Where do you place your camera?

I updated my OR with a rough approximation of where I believe my camera shroud will end up. Keeping in mind that I have 3 sampling holes in my AV bay (center of beige tube aft of the shroud) and this current placement puts the bottom of the shroud about 4.25" from the sampling holes. The original position was roughly 5"-6" higher.

I fly two rockets with Mobius cameras and Landru shrouds, a 54mm MD (Firestorm 54) and a 4" rocket (Binder Excel w/DD). Both do a few turns on the way up but neither one shows signs of coning, in fact the 54mm gets comments from the LCO on just about every flight how straight it is. Most of the Firestorm flights have been on a shortened airframe due to an earlier zipper (first attachment), it was recently restored to something more like its original intent (second attachment which happens to place the shroud roughly at the Cg but that was never my intent, I preferred to have it as high as possible to see as much as it could and to be far from the motor as I've seen other flights where the visual intensity of the flame tends to make the cameras video do bad things during boost). The shroud is epoxied on the 54mm rocket so it isn't moving. I only screwed-on the shroud for the 4", I haven't tried flying without it to see what impact it makes on the altitude, a part of me is tempted for the data aspects but the rest of me just doesn't want to fly without the on-board video. I really like the 4" shots of the apogee separation, I like using the vent-band area for the camera attach since you see apogee (and since it's closer to the side the camera is on I can see my backup drogue charge fire as well), but the camera only faces up while descending on drogue then re-orients towards the ground again once the main pops. Videos from both rockets are on my youtube page linked from below. In fact after my first Excel crashed and I re-built it I ordered a 1" longer vent-band as the Mobius was a bit longer than the stock 4" band, so it fits entirely within the vent band now.

woferry said:

I fly two rockets with Mobius cameras and Landru shrouds, a 54mm MD (Firestorm 54) and a 4" rocket (Binder Excel w/DD). Both do a few turns on the way up but neither one shows signs of coning, in fact the 54mm gets comments from the LCO on just about every flight how straight it is. Most of the Firestorm flights have been on a shortened airframe due to an earlier zipper (first attachment), it was recently restored to something more like its original intent (second attachment which happens to place the shroud roughly at the Cg but that was never my intent, I preferred to have it as high as possible to see as much as it could and to be far from the motor as I've seen other flights where the visual intensity of the flame tends to make the cameras video do bad things during boost). The shroud is epoxied on the 54mm rocket so it isn't moving. I only screwed-on the shroud for the 4", I haven't tried flying without it to see what impact it makes on the altitude, a part of me is tempted for the data aspects but the rest of me just doesn't want to fly without the on-board video. I really like the 4" shots of the apogee separation, I like using the vent-band area for the camera attach since you see apogee (and since it's closer to the side the camera is on I can see my backup drogue charge fire as well), but the camera only faces up while descending on drogue then re-orients towards the ground again once the main pops. Videos from both rockets are on my youtube page linked from below. In fact after my first Excel crashed and I re-built it I ordered a 1" longer vent-band as the Mobius was a bit longer than the stock 4" band, so it fits entirely within the vent band now.

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Good info, where in relation to your sampling holes is the camera mount?

woferry said:

I fly two rockets with Mobius cameras and Landru shrouds, a 54mm MD (Firestorm 54) and a 4" rocket (Binder Excel w/DD). Both do a few turns on the way up but neither one shows signs of coning, in fact the 54mm gets comments from the LCO on just about every flight how straight it is. Most of the Firestorm flights have been on a shortened airframe due to an earlier zipper (first attachment), it was recently restored to something more like its original intent (second attachment which happens to place the shroud roughly at the Cg but that was never my intent, I preferred to have it as high as possible to see as much as it could and to be far from the motor as I've seen other flights where the visual intensity of the flame tends to make the cameras video do bad things during boost). The shroud is epoxied on the 54mm rocket so it isn't moving. I only screwed-on the shroud for the 4", I haven't tried flying without it to see what impact it makes on the altitude, a part of me is tempted for the data aspects but the rest of me just doesn't want to fly without the on-board video. I really like the 4" shots of the apogee separation, I like using the vent-band area for the camera attach since you see apogee (and since it's closer to the side the camera is on I can see my backup drogue charge fire as well), but the camera only faces up while descending on drogue then re-orients towards the ground again once the main pops. Videos from both rockets are on my youtube page linked from below. In fact after my first Excel crashed and I re-built it I ordered a 1" longer vent-band as the Mobius was a bit longer than the stock 4" band, so it fits entirely within the vent band now.

