I could use just a little guidance

Discussion in '[Unrestricted] Staging, Airstarts & Clusters' started by JimJarvis50, Jan 19, 2015.

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  1. Jan 19, 2015 #1

    JimJarvis50

    JimJarvis50

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    If I want to fly any higher than I already have, I'm going to need to fly straighter. Blackrock is a wonderful place, but it's not as big as you might think. It's also rimmed by mountains, and I've landed on two of them. My objectives are modest. I don't need to fly vertical for the whole flight. I'd just like to be there at the staging point for my multistage flights.

    Since I'm not an electronics or programming person, I'm going to use the EagleTree Guardian. It's intended as an RC airplane autopilot. This device is the same control unit that Alyssa Stenberg used for her NAR R&D project. I'm basically going to do what she did with a few bells and whistles (but no LEGO's).

    The Guardian is a pretty interesting device, given that it only costs about $60. It has several operating modes. In 2D mode, it is intended to keep an airplane level (using elevator and ailerons). If you're flying your plane and you get in to trouble, you just let go of the sticks and the airplane goes level automatically. If you mount the Guardian laying flat on a bulkhead, it will try to keep the rocket vertical. That's what I'm going to try, at least to start with. There is also a 2D mode with heading control. In theory, you could also control roll using 4 canards using the v-tail mixer on the Guardian. However, the guardian uses ailerons for heading control and not rudder, so that approach won't work.

    There is also a 3D mode where the Guardian tries to keep the plane moving in whatever direction it is going when the 3D is activated. For 3D mode, you would mount the Guardian vertically, and then try to fly the rocket straight up using rudder and elevator. In this mode, you could use the elevon mixer for roll control, and that might work. Some day I'll find out.

    This project will take a while. There's the electronics aspect, the mechanical design, and test flights to try to figure out how it works. But, I thought I'd start a thread now and just update it periodically. I have my initial pass at the electronics completed, and I put together a little video to illustrate how it works. I can't believe how simple it turned out to be.

    [video=youtube_share;93U7fqSuw1k]http://youtu.be/93U7fqSuw1k[/video]

    Next steps are the mechanical design (mounting the servos, electronics, etc.), and building a bare-bones 4" rocket for testing the system.

    Jim
     
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  2. Jan 19, 2015 #2

    FredA

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    This could be the start of something great....
    Best thread of 2015!

    Go Jim - most interested in your mach-2 controllable fins.....

    FredA
     
  3. Jan 19, 2015 #3

    Tonimus

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    Subscribed!
     
  4. Jan 19, 2015 #4

    GregGleason

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    I'm in.

    :pop:

    Greg
     
  5. Jan 19, 2015 #5

    C.O.B.H.C.

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  6. Jan 19, 2015 #6

    warnerr

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    Great subject! I am in listen mode.
     
  7. Jan 19, 2015 #7

    cvanc

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    Very clever and interesting. Good luck with it!

    Care to share what solid state relays you are using? Do they have a latch-on ability or did you have to make an external circuit for that?
     
  8. Jan 19, 2015 #8

    blackbrandt

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    This will be cool. :)
     
  9. Jan 19, 2015 #9

    tfish

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    I've really enjoyed our time together up in the mountains!

    Tony
     
  10. Jan 19, 2015 #10

    jmattingly13

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  11. Jan 20, 2015 #11

    JimJarvis50

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  12. Jan 20, 2015 #12

    JimJarvis50

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    I got this one:

    http://www.mouser.com/ProductDetail...=sGAEpiMZZMvNy/d/TAiTWbsvWXPeH51IT2FidurMnoA=

    It has the current-limiting resistor built in. You just feed it 5 volts and it works.

    The version they sent me was the SON mount (no legs). Getting that tiny little thing soldered was a challenge, but starting with a stranded and tinned wire made it easier. I'm not sure what latch-on ability is. It stays on as long as my latched Raven output is active.

    Jim
     
  13. Jan 20, 2015 #13

    JimJarvis50

    JimJarvis50

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    I did too. Let's do it again (but not in the summer).

