Prevent lever from flexing

  1. Hi, i was unable to find this answer anywhere else on the internet...so i decided this would be the best


    i have a what essentially can be explained as a lever and i'm trying to prevent it from flexing/bouncing when the car is in motion (i'm only going ~5mph, probably less)

    the lever is a 10 ft steel conduit. 1" in diameter.
    the "fulcrum" if you can call them that are essentially 3 ft apart, on one end of the conduit
    and a load(Canon 40D) hanging from the other end of the conduit, less than 6 inches from the end

    thank you in advanced
     

    Attached Files:

  2. jcsd
  3. Chronos

    Chronos 9,931
    Science Advisor
    Gold Member

    All levers must flex, it's a rule of physics.
     
  4. Simon Bridge

    Simon Bridge 14,797
    Science Advisor
    Homework Helper
    Gold Member

    Welcome to PF;
    Camera mounts on cars have to be much more sophisticated to get a steady pic.
    To avoid excessive flexing, you need to use a stiffer beam - it is that simple.
    You could stiffen the beam by adding bracing of some kind.

    You will still get vibrations from the car though.
     
  5. maybe prevent was the wrong word. i would like to minimize the flex as much as possible without it being bulky/heavy. i tried using some sort of suspension with a post above the camera connecting to the pole near the center with braided steel? cable.
     
  6. russ_watters

    Staff: Mentor

    That is indeed one way to do it:

    [​IMG]

    Another way would be to increase the diameter of the pole or use a beam with a higher moment of inertial. Regardless of the approach, you need more stiffness.
     
  7. SteamKing

    SteamKing 8,789
    Staff Emeritus
    Science Advisor
    Homework Helper

    Nice picture of the car. Not a lot of detail shown for the camera support, though, which makes it kinda tough to see what you've done.
     
  8. Post-production image-stabilization ? ...
    YouTube does it for free ...
     
    Last edited by a moderator: Sep 25, 2014
  9. It don't seems that your question is actually related to the problem you intend to solve. The bending of a beam is explained mathematically by the Euler–Bernoulli beam theory. But don't ask me for details, because I lack the mathematics necessary to understand it. This isn't of practical application to your case either but it's related and may interest you. Note that all real beams bend when given perpendicular load (like the camera). Sometimes it's not noticeable or negligible.

    If it's about recording from the tip of that beam with a car in movement I wouldn't recommend it. A moving car has a lot of high amplitude vibration due to the road imperfections and changing velocity. A beam not only bends but resonates, exacerbating the effect. You'd need a very stiff beam for it to not to bend significantly, but even a perfectly rigid beam attached to your car is going to exacerbate the movement. There's also the problem that the top of the car isn't rigid. If you climb there, you will notice; it may even bulge downwards. The beam works as a lever and the camera is at the far end, so motion is exacerbated.

    If you want to film from a car or other moving vehicle, use a short lens (small focal length) so that the movement won't be so appreciable. Cropping would neglect this advantage. You must take this into account artistically.

    You can also try to move the car slow and then digitally change the speed of the video. This will reduce the shaking due to the beam resonation provoked by car irregular motion, but increase the shaking provoked by wind and similar factors.

    Don't forget to release your work under a free license!. The CC BY-SA is a good idea, see the license of this message (below). Restricting the distribution of intellectual works by Copyright is an anti-service to society taking advantage of a fallacy (that of carrying the concept of property from physical objects to information). It's a fallacy because information intrinsically costs nothing to copy [1] and can be used by an unlimited amount of users, unlimited amount of times in parallel without affecting each other while physical objects can't. Therefore the restriction given by Copyright can't be morally justified on the same basis, and whether it can be justified as an artificial social convention of artificial scarcity that gives a benefit to society is highly debatable.

    [1] There's the Laudauer's principle that says that computation (I.e: manipulation of information) requires a minimum amount of energy and so it can be said to have an intrinsic cost, but it's extremely small. I don't know if copying information is included as a case, but at any rate, current technology is orders of magnitude above this lower bound but even then the current technological cost in practice of copying information is tiny, and it's not intrinsic to the act of copying (because it depends on the state of technology) nor does it constitutes a cost to any parties but those performing the copy which almost never includes the author or the Copyright holder. Landauer's principle don't applies to quantum computing AFAICT.

    Regards.
    ----
    This message is Copyright © 2014 Mario Castelán Castro and it is licensed under the Creative Commons Attribution-ShareAlike 4.0 International license.
     
  10. Thank you for aol the replies. I am not shooting video but taking a picture with a long exposure (~6 second) the vibrations become apparent in the picture due to the light trails and even slight blur of the car. I have realized that pushing the car greatly reduced movement in the lever but there is still some movement
     

    Attached Files:

  11. Baluncore

    Baluncore 2,577
    Science Advisor

    Firstly; the cross trees and tension wires shown in russ_watters post #5 will prevent low frequency flexing. Secondly; counterbalance the short end of the structure so it closely balances the long end of the structure with the camera. Thirdly; allow the beam some movement in gimbals where it attaches at only one point to the car, the small tilt and direction changes of the vehicle will not then significantly influence orientation of camera.
     
  12. I think the problem shown in this picture is not caused by the beam moving but by the camera rotating. If it were simply moving up/down then the foreground would be more severely affected than the background. It looks like it's rotating so that it sweeps out large arcs at distance objects.

    So this is perhaps easier to solve than making a super-stiff beam. Mount the camera on gimbals so that even as the beam rotates, those rotations aren't transmitted to it. Of course this means you also have to drive in a straight line unless you have some springs/dampers to gradually keep the camera in alignment.
     
  13. CC BY-SA isn't really what you want. It restricts distribution unless you comply with certain conditions. You should use CC0 if you're interested in not restricting distribution of the information. CC BY is asking for a kind of social payment and puts an extra burden on anyone else using it.
     
  14. What about attaching two strings to the end of the pole and attaching them to two points on the front and side of the car, say the tow-point and trapped in the door, you then have a tripod stabilizing the camera position where two of the "legs" of the tripod are string which must be in kept in tension by pulling the boom pole upwards.

    [ If the strings are fine, like fishing line, you may not have to photoshop them out , as you have done with the pole ].

    Be careful not to garrote any passers-by.
     
    Last edited: Sep 10, 2014
  15. OldEngr63

    OldEngr63 653
    Gold Member

    Stiffening the system, by a more structurally stiff boom and/or addition of guy wires, etc. will all help. But they will not fully eliminate the vibration. You might do better to look at a vibration absorber (not a damper, but an absorber). Do a Google on "Frahm Damper" (it is misnamed) which is a way to stabilize your camera, at least at one excitation frequency.
     
  16. Use more rigid material, or change the shape to increase the moment of inertia. OR you could do the easiest thing since you already have the materials and attach a strap from the end of the beam (or close to it) to somewhere under your car and tighten it down until the beam is decently bent. Once it's held in its bent shape it won't flop around on you. This of course gives you something rather ugly in your frame, but it's probably the quickest and easiest fix.
     
  17. OldEngr63

    OldEngr63 653
    Gold Member

    Be sure that you understand Stinsonbr's comment to refer to the AREA moment of inertia, not the MASS moment of inertia of the beam.

    Preloading the beam as he has suggested is certainly a simple fix if the visible strap is an acceptable solution.
     
  18. That is an important distinction. My apologies to any professors out there reading this, I know you cringed.
     
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