Rocksim question

Discussion in 'Rocketry Electronics and Software' started by downhill_D, Sep 6, 2018.

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  1. Sep 6, 2018 #1

    downhill_D

    downhill_D

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    i have been using my licensed version of rocksim 9. I only have used it in its infancy long ago but do understand MOST of what I build in Rocksim. That said I know I have a lot to learn on the program. So:
    I built my kit in rocksim yesterday to the best of my ability and all flights are stable but anyone know why I cant get the little parachute to show a perfect flight? I know the 2D flight profile simulation is what is important with rocksim for simulation but it would be nice to get “perfect flights” with the little parachute. I have tried getting the ideal delays and most flights are deployed at a relatively low speed but no “perfect flights”. Anyone have any ideas?

    I built the Alien Interceptor from Mach One Rocketry and weighed and measured each kit piece. Picture of simulation page and rocket to follow. I have rail buttons simulated and all angles and lengths widths are correct to my knowledge. I used the mass override on all parts because the g10 and fiberglass estimates were incorrect due to these kits being very light. Total weight 15.1 oz
     
  2. Sep 6, 2018 #2

    downhill_D

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    Rocksim “Alien Interceptor” file I made
     

    Attached Files:

  3. Sep 7, 2018 #3

    Voyager1

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    Define "perfect flight".

    You might need to attach the sim file for folks to analyse. The screen shot doesn't give us enough information about your model and simulation settings.
     
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  4. Sep 7, 2018 #4

    downhill_D

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    I will look at the rocksim program tonight and find the info that will be helpful-makes sense that would not be enough to go on...
     
  5. Sep 7, 2018 #5

    downhill_D

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    attached is the rocksim file I built
     

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  6. Sep 7, 2018 #6

    downhill_D

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    In looking at my center of gravity it will need to come forward a lot. The payload bay is big and I am tempted to weight the nose cone as my electronics would be minimal. (jolly logic stuff/maybe an eggfinder) The rocket is not built yet- I was waiting on a motor mount.
     
  7. Sep 7, 2018 #7

    downhill_D

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    parachute is just green, no up or down arrow-the program calls this a perfect flight...do you own rocksim as well?
     
  8. Sep 7, 2018 #8

    downhill_D

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    my 2d simulations all run great and stable it just the parachute wont go "perfect flight" (ie without up or down arrows) in the simulation summary page (screenshot above)
     
  9. Sep 7, 2018 #9

    Voyager1

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    Yes, I do have RockSim9, but I generally use OpenRocket.
     
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  10. Sep 7, 2018 #10

    Rex R

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    I looked at the file, not sure why the weight/mass doesn't match. w/o stage override the simulation is 35g under your stated mass...obviously one or more of your overrides does not match reality. undid the stage override and added 35g to the center coupler. only quibble with the file aside from the mass is your chute shroud line length(should match chute diameter). the rocket came down a smidge faster than ideal at 25 f/s, might consider a 24" chute and a chute release(depending on landing surface the 18" chute may work just fine).
    Rex
     
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  11. Sep 7, 2018 #11

    downhill_D

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    Oh dang! Thank you Rex! That is more to go on than I had. I will remeasure/weigh all pieces as I rebuild and double check. Thank YOU!
     
  12. Sep 7, 2018 #12

    rcktnut

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    Getting that "picky" about a perfect deployment speed in a sim isn't going to make a difference in an actual launch. Lots more real variables in the real world than in a sim. Motor delays vary a bit, winds at different altitudes, angle at which the rocket leaves the pad, just to name a few. Getting close to ideal is about the best anyone can do with a sim program.

    I see with your sims so far you are using motor deployment. If you are planning on using electronic deployment set it up in your sims. You might get lucky and see some "perfect" flights by doing that, especially if you choose no wind, no turbulence for your sim flights. Again not the real world,don't worry about perfection, using electronic deployment will be as close as you can get to perfection.
     
    Last edited: Sep 7, 2018
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  13. Sep 8, 2018 #13

    OverTheTop

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    I usually don't bother with the deployment and landing features of the simulations, unless I am trying to do some sort of statistical analysis of landing patterns for high-altitude flights that have the potential to exceed the landing radius of the flight cylinder. Otherwise I see little value in the "recovery" phase of simulations. YMMV ;).
     
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  14. Sep 8, 2018 #14

    downhill_D

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    Thank you! I need to take a closer look at CG once it is built-I really like to know which motors will go how high and why, when and for how long etc. I totally dig the variables I can change in rocksim-it is accurate and fun. On the other hand-I am a beginner with rocksim so a lot could be wrong. Rex (and others) took a look at the rocksim file and it seems I should focus on CG but again...this rocket is not even built yet, only weighed and measured. We get some gusty winds out here at times so having a good flight plan is important to me ahead of even the entire build. That said, I need to start building this rocket-I think tomorrow I will begin fin prep and tube prep. I was not planning on too many electronics right away but dual deployment (JLCR) and an egg finder will have my attention down the road when I am ready to punch a mile or possibly higher.
     
  15. Sep 8, 2018 #15

    Rex R

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    bear in mind that, these simulations are at best planning tools, useful for finding areas that might be troublesome. the reality is that your rockets will likely build out heavier than expected and the cg will shift(shift happens). the really important numbers will be the real ones, and tis likely that your recovery gear will move under thrust(aft usually), and paint is heavier than you think. so build it, paint it, then weigh and measure the bird, plan accordingly, this is called life.
    Rex
     
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  16. Sep 8, 2018 #16

    OverTheTop

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    What Rex said. Refer to my sig for a relevant quote as well ;). It was originally in relation to helicopter flight simulation, but seems to be more and more applicable to many of the complex simulations creeping into our reality these days (weather, CFD, rockets, climate change).
     
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  17. Sep 8, 2018 #17

    Buckeye

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    Agreed. Most of the time, I stop my simulation at apogee.

    For big, outta sight flights, I will tune the descent rates and run the simulation out to landing. Now I have an estimate of when the rocket hits the ground, when the GPS coordinates should stop updating, and when I should start looking for it!
     
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