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Here is the model (yellow line is 1ft) of the gantry crane I used to build the real-life model:

enter image description here

It is a little wobbly now that I've built it. I haven't put the wheels on the ends yet. Can you think of any way to make it more stable and strong? I'm afraid of traversing a drop off with a load like this:

enter image description here

Pretend there are wheels and a chain hoist. For the moment, I've put some screws through with the intention of later drilling holes for some long bolts at yet-to-be-determined locations. Any ideas?

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  • $\begingroup$ Engineering is a site providing answers to focused questions, not overly broad ones like this. $\endgroup$
    – user16
    Commented May 26, 2016 at 23:14
  • $\begingroup$ @GlenH7, what if I ask a question specifically about the bracing of my own design I've made in Rhinoceros 5? $\endgroup$
    – uwemlvxh
    Commented May 27, 2016 at 0:01
  • $\begingroup$ that would potentially be on-topic. SE's bias is towards specific, answerable questions. $\endgroup$
    – user16
    Commented May 27, 2016 at 1:49
  • $\begingroup$ The question is now much improved, but could you give us some details regarding how you've done the connections between the different parts? $\endgroup$
    – Wasabi
    Commented May 27, 2016 at 10:07
  • $\begingroup$ @Wasabi, see my edit. $\endgroup$
    – uwemlvxh
    Commented May 27, 2016 at 15:09

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I have some experience in designing gantry cranes in steel (although not timber) and I would say that for the sort of loads you are talking about this does seem a bit marginal, especially given that the material properties of a going length of timber are inherently less certain than those of structural steel sections.

A lot will depend on how the joints are made, again wood is that bit less predictable than welded or bolted joints in steel so you need extra margin of safety to accommodate this. But suffice to say that if it feels 'wobbly' this is not a good sign.

the situation in the second picture of your question is just bad. This imposes a huge bending load on the upright legs and makes the whole system inherently unstable. If you want to do this you need adjustable legs to keep the legs vertical and the beam horizontal. This sort of lean would not be acceptable for any sort of gantry crane, not matter how well constructed.

In this sort of design the likely failure points are the joints between the beam and the legs and buckling of the legs themselves.

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  • $\begingroup$ Just as plausible a failure point is the beam itself under bending at midspan. $\endgroup$
    – Wasabi
    Commented May 27, 2016 at 20:37
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    $\begingroup$ entirely true, although I am sort of assuming that if you can't account for the loads in the beam there is little point asking the question in the first place ;) $\endgroup$
    – Chris Johns
    Commented May 27, 2016 at 20:56
  • $\begingroup$ Do you know of a good resource on structurally engineering wooden joints/braces/etc for load like this? $\endgroup$
    – uwemlvxh
    Commented May 28, 2016 at 0:21

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