Hey Pumkin,

Can't help you with the theoretical engineering, 'cause I would
probably overbuild it like you anyway.

But a word of warning.

Most "crane" failures, are not from overloading, but from side
loading. Bouncing is nothing compared to a sudden STOP sideways.
They just are not built to take that.

Take care.

Good Luck. Let us know how you made out (pix pix pix)

Brian Lawson,
Bothwell, Ontario.
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On 15 May 2005 10:00:49 -0700, wrote:

Hi everyone -
I have read through quite a few of the strings on inertia and moments
and am a confused lay-person. I believe the entries were repeatedly
saying that it is not as easy to calculate the inertia/mass per length
of moment, especially adding angle .... but forgive me for asking
again.

After a back surgery, I am building avery simple shop crane from square
tube stock. It is modeled mostly after engine hoists, but without the
ram. It is toned down strength-wise because it simply has to hold
250lbs about 45" out on an arm (rather than the 1 and 2 tons an engine
hoist holds) - and I am probably overbuilding.

There are no hinges, tube stock sleeved 20" into larger tube stock will
allow me to make basic angle/height adjustments with a pulley doing the
rest of the up and down work.

I have seen calculations like I=m(r)squared, but am unsure what length
the "r" is. Have also seeen I=(m)(1)squared/3. Anyway, for a simple
structure as this .... ok ... here it goes .... is there a simple way
to calculate aprox. inertia/mass at the end of the arm to ensure the
tube stock can more than handle it (because of fluctuations from
bounces and jostles when moving about) - thanks!