Surfing the limits... flying with an EPIC

Discussion in '3 Axis Gimbal' started by Jonas Rejman, Oct 20, 2012.

  1. Jonas Rejman

    Jonas Rejman New Member

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    Hello,

    we have a C8, 3axis radian setup and we fly almost exclusively with the epic camera. Lift off weight is around 8.5kg.


    I find that we are hitting the limits of the current design of the gimbal, dampeners and radians and I would like to ask for some advise on the following issues.

    These issues may not be observed by users with lighter cameras.

    1. SCREWS

    Due to the weight of the camera, we have to tighten the screws of the gimball very tight. The heads of the screws get very often worn out in this process, as do the hexagonal mounts they go in. Every time before a job, we replace 4-5 screws.

    Would it be possible to know the pitch and the size of the screws used on the cinestar and the gimbal, so that I can go and find replacement screws, but with a torx or a torx plus head, and made of a harder alloy?
    The torx design transfers the torque of the tool much better into the screw, as has been proven on various cinema cameras and tools like steadicam.


    2. ROLL AXIS

    The mount point in the roll axis is getting a lot of stress, when the camera is mounted, and while it not impossible to get perfect balance, the balance shifts after a couple of flights. This then confuses the radians, and a timely re-calibration is necessary.

    Would there be a possible upgrade, to streghten this point in the design?


    3. HORSESHOE ARMS

    The fact that both "arms" that go to the nick axis can be twisted against each other has a quite disastrous effect on the overall balance, if it shifts through time, if there would be a way to link the "horseshoe" that holds the camera, that would be am improvement.


    4. RIGHT SIDE OF TILT AXIS - SOLVED

    Could I order some more components to make the right part of the nick axis as rigid as the left one (with the servo).
    It is held just by the potentimeter in place, and I think the one V-shaped 1 carbon fibre component from the left side, and an axis of the same length would improve the rigidity of the mounting of the camera.

    The solution is here.


    5. DAMPENERS

    The dampeners in their current design do not work with an epic-size camera and the radians. I understand how the two concept are fighting each other: passive vibration reduction dampening and active movement compensation of the radians.

    In order to use the epic and the radian, we pulled the rubbers so that both plates of the dampener touch each other.
    We put a strip of gaffer tape as dampener in between, and another large rubber piece on top of the top plate of the dampener, so that the rubbers hold the entire system together. We then put another rubber piece in each whole between the carbon part and the inner metal part, stiffening the yaw movement of the dampener.

    This allowed the use of the yaw slew with the epic, without oscillations.

    We fly however on very low gain settings (30%). With a 5D we got up to around 120%.

    The main problem is, that with time, the carefully calibrated balance shifts, and the radians get confused and this results in jittery movements in the footage, as the system is trying to keep up with the vibrations.

    I think it would be advisable to consider a re-design of the dampeners for users of the radian,
    particularly those who are using an epic. I have seen in other threads that the dampeners have to be a bit modified, once the gimbal is upgraded to radian.


    6. BELTS AND PULLEYS

    To be able to raise the gain to 30% we need to have the belts very stiff. This causes strain on the pulley wheels of the servos, causig them to twist, as the belt tension is very high.

    Is there a possiblity to have metal pulley wheels, that are stiffer mounted to the servos?

    We have only the yaw servo from freely, it seems we got an older batch of the gimbal - the nick and the roll servos are savox.
    Would it help to have all 3 freefly servos on the gimbal, or go an alternative route?
    There are servos with 30KG torque from savox...


    7. GIMBAL ATTACHEMENT

    It is a bit scary having an EPIC camera mounted on only 8 screws (gimbal mount to dampeners), that are the smallest one's one can find on the c8 system.

    The same screw size is then used when attaching the dampeners to the frame.

    I would prefer a "bigger" screw set on both occasions, which might be an opportunity to look at when considering the dampener re-design for radian and epic use.



    8. FUTURE
    I think the design of the frame is genious. We are putting a lot of strain on it, and it did not fail on us.
    The radian stabilisers are an almost miraculous experience, the precision of the angle-detecion is amazing.