    Jim
     
  14. Jan 20, 2015 #14

    flynfrog

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    Jim (disclaimer I have no idea of any of this in practice) I think the issues you will have its the PID tuning is not sure if its adjustable on the guardian. The guardian and is made for a slow flying plane with larger control surfaces where it has time to correct Im not sure how well it would cope with speeds over mach.

    I have been playing around with an arduino with a 6dof board the last few days at some point will become a quadcopter. The principals are the same using PID loops for the axis of motion. It might be a little more work but would give you more tuning options. You could add a Barro and you dont need the raven and ssrs and you could even fire your charges all with the same board plus or minus a few parts.

    Super interested

    Following...
     
  15. Jan 20, 2015 #15

    flynfrog

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    I have much better luck with solder paste for surface mount stuff.
     
  16. Jan 20, 2015 #16

    EeebeeE

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    I thought that the FAA did not allow guidance systems on amateur rockets. I've seen some with forward fins that will allow the flier to adjust the spin, but that was it. Probably should check into the legality of this before you build.
     
  17. Jan 20, 2015 #17

    jsdemar

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    Active stability control is legal. Guidance for targeting is not.
     
  18. Jan 20, 2015 #18

    jsdemar

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    If you need something soldered, I have a full surface-mount soldering station. Also, if you need an interface circuit designed, or a board layout, just holler.
     
  19. Jan 20, 2015 #19

    JimJarvis50

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    I'm aware of several better options for control, and for several, programming is close to off-the-shelf. I plan to look at those options over time (and it will take me time), but I think the Guardian may do what I need for getting started. In the 2D mode, I think that the response is strictly proportional, and I suspect that too much gain would just lead to oscillation. But my goal isn't to be straight for the entire flight - I only need to get there for staging. On a typical flight, I might have 10 to 15 seconds to turn the sustainer to vertical. My feeling is that there is a gain that would accomplish that without overcontrolling. The nice thing, though, is that both the mechanical design and the control approach can be incrementally improved over time.

    Jim
     
  20. Jan 20, 2015 #20

    gerbs4me

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    Good luck on this endeavor!
     
  21. Jan 20, 2015 #21

    DAllen

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    Quit hogging all the popcorn and let me have some. Sheez.

    :pop:

    There. That's better.
     
  22. Jan 20, 2015 #22

    Andre

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    Jim

    Have you given any thought that maybe instead of a complicated active stabilization system a simple spin stabilization could be used to achieve a more vertical flight. Huge multistage sounding rockets have been flown successfully for decades with only pasive stabilization (fins with a small cant to provide roll).
     
  23. Jan 20, 2015 #23

    bobkrech

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    Guys, you are over thinking the problem. 99+% of our rocket fly straight because they are designed to be aerodynamically stable. The aerodynamic shape and the center of gravity coupled to the forces generated by the fins direct the rocket to minimize the angle of attack of the airflow over the fins. A perfectly balanced rocket do not always ascend vertically due to the simple fact that the axial motion of the rocket and the perpendicular velocity of the wind produce a non vertical minimal angle of attack trajectory solution. And once you are in a non-vertical trajectory, a gravity turn is initiated and the effect will increase as a function of time, further deviating the trajectory off vertical.

    The true trajectory solution is a 6DOF problem: linear velocities and accelerations in the x, y, and z directions, and rotational velocities and accelerations in the x-y (roll), y-z (yaw), and x-z (pitch) planes. In aerodynamically stable unguided rocket flight, the principal forces are generated by the thrust of the motor, the aerodynamic drag of the atmosphere and the gravitational force of the earth. All other motions are cross axis couplings due to wind and imperfections in the rocket shape and mass distribution resulting in non-vertical flight.

    The major instability in most high altitude attempts is coning, or roll-pitch coupling. This coupling causes the base of the rocket to react with an undamped, increasing amplitude oscillation that ultimately upsets the rocket by causing it to turn sideways in the airflow and disassemble. Conversely by controlling and modifying the roll and pitch of the rocket vertical flight can be maintained. Alternatively, one can control the yaw and the pitch of the rocket maintain vertical flight however this method does not stabilize roll, which may or may not be an issue.

