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mpitfield

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I am specifically looking for feedback from anyone who is using a Mobius camera mounted on a 3" Darkstar, although all feedback is welcome. I have a 3" Darkstar and my Mobius camera used to be mounted about mid way on the payload tube. I like to watch the apogee event and see the booster dangling, then touching down. However I would like to move it down a bit but not sure where to place it as I have it in my head that the higher it is the more effect it has on the aerodynamic stability of the flight. I have not facts to stand on when it comes to this as it is more intuitive and maybe I am completely wrong.

Ideally it would be just about the AV band, so about a foot lower than where it was and in a spot where I could still view my apogee event. However in that position it may have an effect on the laminar airflow around my sampling holes, or maybe not, again just a guess.

Down between the fins seems to be a popular spot and based on the 3" Darkstar fin size, it would likely have the least effect on the aerodynamics. However I miss the apogee event.

Any factual substance to my thoughts, where is yours?
 

DavidMcCann

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My screech flights were filmed mounted just below the coupler on the booster. Its a 2.6" so thats a significant drag. You've seen those flights.

I don't know if being close to cg actually helps.... but its not hurting.

I do think the faster flights lead to less issues with it. My villain flights were too windy to get any kind of read on this... I'd love to try testing this, but thats a spendy experiment
 

mpitfield

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My screech flights were filmed mounted just below the coupler on the booster. Its a 2.6" so thats a significant drag. You've seen those flights.

I don't know if being close to cg actually helps.... but its not hurting.

I do think the faster flights lead to less issues with it. My villain flights were too windy to get any kind of read on this... I'd love to try testing this, but thats a spendy experiment
Dave yes your screech flights are dead straight. Where in relation to your CP/CG is your camera mounted?
 

DavidMcCann

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I'd never put the camera in the sim, so I just checked it. It's hard to see in these crops, but it moved the CP forward half an inch



This is a good approximation of where my actual CG is (the above two it's incorrect, I almost never put real CG's into sims, I only use them to check CP, then check when loaded for a real CG)
Here I've adjusted the CG to my memory of it at LDRS last year.


It's ugly there, thats for sure. And missing the apogee event stinks. My real reason for the placement was I wanted it as forward as possible to avoid washout on ignition, and I didn't want the screws sticking through to hang up the main chute. Could have just glued it on, but this works for now. I'd love to test placement..but can't decide how to best do it.... perhaps doing it on my Vulcanite with some G's would suffice.
 
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DavidMcCann

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I typically adjust drag manually... But to see the effect of the camera I took off the override.

on a K1127, with camera it was 7700', without 8475' (actual flight was about 9K)


I need a clear day and about 5 K1127's to settle this ;)
 

Tonimus

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I like to put it well ahead of the break point so that I can see the deployment and if anything goes awry.
 

blackbrandt

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I put it almost at the very bottom, so I don't have a ton of rocket in my video.
 

mpitfield

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I like to put it well ahead of the break point so that I can see the deployment and if anything goes awry.
I put it almost at the very bottom, so I don't have a ton of rocket in my video.
Tonimus and blackbrant, what size airframe are you dealing with? Do you have videos posted that I can review?
 

timbucktoo

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I place it about 8" below the AV bay on booster on my 3" Tomahawk so you cannot see apogee events.
On my 4" Eagle Claw, it's about midway between NC & AV bay on payload.

[video=youtube;otKf8BmMOPM]https://www.youtube.com/watch?v=otKf8BmMOPM[/video]

[video=youtube;C8xC69LnMUg]https://www.youtube.com/watch?v=C8xC69LnMUg[/video]
 

mpitfield

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On my 4" Eagle Claw, it's about midway between NC & AV bay on payload.

[video=youtube;C8xC69LnMUg]https://www.youtube.com/watch?v=C8xC69LnMUg[/video]
Thanks Tim,

Specific to your Eagle Claw I am wondering if the camera location is contributing to the spinning. Here is the rocket I am looking to relocate the camera on and you can see the spin. Although I interpreted my issue as a combination of factors, over-stable resulting in coning being one of them but I also wonder what role the camera position is playing if any at all.

[video=youtube;N4L0TyW7xV8]https://www.youtube.com/watch?v=N4L0TyW7xV8[/video]
 

Coop

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I like having one pointed up from the bottom and down from the top. Lets me see the deployment and if things could be better arranged/situated during flight.


Later!

