The discussion centers on deriving dynamics equations for a two-stage scissor jack, emphasizing the need for understanding rigid body dynamics and moments in mechanical systems. Participants suggest that the equations for such a mechanism are not readily available due to its complexity within the broader field of lever systems. Recommendations include studying intermediate mechanics textbooks and utilizing resources like YouTube for foundational knowledge. The conversation also touches on design considerations, such as the efficiency of screw and nut combinations in jacks, and the potential for hydraulic versions in industrial applications.
PREREQUISITESMechanical engineers, students studying mechanics, and designers of lifting equipment will benefit from this discussion, particularly those focused on scissor jack dynamics and design optimization.
I don't think you are likely to find a 'scissor jack equation' anywhere because such a mechanism is just a part of an enormous field of lever systems. From your question, I get the impression that you are not too familiar with the basics of moments in mechanical systems. I think that you could benefit from an intermediate mechanics textbook with the basics and a number of worked examples. Most of the stuff you find on the net about levers and moments involves the simple see-saw type balance where the forces all act parallel to each other; useful but not enough for what you need here. I found this YouTube video, which gives a way into the topic and there are a number of relevant links leading from it. It's A level physics that you need - GCSE doesn't do 'angles' for moments.bbq_build said:Equations that one could use to simulate the behavior of the jack under different applied forces and loads. One that involves rigid body dynamics.
For a symmetrical (rhomboid) arrangement of four spars and a balanced load,, the problem can be reduced to considering just one spar, with two forces acting at each end. (Assume the jack is massless etc. of course). The calculation should not be too hard with so few variables. Don't ask me to put my money where my mouth is but the relationship between the vertical and horizontal forces with angle is going to involve a tan function of the the angle .malemdk said:I myself worked out the problem -(Mechanical Engineer) since no where I could find the solution to this scissor lift problem- I think Its hard to post here its a lengthy calculation ,
I wonder whether an asymmetrical jack would ever be used. After all, it wouldn't be 'foldable' as a normal jack is and the range of usable angles / heights would be less.malemdk said:Yes it's for simple configuration, but the calculations become somewhat complicated for other configurations
Wow. Never seen one of those; I never thought of that form of asymmetry. Could be very handy in the right conditions.Nidum said:http://www.gustininc.com/norco-82002c-1-1-2-ton-scissors-jack/
A common variant on the scissors jack replaces part of the mechanism with a slide and roller . These can be low height for storage .
sophiecentaur said:But still, there's no Statistics or Integration involved. Just plain old Algebra and a couple of Trig functions.
Nidum said:@bbq_build : Is this a normal scissors jack with hand operated screw and nut drive or is it a more complicated version ? Can you post a picture ?
It's hydraulic power cylinder version, do you design any scissor jack or is it course project?Nidum said:@bbq_build : Is this a normal scissors jack with hand operated screw and nut drive or is it a more complicated version ? Can you post a picture ?
Yes it looks somewhat like, but not exactly what you have shown is small machine, the machine which I designed was for industrial use, the rated capacity of each cylinder is 40 t, there were 2 cylindersbbq_build said:Like the one shown in the photo:
https://en.wikipedia.org/wiki/Laboratory_scissor_jack