    Most of the pitch changes in a rocket flight that result in a non-vertical trajectory occur in the first few seconds where the axial velocity is low and the influence of the crosswind is greatest. Active roll-pitch or yaw-pitch control can prevent this from occurring during boost, or the correction can be applied during coast after boost. The former is preferred if maximum altitude is desired, but the lower energy solution is during coast.

    The average natural angular pitch and yaw velocities of an aerodynamically stable rocket are very low, a few degrees per second or less, due to the large moment of inertial along the axis of the rocket. The rotational velocity of a rocket however can be several orders of magnitude higher, up to over several thousand degrees per second (rotation of 1 Hz is 360 degrees per second.) To control pitch and yaw you do not need a very high frequency control loop. To control roll you need a faster response however the inertial forces are lower and the torque requirements will be lower so from a controls perspective is may be a wash.

    Note that the axial velocity and acceleration is not a significant player. The effect of velocity is that the power that must be developed by the servos is approximate proportional to the mach number cubed (aerodynamic drag forces) however since the motions are slow, the AOA corrections do not have to be large amplitude so the power requirement is not excessive.

    the point I am making is that control actions are not the issue in a properly designed system. The problem remains determining true vertical. With a 6DOF inertial sensor, you should be able to maintain vertical fight with 5 valid sensor inputs, so if the z-axis accelerometer is overanged, vertical determination is still possible. While the correction may be less accurate during motor burn than during coast, it is still better than no correction, and once the motor burns out, you return to full 6 sensor data and have the maximum accuracy.

    FWIW

    Bob
     
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  24. Jan 20, 2015 #24

    Binder Design

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    Can't wait to see what you come up with, Jim.
     
  25. Jan 20, 2015 #25

    VernK

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    Unless I am missing something it seems to me that the pitch and yaw controls do need to be very fast in order to properly correct pitch or yaw when the rocket is rolling really fast. As a rocket rolls, what the system considered a pitch error will become a yaw error and then back to a pitch error again and so on. Consequently, if control fins are trying to pitch the rocket up then those control fins need to go back to a neutral position as the rocket rolls 90 degrees otherwise they will be yawing it right or left rather than pitching it up. As the rocket rolls another 90 degrees those control fins then need to swing in the opposite direction to pitch it up and so on. I have a mental image of the control fins swinging back and forth as the rocket rolls. The speed they need to move back and forth depends on the roll rate. (I think.)
     
  26. Jan 21, 2015 #26

    Titan II

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    Looking forward to your progress. I am working on a version with parts I had available. The assembly will also be going in a simple 4" rocket. My next version will have individual servos as you have done. My primary goal is to fly at slower speeds. Thanks for posting your thoughts and your build.

    002.jpg

    103.jpg
     
  27. Jan 21, 2015 #27

    JimJarvis50

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    Well, I don't know a lot about spin stabilization, but my belief is that it would be more difficult for me to implement thay than the active stabilization approach I'm trying. I don't know how spin stabilization helps when a rocket weathercocks shortly after leaving the rail. Also, the long-burn motors that lend themselves to survivable flights are moonburners, and I don't think you can spin those. And then there's the despin system. I have also googled spin stabilization several times and have not found much practical information. If anyone can share a reference, I like to read more on the subject.

    Jim
     
  28. Jan 21, 2015 #28

    JimJarvis50

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    Vern, I see it the same way. Hopefully, it would only be necessary to swing back and forth at relatively small angles (say, plus or minus 10 degrees and likely less). I don't think this will be a problem.

    Jim
     
  29. Jan 21, 2015 #29

    JimJarvis50

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    Feel free to post additional pics and descriptions of what you're doing. Looks like 6 canards?

    Jim
     
  30. Jan 21, 2015 #30

    mpitfield

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    Hi Jim,

    I have been following your progeress and any thread related to active vertical stabilization with interest, albeit I am likely at least a year or two away from your stage. Where do you plan on using the active stabilization, booster fins, fins on the upper stage like forward canards, some added forward canards, or in multiple areas. I was wondering what advantages/disadvantages each scenario would have. For instance booster fins obviously means you leave the active stabilization on sep, however I wonder if booster active stabilization would be more responsive over stabilization mid airframe.

    I am sure you have thought of or simply researched these questions and more so any insight you can should would be interesting.
     

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