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Thread: Vehicle lift

  1. #41
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    Hi, I'm coming up with 30,000lbs, you have 2500 each at the top pins and 10,000 at the center, should this be 5,000?

    I've shortened the arms by 2.5" and increased the vertical sleeves length 3" and now have the arms angle at 21 degrees. Still have enough travel on the cylinder. Huge difference and it's under 15000 per corner now.....I hope.

  2. #42
    Lead Engineer
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    Bart, the 10,000 lb load is correct, think of beams as crossed levers with the center pin as a common fulcrum where the load on the center fulcrum from each lever is 2500 lbs x 72 /36 = 5000 lbs and the sum for the two levers is therefore 10,000 lbs. The anaysis is pricipally the same as if I had ignored the loading on one arm end and applied the full 5000 lb loading on the end of one arm as I have done on my earlier analyses.

    On your new design is the cylinder still located in it location between two of the beams or have you moved it to the horizontal position of the latest analysis? Let me know so I can run a revised analysis to confirm your results.

  3. #43
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    Well dang it all. I've been using the Scissor Lift Jack Force Bottom Load Calculator located here at this site and a have set my lift up exactly like it except for being upside down. What am I doing wrong. sigh.

  4. #44
    Lead Engineer
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    Well, then maybe I am the one doing something wrong because it should be valid for your case at the top as well as at the bottom. How can I access the calculation you have used?

  5. #45
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    See above post
    the pictures didn't attach for some reason.
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  6. #46
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    I bet its me.....I can't link it but I can send a screen shot.
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  7. #47
    Administrator Kelly Bramble's Avatar
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  8. #48
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    Bart, I found the link and have reviewed the above calculator and the equations used and the review of the equations clearly show there is an error in the calculator description where it states "the angle between scissor arms" the correct angle is the angle between each arm and the horizontal line in the diagram indicated by the angle symbol "psi" in the diagram (ie 1/2 of the angle between the arms).

    If you enter the 9.68 degree angle value that I used in my last analysis in the calculator, then their calculated horizontal cylinder force is exactly 1/2 of my value; and, that is where I am a bit conflicted with their result because in their equations they analyze each arm individually and then say the horizontal reactions of each arm are not additive.

    Unfortunately, I cannot really state for sure which of our calculations is correct and we need really need an independent opinion from a third party to help resolve this issue.
    Last edited by JAlberts; 11-19-2013 at 08:53 PM.

  9. #49
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    Well, that answers why I've been thinking I could make this work.

  10. #50
    Quote Originally Posted by JAlberts View Post
    Bart, I found the link and have reviewed the above calculator and the equations used and the review of the equations clearly show there is an error in the calculator description where it states "the angle between scissor arms" the correct angle is the angle between each arm and the horizontal line in the diagram indicated by the angle symbol "psi" in the diagram (ie 1/2 of the angle between the arms).
    The equations have been proven and the calculator was incorrect as you indicated. I have updated the calculator to show the the angle as Theta to the horizontal.

    Sorry folks...

  11. #51
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    Bart, sorry it appears I have misled you and have been in error on my latest calculations, so from now on you (and I) both should use the corrected on-line calculator for our future analyses.

    Kelly, thanks for your input, it looks like I need a refresher course on statics and vector analyses.

  12. #52
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    Hello, no worries here. It's been a very enjoyable experience. I have learned so much about force and angles. I don't know what your referring to, being in error on your latest calculations. Your calculations showed that the calculator input angle for the scissor arms was incorrect. This will be very helpful to folks in the future. Back to the drawing board!

  13. #53
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    Bart, I am glad I was able to spot the error in the calculator but that does not negate the error in my calculation. Just for your information, I was so focused on resolving the horizontal forces at the lower legs that I failed to include the vertical load reactions as well, which was a definite error on my part because if I had I would have immeadiately seen that the 10,000 lb downforce was an error because dividing between the two legs would have resulted in a vertical downforce reaction of 5000 lbs per leg which is twice the platform loading and obviously wrong.

    While I am communicating with you I would like to address another issue related to the safety latching of the platform in its raised positons. While your hydraulics friend is correct in stating that pilot operated check valves will protect you from hose failures there is also an issue related to the wearing of the cylinder piston sleeves and/or check valve seats that over time, while it will not cause a sudden drop of the platform, can result in a very slow lowering of the platform that is nearly imperceptible on a day to day basis, until one day you might discover that your truck with a top load doesn't quite fit under the platform any more. For this reason, I still recommend that you include mechanical hard safety stops at your two lift height positions.

    Another issue about your hydraulics is that you are placing your cylinders on the platform rather than at the floor level. While I understand that you are doing this to minimize floor space intrusions of your equipment also be aware that this is going to result in your having to deal with 12 ft lengths of hose at each corner that will be hanging from the platform and have to be controlled to prevent tight bends and kinking that can danmage the hose when the platform is at its 8 ft height and more so when the platform is at its bottom position. Placing the cylinders at floor height will eliminate this issue and since it appears you have not yet installed your garage floor you might consider looking placing the cylinders and lower arm connections in troughs below the floor height with floor level removable trough covers. This would keep both you equipment and the hosing out of the way of garagfe foot traffic. Just a thought you might consider.

    I am glad to see that it appears you are beginning to close in on a possible design for your lift; and if you have any more questions I will be glad to help.

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