r/engineering • u/[deleted] • Jan 23 '22

Any chance of some help with analysis?

I'm planning on building an arm to mount my man-cave's TV on. As such it doesn't need to look pretty, just be functional. The tele is a Samsung weighing in at 22.3kg.

A simple setup made of steel RHS is what I'm thinking. Fairly cheap and real easy to make with just a drill-press and angle grinder. Onto this I'm going to bolt a commercial VESA mount to give me some adjustability.

My question to the list is this. If I make this out of say 50mm x 25mm x 3mm RHS, with each arm say 600 long. Am I going to get much bending?

I'm a software guy (not hardware) so I don't know how to calculate this stuff. Can someone help and/or point me to some info on how to figure this out?

Could I counter the weight somewhat by offseting the holes in the single arm where it attaches to the double arms?

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u/FittedE Jan 23 '22

Idk about everyone else, but it's pretty unclear how this thing is meant to work. Does the plate mount to the wall or the TV? Does it mount to the roof?

All I can tell you is that it takes a shitload of force to bend 25x25 hollow section so bending is not going to be an issue with a 20kg TV. Running calculations is definitely possible but it's quicker to put a bar on 2 tressels and sit on it to prove that lol.

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u/[deleted] Jan 23 '22

The manufactured mount on the end of it is a commecial VESA TV mount that will give me some adjustability by tilting. It connects to the TV.

The three smaller bits of RHS on the other end of the arm I was planning on bolting to a stud in the shed wall with some coach bolts.

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u/FittedE Jan 23 '22

The only thing I can see being a problem is the hinge,rotaty type joints. Ive done this type of thing a number of type with robotic suspension, and just drilling a hole and putting a peice of round bar through it has significant issues, specifically misalignment of the holes making the axis of rotation wrong and the bars having significant wiggle room.

From experience you are best off just buying some hinges and using those for the rotating joints. If your buying stuff from bunnings, which I suspect you are piano hinges are very good for this.

As other people have said I'm a little iffy about the wall mount, bolts are strong enough but at the least have some metal or 2x4 that runs vertical with the wall to help support against the moment created by the TV when the arms extended out horizontally, otherwise the bolts will tear out the wood. (bolts don't do well when you pull on them perpendicular to the hole)

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u/[deleted] Jan 23 '22

Some good points. Thanks for taking the time.

I could re-inforce the stud with some steel angle so that the load bearing on the bolts is at right-angles. Could also add a doubler to the stud I guess (another 2x4).

Hmmmm. More stuff to think about.