[HELP] Strong Crane Boom Concept

[Cumulonimbus]

The boom bends because the bottom is compressed and the top is stretched. So if you awnt to minimize the bending, try to minimize the amount that the bottom will compress, and the amount that the top will stretch. If the bottom and top are further apart, the same amount of stretch/compression will result in less bending.

So, strengthen the bottom and the top, and keep them at the right distance by vertical bracing of any kind. It doesn't have much use to strengthen the center, as long as the center is there as a spacer for the bottom and the top.

By the way - that's also why real crane booms are half-oval shaped - with a round bottom and a flat top. A rounded surface has a better resistance against compression then a straight surface, so that's why it'sround at the bottom, and for tension it doesn't matter, so as much material as possible is put at the top, hence the flat top.

Nice explanation, this is the best description in layman's terms of moments of inertia of a beam I ever read.

[efferman]

Erik, thanks for this perfect explanation. a one piece boom would be perfect, but when i do this, it would not longer be lego.

jdc, this should help a lot but unfortunately this wouldnt fit to my Recovery truck which i want reactivate

picture source

Bricktrain, my second boom is 20 percent of the full length overlapped. this should be enough.

Now the actual standig. it is a hybrid of a box and a lattice boom. on a short test without the actuator it bends on the whole length.

lxf

iam very interrested to see whats happens with actuator

edit:

it works. no bending on the mainboom

Edited September 27, 2014 by efferman

[Leif]

just my 2 cents, I'm pretty sure you read most of the posts at the forum, but my boom, a modifed version of afol1969 is pretty strong.

At least 1.2 kilogram without extending boom, and at least the unimog cab while fully extended

details here: http://www.eurobricks.com/forum/index.php?showtopic=85388&st=400#entry1996084

I am all for stronger, bigger stuff so please let me know your progress and if anything of my build is good input for you!