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Congrats. Hope your results are that great when you get to your max motors and three stages!
I don't think it would make any sense to put this on the top of a three stager. It wouldn't work that well, and there would be a weight penalty for the entire flight.Congrats. Hope your results are that great when you get to your max motors and three stages!
I was able to do the flight today (the M3100 to M745 test rocket flight). It went quite well. I did the boost with roll control only (since yaw/pitch wouldn't do much with the longer stack anyway), separated the stages at 3 seconds after a 2 second burn, and then turned on yaw/pitch at 4 seconds. You can clearly see the yaw/pitch control come on in the video...
Jim
PS - The spin can got a thorough workout on this flight. Lots of wind shears on the way up.
I don't think it would make any sense to put this on the top of a three stager. It wouldn't work that well, and there would be a weight penalty for the entire flight.
Just in case you missed it, though, I did use the system on the three stage flight at Balls in 2018. It was located between the first and second stages, and then was separated after the first-stage coast (before lighting the second stage). It actually worked quite well. With respect to the distance of the recovery, if you consider the angle that the rocket would have been at after the coast versus the actual angle, it was the difference between a recovery 20 miles out versus the actual 3 miles.
Jim
These are different ways to solve the same problem. Spinning a rocket helps to reduce dispersion but is not used with active stabilization. Spinning introduces a new set of difficulties.A very pretty rocket. Thanks for that.
BTW, can you explain again what is the advantage of a spin can rather than having just the entire stage spin?
Bob Clark
I'm not familiar with this particular launch. I know TU Wien had a failure on the boost of their two-stage around this time?Pretty impressive you were able to get ignition at high altitude. As you know, that has been a problem with other amateur teams.
An additional university team recently had a failure at a high altitude launch due to this:
https://m.facebook.com/story.php?story_fbid=2929589837068469&id=245686032125543
Anything you would want to discuss?
Bob Clark
Pretty impressive you were able to get ignition at high altitude. As you know, that has been a problem with other amateur teams.
An additional university team recently had a failure at a high altitude launch due to this:
https://m.facebook.com/story.php?story_fbid=2929589837068469&id=245686032125543
Anything you would want to discuss?
Bob Clark
Bob,
In 2018, their failure to ignite the sustainer had nothing to do with high altitude. They had a wiring problem. That’s briefly mentioned in this report which discusses their 2019 failure.
https://spaceteam.at/2019/10/31/final-report-the-hound-2019/?lang=en
Bob, I do a few things to help get motors lit at high altitude. These include things like propellant selection, igniter strategy, etc., most of which I have posted here on this forum. I know I can get the motors to light, albeit with a few seconds of delay, which I account for in the flight profile. Perhaps the actual correlation is that I often have rockets at high altitude, in a position to be lit, with tested electronics to accomplish that?Jim may be the only amateur in the world able to do successful ignition at high altitude.
It’s an important accomplishment for amateurs to reach, for reasons I have discussed before.
Robert Clark
Actually, there may be another variable at play. If you look at the video (and other recent videos), it appears that the spin can locks up under boost. You would expect it to be turning at some point during the burn, but it doesn't. Then, at burnout, the spin can starts to spin, even though the velocity is still high. I would speculate that the fin can is drag separating from the air frame such that the downward force is reduced to the point where the fin can can spin. At least I didn't spend many $'s on the spin can! So, it is possible that the spin can is just acting as a set of fixed fins during the boost, and that the roll at that point is caused or confounded by the action of the canards. I'm not sure how to sort this out, but I think I need to find some metal bearing surfaces.Hi Jim,
Very nice result. Your initial roll looks like it could just be a typical transient response [saturated or not]. If it is saturating like you suggest, reducing the control travel limit for pitch a little would be expected to improve it and should get you closer to the sweet spot for overall control balance for this rocket. If that does not help then raising the roll gain a little [especially if you have recently reduced it] would be another candidate.
br/
Tony
Actually, there may be another variable at play. If you look at the video (and other recent videos), it appears that the spin can locks up under boost. You would expect it to be turning at some point during the burn, but it doesn't. Then, at burnout, the spin can starts to spin, even though the velocity is still high. I would speculate that the fin can is drag separating from the air frame such that the downward force is reduced to the point where the fin can can spin. At least I didn't spend many $'s on the spin can! So, it is possible that the spin can is just acting as a set of fixed fins during the boost, and that the roll at that point is caused or confounded by the action of the canards. I'm not sure how to sort this out, but I think I need to find some metal bearing surfaces.
