will shift, moving it closer to, or even worse, BEHIND the center of pressure. If this happens, the rocket WILL be unstable. The closer together the CG and CP are, the more aero-effect the camera will have on the rocket as well, because the fins won't be able to generate enough corrective force through the shortened moment arm of inertia to overpower whatever aero effects the camera induces on the airframe. (the fins have less "leverage" to keep the rocket flying straight, thus allowing the small aero effects to have more influence on the flight path... and in the case of mounting the camera on a boom behind the rocket, at the same time giving those aero effects a longer moment of inertia-- more leverage!)

Now, cameras HAVE been mounted on long booms out to the SIDE of the rocket, filming the rocket from an external "chase plane" perspective... BUT, generally speaking, the booms extend from the nosecone or forward end of the rocket body tube, and the camera is usually located at some point forward of the present CG, or in a plane close to it. Thus, the CG will either not move at all or slightly (proportionally) forward, depending on how far forward of the present CG the camera's mass is. As already said, this tends to increase the stability margin by increasing the distance between the CG and CP and giving the fins "more leverage" to correct the flight path, which usually is capable of overpowering any aero-effects from the camera and booms. One other important consideration is, that an equivalent "dead mass" is placed on the opposite side and location of the rocket (axi-symmetrically) to ensure that the off-center mass does not move the CG outside the diameter of the tube, wrecking the stability of the rocket. This usually also closely mimics the aero-effects of the camera being out in the slipstream on the end of the boom, helping to "cancel out" the aero effects as well (but doubling them overall, so care is still required).

Generally speaking, however, the placement of the camera's mass and its effect on the CG location has more to do with stability impacts than aero effects from the camera and any "opposing dead mass" used for balance. In short, the further forward, the better, generally speaking, just as with any other payload.

Remember to check the stability in both a "loaded for launch" configuration (motor installed full of propellant) and the "burnout" or "coast" configuration (basically, empty motor casing). (The CG is located the farthest aft at liftoff on model rockets powered by solid propellant motors, and moves forward as propellant burns off until all the propellant and delay grain are consumed and only the empty casing remains. (in a similar manner, CP is also at its most forward location when the rocket is sitting still, and tends to move aft as the fins generate the most corrective force as airspeed increases to maximum in flight, then shifts back forward again as the rocket decelerates during coast... IOW, CP location is also influenced by the airspeed of the rocket (as well as the angle of attack).

Hope this helps! OL JR :)
Great information! You just answered a question I’ve not yet asked.
 
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