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I am relatively new to HPR so forgive me if I am missing something. You fly the middle example with a stability of 9?

Buckeye said:

More specifically, why and how? My specific interest in this discussion is to minimize roll with the camera aboard. Ascent only.

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Aside from fastidious fin alignment and not flying at stupid fast speeds the only option for a rock steady ascent is active roll control with winglets and stabilization. In years past, I believe mechanical R/C gyros were modified to damp out rolling.
Various online videos are out there. I remember the Dr. Rocket fellow (of motor fame) flew a large project and had videos with stabilization on and off. Others out there have had similar projects.
People can pontificate about what one can do to minimize roll but after all is said and done, one has to fly the rocket and see what happens. Kurt

ksaves2 said:

Aside from fastidious fin alignment and not flying at stupid fast speeds the only option for a rock steady ascent is active roll control with winglets and stabilization. In years past, I believe mechanical R/C gyros were modified to damp out rolling.
Various online videos are out there. I remember the Dr. Rocket fellow (of motor fame) flew a large project and had videos with stabilization on and off. Others out there have had similar projects.
People can pontificate about what one can do to minimize roll but after all is said and done, one has to fly the rocket and see what happens. Kurt

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While I agree that this will have to be a trial and error process, as simulations seem to be unable to predict this, I am not convinced that we will not be able to come up with some basic guidelines, kind if like minimal margin for stability rule.

I am aware of the active stabilization discussions and have been involved in some, and I would love to see a model that could be widely adopted, however arguably this adds a layer of complexity that I personally would like to avoid for this specific application.

Without adding anything to the rocket, ideally I am just looking for a guideline on building a rocket when it comes to placing a camera on the skin.

mpitfield said:

Good info, where in relation to your sampling holes is the camera mount?

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On the 54mm the AV bay is waaay above the camera mount (in the DD configuration, the SD configuration was motor-eject only, I flew a TRS in the nose but used it for logging/tracking only, never for deployment). On the 4" the mount is on the vent band, there are 4 sampling holes 90° apart (4x 1/8" holes for a ~4"x14" volume), one is directly underneath the camera, so there's also one opposite and two 90° away. The one right under the camera probably isn't so hot for ascent but I figured the others would make up for it, the main reason for multiple holes as I understand it is to deal with cross-winds on the ground that could confuse the altimeter by causing pressure changes if the wind hit it right, so it basically allows for any pressure spikes/dips at one hole to be equalized by the others. 3 holes 120° apart with one directly opposite the shroud might have also been okay, or it might put the remaining two too close to the shroud, not sure.

dhkaiser said:

I am relatively new to HPR so forgive me if I am missing something. You fly the middle example with a stability of 9?

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Flys great! Wouldn't be the wisest idea to fly it in a decent wind with a slow-off-the-pad motor, but in light winds on motors that hit at least 50 ft/s off the rail I've never had a problem, and generally (IMO) some weathercocking isn't such a terrible thing since it points the rocket into the wind, so the descent takes it back closer to where it started rather than purely blowing it away. Of course the less vertical the flight is the lower the max altitude will be, so if you're shooting for altitude records it's not so great, I'm not trying to break any records with this and my flights have always come in right about where my sims say they should (most recent flight was at LDRS 35 as configured in the above screenshot, sim predicted 3538' on an I303BS and I actually got 3356', only 5% off which is well within the allowed motor tolerance). It landed ~438' from the pad though the main failed to deploy, had it deployed the rocket probably would have drifted a bit farther away. That flight's video (pad, handheld and onboard) starts here, you can see from the on-board that it was barely even arcing at apogee (I lost visual on the ground camera before apogee unfortunately). The sims say the I303BS would have reached ~68.7 ft/s before leaving the ~6' rail, though it was also pretty calm when I flew it. I'll likely fly it again this weekend.

I generally place the camera near the CG, but I don't worry about it too much. I think you'll find that rockets that fly straight without the camera will fly straight with one.

