Help with Cherry Picker

[Paul B Technic]

Hi all.

I am hoping for some advice on a problem I have come across with my latest MOC, this is a cherry picker. In basic terms when it gets to a given point of raising the arm it gets a "twist" at the bottom near the large LA which makes it fall out of alignment much worse at the top. When it is higher or lower it is fine, just at this given point.

Having looked at it on and off for the past few weeks I have gotten to the point where I am not sure how to fix it. If I was to use two LA's I think that would fix it but this is not something I can do and it seems like overkill.

Has anybody else built a cherry picker and had this issue?

Paul

[Balrog]

Without seeing what you have built, I would assume that your lifting geometry is a little off and that when you hit this spot it creates a little "bend" on the pieces. Can you post some pics with highlighting? It's very hard to debug a problem without seeing the problem.

[Paul B Technic]

My photos didn't work, will take some tomorrow.

[_Ben_]

Without seeing the problem, it is indeed difficult to help. However, from an engineering viewpoint, it sounds like the beam you're using is not torsionally stiff enough for the given length and mass you're asking it to lift.

There are two solutions to this: 1. shorten the beam; or 2. make it stiffer.

You could achieve 2. by increasing the depth of the beam.

Edited April 21, 2016 by _Ben_

[Paul B Technic]

Thanks.I can't post any photos until the weekend but I think you are right with number two, I might need to add a second row to make it stronger.

[Myers Lego Technic]

I am young, but have been building technic all my life. If I could see some pictures, I might be able to help. Is the problem caused by to much fiction when the angle reaches a certain point? Maybe.