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Gas spring solution for flap needed.

  1. Oct 9, 2011 #1
    I want to build some kind of large box with flap door. Please see attached simple drawing.

    I have a problem with gas spring location, now I made few experiments, but doors still are to heavy to easy lift.

    Can somebody help?

    Sorry for weak English.
    http://img843.imageshack.us/img843/2007/flapg.jpg [Broken]

    Uploaded with ImageShack.us
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Oct 10, 2011 #2


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    You could try a spring in torsion along the hinge.
    To give you and idea of the size of spring, and you would have to modify for your setup:
    Take a look at cube delivery trucks. To open the doors on delivery cube trucks, with the doors that slide up and curve around underneath the top of the box, there is a spring in torsion that helps move the heavy doors. Some garage doors use this pactise also.
  4. Oct 10, 2011 #3


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    Agreed. That, or even a simple counterweight and pulley, would probably be the best approach. It will also give the advantage of allowing easy manual operation in case of an actuator malfunction.
  5. Oct 11, 2011 #4
    Gentleman, I'm affreid my english is to weak for good understanding.

    Can You explain this idea maybe little more? Or simple sketch can be usefull.

  6. Oct 14, 2011 #5


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    Rather than go into a more elaborate explanation, I suggest that you look at how a gas strut assists in the opening of a car hatchback door. Same idea.
  7. Oct 17, 2011 #6
    What language can you manage? Dutch or German?
    Otherwise the use of basic english is preferable.

    I can help you.
    You only have to determine some forces with the help of a scale and to measure some distances. All at 2 specified opening angles.
    Furthermore I need the expected environmental temperature (range).

    After that I will do the math for you so we can select the proper gas struts (depending on your local supplier) and their mounting geometrie.

    Are you still waiting for a solution?
    Please let me know.
  8. Oct 17, 2011 #7


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    I just realized that I misread the original question. I was thinking that the sought-for information dealt with a pneumatic actuator rather than a strut. My answer was therefore irrelevant. Sorry about that.
  9. Oct 2, 2012 #8
    Hi Techvogel,

    I am trying to design a similar situation and would appreciate if you could help with me with the math required to size a gas strut/spring. I've read a lot about it but I can't find a definitive source for the calculations required or the best placement of the strut. The final design intent is a trap door (in the floor) that will be flush with the floor. The SOSS integrated/invisible hinges will allow a minimal gap for the opening and allow the door to sit flush with the floor. I am worried about the weight required to open the door by a small handle. Thank you in advance for any help you can offer.

    https://dl.dropbox.com/u/72370540/Feldstein%20-%20Trap%20door%20hinge%20sketch.jpg [Broken]
    Last edited by a moderator: May 6, 2017
  10. Oct 2, 2012 #9
    Hello Smarchy,

    First I want to make sure that my calculations will be based on the right behavior (in terms of moment change) of the flap during the complete rotation of 90 degrees.

    First question: Is it possible to open the flap that far so it will stay in balance on the hinges?
    If so: At what opening angle can you reach this situation?

    When it 's difficult for you to measure this angle please do the following:
    - measure the horizontal distance from the center of the hinge-line to the rim of the opening in the floor (must be a bit more than the 27,5 inch).
    - measure the thickness of the flap
    -measure the distance from the center of the hinge-line to the top side rim of the flap (should be 27,5 inch).
    - with the flap in balance on the hinges: measure the distance from the rim of the opening at floor level, to the closest rim on the flap (bottom side).

    With these figures I can calculate the opening angle according to the balance situation.

    For lifting the flap from fully closed we choose a force needed of 20-30 Newtons.
    And for closing the flap from fully open position we choose a force of 50 Newtons.
    For the operating temperature we take 22,5 'C as an average value.

    Furthermore we take into account that over the years there could be a decrease of 15% in extension force.
    With 15% loss of extension force and an environmental temperature of lets say 0 'C, the struts must do the trick.

    Do you have a preferred supplier for the struts? (make)

    Best greetings,

  11. Oct 2, 2012 #10
    Hi Techvogel,

    Thank you for the quick reply.

    The distance is 26-1/2" from the center of the hinge to the inside edge of the opening of the hole between the door supports. If you were referring to the opening of the actual floor/door then the dimension is 27-3/4" The thickness of the door is 2-1/4". The distance from the hinge line to the top side of the door is 27-1/2". With the door on the hinges - I assume you mean open at 90 degrees - 9/64" is the distance between the floor and the bottom of the door.

    At what angle will the strut take over from the manual force required to open it?

    How does one figure out the best location to mount the strut onto the door and the frame?

    Just in case I need to clarify, the door should stay closed with it's own weight. The door should open itself after being lifted to about 20-30 degrees and stop and hold itself open at 90 degrees. The door should self close slowly after being pushed down somewhat.

    I do not have a preference on manufacturer, just looking for something reasonable and that ships to the U.S., preferably quickly.

    Thanks again.
  12. Oct 3, 2012 #11
    Hello Smarchy,

    I made a drawing for you to check if I got it all right and for you to determine a weight.

    After I have completed the calculation I can tell you where the gas springs will take over.
    30 degrees is a good guess.

    The best location for fastening the gas spring to the hatch and against 'the world' is part of the results from my calculations.

    At first the calculation will be based on strut lengths and possible extension forces taken from the site of a well known deliverer here in the Netherlands.
    Secondly we shall try to find a good equivalent of the best suitable gas spring selected by me.
    A type, easy for you to buy nearby where you are living.
    And I will recalculate the mounting positions, if needed.

    Looking forward to your reply,
    The Netherlands

    Attached Files:

  13. Oct 3, 2012 #12

    I apologize if I didn't make it clear but this isn't built yet. I am trying to make sure it can be solved before it is built next week. All of your dimensions are correct.

  14. Oct 4, 2012 #13
    Mathematically I think the weight at that point would be 37.813 lbs. 33 lbs at the opening end, 33lbs x 27.5" = 907.5 / 24" = 37.813lbs. Unless leverage is a factor?
  15. Oct 4, 2012 #14

    You did mention it in your first posting: You were trying to design a similar situation.
    My fault. Should have taken a closer look.
    Anyway, I did some calculations in advance so you will not have to worry about the force required to open and close the hatch.

    To open you will need 30 Newtons (or less if you prefer).
    To close the lid you will need 50 Newtons (I choose a higher force because of safety reasons).
    The maximum force occurring during the full cyclus (closed -> fully open) is 42 Newtons.
    From fully open to horizontal it will be a bit more due to friction in the gas springs.

    The maximum force on the hinges = 380 Newtons.

    For how it could be look like: See the drawing attached.

    Conclusion: Build your hatch and after all is finished collect (check) some measurements and perform the trick with the scale.
    Based on these figures I will calculate the best solution for you.

    Succes !!

    Attached Files:

  16. Oct 5, 2012 #15
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