Boom strength calculation

[parkland]

TL;DR Summary

Potential project/ learning about steel strength

Hi all,
I was hoping a guy with limited engineering skills might find a little help and understanding...
I'm not formally trained but am somewhat mechanically inclined. I build things, and usually have good luck estimating strengths and designing things without doing the math or science behind it.
That being said, here is my story...

A little while back, me and my friend started talking about starting a little tree limbing business. We wanted to buy an old telehandler, manlift, or bucket lift system and install an electric chain saw at the end so we can cut limbs from the ground. (Thus not requiring xray inspections for human riders, and inherently safer.)

So we started looking at equipment, quickly ruled out telehandlers as the boom is fixed to the body, meaning that you'd have to drive to pivot the boom.
We think man lifts would be the best in theory, but they are super heavy and would need a semi truck and trailer to pull around.
That leaves us with bucket boom trucks. They seem to be available and relatively inexpensive, but there is still issues...

First of all, seeing as they were designed to move people around, the hydraulic system must have a very small pump meant for slow actions. I suspect it's not just a small pump but small lines and controls as well.

Also, from what we've seen so far, it is very hard to find a used for sale unit with long reach. Most are around 45 ft, and that isn't enough to limb high trees.

So what I'm getting at slowly here, is that we started discussing if it would be reasonable to build our own boom system?
It's not exactly a high tech design, but we can't just take an existing design and make it bigger as we don't know the grade of steel used in these booms.

Am I correct in thinking that if steel is 40,000psi strength, you can apply 40,000psi to a 1x1x1 cube and it would never become permanently deformed from that? And the same for tensile strength?

How would a boom be designed for something like this? If we have a 40ft long box beam, 3x8 inches and 1/4 inch wall thickness, and the hydraulic ram is attached 5 ft from the fixed end of the boom, how are the stresses calculated? Looking at the cross section of the beam, 3x8 1/4 wall , do we figure out the compressive strength of the bottom half and tensile strength for the top half, and add safety factor to that?

I just want to figure out how that works. I could keep blabbing but I'll wait and see if I'm blabbing in the wrong direction first.

 

[berkeman]

Welcome to the PF.

Maybe you should think a bit farther outside of the box on this. After all, technology has advanced a lot since those "Cherry Picker" type systems were developed. I'm thinking it might just be easier/safer to attach a chainsaw to a medium-size drone...

 

[jrmichler]

Definitely a fun possible project. Add one more constraint: Any part of the machine on the ground should not be underneath the branch being cut.

There is a challenge in mounting a chain saw at the end of a long boom. The boom is flexible, and wants to bounce when the chain saw starts to cut. Controlling that will be a challenge.

Have you considered making some sort of tree climbing machine with a chain saw on a short boom? It could go as high as you make the power / control cable.

 

[Baluncore]

The problem with such a long and slender design is that it will sway around, and so be quite uncontrollable. You will have trouble seeing what you are doing, or be unable to apply the cutting pressure needed with the saw.

“Column stability” will see it buckle and collapse, or it will simply form a horseshoe shape, with the head remaining on the ground.

Look for telescopic crane boom designs that have a truss or employ external wire bracing.
Google images 'concrete pump'.

 

[berkeman]

Add one more constraint: Any part of the machine on the ground should not be underneath the branch being cut.

https://www.dreamstime.com/cutting-...enery-young-man-making-mistake-image107873820

 

[parkland]

I hear you all. Ok I actually want a grapple to grab the branch then cut with saw, and bring branch down or even logs, but just in chunks that a few hundred pounds. They make grapple saws like this but they are heavy duty forestry saws that can lift thousands of pounds and would be too heavy to lift with anything like this.

Also we would install multiple cameras on boom to allow seeing from a screen at the ground.

The drone idea is interesting but I feel like we're a ways away from it being practical quite yet. I'm not rich lol. I'm sure it could be done if someone had deep pockets.

 

[parkland]

Also we have looked at crane masts, it could be a possibility but a lot more work to build, and more limited angles

 

[parkland]

Maybe something Similar to these booms, but without the leveling hold back arms, or whatever that's called

 

[Baluncore]

Ok I actually want a grapple to grab the branch then cut with saw, and bring branch down or even logs, but just in chunks that a few hundred pounds.

Cranes are a very poor choice when it comes to disassembling standing trees. It is extremely difficult to judge the weight of a branch with foliage before it is cut. Crane failures are not gradual, they tend to be catastrophic, and catch out experienced operators. Without some form of limiting, bigger branches will be cut, to see what you can get away with, until the crane topples over or the boom buckles and collapses. That is a very real safety issue.

 

[parkland]

Can always have load sensors on outriggers to trigger the grapple to release 🤔

 

[berkeman]

Without some form of limiting, bigger branches will be cut, to see what you can get away with, until the crane topples over or the boom buckles and collapses. That is a very real safety issue.

Can always have load sensors on outriggers to trigger the grapple to release 🤔

Okie dokie, we gave it a try. Thread closed now per the PF "no dangerous discussions" rule. Thanks everybody for trying to help. Especially whoever suggested the drone... 😉

 

[anorlunda]

If you're thinking about large heavy trees, that is the most dangerous, most difficult, and the lowest paid part of the industry. Trimming thin branches near power lines is easier, safer and is worth more money. Utilities spend lots of money for tree trimming contractors.

Inventive people find clever ways of doing that too.

But making something like that takes more than ideas and invention, it takes engineering skills and hard work. If you want to do things like that, study hard and get an engineering degree first.

There are also low tech ways to do it. Go out, find some of those tree trimming teams and watch them. See what tools they use. Perhaps you could even get a job with them to learn the trade and the tools.