Cluster Alignment

Discussion in 'Low Power Rocketry (LPR)' started by jqavins, Mar 6, 2019.

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  1. Mar 6, 2019 #1

    jqavins

    jqavins

    jqavins

    A True Homebert

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    Let me start off by saying that I really stink at doing things by eye. What other people look at and align or cut or mark or whatever freehand and eyeballed, I will mess up reliably. I need jigs and guides to mistake-proof my my builds. So, that said...

    Has anyone got tried and proven methods of assuring that the motor tubes in a cluster are parallel? Introducing a radial cant is a good way of introducing spin if spin is what you want, but I want tubes dead parallel.

    Please start with methods that you've used or seen used before inevitably going off into brainstorming new ideas.
     
  2. Mar 6, 2019 #2

    Wallace

    Wallace

    Wallace

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    If you have 3 or more motor tubes you can find a larger tube they fit snugly in. That'll keep 'em parallel until the glue dries.
     
  3. Mar 6, 2019 #3

    prfesser

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    Isn't there something about canting outer tubes inward a bit? Preferably having them point closer to CG, so that if there's off-center thrust or if one motor doesn't light, it affects the flight less?

    Best -- Terry
     
  4. Mar 6, 2019 #4

    dr wogz

    dr wogz

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    to me, the obvious.. (From a 3 motor 'D' cluster I built a few years ago..)

    place the 1st MMt tube on the table top. Bonus for pressing against a stop-block to stop it rolling away..
    place the 2nd tube against the 1st, and flat on the table top. glue in place. (These two should be parallel, due to the table / surface they're sitting on..)
    place 3rd on top of the first 2 tubes. glue in place.
    add CRs...
     
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  5. Mar 6, 2019 #5

    jqavins

    jqavins

    jqavins

    A True Homebert

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    I'm thinking about SU Aerotech motors (maybe I should have posted in mid power) so I need space between the tubes to accommodate the thrust rings. Dr. Wogz's and Wallace's methods both work great if the tubes lie against one another. The good doctor's method should be adaptable. I can think up ways to adapt it, or other potential methods, but as I said I'm looking for proven methods first.
     
  6. Mar 6, 2019 #6

    Nytrunner

    Nytrunner

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    Stack and align centering rings, Mark for locations, use drill press through stack.

    If still concerned, make a square keying notch with with a rib that runs down the whole stack (squares don't twist as easily as round tubes)
     
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  7. Mar 6, 2019 #7

    heada

    heada

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    Mark a line on one of the MMTs using the Estes doorjam method. Also, stack the CRs and mark them along an edge. Install the MMT into the CRs with all the marks lining up. Now that you have the CRs 90 degrees to the MMT, you can install the other MMTs and they'll be parallel to the first MMT. Bonus points if you drill the center of the CRs and install threaded rod to act as your positive motor retention.
     
  8. Mar 6, 2019 #8

    jqavins

    jqavins

    jqavins

    A True Homebert

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    I'm missing something here. So I have a straight line up the side of a motor tube. I have a tick mark on the edge of a CR. What causes the marks to wind up aligned, given there are no calibrated eyeballs involved?

    So, suppose I mark the insides edge of a hole in the CR, then transfer that mark around the corner to the face. That's a mark I can align to the line of the MMT tube. What assures that the tube at this point is normal to the CR and not tilted a few degrees? (I know it can tilt at this point, because I've done it when spin was what I wanted.)
     
  9. Mar 6, 2019 #9

    heada

    heada

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    Yes, extend the mark on the CRs to the MMT hole on the CRs. Then all 3 lines should match up. If you've twisted/tilted the MMT in relation to the CRs, the MMT wont stand flat on a surface. Rotate the CRs/MMT until all the marks line up and the MMT stands flat on a table. It's hard to describe without showing in person.
     
  10. Mar 6, 2019 #10

    jqavins

    jqavins

    jqavins

    A True Homebert

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    I think I've got it now; the stand flat part was critical and missing.

    Mark lines straight up the sides of all the motor tubes. Also, mark circles around the circumference of each tube a measured distance from one end.

    Stack the CRs and mark a line straight up the inside edges of each of the through holes. Separate the CRs, and transfer the marks to the surfaces adjacent to the holes.

    Insert the tubes in the CRs, with the lines on the tubes matched to the matched to the marks on the CR faces, and the circumferential lines on the tubes aligned to one surface of one ring, assuring equal protrusion from that ring.

    Stand the assembly on a table. Holding the lower CR, rotate the upper CR until the tubes all stand squarely on the table, as judged by leaving no gaps.

    Sounds good.
     

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