Mounting Arm Torque for Short Throw Projectors on Different Walls

[SaiQmon]

Hi there,

I'm going to install same kind of short throw projector in multiple locations, with different wall materials. Projector has integrated wall mount arm (see picture).

- How to calculate total torque affecting mounting plate top row screws?

Some locations have plasterboard walls. Board itself will handle this load, but mounting screws can take only 0.15kN / each for plasterboard.

 

[BvU]

Hello SaiQmon, $\qquad$ $\qquad$ !

Load per screw 150 N probably means in the vertical direction ? so with 8 kg no problem expected in the vertical direction. But:

As you may know, torque = force $\times$ perpendicular distance, so the loads will add up to a torque of
$(2.5 * 0.32 + 5 * 0.665 ) * 9.81 = 39$ Nm wrt the wall.

The mounting screws will have to counteract this, and if we pick the lower row as axis of rotation, that means a pulling force on the top row of $39/0.2 = 200$ N or 67 N on each of the three screws. Problematic for the plasterboard ? It at least deserves some attention.

 

[SaiQmon]

Hello SaiQmon, $\qquad$ $\qquad$ !

Load per screw 150 N probably means in the vertical direction ?

150 N is actually pull / tension force ("Sormat OLA" board anchor + Gypsum board standard, thickness 12,5 mm), vertical forces up to 250 N.

Thanks for this, it confirmed my calculations.

 

[BvU]

Okido. Don't go and sit on such an arm !
Not worried about cats or kids jumping on them ?

 

[SaiQmon]

Okido. Don't go and sit on such an arm !
Not worried about cats or kids jumping on them ?

Not really, these are going to be at Tech exhibitions, most likely no cats or kids involved - I'm more considered about drunken engineers

 

[anorlunda]

Some locations have plasterboard walls. Board itself will handle this load, but mounting screws can take only 0.15kN / each for plasterboard.

Be careful. Unless the screws go into the wood studs behind the plasterboard, this is risky. Are you using anchor screws like this?

 

[jrmichler]

I have put screws into plasterboard. A particular screw, perfectly installed in exactly the correct size hole, may hold the rated 150 N if the load is perfectly applied. In the real world, expect an occasional failure. I would want to see screws at least 25 mm into a wood stud, or the anchor shown by @anorlunda. That goes double if you have drunken engineers in the area.