--Coop
 

timbucktoo

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Thanks Tim,

Specific to your Eagle Claw I am wondering if the camera location is contributing to the spinning. Here is the rocket I am looking to relocate the camera on and you can see the spin. Although I interpreted my issue as a combination of factors, over-stable resulting in coning being one of them but I also wonder what role the camera position is playing if any at all.
Yours looks a bit more like coning but I don't think thats from over-stability. Isn't coning a result of motor being off center or some element within say the AV bay where there is more weight on one side vs. the other? I would think the camera would tend to help reduce any spinning. The Eagle Claw has a lot of "fin" and it tends to spin more with wind. I have several launches of Eagle Claw with & without camera & I can see it spin right off the pad.

Another guy I fly with has added tape to the trailing edges of his fins on one side only to counter the spin and has actually shown a reduction in spin.
 

Buckeye

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Thanks Tim,

Specific to your Eagle Claw I am wondering if the camera location is contributing to the spinning. Here is the rocket I am looking to relocate the camera on and you can see the spin. Although I interpreted my issue as a combination of factors, over-stable resulting in coning being one of them but I also wonder what role the camera position is playing if any at all.
I am wondering the same thing. My videos, on two different rockets, have a fair amount of roll. It sucks and makes the video hard to watch. I think my fin alignment is pretty good, too.

Any rocket aerodynamicists care to comment on the factors that affect roll? I am thinking these are factors:

  • Fin alignment
  • 3 fins vs. 4 fins
  • camera frontal area vs. rocket frontal area
  • angle of attack
  • camera off-center mass
  • position of camera along rocket length
  • rocket speed (my spinning flights used fairly high thrust motors and fast speed off the rail)
 

markkoelsch

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Simple to test. Get another shroud and mount it 180 degrees from the first shroud. That would likely cancel out the roll if it were caused by the first, single shroud.
 

mpitfield

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Yours looks a bit more like coning but I don't think thats from over-stability. Isn't coning a result of motor being off center or some element within say the AV bay where there is more weight on one side vs. the other? I would think the camera would tend to help reduce any spinning.
From what I was told the term "Conning" is not the technical term for the phenomenon but it is something like roll-pitch coupling, or something like that. My understanding of it is that an over-stable profile can be a factor.

This particular rocket is pretty balanced along its vertical axis and the motor was a ATK700 which has a center core, not off-set. Even the dual electronics are centered on the sled with evenly distributed configurations on the sled. The only unevenly weight distribution is the airfoiled rail buttons and on the opposite side, and end, the Mobius action cam

I am wondering the same thing. My videos, on two different rockets, have a fair amount of roll. It sucks and makes the video hard to watch. I think my fin alignment is pretty good, too.

Any rocket aerodynamicists care to comment on the factors that affect roll? I am thinking these are factors:

  • Fin alignment
  • 3 fins vs. 4 fins
  • camera frontal area vs. rocket frontal area
  • angle of attack
  • camera off-center mass
  • position of camera along rocket length
  • rocket speed (my spinning flights used fairly high thrust motors and fast speed off the rail)
Yes I would love to hear from someone knowledgeable on aerodynamics, and possibly help us with a rule of thumb.
 

mpitfield

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Simple to test. Get another shroud and mount it 180 degrees from the first shroud. That would likely cancel out the roll if it were caused by the first, single shroud.
Hi Mark,

I am in the process of repainting that rocket, and mounting something on the opposite side would likely mean some body work (which I just did) followed by a paint touch up. Another way around this would be to setup different configuration payload tubes. However my biggest issue is that I do not have a local field to launch from, so trial and error would be a very drawn-out process for me.
 

DavidMcCann

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From rocket reviews- https://www.rocketreviews.com/coning.html

I think it's less about spin, and more a question of "does having more drag on one side of the rocket affect flight path" and "does having that drag further from the cg affect the path more than being close to the cg?"

I think because of the spinning it's manifesting like coning, but it's possible that the drag of the camera is as strong, or stronger than the corrective force of the fins.

Watching my Screech flights you can definitely see some corrections by the fins going up. Slight, but there's some butt wiggling. My guess is that the drag forces pivot the rocket about the cg, and the forces on the camera are slight being so close to it, while the fins are greater being further away. I could be totally wrong, and it was not my intent while mounting it, but my armchair guess.