    The gimbal itself, however is not stiff enough for an epic. Sure, we are trying to make it work, the best we can, but in the very, very end, I think we are asking too much from it.

    I hope that tabb will consider a new "cinema" mount like the hero3000 for his next gimbal design, and we would hereby like to apply as betatesters. Hopefully the pricepoint will be a bit less than the 25K pounds, photohigher is asking.

    Having experiences the radians, I also surely hope that tab will consider his own flight controller.
    :-D




    Thanks for reading.

    Jonas

     
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  2. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    H Jonas:
    It sounds almost silly, but the only question I can respond to is:
    Would it be possible to know the pitch and the size of the screws used on the cinestar and the gimbal, so that I can go and find replacement screws, but with a torx or a torx plus head, and made of a harder alloy?​

    They are M3 x 0.5 x 6mm BHCS (Button Head Cap Screws). These are the screws that attach the gimbal's star plate to the vibration isolators' thread aluminum hex stand-offs.

    One concern with moving away from BHCS is that when the C8 is on the ground there is not much clearance between the underside of the those BHCS and the pan servo small pulley, so you may find that you have a different problem if you have screws with large heads.

    As to the rest of your posting (which I read with great interest), could you possibly upload an image of your vibration isolators. I think there is more than one forum member who would be interested to see what you have created.

    The remainder of your comments are, I suspect, more properly addressed by Tabb.

    In anticipation of Tabb's comments: Can you clarify that the "horseshoe arms" are the two side booms running fore and aft. One of them holds the nick potentiometer and the other has the nick servo and pulleys on it? I've not heard them called "horseshoe arms" before -- so I've resorted to calling them "the side booms."

    Thanks
    Andy.
     
  3. Rick Marcus

    Rick Marcus New Member

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    Hi Jonas,
    Are you running Mikrocopter, or some other Flight Controller and Power Distribution. I am also curious as to the motors that you are using. I am trying to get a Red in the air and am having major overheating issues with the MK PDB.

    Thanks,
    Rick
     
  4. Jonas Rejman

    Jonas Rejman New Member

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    Hello,

    @Andy
    Thanks for the reply. I looked at different screws, and the variety is overwhelming. The pan servo is making us headaches with the current screws anyway. It seem to be impossible to get proper clearance.

    I found these titanium screws, but they are unfortunatelly too long, and smallest size is M3.
    http://www.pro-bolt.com/titanium.html?thread_pitch=319

    Another screw set with torx would be these, but there is no description of the pitch. Is "machine" screw the correct pitch?
    http://www.shop4fasteners.co.uk/acatalog/Torx_Pan_Head_Machine_Screws_DIN_7985_Stainless_A2.asp
    The screw number: TMSPH-A2-M36

    Could you also tell me the sizes of the other screws that are used in the gimbal?
    There are certain areas that get so much tension, like the center of the "back boom" (the horizontal boom), that I would like to replace the current screws with titanium screws.


    "Horseshoe arms" are "sidebooms". :-D


    I will post a picture of the modified vibration isolators, but it is a hack, not a solution.
    I have looked at these, but I think they would be too soft for the radians, resulting in oscillation movements.

    We made custom-cut side booms, that are a bit longer, so that the epic can tilt in the full area. This mod of course puts even more strain on the back boom attachment to the vertical boom.

    One extremely important addition seem to be a cabletie that runs inside the vertical boom, over its attachement to the "upper boom" (one of the 3 that go from the center plate", and then on the outside down along all the mountings. This is to be seen as a safety, because there is no other precaution that would prevent the vertical boom to slip out of its top mounting. It almost did happen to us with a c300, the screws were tight, but just not "tight enough"...

    To balance an epic around the yaw axis, it also seems necessary to pull the "vertical boom" as far on the outside towards the leg as possible. Even then, I can feel, that the CG is not exactly around the yaw axis. I think we will try to enhance this boom as well, by around 1cm.



    @Rick
    The MK esc's are very robust, and the compactness of the system is convenient, as well as the log feature and the telementry downlink. MK in 4S power and an epic is really pushing the limits. A separate power circuit from the FC and navigation seems the better solution.

