Calculating maximum load and counterweight of a tower crane

[mehagar]

Homework Statement

The object is a crane arrangement of pipes that falls forward without any loads or counterweights on it. We can take it apart measure the weight and the length of the individual pieces.How much weight can a tower crane lift without tipping? I just need a general way to solve this problem, not specific numbers.

Homework Equations

moment/torque = force X distance
ƩF = 0
ƩMoments = 0

The Attempt at a Solution

I drew a free body diagram of the crane with downward forces to indicate the load, the counterweight, and the center of mass. The upward force was the normal force and one of my equations involved adding the forces together to equal 0, with a variable (l) for the load.
I don't know how to calculate the center of mass though, and I'm confused about where I should be taking the moments from. Thanks for your help.

 

[Camille]

If I have got the right picture of the problem, then probably it is enough to calculate moment on the right to the point of support of the crane and moment to the left of that point. They have got to be equal, otherwise one arm would be loaded more then the other and the crane would collapse.

So, from the equality of moments you should be able to calculate loads.

 

[mehagar]

Okay, but how can I find the center of mass? I tried to add up all the halfway points of the horizontal pieces and for each one multiplied by it's respective mass. But I was unsure how to factor in the vertical beam, as it wasn't symmetrical.

 

[Camille]

Do you have any picture of this crane?