Statically inderterminate analysis

[jpmpack]

I am trying to solve for forces in a wheelchair lifting device that mounts to the rear of vehicles. The only known force I have is the wheelchair weight. I am not looking for information on computer software, just some resources on solving by free body diagrams and hand calculations.

 

[desertfox]

Hi jpmpack

Can you supply more information on how this device is fastened to the vechicle, if its just bolted on with say two
rows of fixings like a wall bracket then the calculations are not that difficult and I may be able to help you further.

regards

desertfox

 

[jpmpack]

The lifting mechanism is more complex than I indicated, basicly it is a 4 bar linkage that helps lift the platform from ground level to several feet off the groud. I am able to figure the stress at the mounting position.

 

[desertfox]

Hi again

So are you looking to calculate the forces in the four bar linkage? What does the linkage look like ie:- does it form
a scissor type mechanism? its difficult to help when we don't know what the configuration is other than a four bar mechanism.

regards

desertfox

 

[jpmpack]

Let me try this, picture a rectangle with one short end fixed to the vehicle and the other short end supports the platform. The platfrom and the two long sides members rotate as the lift raises and lowers by means of a strap attached to the platform powered by a motor. All 4 corners are pinned rotating joints.

Thanks

 

[ludvik]

The structure the way you described it sounds suspiciously determinate. Why do you think its indeterminate? Its all pinned right? Can't you just analyze the arms of this rectangle thing as cantilevers?

Do you have a text book on structural mechanics? That's the kind of reference you will need for hand analysis of this kind of problem.