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Anyone had this problem before?


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#1 Bradley Crosbie

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Posted 05 February 2013 - 08:20 PM

I can balance up my PRO/XCS rig perfectly, as it is stationary, sitting level fore to aft and side to side. When I check my drop-time (3 seconds), the rig does not swing down in a straight line, it wants to swing ovals from side to side. If I spin the rig to check dynamic balance it spins like a top. I have sent my gimbal to Greg Bubb at XCS to be serviced and checked, and he has assured me that there is nothing wrong with the gimbal. Has anyone ever encountered this before with their sled, where the rig balances horizontally with the post vertical, but the balance horizontally goes out as it is dropped from 90 degrees?
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#2 Rich Cottrell

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Posted 05 February 2013 - 09:31 PM

What batteries are you flying? I used to fly the large pro-pacs and one was a re-celled battery. The cells inside that battery were always shifting.

On my model two with the battery hanging off the AB plate I never had a problem. When I went to the XCS with the AB batteries hanging in a more tabled manner that battery always drove my crazy as the slight shifting in the battery threw off the sleds ballance.
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#3 Bradley Crosbie

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Posted 06 February 2013 - 01:49 PM

Thanks Rich, it's a pro, with AB's and I don't feel any shifting.
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#4 Jerry Holway

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Posted 06 February 2013 - 02:38 PM

Bradley-

When you spin balance, do you do it at a slow speed?

At high speeds the spinning forces overwhelm the "static" ones by several orders of magnitude, which may mask issues that become apparent in slow moves, like when you do the drop test.

Did you check the gimbal at 0, 90, and 180 (might as well do 270) degrees and make sure it stays level in all directions? Anything else loose?

Jerry
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#5 Richard James Lewis

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Posted 06 February 2013 - 03:22 PM

I think I know exactly your problem.

I too have had the same issue with my PRO / XCS conversion, and I'm surprised that this hasn't been discussed before. I thought my gimbal was misaligned too. It went back to Greg a few times to be checked.

The issue i found is with the interconnection between the PRO and the XCS post. I feel that there is some mechanical discrepancy with the thread pitch on the ring and also the XCS post end. Try taking off the j box. If you settle it down on the 3 pins that go into the post, you might find that it rocks a little. One of the pins on the j box assembly may be longer or shorter than the others this causes it to rock.

What i had to do was cover the threads with plumbers PTFE tape and then rock the top stage as i was tightening the ring down as you get tighter with the ring the rocking slowly disappears. I'm talking TIGHT.

Since i did this the issue has gone away and i can swing and flip the sled around as much as I like and when I bring it back to static balance everything is still fine. I can work with a neutral drop time and doing 180 or 90 degree static balance tests everything stays absolutely perfect.

It's a shame this is the case, because it kind of rules out the ability to swap out to super posts. I also found that having the gorelock docking ring around the locking ring would with repeated docking start to shift the ring and ultimately lead to the play returning, so that's now back on the post.

I'm not really sure who is at fault here. Maybe if i changed the J box to one with 3 level pins in the connection them my issue would vanish, but because it's not an all PRO sled I can't really go to jack and make a presumption about a defect as I'm mixing manufacturers, although i expect the play has something to do with it.

Try wrapping the threads with plumbers tape and see if it sorts it out.

Good luck!

Rick.
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#6 thomas-english

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Posted 07 February 2013 - 03:15 AM

Thanks to Richard I use PTFE tape in a few places where I don't wan't any play in the threads or I simply don't want the threads coming loose. Its really a great tip.

This issue you have is indicative to me of the base being out of line with the top stage. You can balance it fine but it will fall funny. I think that tallies with what Richard is saying.
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#7 Bradley Crosbie

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Posted 01 March 2013 - 09:54 PM

Thanks for the replies guys. I have the gimbal back from Greg, and built up the rig and it is still doing the same drift.  I checked on my own how the level was facing all different degrees like Jerry suggested.  It goes out of level as soon as I pan.  I decided that somehow the centre alignment of the gimbal must out; but Greg had just checked it with a five second drop time and it was fine.  I never even considered the PRO top stage not lining up with the XCS post.  I will get to work on that next.  Thanks for that Richard, I appreciate it.  Off to the garage to get the plumbers tape.


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#8 Richard James Lewis

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Posted 03 March 2013 - 07:50 AM

It's not a matter of it being out of line, it's about movement caused by all three mating pins possibly not being the same height, mixed with tolerances with the threaded post ring. Make sure to rock the top stage for and aft in relation to the post as you tighten down the ring once the opposing threads are covered with plumbers tape, and the issue should go away.

I will get an engineer to have a look at the issue and find a more permanent solution when i have time.

 

Good luck!

 

R

 

Thanks for the replies guys. I have the gimbal back from Greg, and built up the rig and it is still doing the same drift.  I checked on my own how the level was facing all different degrees like Jerry suggested.  It goes out of level as soon as I pan.  I decided that somehow the centre alignment of the gimbal must out; but Greg had just checked it with a five second drop time and it was fine.  I never even considered the PRO top stage not lining up with the XCS post.  I will get to work on that next.  Thanks for that Richard, I appreciate it.  Off to the garage to get the plumbers tape.


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#9 Richard James Lewis

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Posted 03 March 2013 - 07:53 AM

Ohh and also try doing the pan test but turn the rig really, really slowly as you reposition it. Also if you are using a video camera with a sony plate then thats probably causing some issues too.

The XCS gimbal is so sensitive that it caught me off guard after coming form a V2 MK-V. Lots of little things that didn't matter before now do! 


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