# Boom Arm Math

• Jun 26th 2010, 11:32 PM
Gromit
Boom Arm Math
Hi
I'm desgining a projector screen boom arm for a college project and need help with some math.

http://i54.photobucket.com/albums/g1...oomarmhelp.jpg

I need help in working out B and D from the image I have attached.

The load is 30kg and the span in 12'

Any help work be great!

thanks
Michael
• Jun 27th 2010, 04:44 PM
bjhopper
Hello Michael,
A similar problem
A 2000 lb weight is attached to a 20 ft boom which is supported to wall and by a cable attached 11.5 ft above the lower mount. A force diagram shows a 4000lb tension in the cable 2000 lb downward force at the beam attachment and 3464 lb compression in the beam . This is what you need to do for your problem.The distance between the supports must be determined by you .You might try 4 ft. Stresses at the hinges and wall supports have to be calculated
• Jun 28th 2010, 09:44 AM
Gromit
bjhopper

Thanks for the help.
How did you come up with 4ft?
Sorry but i'm really rusty with my maths!
• Jun 28th 2010, 10:36 AM
bjhopper
Hi Michael,
As the designer you have to make the decision based on wall or structure attachment and secondly to minimize the costs of materials,4 looks a reasonable start

bjh