Boomilever B/C

[iwonder]

But remember that you need to hold somewhere about 45kg (it's a tad less, round up for safety factor) in compression. I've used 1/8"x3/8" compression members with a 1.5" bracing interval with successes. It's not super light, but it's reasonable (my boom with those members weighed a tad over 15g). Oh, and that's for C divison, I'm not sure of the B div rules...

However, your math is almost spot on for what you were trying to solve. If something buckled at 1 kg then 4 braces on it would bring it up 2^4 times, to 16kg. You'd end up with an 11cm bracing interval (the units were the only issue ).

[balsaandbass]

Hi, this is my first year doing Boomilever, and I was wondering how wide you would recommend to make it? I would guess somewhere between 4cm to 3in?

[iwonder]

Typically the ones I see are pretty close to 5cm wide. Any wider and they could bow under the weight (when you're looking down the length of the compression member) and any narrower and it's hard to glue the tension members on.

[jma]

But remember that you need to hold somewhere about 45kg (it's a tad less, round up for safety factor) in compression. I've used 1/8"x3/8" compression members with a 1.5" bracing interval with successes. It's not super light, but it's reasonable (my boom with those members weighed a tad over 15g). Oh, and that's for C divison, I'm not sure of the B div rules...

However, your math is almost spot on for what you were trying to solve. If something buckled at 1 kg then 4 braces on it would bring it up 2^4 times, to 16kg. You'd end up with an 11cm bracing interval (the units were the only issue ).

Thanks Iwonder. I updated the unit to cm.
Is 45 kg for divison C? We did some calculations and we got 32 kg (16 kg for each individual member). Could we have made a mistake?

[fanjiatian]

My compression members buckle at 1.17 & 1.22 kg so I need to have about 4 X-bracings to increase their strengh to 16 kg. Do you think that an 11-cm bracing interval will work? I would appreciate any advise. I'm using 1/16 square.

If you don't mind me asking, how did you pull that off? That's seriously impressive
Did you use dense wood to compensate for the smaller cross section?

[fanjiatian]

I've got an L-Shaped jig and all I have to do is align and tack down the compression member in place, set my base in place (probably take a third hand this year) and then I can glue the tension members onto the distal end and the base at the same time, no worried about angles and lengths being wrong.

That's really cool! An accurate and efficient way to connect the bases
But does that mean you have to take the boomilever off the jig before you can attach bracings to the compression members? How would you attach the bracings without flipping over the jig itself?

[jma]

My compression members buckle at 1.17 & 1.22 kg so I need to have about 4 X-bracings to increase their strengh to 16 kg. Do you think that an 11-cm bracing interval will work? I would appreciate any advise. I'm using 1/16 square.

If you don't mind me asking, how did you pull that off? That's seriously impressive
Did you use dense wood to compensate for the smaller cross section?

1/16 is for bracing.

[iwonder]

That's really cool! An accurate and efficient way to connect the bases
But does that mean you have to take the boomilever off the jig before you can attach bracings to the compression members? How would you attach the bracings without flipping over the jig itself?

I assume you mean bracings on the compression member? I attach those before I put it on the jig, so I build the entire compression truss then add the tension members after it.

Is 45 kg for divison C? We did some calculations and we got 32 kg (16 kg for each individual member). Could we have made a mistake?

So here's my math, it could be just as flawed. You have a 15kg load at the distal end, and an angle between the compression and tension members of about 19 degrees. Picture the forces acting like a right triangle (it's a equilibrium problem like in a first year physics course), with 15kg on the opposite leg, and a 19 degree angle between the adjacent leg and the hypotenuse, the force acting on the adjacent leg (that's compression, the hypotenuse is the tension member) becomes the force on the opposite leg divided by the tangent of the angle, or 15/(tan(19)), which is 43.56, I round to 45 for a small margin of error.

[chinesesushi]

Hello guys. I have 2 questions and I would be extremely appreciative of anyone who might reply.
1. What's your guys' weights of the base/how are you constructing it? I don't know how much a base should weigh in order to yield the greatest efficiency.
2. What's the type of wood and the dimensions of the wood of your guys' tension members? The last boomilever I built failed because of the tension members snapping. I used 1/16" X 1/16" basswood.

Thank you!

[iwonder]

Have you checked out Aia's boomilever guide? It's on the wiki (there's a link at the bottom of the boomilever page) and it answers both of those questions really well!