If you want less of the rocket in the frame you can shim the bottom rear of the housing to point it away from the airframe like I did with the Sony camera in the second video.

[YOUTUBE]ahpt81EWN40[/YOUTUBE]

[YOUTUBE]xV9GPbGtnHo[/YOUTUBE]

Very straight! Nice.

The camera doesn't need to be near the CG. I used to mount cameras in crazy places back when I built LPR rockets. Here is one I did mounted 6 inches below the rocket:

[video=youtube;-YwlQI3FTbM]https://www.youtube.com/watch?v=-YwlQI3FTbM[/video]


And here is another one mounted above the rocket:

[video=youtube;uG7OpyEaNSg]https://www.youtube.com/watch?v=uG7OpyEaNSg[/video]

Nathan said:

The camera doesn't need to be near the CG. I used to mount cameras in crazy places back when I built LPR rockets.

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Pretty cool perspectives and videos!

Too funny...I remember watching those videos when you posted them and I completely forgot about them and didn't even know who you were at the time.

However as cool as they are, and they are, it is really hard to tell from that perspective how stable their flight was. Remember we are not talking about if a rocket can fly or not with a camera attached to it, but rather if the camera has an effect on the stability of a flight, especially when the rocket design is over stable to begin with.

So at what point, if any, does it have an appreciable effect.

A view with an 808 cam from about 9 feet up on a 11.5' rocket:

[video=youtube;QBnYac-Dn3c]https://www.youtube.com/watch?v=QBnYac-Dn3c[/video]

Below is where I am leaning towards relocating my camera, first pic. This is roughly 2" above the sampling holes which can bee seen at the bottom of the ruler, there are 3 holes 120 degrees apart. Ideally I would be flush with the bottom of the AV bay ring, however I am concerned about any effect the shroud will have on the laminar air flow as it pertains to the sampling holes. In this place the shroud is roughly 10"-13" forward of where my CG is typically, vs. 17"-20" of where it was originally; dependent on motor choices.



Here is a picture of where the camera shroud was originally, which is about 9" from the sampling holes.



Thoughts?

I think you'll be alright. Looks like you have at least 3 holes.

Tonimus said:

I think you'll be alright. Looks like you have at least 3 holes.

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You got me thinking. If I center this over one hole then the other two holes will be far enough around the airframe that if there are any issues due to pressure differentials or laminar airflow, that they are very unlikely to be subject to them.

So below is my current mindset, 3" above one sampling hole, and still above my AV bay so I can capture my apogee event. I am also thinking of using epoxy to bond this in-place instead of using machine screws and self-clinching nuts. If so I will blend the corners so it looks more integrated into the airframe.

mpitfield said:

Thoughts?

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My elbows hurt just looking at that.

DavidMcCann said:

My elbows hurt just looking at that.

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Well try using your eyes instead then.

mpitfield said:

You got me thinking. If I center this over one hole then the other two holes will be far enough around the airframe that if there are any issues due to pressure differentials or laminar airflow, that they are very unlikely to be subject to them.

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I think your previous placement was better. All 3 holes were probably fine. In this last scenario, you absolutely, positively, compromised one of the vent holes, giving spurious pressure fluctuations into your ebay.

Edit: Looking again at your photo, 3'' may be sufficient distance for the wake off your camera to close, but still risky.

Buckeye said:

I think your previous placement was better. All 3 holes were probably fine. In this last scenario, you absolutely, positively, compromised one of the vent holes, giving spurious pressure fluctuations into your ebay.

Edit: Looking again at your photo, 3'' may be sufficient distance for the wake off your camera to close, but still risky.

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I completely agree that Your concerns are valid, at least from my limited perspective.

However as you pointed out I have moved the camera up 1" to 3" from the hole, in an effort to mitigate any pressure differentials the wake may cause around that sampling hole.

Realistically at the hobby level I understand enough to know that this is a best guess. However one thing I am fairly certain about is that the other two sampling holes are far enough away and around the airframe that they should not have any appreciable effect by the camera placement. If true then this current location is better mitigated that the original one. It really comes down to potentially having an effect on 1 hole vs. two holes.

I welcome input as my knowledge on the topic is average at best and I am basing it on assumptions and intuition, which may be way off.