Results 1 to 12 of 12

Thread: Help Plz!!!

  1. #1
    Associate Engineer
    Join Date
    Jul 2012
    Posts
    4

    Bang Head Help Plz!!!

    Looking to build a scissor lift that will be mounted to the ceiling and able to manually retract a 10lb, extended length at 5' (width not a issue). Hopefully able to make the legs out of wood.

    I dont know much (Freshman), additional and helpful tips greatly appreciated (personal project)
    if needed any more information please ask.
    Last edited by luigifan1300; 07-18-2012 at 12:10 AM.

  2. #2
    Senior Engineer
    Join Date
    May 2012
    Posts
    33
    Sounds like a fun project, can I assume you are powering this lift with man power? or do you plan on hooking up some sort of actuator? Keep in mind that a scissor lift will require you to have a track for 2 of the 4 legs on the ceiling and that may require some metal if your looking for the best performance. If you are looking for simplicity, and to make it out of wood, I might recommend a cantilever lift.

  3. #3
    Technical Fellow jboggs's Avatar
    Join Date
    Mar 2011
    Location
    Myrtle Beach, SC
    Posts
    781
    Normally scissor lifts are used in compression, not tension. That means they are usually pushing something, not pulling something. I applaud your creativity, but why not just use a winch?

  4. #4
    Associate Engineer
    Join Date
    Jul 2012
    Posts
    4
    Thanks, however I am really trying to mimic the idea from a show (Doctor Who), in which he used a scissor lift which could be manually/automatically brought up or down. I was planning to first make it with a spring, and add an actuator in later.

    My main concerns are that:
    It will be able to hold 10lb
    When contracted it the legs shouldn't drift downward
    Last edited by luigifan1300; 07-18-2012 at 11:15 AM. Reason: Reply

  5. #5
    Technical Fellow
    Join Date
    Feb 2011
    Posts
    1,043
    What episode of Dr. Who?

    You could make a normal scissor lift on the floor, then invert it and hang it form the ceiling, but the main issue is that the scissor lift is designed for mechanical advantage while lifting. However, given the load is only 10-lbs, you would not really have a problem. Do some research on scissor lifts and replicate one of them, just make sure that track the wheels run in capture the wheels so they can't fall out when inverted.

    Generally the wheels run in a track (as WD mentions) and usually that will be open-topped as the load is pushing down on the scissor lift base and track. In your case the lifting load needs to be in the other direction so a captive track for the wheel is a must when operating inverted.

    You could use something like garage door track and rollers. Very low-cost parts at the Hardware store.

  6. #6
    Administrator Kelly Bramble's Avatar
    Join Date
    Feb 2011
    Location
    Bold Springs, GA
    Posts
    2,237
    Well, the applied forces of a scissor lift in tension vs compression are equal but opposite. So, the math and design is roughly the same whether lifting + or -.

    However, when a load is being lowered or lifted from an elevated location I believe a block and tackle or pulley lift system is more cost effective and makes better sense.

    Scissor lift:

    http://www.engineersedge.com/mechani...issor-lift.htm

    Block and tackle (Pulley System):

    http://www.engineersedge.com/mechani...advantage3.htm
    http://www.engineersedge.com/mechani...advantage2.htm

  7. #7
    Senior Engineer
    Join Date
    May 2012
    Posts
    33
    I do not understand what you are trying to accomplish with the spring. Can you explain where you want to attach the spring? would it be a compression or a tension spring, or even a torsion spring for that matter... these all depend on if you want the natural state of your device to be retracted or extended. Gravity will want it to be extended.

    That being said, here are a few things to think about with respect to your scissors. Trigonometry will tell you what length to make your legs, and also how long your tracks have to be. For instance if you decided that your max angle with respect to the ceiling would be 45 degrees, your equation for length of individual legs is: L =60"/(X*sin(45)) where X stands for the #of leg "sections" you want to have.

    In my opinion if you are looking to make it look cool, be more compact, and have a smaller stroke on your track system, I would have a bunch of small scissors... However the other side of the coin is that the more scissors you have, the harder it will become to control the motion of the system because it will become less rigid. and your track motion becomes less... off the top of my head, I think your track motion equation would be something like: Track stroke length = L - (60/X) but that is an estimate, the true motion would be slightly less I think.

    as far as material, I would use something like 1x2 lumber? and as far as the tracks, I like the suggestion of using a garage door track. However I do think it would be pretty easy to make a track out of wood and bolts.

  8. #8
    Associate Engineer
    Join Date
    Jul 2012
    Posts
    4
    Attachment 371Attachment 372

    Heres a scene from "The Impossible Astronaut"
    I'm gonna take up the track idea, considering that The Doctor is able to move it around the console

  9. #9
    Associate Engineer
    Join Date
    Jul 2012
    Posts
    4
    The natural state would be retracted, but is it possible for me to be able to pull it down 3' and have it stay put, same with any other distance?

  10. #10
    Senior Engineer
    Join Date
    May 2012
    Posts
    33
    ya. a mechanical stop. probably something like a hand knob screw that can be positioned on your slide, or on a pivot point in your scissors.

    video didn't work for me btw

  11. #11
    Technical Fellow
    Join Date
    Feb 2011
    Posts
    1,043
    Ahh, OK, that is not a scissor lift it is a concertina support, sometimes called a scissor arm. Much easier to make.

    Study this...
    http://www.vandasye.com/wp-content/u...Absperrung.jpg

  12. #12
    Technical Fellow
    Join Date
    Feb 2011
    Posts
    1,043
    Quote Originally Posted by Kelly Bramble View Post
    Well, the applied forces of a scissor lift in tension vs compression are equal but opposite. So, the math and design is roughly the same whether lifting + or -.
    Kelly, I don't want to get into another lengthy debate on scissor lifts, but the lifting load on the lead screw is greatest when the scissors are all collapsed. As the arm-angles approach zero, the resultant lift force increases as in a toggle. The forces are not multiplied by the number of scissors, but the effort on the lead screw is much reduced approaching full extension at the expense of lift-inches per degree of scissor angle.

    Not an expert on scissors lifts, in fact I seem to recall my very first post here was actually asking about scissor lifts. That should say it all.

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •