5D MK III : Anyone successfully balanced it in the tilt axis?

Discussion in '3 Axis Gimbal' started by Andy Johnson-Laird, Sep 19, 2012.

  1. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
    Staff Member

    Joined:
    Jul 31, 2012
    Messages:
    10,351
    Likes Received:
    1,160
    I've been experimenting for an hour or more trying to balance the 5DM3 with 24-105 lens in the tilt axis. I've locked the roll axis horizontally using a lab clamp so that it's not a factor in my experiments.

    My mental model is that the potentiometer on the left hand side as you look at the gimbal from the front forms a "tilt axis" with the shaft/pulley on the right hand side.

    As far as I can tell, the CoG of the camera + lens is above the tilt axis line when the camera/lens is horizontal. Thus, while I can get the camera to balance horizontally (with its CoG right above the tilt axis), the moment I tilt the camera/lens slightly forward the CoG rotates around the tilt axis and comes forward of the tilt axis and the camera/lens nose dives. Similarly, if I tilt the camera/lens back, the CoG now rotates above and behind the tilt axis and the camera/lens tail dives.

    Unless I can get the CoG of camera/lens to be co-located right on the tilt axis, it doesn't appear that is any way I can achieve a stable balance in tilt at all camera/lens tilt angles -- the physics doesn't seem to work.

    To bring the camera/lens CoG onto the tilt axis, I think I need to lower the camera plate by lengthening the tilt arms (which clamp to the front transverse boom).

    I did try displacing the tilt arms away from the vertical towards me (looking at the gimbal from the front) and re-level the camera plate, but that *raises* the camera/lens CofG even higher above the tilt axis and brings it forward of the tilt axis (and can, of course move the camera on the plate, but while the CoG is above the tilt axis, it's not going to help). Similarly, displacing the tilt arms backwards, *raises* the camera/lens CoG even further above the tilt axis and moves it away from me.

    I've got a 24mm prime inbound, and when that arrives I'll try with that, but I'm concerned that that's not likely to lower the CoG of the camera/lens combo towards the camera plate and thus onto the tilt axis line. I suspect it's just likely to shift the CoG fore and aft.

    Am I missing something? Anyone successfully done this with the 5D Mark III?

    Thanks
    Andy.
     
  2. Howard Dapp

    Howard Dapp Active Member

    Joined:
    Aug 18, 2012
    Messages:
    977
    Likes Received:
    111
    Kenny Chen likes this.
  3. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
    Staff Member

    Joined:
    Jul 31, 2012
    Messages:
    10,351
    Likes Received:
    1,160
    Thanks, Howard. I was wondering about that, but quite a few folks seem to have balanced the 5D Mk II so I thought I'd as first. I'll call QC now and order up a set, because, as you say, that seems to be the way to lower the camera/lens CoG.

    Andy.
     
  4. Tabb Firchau

    Tabb Firchau Administrator
    Staff Member

    Joined:
    Jun 28, 2012
    Messages:
    910
    Likes Received:
    472
    Hi guys, the Epic tilt bar is made for the EPIC to be top mounted. If you try and run it the other way it will hit the back of the gimbal unless you stretch the side arms.

    We have adjustable tilt bars on the way for you! I will update when they come in.

    Thanks
     
  5. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
    Staff Member

    Joined:
    Jul 31, 2012
    Messages:
    10,351
    Likes Received:
    1,160
    Uhoh....sounds like I should NOT have ordered them..... :(

    Andy.
     
  6. Tabb Firchau

    Tabb Firchau Administrator
    Staff Member

    Joined:
    Jun 28, 2012
    Messages:
    910
    Likes Received:
    472
    Andy, you can make them work...might just have to extend the side arms of the gimbal a bit. They both arrive at the same destination just a little different route.
     
  7. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
    Staff Member

    Joined:
    Jul 31, 2012
    Messages:
    10,351
    Likes Received:
    1,160
    Aha. OK. I'll search the quadrocopter.com site for something a little longer than the existing 200mm side arm booms.

    Thanks
    Andy.
     
  8. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
    Staff Member

    Joined:
    Jul 31, 2012
    Messages:
    10,351
    Likes Received:
    1,160
    OK, I've now unconfused myself. QC has the 200 mm booms -- the standard gimbal side arm booms are 120 mm -- so the 200's are perfect for the application at hand. Thanks for your help Tabb.

    Andy.
     
