scissor lift design help

Dear mo:
How do you intend to power this?
Can you use an overhead crane affair?
Is the 400 pounds "live load"? (People, or animals that move around.)
I replaced a scissor lift system, because the bearings were nearly impossible to properly service. I did it with direct lift at each end of a table, like a hammock. I used a simple op-amp circuit (at first) to correct for tilt in the table. But I used electricity.
David A. Smith

David
Power is manual, the estimated weight of scissor lift and platform it lifts is 400lbs.
Both of which arre aluminium. the load bearing will be in the scissor arms which will be designed to 2000 lbs.
It has to be a scissor due to collapse height and storage needs.

Dear mo:
OK, so what kind of mathematical model to you have knocked up so far? Each "leg" of your scissor is at most 66", and you need a 72" lift. So you will have to have two pairs, right?
How tight a stack (vertical) do you need?
I'm afraid aluminum in toto will be inadequate, but then I never did much like aluminum. Too much analysis required...
David A. Smith

Each arm overall is 64" pin to pin is 61". Yes it is two pairs , I have cad mock up of tow cylinders attached to base and then to second pair of arms, when folded the cyliders are at 9 degrees to horizontal, i calculate loading to 1917 lbs at thisposition so 958 per cylinders.
I plan on use 4x2 Al 6061.
I need help with bearing /bushing selection and force calc .

Dear mo:
=2E.. Limit your model to the very lowest triangle. Have the downward force, and an unknown (for now) couple acting at the apex of the triangle. You have a "four bar mechanism", and I suspect you can find your exact solution on the internet. You are describing a "crank- slider".
Personally, I like the cylinder to act horizontally. It minimizes stroke, and the vertical component at the deck is always down, supporting weight. If you push into the "fulcrum", the parallel members are in tension, fighting the cylinder(s).
David A. Smith