this is my first time posting on here and I have a question regarding the structural properties a beam will need in order to fulfill some requirements we have for our robotics team. The scenario is as follows: Our robot has two wings that drop to our sides in order to support two other robots in order to simultaneously lift all three. The situation results in the lifted robot applying a large amount of force on the top of two beams supported only from the side of the wing held against the robot frame. The current wings we have are made out of 1/16in aluminum tubing, which has ended up being heavy and not sturdy enough for our needs.

We have been doing research on potentially using fiberglass or carbon fiber rods. We think that 3/4in OD solid fiberglass rods will be strong enough for what we need, but are not sure. I understand that fiberglass is very flexible, and while this normally would be good we only have room for about an inch of bending. This is because all three robots must clear 12 inches while being lifted, and we lift ~15 inches up. This only leaves 3 inches of clearance, and we would like to keep as much wiggle room as we can for any tilting/unbalancing after lifting.

Because of this, we looked to hollow carbon fiber tubes. We can afford .625in OD .515in ID Pultruded rods, but after doing research we believe these will be ineffective, as they focus on tensile and compression strength, while the force we are dealing with is transverse on top of the tube. As roll wrapped rods are quite expensive, the largest tube we can afford is .422in OD .372in ID twill rods. I understand because the way the fibers are directed, roll wrapped rods are much stronger in dealing with perpendicular or twisting forces, but believe the size we will need to support the robot is outside our price range.

Obviously this quite a lot and I dont expect anyone to completely solve our problems. I have presented all this information in hopes someone can provide the methods we can use to calculated the type of rod we will need and its amount of deformation, bending, breaking point, etc. We are currently planning on using the previously mentioned 3/4in OD solid fiberglass rods from goodwinds composites, held by an aluminum holding piece that attaches the rods to the frame. Below I will attach some pictures and diagrams to better express the forces involved and our setup. Keep in mind that weight is a huge factor as well, but we think we any composite used will be lighter than our original wing. Currently each one is around 5lbs

Thanks guys!


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  • $\begingroup$ This is a fairly common type of engineering calculation . Check this out and see if you can work through to the solution: mechanicalc.com/reference/beam-analysis. You'll need to look into yield criteria to find the breaking point, after you've calculated the extreme loading cases. $\endgroup$ – C.R Mar 18 '18 at 6:42

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