  9. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
    Staff Member

    Joined:
    Jul 31, 2012
    Messages:
    10,351
    Likes Received:
    1,160
    Just to update this thread. Thanks to USPS Express Mail and the superb support of Karsten and Sarah at QC (shout out to both of them!) , I got the Epic Tilt Bars and the 200mm carbon fiber tubes and installed them this evening.

    The bad news: the Epic tilt bars allow you to lower the camera plate below the tilt axis in increments of 8mm at a time. So for the 5DM3 you can use the second set of holes down (the first ones match the standard tilt bars). But now the camera/lens CoG is below the tilt axis so, as you would expect, the camera acts like a pendulum and wants to revert to horizontal. Balancing it to remain in any position is not possible "as is." But wait, there's more -- the good news is that now you can use Joe's approach of using washers as shims to elevate the camera plate up to intersect with the tilt axis exactly, so all is not lost!

    I'll hit up Ace tomorrow to see what they have in terms of small, thin, washers -- hopefully I can use those to shim it exactly. Who knows they might even have M3 fully threaded rod so I can make up a fully adjustable method of raising/lowering the camera platform using M3 nuts above and below the boom clamps. Then, onwards to the roll axis!

    Thanks
    Andy.
     
  10. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
    Staff Member

    Joined:
    Jul 31, 2012
    Messages:
    10,351
    Likes Received:
    1,160
    OK, here's the trick for the 5DM3 with the 24mm prime lens. See the image. You need to change the side booms for 200mm ones from QC. You also need to order up the Epic tilt bars as Howard suggested.

    Then you need some M3 x 40mm screws (which I got from http://www.fastener-express.com/m3-x-5-x-40mm-socket-head-cap-screw-stainless-steel-qty-20.aspx ) and some M3 washers which I found at Ace Hardware, part 06840, 3mm metric flat washers, zinc.

    The image tells the rest of the story -- basically you need to use the washers to do to things:
    1. Shim the head of the screw to prevent surplus thread sticking through the threaded insert and damaging the camera's underside.
    2. Shim the camera plate to raise it up to the point where the camera/lens CoG is on the tilt axis.

    In my case I used three washers at the screw head (plus the one that was already there) and seven to shim the camera plate.
    As we say on the internet: YMMV. Your mileage may vary -- or in this case, YWMV -- your washers may vary.

    To figure this out I did a first order approximation with 1/4" washers on the 1/4-20 camera screw to raise it up more or less to the point where the camera/lens CoG was on the tilt axis. It was easier to do this than futz with the four screws on the boom and the camera plate. I then calipered the total thickness of the 1/4" washers and replicated that thickness with M3 washers.

    I used vinyl electrical tape -- just a small piece of it to wrap around each "cylinder of washers." I only arrived at this after spending a few minutes in the loop of: 1) stack washers, 2) put them on screw, 3) drop one/several/all, 4) utter obscenities, 5) repeat from 1.

    This *only* statically balances the camera in tilt. Onward to roll!

    Hope this helps someone else with a 5DM3 -- although the principle's the same for any camera. You might also get lucky and find that you can replace the stacks of seven washers with a metal standoff.

    Oh...and if you're tempted to buy a box of 100 at Ace, be sure to count them out -- I've learned that lesson and this time my box of "100" had only 61 in it. ;)

    Andy. 5DM3 statically balanced on 3-Axis Gimbal.png
     
    Kenny Chen and Morgan Friedland like this.
  11. John Gore

    John Gore Member

    Joined:
    Jul 24, 2012
    Messages:
    93
    Likes Received:
    15
    Hi Andy. I was just wondering how much of a difference this made to your footage (having the vertical CG on tilt perfect). Did it also improve roll ?

    On my setup (7D on 2-axis CS gimbal) the 7D is also a little top heavy on the tilt axis, but setup correctly for roll (which allows more adjustment). My tilt is pretty much perfect, right out the box, using 100% gains (so at this point I am not too worried about the tilt axis being top heavy, as it does not seem to affect performance). tks
     
  12. Katya Nelhams-Wright

    Joined:
    Jul 8, 2012
    Messages:
    216
    Likes Received:
    9
    My question is you get it all balanced in the gimbal with the tilt and roll and then how on earth do you then get the pan balanced perfectly through the full 360 once you start adding batteries and video rc to the legs because it then throws everything out. Do you then re-balance the gimbal and camera, don't know where to begin on that one!
    Kat
     
  13. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
    Staff Member

    Joined:
    Jul 31, 2012
    Messages:
    10,351
    Likes Received:
    1,160
    John: On the RTF frameset I was using, I had some lateral vibration so I've not yet had a chance to fly a payload camera and see whether that improves things. I'll let you know. What I really was looking to have was longer gimbal battery life -- and that I am seeing -- the servos don't have to work as hard because they're not having to provide counterbalance force -- just motion force.

    Katya: To balance the gimbal in pan, I just stand the Cinestar on end (so the plane of the booms is vertical), and then slide the gimbal's down-post along the the short boom to balance the boom in pan.

    For example, put a towel or something soft on a desk/table. Lift the C8 so the booms are vertical. Note which way the gimbal rotates. If it's camera heavy, slide the down post out away from the pan pulley until you find a balance point. If it's "rear of gimbal" heavy, slide the down post along the boom towards the pan pulley. I've only done this for a 5D Mk III and a Sony CX760 (the USA version of the 730). I'll be interested to know if you can do it for the C300 -- there's not that available motion for the down post along the boom and that might be a limiting factor.

    It works better if you have a helper to hold the Cinestar on end, or you'll end up just barely loosening the down-post on the gimbal and "walking" it along the boom to find the balance point. It obviously wants to rotate around the long axis of the boom and you really need both hands. It's easier to balance it with the camera on your left so you have the 2.5mm bolt heads facing up.

    So the short answer is: don't move anything other than the down-post to bring the gimbal pan into balance.

    Hope that helps.
    Andy.
     
  14. Katya Nelhams-Wright

    Joined:
    Jul 8, 2012
    Messages:
    216
    Likes Received:
    9
    I have done that but now that I have added 2 batteries to the legs and the mondo stinger it's no longer balanced!:)
     
  15. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
    Staff Member

    Joined:
    Jul 31, 2012
    Messages:
    10,351
    Likes Received:
    1,160
    Ah yes....that is the problem. There comes a point where the combined gimbal/camera centre [sic] of gravity is just too far offset that moving the down-post just will not bring it back to the centre [sic] of rotation.

    The physics of the problem suggest either (a) getting a longer rear boom for the gimbal (assuming that you're camera heavy and need to move the rear of the gimbal further away from the pan pulley) or (b) redistributing the mass on the gimbal (if you're rear-of-gimbal heavy and already have the down-post as close to the pan pulley as it will go).

    Andy.
     
  16. Katya Nelhams-Wright

    Joined:
    Jul 8, 2012
    Messages:
    216
    Likes Received:
    9
    Having spent hours making sure my gimbal is centred perfectly I don't think I can cope right now with doing it all again!:)
     
  17. Pavlos Antoniou

    Joined:
    Oct 6, 2012
    Messages:
    321
    Likes Received:
    18
    Andy when you say down post what do you mean?? thank you!
     
  18. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
    Staff Member

    Joined:
    Jul 31, 2012
    Messages:
    10,351
    Likes Received:
    1,160
    The "down post" is the name I gave to the vertical boom at the rear of the gimbal on which the roll mechanism is mounted. The term "post" tends to mean anything that is vertical.

    Sorry if I caused confusion, but there is no published list of the various parts of the gimbal so I'm making them up as required. Tabb may have different names for them...

    Andy.
     
  19. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
    Staff Member

    Joined:
    Jul 31, 2012
    Messages:
    10,351
    Likes Received:
    1,160
    I can empathize with you on that. This is where that Hitachi electric screwdriver with the 2.5mm bit makes life a lot easier.

    But there's no getting away from the process of "fettling" the gimbaling (also known as "tweaking," "adjusting," or "working on the gimbal when you could be drinking wine or beer...." :rolleyes: )

    Andy.
     
  20. Philip Ellerbroek

    Joined:
    Oct 8, 2012
    Messages:
    139
    Likes Received:
    7
    Katya,

    I feel your pain. I got my Mark 3 a few weeks ago and recognized that I had to move some weight around so that things were more balanced. What I did was move my lipo that powers my radians to one of the front legs from the rear leg of the axis. Then, I place my Mondo Extreme downlink on the remaining leg. It helped a little to move that weight from the rear leg. The pain involved having to rewire and solder everything.

    Andy - Did you ever try sliding the camerd forward or backward on the sear plate? I noticed this dramatically affects the overall positioning and balancing of the Mark 3 in regards to roll/tilt. I did notice that i had to position in parallel tilt bars to an aggressive upward position. When done, the top of the Mark 3 (where the external flash tower mounts) had approximately 1" of clearance from the piece of the 3 axis gibmal where the booms come together and meet (boom "hub")

    Phil
     

Share This Page