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Thread: Norman's Jib Crane adventure

  1. #31
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    Quote Originally Posted by BCRider View Post
    Norman, your reply above to my post shows you've given this a LOT of thought and have most of the bases covered. From your load testing which seemed fairly recent I didn't think you were that far along with the idea.
    I am getting closer to having the bases covered in so far as desirability of each of the generally available options. That said, I do not yet have any math to fully confirm the flex issues of the beams. If you have any good places to look that actually provide answers in the context that I need them them please do let me know ... it is my next port of call.

    Quote Originally Posted by BCRider View Post
    I do agree that the RHS tube would be a lot stronger in torsion. But doesn't that cause problems with moving items long the length of the boom? Would you add a track of some sort or will it have a larger section that wraps around and wheels that ride along the top of the RHS?
    If I settle for a boom that is of fixed length (without articulation) then it makes sense to use an I or W-beam and run a girder trolley.

    That said, the more I have looked at the articulated version the more I like that style. The articulated style allows reach into the corners of what is essentially a square space, whereas the fixed boom can only cover a circle (an arc) from the mast.

    There is need only for a single hook point at the end of the second boom on the articulated type. That hook can reach anyplace by folding the booms and swivelling the mast.

    The image below is close to the desired outcome save for the mast hinge points. It has a boom that is fixed to a swivelling mast. The mast swivels and the first section of boom travels with the mast an arc. The articulated section of the boom swivels independent of the fixed section of boom; to go both inside (closer to the mast) and outside (go beyond) to extend the fixed section of boom. That articulating action allows you to step around obstacles and reach into corners.

    For the design under consideration the hinge points differ from the image in that one would be at bottom of the mast (on the floor) and the other at the top of the mast (connected to a roof beam). More of an axle action rather than a gate action.



    Quote Originally Posted by 754 View Post
    I dont think the 4 ft deep anchor would have been a problem, if the floor was not yet in.
    So i had this thought, if you had a 12 foot wide door at one end of the shop, and could live with your lathe and mill there....could you mount the crane outside the end of slab (with proper anchor), and be able to swing inside to the machines.? I know it doesnt reach much of the shop.
    There is already enough floor strength for a floor mounted column type. Just am not looking to go there just yet.

    Do agree we do not want the crane outside of the shop for all the reasons you mention.

    Norman

  2. #32
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    Not my idea, but I think this would work better to distribute the load on the building structure.
    http://www.homemetalshopclub.org/pro...ane/crane.html

  3. #33
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    With the way that forces grow and pull on the metal when you go with longer lengths and spans I can't help but think that the size of RHS needed to withstand the twist will not be small or light. That example image is quite small by the looks of it and not a lot of reach. That's a whole other animal. You're talking about lifting a couple of hundred Kg's on a boom that is 3 or 4 meters long with a jib off the end that is another 2.5 to 3.5 meters so you can reach the whole area. I'd feel a strong urge to have someone that knows their engineering run the numbers on that sort of design.

    The good news is that with the style of building you posted if that's what you're using the peak on the inside is tailor made for the boom to have a diagonal brace that matches the ceiling angle. That would greatly aid in reducing the size of the boom you need. It also supports the idea of using an I section so you can use a rolling carrier. And it doesn't eliminate the idea of a hinged jib extension being pivoted into place to reach the darker corners.

    There's not much doubt on which option I would fee comfortable in doing my own "engineering". I can handle learning about and running the numbers on a simple bending and triangulated extension setup. I would not be so good with trying to wrap my head around the torsion issues of a longer jib setup as you are considering.

  4. #34
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    Determined that more tests were required so setup this rig in the tow slot at rear of forklift.

    The RHS beam is 150mm wide x 50mm high x 5mm; it is 3 meters long though not quite all of it is used in the test.

    The beam is held to the top of the slot by 2 x short lengths of pipe that I trimmed to length in lathe to create a tight fit ... they stand on their end and were banged in with a hammer.

    I will call the pivot point as being 250mm from the back of forklift.

    All'n'all I was pretty happy with this fit ... it all felt good, snug and well held.



    Time to apply some load. With a trusty assistant and a bar we carefully lowered this known 80kg lump of steel onto the end.



    Of course there was some deflection. I know yous are all keen to know the stats so here they are.

    Do remember this is ONLY a 50mm profile. The person on this side of the screen does realise that a 50mm profile will not fly for the real implementation ... we are just working to get more feel for what is possible and practical.

    [EDIT] my original measurements here did not take into account the "lift" to back of forklift etc, so I reworked them with a string line. With string line there is around 7mm deflection along 2600mm of 150mmx50mmx5mm RHS on its SIDE.

    Norman
    Last edited by Norman Bain; 04-22-2017 at 12:52 AM.

  5. #35
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    So now onto torsion ... the ability to resist twisting.

    An anchor point was created at the end of the 3 meter beam. At a right angle a 75mm x 55mm x 4mm RHS beam, lying on it side, was attached with a few G-clamps.

    Having this second beam on its side was to create a larger flat surface at the join with the main beam onto which to attach the G-clamps.

    The 80kg weight was placed at 1000mm from the pivot point.



    The 80kg weight was placed at 1500mm from the pivot point.



    The 80kg weight was placed at 2000mm from the pivot point.



    I am sure yous can all see from the images that the weight got itself closer to the slab surface the further we moved it from the pivot point.