    We are currently switching to KW10 motors, their custom 80A esc. A engineer friend is designing a custom 500A power distribution board for us, that would fit the C8 mounting points. The whole system will be both crimped and soldered to aeronautic standards, there will be no disconnectable points apart from anderson power poles on the batteries.
    The whole system will run at 6S, powered by 2x 5000mAh 45C/90C burst batteries and DJI wookong FC (once their recall of the GPS unit is over). The goal is to hover with an epic at 1/4 of trust, without any component getting hot.

    We tried APC and wooden propellers and ended up with carbon fibre ones. They give around 0.3kg more trust than the APC.

    Stay away from Deans connectors. They have only little solder on them, and they melt. We used EC5, but even there, after one landing, the solder in the connector became liquid.
     
  5. Howard Dapp

    Howard Dapp Active Member

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    Jonas, Tabb will certainly be chiming in soon. One question, what was your conclusion regarding wooden props? (Xoars)

    Tabb has confirmed, though not in so many words, that he is working on/testing a more robust gimbal for C300/Epic sized cameras.

    I hope that statement doesn't bite me in the ass later.
     
  6. Jonas Rejman

    Jonas Rejman New Member

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    I sure do as well. The current gimbal is simply not "hardcore" enough to get out of the way, so that one can just trust it and focus on the filming. I certainly would love to get on the betatester list for the new design. I trust the rumours to be true.

    We found the wooden props enhanced the stability and agility. The reactions of the C8 were "faster" as the wooden props do not bend, in contrary to the APC props. Changing to the carbon fibre props was another big step. The control is even more direct, it feels like a "better' machine - less "in between" the operator and the flight.

    The power spikes rise as well though, because the pitch of the carbon fibre one's is very aggressive, demanding torque from the motors. They are worth their money in my opinion.
     
  7. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    It might be worth contacting the company anyway -- they might be able to order in what you need.

    I'm afraid there is no way of knowing what pitch those are. "Machine screw" really doesn't say anything about the pitch. I suspect you will have to call or email. Please post a message on this forum when you find out.

    I'm pretty sure they're all M3, 0.5, and they vary in length. I'm afraid I don't have a list, but you can get this information by looking through the Cinestar build manual at the different sizes -- there are not that many variations.
    Also, there appears to be a list on the Cinestar 8 kit page.

    That makes sense. With the Epic's weight that has to put additional stress on quite a few places.

    Good to know!

    I'm not sure it's the softness of the vibration isolators that cause the oscillation so much as the sensor gain.

    How long did you make the side booms out of curiosity. Quadrocopter sells 200 mm booms.

    Ouch! I don't even want to think what that would look like from the ground. As you say, cable ties are the way to go there.

    Yes, I could see how that would be necessary. You might need to start with a Cinestar 8 full-size boom and cut it down to size. (That's odd, I cannot find the link to the replacement booms on quadrocopter.com -- you'd think that searching for "boom" would find it, but it does not.)

    Wow! You melted a EC5 solder joint. There should be a prize for that! :)

    Hope the above helps.
    Andy.
     
  8. Emanuele Chiocchio

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    Jonas, it seems that we're looking for the exact CS8 upgrade. We too have a CS8/360 w/ a full Radian and are interested in a top-of-the-line heavy duty configuration.
    It would be interesting to know what CF props did you chose and if the power distribution board could be available for purchase...
    As for batteries, we're currently using QC 5s 6200 and we're very happy with them: this week we espect a delivery of 5 of them because we want to try to fly w/ 4 of them simultaneously.
    Currently we're running onto MaxAmps 11.000 4s: we use two of them in parallel and we can fly w/ a GH2 (or similar camera) for 10 to 11 minutes. We've already replaced the standard Deans w/ EC5s but we could employ the Andersons as per your suggestion.

    One for Tabb here. Your 3-axis gimbal and Radian are just perfect for us: what we really appreciated is the fact that adding the Radian to our current set-up upgraded our copter without the need to change the whole gimbal. Thank-you!!! If you'll sell a bigger gimbal, we hope it will be possible to use our current Radians on it.
     
  9. Thijm

    Thijm Member

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    Hi Jonas,

    Also had similar experience with the cs mount. Using it with Epic/Scarlet from march '12
    Last week finally had some time to upgrade...No Red test yet, but i have a good feeling it will be allot better.

