Boomilever B/C

[TheChiScientist]

We tried using the base with the hole as described in Aia's guide but I don't think that will work with the hooking mechanism. We always have issues with setting up the boomilever or with it breaking where the tension cords attach to the base since there is no way to rotate the boomilever if you have such a rigid base.

I think we will switch to a base where we just use a thicker stick of balsa/basswood or a dowel like you suggested. As long as it is sufficiently thick then it should do the job since it's unlikely it will snap if it's just 5cm long. The joints will still be an issue though since there is less gluing surface area.

Yea I encountered the same issue initially. Just curious to see how others are resolving this problem... Has anyone figured out how to do a proper boom set up using the bridge/tower loading device?

I can't seem to understand why so many people are stubbornly trying to make bases designed for bolt attachment work with J-hook attachment....

*COUGH* Aia's guide to making a Boomilever *COUGH*

[rschmitz]

I built the testing wall, however I am concerned about how far out the inside diameter of the j-hook should be. It only mentions the opening needs to be 2.5cm from the wall. I bought the J-hook from Lowes. It has a straight part to it before it curves. The parameters do not say how long that can be. In particular the distance from the wall to the inside diameter of the j-hook distance can change due to style of J hook. Mine is 4.4cm from wall to inside of Jhook.

I believe the rules go into pretty deep detail, identifying the exact sku # and manufacturer of the specified hook, so technically they should all be the same, but you are correct, there will always be those out there that think that all 1/4" J hooks are the same. The only way to be sure is to check with the E/C well before the competition for his specific hook dimensions.

Thank you, somehow I missed that. I looked at Lowes and the stock number is not exactly the same. Checked Amazon and they want $4.95 for each J hook. did a google search, found them for $0.50 at the following website. I ordered 12 and payed $13 in shipping (still better than $5 each)
https://www.hardwareworld.com/pc44398/J ... nc-1-4-x-4
Once I get these in I will check to see if the Lowes J hooks are an "exact equivalent" as stated in 5.a.ii

I have checked. the ones I bought at the local Lowes are the exact same as the ones I ordered on line. The ones at Lowes were only $0.92 (and no shipping lol)

[dholdgreve]

Keep in mind that you are dealing with Mechanical "Disadvantage" here... You have a 15 KG load applied vertically to the distal end of the boom, but at a 2:1 ratio (40 cm out, 20 cm up) that works out to a 30 kg compressive force (147 Newtons) applied to the wall and and equal tensile force.

With Div C being even shorter in height, the forces increase to 40 kg. in both tension and compression.

You can use these values to plug into Euler's buckling theorem along with SFPD values to determine bracing and support spacings...

This of course is dependent on the cross section shape of your compression beams. If they are square, you are golden... If they are rectangular, the SFPD value used will in all likelihood be for only for the smaller of the 2 dimensions. This will help you design the bracing for only one axis... You will need to create a way to test the SFPD of the stronger (wider axis) or just go with calculations determined from the weaker axis, and improvise as your design matures should you determine that your calculated and braced smallest dimensional axis is now stronger than the larger axis. Then adjust your bracing in that plane accordingly.

[Cow481]

What scores have you all been getting so far. I made 2 so far with one disappointing result at around 350 and one decent result at 700.

[TheChiScientist]

What scores have you all been getting so far. I made 2 so far with one disappointing result at around 350 and one decent result at 700.

Trust me you're not alone. I started out exactly the same way. Now my scores are 800+. average. This is why I think competitive scores will fall in 1000+.

[cheese]

Yeah I think a lot will be just refining minor parts. I have found that an imbalance in how long your tension beams are can result in crazy twisting.

[TheChiScientist]

Yeah I think a lot will be just refining minor parts. I have found that an imbalance in how long your tension beams are can result in crazy twisting.

IKR!!!!!! AGH!!!!!!!! What other build problems have people faced? Best to address them now vs later.

[cheese]

I think, to a point, you need to be ultra precise on how even your column pieces are as well as your tension pieces. It will be very similar to towers, where if your tower wasn't perfectly level, there will be an imbalance which may cause the death of your boom.

[Cow481]

I think that the angle of the tension pieces compared to the compression pieces is very important and you need to be very accurate with it

[dholdgreve]

Boom has been an event before. In 2014, here were the primary reasons for failures:
Compression Beam failures (Buckling). 43%
Wall Attachment point failures 39%
Tension chord failures (Sear parallel to grain) 11%
Load point failures (Distal end snap offs) 5%
Twisting and torquing due to symmetry issues 2%

If you pay attention to issues relating to the most prominent failures above, you are almost home!