[youtube]2LlFECiy5oc[/youtube]

[youtube]bVJD1Akxh-U[/youtube]

However....My Villain is located in the same place. It has coned like crazy. It's in much winder conditions (and not an over-stable rocket) so I'm not sure it compares, but for full disclosure-
(also the screech flights were over M1, the Villain were not)

[youtube]euJD8tX0Sew[/youtube]

The second and third flight of the Villain are in this video. Slightly less wind, less coning, some visible correction, but still to windy to be certain-
[youtube]Xcxv8gxVgNs[/youtube]


Villain Flights- (some visible issues)


Screech-




Overall, for myself, I think I could check the Villain with two more 54/1200 flights. One on a calm day, and one with the camera mounted higher. The Screech, I'd like to fly another K1127's with different camera locations, and with no camera.
 
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mpitfield

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I recall reading that one, thanks for reminding me. I interpret that as an over stable rocket will be more prone to coning. Which in the case of my 3" Darkstar it had close to a 7 caliber margin. Hopefully chopping 5 inches off the rocket over the winter will help with these numbers.

I think it's less about spin, and more a question of "does having more drag on one side of the rocket affect flight path" and "does having that drag further from the cg affect the path more than being close to the cg?"

I think because of the spinning it's manifesting like coning, but it's possible that the drag of the camera is as strong, or stronger than the corrective force of the fins.

Watching my Screech flights you can definitely see some corrections by the fins going up. Slight, but there's some butt wiggling. My guess is that the drag forces pivot the rocket about the cg, and the forces on the camera are slight being so close to it, while the fins are greater being further away. I could be totally wrong, and it was not my intent while mounting it, but my armchair guess.
My intuition would agree, however rocketry and aerodynamic forces have already proven to be anything but intuitive. I am really oping that someone with knowledge on the topics will step in and set us straight.

However....My Villain is located in the same place. It has coned like crazy. It's in much winder conditions (and not an over-stable rocket) so I'm not sure it compares, but for full disclosure-(also the screech flights were over M1, the Villain were not)

The second and third flight of the Villain are in this video. Slightly less wind, less coning, some visible correction, but still to windy to be certain-

Overall, for myself, I think I could check the Villain with two more 54/1200 flights. One on a calm day, and one with the camera mounted higher. The Screech, I'd like to fly another K1127's with different camera locations, and with no camera.
Looking at the Villain vs. the Screech, there is a noticeable difference in the fin design, tapered swept vs. a trailing delta. I know with a swept fin the CP moves aft and this may help to support any CP/GP relationship, over stable theory.

In my case the Darkstar, as you know, has a spit fin but overall looks more like a clipped delta design, however my particular rocket seems to have been longer than stock. I miss quoted the length of it in my video as I went off the Open Rocket File. I will have to check but I took over 5" off of rocket between the booster and payload tube, which shaved off close to 2 calibers.

My hope is that with this change along with moving my camera further aft it may help to stabilize the coning. I think I need to grab another K700 as a fair test, even though I have my sights on L1040...ah I will just do both ;)
 

DavidMcCann

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I'll have to measure my ds booster. It's very overstable loaded... NC is almost a pound the way I did it. K805 may have coned slightly looking at photos , but K1100 nailed it straight up. sadly this was before I got into video, so neither had a camera on it.

Sorry if I'm dumping too much into this thread, but its a question I'd love to know the answer to. I may attempt some scale A8-3 tests. I'm also curious what the overall effect on altitude is.
 

mpitfield

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Sorry if I'm dumping too much into this thread, but its a question I'd love to know the answer to
"dumping", you mean contributing, and thank you. The dialogue is welcome and the more dialogue the more chance we will put this one to rest, so bring it on!

I have tried to get this answered once before and I know at least one other person also made an attempt. I am hoping for a basic guideline, such as don't mount it x calibers above the CG and drop a caliber for every x calibers of stability...or something like that. Possibly this is a bit naive on my behalf and every case is different.
 

DavidMcCann

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Well....I've got a pile of various G motors.... And a vulcanite. I'm thinking either july or august I'll try flying it a few times with the camera in various positions. The rocket is fairly over stable, and the camera on the payload will certainly make it even more so

My DS Booster is roughly 44"
 
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EeebeeE

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A couple thoughts... Placing it aft would hypothetically increase base drag. You can also get videos without the rocket in them. Having it close to the nose cone is more aerodynamic because the air tends to move wide around the point where the nose cone and airframe come together. You can also get nice shots of apogee separation. It still slows the rocket a little but if your mounting system isn't big and bulky like some of the 3D printed ones I've seen that look like a storage shed mounted on a rocket, it shouldn't make much of a difference in the stability of the rocket.
 

DavidMcCann

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I believe we're discussing the best position to mount a storage shed to carry a mobius externally.

