# 4 bar linkage question



## gooffy87 (Oct 18, 2011)

Hi all, starting Haunt 2012 today!

starting with a JIB, i am using some very sturdy metal from an old piece of workout equipment (elliptical with no motor or electrics). I thought at first that the lift bars were double up for sturdiness but the bar is nearly 1 and a half inch thick, do i still need to double the lift bars or will it be fine single. or better yet, is their any technical reason for the doubled up lift bar. thanks!


----------



## gadget-evilusions (Jan 26, 2007)

Are you planning on building a 4 bar lifting mechanism? I assume JIB is jack in a box?

What are the exact dimensions of the steel? I'll help you out anyway I can with design specs.


----------



## gooffy87 (Oct 18, 2011)

thanks gadget, i figured it out already but thanks for responding!


----------



## Dead Things (Apr 4, 2009)

I have a question, Brian. I want to build this




I am thinking of using pvc (reinforced with copper pipe or metal conduit) as the 4 bar. Prop would be built as light as possible. I have a cylinder with a 1 inch bore. Would that provide enough force to lift the prop?


----------



## gadget-evilusions (Jan 26, 2007)

The best I can do is maybe.

I build a very similar mechanism, http://evilusions-shop.com/Casket-Jumper-Mech-PNME-001.htm , but mine is built with 1" square 1/8" wall steel. I use a 2" bore x 9" stroke cylinder to operate it.

Your much lighter build may work with the smaller cylinder. What stroke is your 1" bore cylinder? One thing that would help is if your cylinder has a long stroke, that will allow you to mount it farther away from the pivot point, which will increase its mechanical advantage. If your cylinder has a shorter stroke, you will have both a smaller bore and smaller stroke working against you. Try it, if it doesnt work you can adjust the mechanism or find a bigger cylinder. Experimentation = Research and Development.


----------



## Dead Things (Apr 4, 2009)

The cylinder i have has a 12" stroke. On the mechanism in the video, the base of the cylinder is mounted under the pivot point which places it at an angle, connecting to the lever arm . Perhaps a bracket that places the cylinder in a vertical position under the lever arm. I found i had to move the position of the cylinder on my coffin leaper. I had found a 4 bar calculator somewhere on the net but it was on a laptop that was "liberated" from my car last year.


----------



## gadget-evilusions (Jan 26, 2007)

I have found the best angle to mount the cylinder at is one that places it at 90 degrees when the cylinder is at half stroke. This causes the angle at which your force is applied to be more even. For example, -22 degrees when retracted, and + 22 degrees when fully extended. It helps to smooth out the movement and try to keep the rate of extension as even as possible.

With a 12" stroke it may work, especially since you can mount the piston rod connection a little farther from the pivot point of the mechanism.


----------



## Dead Things (Apr 4, 2009)

I took a look at some of your designs and I see what you mean. At half stroke the lever should be at 90 degrees to the cylinder, and that lever should also be at the mid point of its travel. Thans for all your help, really appreciate the fact that, even though this is how you make your shekels, your willing to offer advice. I can't wait to start this build!


----------

