# I could use just a little guidance

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#### BABAR

##### Builds Rockets for NASA
TRF Supporter
Congrats. Hope your results are that great when you get to your max motors and three stages!

#### JimJarvis50

##### Well-Known Member
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.

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

#### BABAR

##### Builds Rockets for NASA
TRF Supporter
Thanks for reposting, very cool. Especially was interesting how the rocket started tumbling but still ascending from 140k to 175k Apogee, I guess because it there was so little atmosphere at that point that the only effective forces were kinetic energy (momentum) vs gravity, minimal atmosphere so minimal drag, so orientation of the rocket didn’t matter.

I guess your pitch/yaw/roll control surfaces have the same issue, they become less effective per square inch of surface area the higher the altitude.

#### RGClark

##### Mathematician
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.

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

#### Charles_McG

##### Ciderwright
I can answer this one. Jim is using active correction- if he spun the whole booster, the pitch and yaw axes would spin with it. That would complicate controlling those axes - to say the least. It might not be possible. So he controls roll, which keeps the pitch and yaw axes pointed mostly in constant directions. That means he can then control them when the time comes.

But experimentally, he discovered that the control vanes, when controlling, kinda torque the slipstream of air flowing around it so it doesn’t hit the aft fins symmetrically. That caused a reverse roll. So he made the aft fins spin freely in roll. They still function to keep the rocket stable in pitch and yaw, but are free in roll so it doesn’t cause the control reversal.

His unit looks a lot like the S19 sounding rocket boost guidance module. There has been a recent picture posted on YORF of an unidentifed Honest John-Nike rocket with, perhaps, an S19 test unit on top. That version appears to have strakes immediately aft of the control vanes, and I wondered if that was an alternative solution.

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#### RGClark

##### Mathematician
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

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:

Anything you would want to discuss?

Bob Clark

#### JimJarvis50

##### Well-Known Member
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
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.

For active stabilization, the spin can reduces the effect of control reversal, as Charles mentioned. Here is a video that really showed what happens with control reversal. The rocket was spinning the opposite of the desired direction during the boost, but then roll-stabilized as soon as the lower booster fins were separated. I started building the spin can as soon as a realized what had happened on this flight.

Jim

#### JimJarvis50

##### Well-Known Member
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:

Anything you would want to discuss?

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?

People say I get lucky that my upper stages light. Hmm. My interpretation is that I make arrangements for them to light, and then they do.

Jim

#### Steve Shannon

##### Well-Known Member
TRF Supporter
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:

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

#### Reinhard

##### Well-Known Member
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
The statement Bob Clark is referring to, is also from 2019. It was written right after the launch without much data at hand, but already then "upper stage didn't ignite" was admittedly an euphemistic way to put it, considering we already knew that we lost telemetry on the sustainer.

Reinhard

#### RGClark

##### Mathematician
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

#### JimJarvis50

##### Well-Known Member
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
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?

Techniques to light motors properly at high altitude are not secret so far as I know. Any serious university team would have the manpower, time and resources to do the required testing for their motor style. They should do that and not worry about what I do.

Jim

#### JimJarvis50

##### Well-Known Member
I had a chance to fly the stabilization system again last weekend. It was an L-1050 to about 7,800 feet. We set up the rocket at a tilt of about 7°. I wanted to set it at 10°, but it was pointed into a pretty brisk wind, and setting a higher angle than we did just didn't pass the smile test (and at 10°, the pad probably would have fallen over). Looks like the rocket weathercocked to around 20° and then corrected to vertical after 5 seconds.

The flight does show some roll early on. I think that when the canard angle is high, it is easy to induce some roll if things aren't aligned perfectly. Then, there is relatively much less control action available for roll control, so it's difficult to completely eliminate roll. From that perspective, I think the system worked pretty well.

Here's a short flight video.

Jim

#### TonyL

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

#### JimJarvis50

##### Well-Known Member
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 $'s on the spin can! So, it is possible that the spin can is just acting as a set of fixed fins during the boost, and that the roll at that point is caused or confounded by the action of the canards. I'm not sure how to sort this out, but I think I need to find some metal bearing surfaces. Jim #### Chad ##### Well-Known Member Actually, there may be another variable at play. If you look at the video (and other recent videos), it appears that the spin can locks up under boost. You would expect it to be turning at some point during the burn, but it doesn't. Then, at burnout, the spin can starts to spin, even though the velocity is still high. I would speculate that the fin can is drag separating from the air frame such that the downward force is reduced to the point where the fin can can spin. At least I didn't spend many$'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 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

#### UhClem

##### Well-Known Member
The servo control code in MatrixPilot is designed in a way that will induce unwanted motion. That is because it sends out the servo control pulses one at a time. That delay means that opposite fins are not always working together which will add roll when only pitch or yaw is commanded.

Roll corrections of course result in unwanted pitch and yaw motion.

It isn't that difficult to send the servo pulses out simultaneously.

#### JimJarvis50

##### Well-Known Member
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
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.

By the way, there are lots of pictures of the spin can design earlier in this thread.

Jim

#### TonyL

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...

#### JimJarvis50

##### Well-Known Member
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...
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.

Jim

#### JimJarvis50

##### Well-Known Member
I had a chance to fly my stabilization system last weekend. It was a pretty severe test of the system with the rocket launched at about 12° into a brisk wind. Thge rocket weathercocked initially but then went vertical. The on-board video is interesting because you can clearly see the rocket go vertical from the smoke trail. Everything came back fine, so I get to fly it again.

Jim

#### ksaves2

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

#### JimJarvis50

##### Well-Known Member
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
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"....

Jim

TRF Supporter
Nice flight!

#### JimJarvis50

##### Well-Known Member
Nice flight!
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.

For the next flight, I was thinking about doing a flight with roll control only. On many of my flights, it doesn't appear that the roll control part of the flight is working as well as it should. The problem is that vertical stabilization takes relatively large canard movements, and if things are not perfectly aligned with respect to roll, then it is hard for the relatively small canard roll movements to counteract that. I'm surprised it works as well as it does. So, I'm thinking of doing a flight with roll control only, just to show how it works when it doesn't have to fight the vertical stabilization.

Jim