Jim
The spin can does have ball bearings, probably 150 or them or so (I use two sizes and don't remember specifically how many of them). However, they are between two fiberglass surfaces (the flattened ends of two fiberglass tubes). I suspect that this fiberglass deforms just enough under load to reduce the spinning freedom of the spin can. I know it still turns under the load, but the force required may be more than what is required during flight.the R/C car hobby uses very good (and small) metal ball bearings if you want to incorporate those to your spin can to keep it from binding under acceleration. Edit: i just realized they probably won't help at all. The motor is where the bearings would be hah
Right now, the upper and lower bearing surfaces are the ends of fiberglass tubing. I'm sure things would work better if I could replace that with metal tubing. Unfortunately, the standard 4" aluminum tubing doesn't quite fit.Certainly without something comparable to a thin section bearing under it, it is is almost assured to lockup until the axial forces on it are low enough. If you are controlling 3 axes, then the system would seem to work without the spin can given a bit of tuning...
There's things I've done in rocketry, caught on keychain cameras, that I don't think could be repeated! I had a flight where stages collided, and I remember telling Stu "you're not gonna believe this"....That is really cool Jim. I know the reason for the spin can but by mere chance I built a 4 inch rocket with plywood fins that apparently ended up mis-aligned “just right” and the rocket didn’t spin on the J motors I flew it on. Keychain camera video was was interesting. I couldn’t repeat this feat in a million years. Gotta go dig out the video. It’s stashed on a loose hard drive in the basement. Kurt Savegnago
Thanks! I wish I had a better ground video of this flight. It was very interesting how the rocket just did this graceful arc upwards to vertical. Unfortunately, when the button get's pushed, it's hard for me to focus on video.Nice flight!
I think the spin can helps to avoid control reversal, but it actually makes roll control much more difficult because the moment of inertia of the air frame is lower without the fins being attached. If the fins were attached, and if control reversal could be avoided, roll would be more damped and more aesthetic for side-looking cameras.Wow!
The fin can “absorbed” the roll while the fuselage and camera kept the orientation solid.
What, you don't have a transonic wind tunnel laying around?I think the spin can helps to avoid control reversal, but it actually makes roll control much more difficult because the moment of inertia of the air frame is lower without the fins being attached. If the fins were attached, and if control reversal could be avoided, roll would be more damped and more aesthetic for side-looking cameras.
The heading hold capability is interesting. There are two terms contributing to the position of the canards for roll. The first term, which we had previously, generates a canard response in proportion to the roll rate. So, if the rocket starts to roll, the canards resist that roll, but this term doesn't try to hold a specific roll position. The second term generates a canard response that increases as the difference from the initial position increases. For example, at the initial roll position on the pad, this second term is zero. If the rocket turns from zero to 180 degrees, the canard response goes from zero to the max allowed, in an effort to return to the initial roll position. If the roll ever exceeds 180 degrees, the maximum canard deflection is retained until the rocket starts to rotate in the other direction. At that point, there is a new heading established that is 180 degrees away from the point where the roll direction reversed. But as long as the rocket doesn't turn more than 180 degrees, the original heading is retained. In the flight, the roll angle never exceeded 70 degrees. It is also interesting that the first term of the roll feedback dampens the second term. That is, if the heading hold response is high, due to a roll position that is well away from the initial point, the canard angle generated from this would be offset by the first term if the return roll rate is high. This helps to keep the roll rate from getting too high. Bench testing all of this is pretty weird.
Jim
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