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roban 500 size cobra help

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  • #1

    roban 500 size cobra help

    A fellow club member has the roban 500 cobra which im trying to help him set up.
    It has t rex 500 machanics and has a mini v bar.
    The problem were having is it wobbles badly from side to side and when the wind hits it then it becomes even worse.
    I have tried increasing and decreasing headspeeds ,main rotor gain and tail gain,with no change.
    Re mounted the v bar as it was not very solid on mount but no change.
    Thought maybe a bent shaft but that is all new.
    Has any one else had one with these and had these issues.
    Don't know if this vid will help you to see whats happening.

    https://www.youtube.com/watch?v=yECa1OVLb38

    Any ideas please guys

    Ian
    Last edited by chopper1; 04-05-2015, 01:20 AM.
    Tags: None
  • #2
    Dfc head yes?

    Comment

    • #3
      Yes he does have the dfc head on it Chris,
      What are you thinking mate .Possible wrong head settings in v bar?

      Comment

      • #4
        No wrong head,my guess is low headspeed,hard damping,rigid links,mass of Fuselage could all contribute to this.

        IMHO thats 100% a mechanical damping issue nothing adjusting V Bar will cure.If it was mine i would be converting the head to standard design,i think its hit and miss if you get this problem or not on any specific heli but thats exactly how my DFC heads react when i run my HS too low.

        Quotes from scale forums.

        doorman
        rrProfessor
        Sherwood, Arkansas
        My Posts: All Forum Topic
        Agreed
        I think that the lower HS is going to cause the infamous "wobble"
        If you don't mind the much higher HS, you might be OK, but then you might find some very UNWANTED harmonics building up and trying to shake your heli apart...
        As Grim said... proceed with caution....
        Good Luck, Stan
        AMA 2918-Team JR, Spin Blades, East Coast Scale Helicopter,Castle Creations,

        Its been my experience that stiff dampening and scale heils are tricky to tune. The resonant caused by ridged rotor head can cause “odd issues” with a fuse hanging below the head.
        I have woof and proofed TWO heils due to the head being to ridged, and flying with a higher head speed.
        I don’t think anybody’s saying you cannot do this.. just proceed with caution. I can however say.. I will not fly a DFC head on my scales. The minor (looks?) are not worth the flight risk.. to me..
        Keep us posted.
        Grim
        Michael J Zaborowski
        04-24-2014 Over year old.
        Last edited by ChrisB; 04-05-2015, 12:23 PM.

        Comment

        • #5
          Actually that makes a lot of sense to be honest Chris and now you have said it I can remember yours doing just that.Cheers buddy .Hey its funny how a fellow mate and club member comes up with a possible answer when I've put it out to a wider audience .Top man ,I will let him know and see if we can try another head .
          Thanks
          Ian

          Comment

          • #6
            No worries Ian ,i was not aware Nev was having the issue as you described above.

            Will have a look at it with you when at the field ,how high have you tried running the HS up to?

            Nev's 500 was OK as Pod n Boom wasn't it? Has he run a like for like HS?

            But as some say on scale forums ,the extra Mass of the Fuse can induce harmonics that maybe punishes you with hard damping,i expect its one of those things that will effect some but not others.

            Comment

            • #7
              Originally posted by chopper1 View Post
              Actually that makes a lot of sense to be honest Chris and now you have said it I can remember yours doing just that.Cheers buddy .Hey its funny how a fellow mate and club member comes up with a possible answer when I've put it out to a wider audience .Top man ,I will let him know and see if we can try another head .
              Thanks
              Ian
              Nice to see the question asked non the less Ian. Now others can benifit from the replies.
              Ron

              hobby-hangar.co.uk
              SWRCH-GO big or Go home!
              http://www.ultimatebuildandfly.co.uk/

              Comment

              • #8
                It certainly is Ron.If it helps others too then that's great .I will of course post up our results .There's always something to learn in this hobby and that's part of the fun and also where I believe these forums help so many people and come into there own .
                Fingers are firmly crossed that I can now help my fellow club member resolve this problem and start enjoying it..
                .
                Must add also that its a great looking model .

                Cheers,
                Ian

                Comment

                • #9
                  Well one week later and all sorted.
                  We changed the head over to a dominator 500l with phasing arms ,ie not the dfc one .
                  All the troubles went away.Brilliant .
                  Thanks for your advise Chris B. Top Man
                  Hers a short vid of it.
                  https://www.youtube.com/watch?v=x1ZscJ9qU0o

                  Thank you

                  Ian

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                  • #10
                    It was great to see Nev enjoying it for sure

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