    Not all that "droop" was a result of twist in the 150mm x 50mm x 5mm RHS. We ran a string line under the right angle beam and recorded that it was 10mm drooped over the 2000mm with 80kg added.

    I tried to get an image of the twist in the 150mm x 50mm x 5mm RHS. It is twisted but not massively so.

    The beam did return to "normal" non-twisted state when the load was removed; so I presume this means we did not overload to go beyond some elastic/spring point.



    The stats were all measured at a common point; that being the end of the beam that is hanging out at right angles:
    400mm when unloaded.
    340mm when 80kg added at 1000mm from twist pivot.
    295mm when 80kg added at 1500mm from twist pivot.
    240mm when 80kg added at 2000mm from twist pivot.

    Some right angle triangle math using the 2000mm length and 160mm droop tells me that the beam under torsion is twisted 4.57 degrees.

    Apply similar triangle math and 4.57 degrees to the 150mm width of the beam and result is there is a 12mm twist in the overall length of the beam.

    Given the beam is 3000 mm long I have it that we have 4mm twist per meter.

    I really would like someone to point me at an online calculator into which I could punch in the numbers and get theoretical answer that somewhat matches my observations. That would get me a long way along the path to the goal.

    Norman
    Last edited by Norman Bain; 04-21-2017 at 07:54 PM.

  6. #36
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    This is even better than all that math stuff....

    So now you know it's good for 80Kg at 2 meters with that size of RHS. Will 2 meters serve your needs for the pivoting jib? What about the 80Kg? Is that going to be enough to serve your needs? Still questions you need to get answers for. But this is an excellent start.

  7. #37
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    Lurkers, I just could not find any "calculator" that would agree with my measurements in post #35.

    I did surf around a lot and got lotsa conversions going that allowed me to enter data into the myriad of calculators out there.

    I am not yet fully conversant with the calculators; but the results are always way off my 70mm measured ... so how come.

    Went back to the setup and looked for "flaws" in the approach. Biggie was that the forklift did lift some at the rear as it unloaded the tyres etc.

    Reworked the test by setup of a string line under the beam and applied the 80kg weight again.

    Measured the distance between the string line and beam ... now get around 7mm ... that is a BIG difference from the 70mm of the post #35 approach.



    That is enough for one day. Will need to go at it again tommorrow with the calculators.

    Will add some [EDIT] comments in post #35 so the new visitors don't get alarmed.

    Norman

  8. #38
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    You should consider using your original design and add a telescopic beam on top of your main beam to get into your corners.Have a girder dolley that would roll on the top of the upper I beam and the two I beams would be similar in length,it would be similar to full extension drawer slide.

  9. #39
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    Have done the "overnight cogitation" thing and managed to work up a solution to the deflection measurement hassle of earlier posts.

    Setup a light wooden beam that is fully anchored at the forklift end by a G-clamp to the beam. Idea is that this wooden beam (which is not attached elsewhere to the beam) will stay parallel to the beam at the anchor point; thus allowing a measure of the true deflection when a load is applied.



    The 80kg weight is then applied to the end with result the beam heads some in the downward direction.



    Go figure ... the measured deflection (32mm) is different than all previous approaches.



    Stats are:
    3000mm of beam of type RHS 150mm x 50mm x 5mm lying on its side.
    80kg of weight applied at 2800mm from the rear of forklift
    32mm deflection measurement taken at 2600mm distance from rear of forklift.

    Norman

  10. #40
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    All day yesterday I was surfing the web trying to improve my knowledge of the modelling variables and application of them in manner that would be a reasonable match for engineering calculations.

    Good news ... I believe I have the answer.

    Raw stats for my latest forklift and beam rig were:
    3000mm of beam of type RHS 150mm x 50mm x 5mm lying on its side.
    80kg of weight applied at 2800mm from the rear of forklift
    32mm deflection measurement taken at 2600mm from rear of forklift.


    To work from the theoretical (using available online calculators) to get the answer there was need to do it in two steps.

    Step #1: Input the beam RHS dimensions and the steel density and push the Calculate button.

    http://www.amesweb.info/SectionalPro...Rectangle.aspx




    For Step #2 we need to get the "Second moment of Area" value from Step #1.

    The "Second moment of Area" value for the beam on its side is 81.583 cm^4; it is shown at the first red arrow in the result.

    The deflection calculator will also require a value for "Distance from Neutral Axis to Extreme Fibers".

    The Neutral Axis (for a simple beam like this) is at the center as if you'd drawn an X from corner to corner looking at the end of the beam. The idea is that the Neutral Axis is the line along the beam that does not undergo compression or stretching change when the beam is loaded.

    The Extreme Fibres value is ASSUMED by me to be the distance from the Neutral Axis to the outer edge of the beam. I say assumed because I could not find anything that said it is exactly that; all the verbage sorta talked around it; talked heaps about the Neutral Axis and sorta assumed you knew about the other.

    For a consistent beam like RHS the value (50mm beam height - 25mm beam neutral axis) = 25mm; that equates to the "ycog" value in the results ... hence I suspect that is our number. Input please from the HSM wizards out there on this.

    Punch in the beam stats and load numbers into the load calculator and push the Calculate button.

    80kgs = 0.784 kN
    The Modulus of Elasticity of steel is 200 GPa

    http://www.amesweb.info/StructuralBe...ratedLoad.aspx



    Our theoretical deflection value is shown as 31.392mm at the red arrow in the results.

    Finally I have a very good theoretical match for the physically measured 32mm.

    Norman

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