I've actually checked all over NASA. there has to be a search term I'm missing. If they have papers on split washers they have to have something on this.
 

ksaves2

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I asked this question some years ago and the response I received was it doesn't matter where one puts it. That said, I've noted some rockets are better camera platforms than others and it doesn't matter where the camera is placed.
I've seen a rocket that spins like crazy after apogee on descent. Nauseatingly dizzy. No swivel and once it's wound up all the way, it starts unwinding in the opposite direction. The camera is looking down on the sustainer aft of the ebay
separation point.

Some rockets just give the camera a better ride than others. I especially impressed with this video just posted: https://www.rocketryforum.com/showt...-GoPro-Complex-M-Flight&p=1602491#post1602491
Gives a nice easy panoramic view. The only thing better would have been to have a downward camera to catch the airstarts. That's really cool when it's captured. Kurt
 

Buckeye

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Some rockets just give the camera a better ride than others.
More specifically, why and how? My specific interest in this discussion is to minimize roll with the camera aboard. Ascent only.
 

DavidMcCann

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I think part of the difficulty is it's hard getting info on how rockets fly without the camera. With it's pretty obvious how it flies.

What I haven't seen is a 'smoking gun' a rocket that flies straight without a camera, and cones with it on, on the same motor. And on such a rocket, does it cone with it on the payload, and less with it on the booster?

I'm sure there are many things going on with this. I tried looking at canards and their aerodynamic properties. I succeeded in confusing myself more I think....


I went back through my photos to see if that K700 really coned that much, as the video doesn't look too bad.


The funny thing I noticed digging back in the photos is that a week after I saw your Tomach fly, I had one on my workbench :)
 
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Buckeye

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I'm sure there are many things going on with this.
Yes, and I threw out a bunch of possibilities in post #13. Hmm...sounds like experiments are in order.

I will try to dig into "Advanced Topics in Model Rocketry" and see if I can find anything related to roll or pitch/roll, especially with a shed-like pod attached!
 

mpitfield

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I think part of the difficulty is it's hard getting info on how rockets fly without the camera. With it's pretty obvious how it flies.

What I haven't seen is a 'smoking gun' a rocket that flies straight without a camera, and cones with it on, on the same motor. And on such a rocket, does it cone with it on the payload, and less with it on the booster?

I'm sure there are many things going on with this. I tried looking at canards and their aerodynamic properties. I succeeded in confusing myself more I think....


I went back through my photos to see if that K700 really coned that much, as the video doesn't look too bad.


The funny thing I noticed digging back in the photos is that a week after I saw your Tomach fly, I had one on my workbench :)
Yes in the on-board video it is hard to tell. However it is pretty obvious in your pic and if you look at the video Coleman put together for the club launch. Below is the club video starting at the same launch as my on-board, but from the external perspective, and you can clearly see the oscillations increase as the motor burns the propellant, moving the CG forward and increasing the over stability...at least that is how I interpreted it.

I recall commenting out loud, when it launched, "man did that ever cone", it was that obvious.

[video]https://youtu.be/pc4m1xoCLTM?t=283[/video]

I just measured my components and here is the before and after.

Was
Booster 44”
AV Band 1.5
Payload 23
Nosecone 18
With K700 6.4 over-stable

Is
Booster 41.25
AV band 1.5
Payload 20
Nosecone 18
With K700 4.9 over-stable

So I shaved off 1.5 calibers by shedding 5.75 inches. This number may change as the new sim is not corrected with the camera remounted, but it still should be 1.25ish as the camera will be mounted lower this time. My suspicion on this whole topic is that, as in the opinions ksaves2 solicited, in the grand scheme it may not make a difference, unless your rocket and flight profile put you on the edge of being too over-stable. However I think as you and Buckeye have pointed out this may take some actual test flights to vet out and come up with some guidelines. We could also gather some statistics on launches with external cameras measuring CG/CP and where the camera is mounted in relation to them. Of course this is not likely to paint a full picture, as fin shape and rocket design likely also play a role, however it may help.
 

DavidMcCann

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I'm not sure if it would translate, but I've got a mean machine I've never flown. I need to see how many D12's I have, rig up a dummy shroud, and see what happens.
 

T34zac

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Im currently working on a 3" darkstar and plan on sticking a camera near the CG. Thats where I put it on my 4" Frenzy XL and have only had straight flights so far, but thats also a larger rocket than the Darkstar. I plan on putting two cameras on my darkstar Jr later this month (one camera for each stage), one camera at the sustaimer CG and one at the booster CG pointing up to (hopefully) catch sustainer ignition.

I am using an 808 camera, but it has a cowling very similar to the mobius camera ones.
 
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