Boomilever B/C

[fishman100]

Got my rules, here are the 2013 Boom specs!

• Boom can't contact the wall more than 20 cm (Div B) and 15 cm (Div C) below the centerline of the attachment holes, however, there is no limit to the height of the boom above the testing wall.

First of all, thanks so much!
However, what does this spec above mean? Does it mean the boom can't be more than 15cm tall (for div. C), if so, what does the second part mean (no height limit above the testing wall)???

I can post my own idea, but you're better off submitting an official clarification.

Anyways, I think you're right, you can think of the 15/20 cm as the "height" of the boom (like the 15cm max height in 2008), but since the boomilever can extend above the testing wall (and above the attachment holes), there technically is no "maximum height".

[fanjiatian]

I think it means that the bottom point of the boom can't be more than 20/15 cm below the holes in the base, so it's probably referring to height.

Question, what kind of advantages would a shorter vertical member have vs. a longer vertical member?

[iwonder]

What do you mean by long/short vertical members? And I think the rule in question is the same as the second to last bullet in the original post.

[Faustina]

The part that makes me scratch my head is that the "center of the loading block must be between 40 and 45 cm from the testing wall for both Divisions." Why would there be a range (40-45 cm), instead of a minimum distance (>40 cm)?

[retired1]

Height makes a major difference because if the top is the tension member it has a large(better) angle. IE it can hold more. pure vertical would be optimum, but impossible.

The distance from the center of the bolt (hole) to the bottom is the 20/15. 1mm over and you are dropped a tier. It can go as high above the hole as you want. While this makes your angle better, it adds weight and adds a bending moment to the tension member support. IE: till I see a good representation, it will cause problems in my mind. Obviously, you have to have a bit of height above the bolt hole.

The 40 to 45 distance meant something to one of the rule writers. To the rest of us, it is a minimum of 40.0 cm and not 39.95cm. do not worry about it.

[chalker]

The part that makes me scratch my head is that the "center of the loading block must be between 40 and 45 cm from the testing wall for both Divisions." Why would there be a range (40-45 cm), instead of a minimum distance (>40 cm)?

Giving a narrow range makes it easy to setup the testing rig to handle all possible boomilever configurations. When you say just >40, that means you potentially have to be able to support something 50 or 60 or more cm long.

[thsom]

Height makes a major difference because if the top is the tension member it has a large(better) angle. IE it can hold more. pure vertical would be optimum, but impossible.

The distance from the center of the bolt (hole) to the bottom is the 20/15. 1mm over and you are dropped a tier. It can go as high above the hole as you want. While this makes your angle better, it adds weight and adds a bending moment to the tension member support. IE: till I see a good representation, it will cause problems in my mind. Obviously, you have to have a bit of height above the bolt hole.

The 40 to 45 distance meant something to one of the rule writers. To the rest of us, it is a minimum of 40.0 cm and not 39.95cm. do not worry about it.

but if there is a bolt, how can the height be above 15/20 cm.
The setup i see is:
bolt and base



bolt(not necessary)------------------------------------------------------Tension-compression connection

and then connection between the tension-compression joint and the base. difference between top bolt and optional bottom bolt is less than or at 15/20 cm. So, how is it possible to have a boomilever with height above the bolt hole, how is it possible to make one taller than 15 cm?

[chalker]

So, how is it possible to have a boomilever with height above the bolt hole, how is it possible to make one taller than 15 cm?

Someone could easily put a spar sticking straight up at the point of attachment to the bolt hole and try to use it as a higher anchor point for the tension member.... obviously that's not a good design as the spar would snap very easily due to the side load on it, but what you asked was how it's possible, not whether there is any advantage.....

[dholdgreve]

The part that makes me scratch my head is that the "center of the loading block must be between 40 and 45 cm from the testing wall for both Divisions." Why would there be a range (40-45 cm), instead of a minimum distance (>40 cm)?

Giving a narrow range makes it easy to setup the testing rig to handle all possible boomilever configurations. When you say just >40, that means you potentially have to be able to support something 50 or 60 or more cm long.

When I first read this, I too questioned the need for a maximum length, until I remembered a time when a boomilever nearly tipped the testing table over. The further out the load is suspended, the more counterbalance is required from the testing table. Hopefully, all the Event proctors can now test their tables for worst case scenario (15 KG @ 45 CM out) and confirm that the rig will support the boom without it tipping over, or at least know that they need to add ballast to the other end of the table.

[LAndrus]

I cut a piece of 3/4" plywood for my testing wall at school. Does anyone have a good idea how to build the attachment point so I can attach the wall to a standard science lab table.