Subject:
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Re: 8860 Scissors lift
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Newsgroups:
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lugnet.technic
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Date:
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Mon, 21 May 2001 15:08:25 GMT
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Viewed:
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1660 times
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> I have trying to build a scissors lift robot (really just using the RCX for
> remote control) but I am having problems with powering the lifting action.
> I can't get enough power to lift any thing substantial (more than 4 layers
> of X's). I am using a mechanism similar to:
>
> http://carol.wins.uva.nl/~leo/lego/piston.html
>
> but the model just wants to fall apart or the motor just stops and hums.
I recently needed a compact rotary->linear motion converter and tried the
electric piston referenced above. It works great for small loads, but if you
try to apply any force the bushings slide on the axels. So I modified the
design slightly. I ended up using a sliding worm gear on a rotating axel.
The work gear road against technic gear racks (3743) which converted
rotation of the axel into translational motion of the worm gear. The worm
gear pushed against a perpendicular axel joiner (6536) which was attached to
what I wanted to move. I also used a geared 9v motor as opposed to the
micro-motor. Below is a sketch. If makes no sense, try changing to
uniformly spaced fonts. If it still makes no sense I'm sorry.
\ <- Linkage to force application point
\
O Worm Gear
------[ ]\\\\\----------Axel
^^^^^^^^^^^^^^^
Rack
Now you just have to determine where to apply the force. An initial impulse
may be to apply the force to the bottom of one of the sissors. This is
where we apply the force when we manipulate one of these mechanisms manually.
\ /
\/__Pivot
/\
Fixed leg / \<- Apply force here?
--O////--- <- Electric Piston
The problem is that when the sissors are collapsed (jack in lower position),
a force applied at this point results in a small moment about the sissor
pivot. So you get a lot of force trying to tear the jack apart, and very
little force trying to raise the jack.
A better idea is to apply the force higher up in the jack. You want the
linkage attaching the piston to the jack to be at about 45 degrees. It's a
weight/travel trade off. Much less than 45 and you can't lift as much, much
more and you can't lift as high.
Hope this helps.
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Message is in Reply To:
 | | 8860 Scissors lift
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| Hi all, I noticed that the box for the <set:8860> car chassis has a scissors lift. The scans of the instructions on brickshelf: (URL) do not have any instructions for the scisssors lift. Was there a second book in the box or was this just a (...) (23 years ago, 16-May-01, to lugnet.technic)
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