    Alu plate behind clamps centerboom
    Extra 4mm screw 360pan > copterplate
    Added xtra support epic tiltbar
    Xtra clamps sideboom
    Replaced all Carbon booms with 25(od) 22(id)
    Replaced pot with http://www.1001copters.com/fr/nacelle-gyro-stabilisee/88-pieces-cinestar-pour-skyline.html (not the same quality as CS, but it works for now

    TFCM

    Edit; I know some carbon replacement parts could be made/cut cleaner (used carbon from leftover cs bottomplate), but they are still wider than the original. If the parts would be available in the shop, i would order them asap.
     

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  10. Thijm

    Thijm Member

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    New mods work great. tested with a Epic today.Only the tilt bar has a little flex
     

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  11. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    What does the gimbal + Epic weight, now, TFCM?
    I'll be curious to hear what flight times/battery combos you fly with, too.

    Andy.
     
  12. Jonas Rejman

    Jonas Rejman New Member

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    We are using the aerobot 13x6.5 carbon fibre props v2.

    We had a look at the PowerHungry distribution board. I am sort of against anything that can be disconnected on the copter. We have a design in mind, where cables are routed back through holes in the board and then crimped tight together. The whole assebly is then soldered. This is used in real helicopters. In case of a high-current event, even when the solder becomes liquid, the connection still holds,
    and gives a bit more time for emergency procedures. It will take some time to make it, at least a month, but if there is interest, we can work something out.

    I got in touch with an ex-ducati race driver, who is now a titanium metallurgist - making racing bolts and screws for the racers. He can manufacture any type of screw. We will start with replacing the bolts that hold the gimbal to the frame, hopefully be able to make them M4 and with a wider head and torx. If there is any interest, we can make more of those screws. Being handmade and of titanium, they have their price.

    TFCM, thank you for sharing the images! Great additions. I will try to understand your mods more and to source these parts for us as well. I surely would welcome, if Tabb could these parts as an intermediate solution for those who wait for the new gimbal. I am sure there are more people looking for a more sturdier gimbal.

    I am away from the copter, but will post images of the vibration isolators within 2 weeks.
     
  13. Thijm

    Thijm Member

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    Total is 5.4 kg (incl. Lens, ssd, 2x 2s 3300mAh lipo)
    FT = 7min.
     
  14. Thijm

    Thijm Member

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    @Jonas
    I have always used a herkules 2 board with 2x 6s 5800mAh and ec5 connectors and never experienced hot or melting connectors! It's all motor prop combination!
    Just got the New Herkules III board :) and motors > digitech X-140 (kw10) underway. will post the results.
    If a screw fails you also have to replace the press-nut, its the weaker part here.

    Nice! keep us posted!
     
  15. Thijm

    Thijm Member

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    Btw; the most effective and easy mod is the 1mm Alu backplate at the "horseshoe" center fix.
     

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  16. Jon Fredericks

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    Interesting - I would have thought the gross weight to be more.....what is the actual camera weight?
     
  17. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Could I also confirm a couple of things:

    You said 2 x 2s 3300mAh? Did you mean 2 x 4s? 2s would only give you 7.24v nominal.

    Also, the backplate -- do you mount that on the front face of the down post where the roll pivot point is? I just cannot quite see it in either of the the images you posted in message #10 but I could be looking in the wrong place?

    Thanks
    Andy.
     
  18. Thijm

    Thijm Member

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    2kg Mount incl lipo
    3kg Epic-m
    2,8kg Epic-x
    2.5kg Scarlet

    btw without lens
     
  19. Jon Fredericks

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    TFCM - When you say "2kg Mount incl lipo", is that your gimbal + lipos? Where does the copter weight come into play?
    For example, our CS8 copter basic empty weight = 3.9kg and (2) 5400 lipos = 0.9kg. If we add an Epic X to that, our all-up weight is 7.6kg.
     
  20. Thijm

    Thijm Member

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    To power the mount and the Epic i'm using 2x 7,4v lipo (7.4v to radian with ubec, 14.8v to cam) post a better pic tomorrow
     

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