Boomilever B/C

jinhusong
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Re: Boomilever B/C

Post by jinhusong » March 3rd, 2020, 11:33 am

scioly2345 wrote:
March 3rd, 2020, 9:36 am
jinhusong wrote:
March 3rd, 2020, 9:33 am
MadCow2357 wrote:
March 3rd, 2020, 7:58 am

It could be the base of your boom compressing, which is rather likely if you are using balsa.
We use basswood base and pre-dented with 40kg pulling. The distal still went lower more than one cm before the boomi broke at 9kg.
Mostly is because the stretch of the tension.
Wdym by “40kg pulling”?
We put a 1/4X1/2 stick on the hook, then pull the hook with luggage scale to 40kg. It will leave a dent on the stick, then we cut the stick around the dent to make the base.

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Re: Boomilever B/C

Post by MadCow2357 » March 3rd, 2020, 2:05 pm

jinhusong wrote:
March 3rd, 2020, 11:33 am
scioly2345 wrote:
March 3rd, 2020, 9:36 am
jinhusong wrote:
March 3rd, 2020, 9:33 am


We use basswood base and pre-dented with 40kg pulling. The distal still went lower more than one cm before the boomi broke at 9kg.
Mostly is because the stretch of the tension.
Wdym by “40kg pulling”?
We put a 1/4X1/2 stick on the hook, then pull the hook with luggage scale to 40kg. It will leave a dent on the stick, then we cut the stick around the dent to make the base.
How much does your base weigh just curious?
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Re: Boomilever B/C

Post by scioly2345 » March 4th, 2020, 6:31 am

jinhusong wrote:
March 3rd, 2020, 11:33 am
scioly2345 wrote:
March 3rd, 2020, 9:36 am
jinhusong wrote:
March 3rd, 2020, 9:33 am


We use basswood base and pre-dented with 40kg pulling. The distal still went lower more than one cm before the boomi broke at 9kg.
Mostly is because the stretch of the tension.
Wdym by “40kg pulling”?
We put a 1/4X1/2 stick on the hook, then pull the hook with luggage scale to 40kg. It will leave a dent on the stick, then we cut the stick around the dent to make the base.
Oh, so no drill and just that dent? Interesting, would’ve never thought of that. Is the stick bass or balsa?
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Re: Boomilever B/C

Post by BigBootyBason » March 4th, 2020, 7:42 am

if one were to use 1/16 x 1/16 bass for tension from a 24" stick. What weight would be ideal for a 24" stick

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Re: Boomilever B/C

Post by jinhusong » March 4th, 2020, 9:04 am

scioly2345 wrote:
March 4th, 2020, 6:31 am
jinhusong wrote:
March 3rd, 2020, 11:33 am
scioly2345 wrote:
March 3rd, 2020, 9:36 am

Wdym by “40kg pulling”?
We put a 1/4X1/2 stick on the hook, then pull the hook with luggage scale to 40kg. It will leave a dent on the stick, then we cut the stick around the dent to make the base.
Oh, so no drill and just that dent? Interesting, would’ve never thought of that. Is the stick bass or balsa?
Basswood. Normally down to 0.4g.

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Re: Boomilever B/C

Post by jinhusong » March 4th, 2020, 9:06 am

BigBootyBason wrote:
March 4th, 2020, 7:42 am
if one were to use 1/16 x 1/16 bass for tension from a 24" stick. What weight would be ideal for a 24" stick
1/16 X 1/16 cannot hold while weight from our experience. Now we use 1/32X3/16. To be safe, I saw many people use 1/16 X 1/8 or 3/32 X 3/32.

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Re: Boomilever B/C

Post by TheRarePinkSheep » March 4th, 2020, 4:15 pm

I recently made a classic tension boomilever. It failed very early with one side of the compression shattering on the wall. For the bottom I used a diagonal and then a straight trusses to connect the compression but I didn't go to the very end at the far wall, and I did triangles for the sides and I tapered the compression but not the tension. Would be the failure be due to faulty balsa or bad design?
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Re: Boomilever B/C

Post by dholdgreve » March 5th, 2020, 5:11 am

BigBootyBason wrote:
March 4th, 2020, 7:42 am
if one were to use 1/16 x 1/16 bass for tension from a 24" stick. What weight would be ideal for a 24" stick
1/16" square WILL hold full load on Div B designs... Gets a little sketchy on Div C designs. We buy our 1/16" squares in 48" lengths ranging from 1.07 to 1.57 grams. Even the very lightest holds with our design, which utilizes 2 tension rods. The key is to keep the rods perfectly straight and create a design that distributes the load gradually over 4 or 5 cm of the rod. Last weekend we tested multiple booms that have carried full load in the past just to see what the max would be, and they consistently broke between 18 and 21 KG

For Div C, I'd recommend going to 3/32 x 1/16"
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Re: Boomilever B/C

Post by michiganmarc » March 5th, 2020, 5:40 am

dholdgreve wrote:
March 5th, 2020, 5:11 am
BigBootyBason wrote:
March 4th, 2020, 7:42 am
if one were to use 1/16 x 1/16 bass for tension from a 24" stick. What weight would be ideal for a 24" stick
1/16" square WILL hold full load on Div B designs... Gets a little sketchy on Div C designs. We buy our 1/16" squares in 48" lengths ranging from 1.07 to 1.57 grams. Even the very lightest holds with our design, which utilizes 2 tension rods. The key is to keep the rods perfectly straight and create a design that distributes the load gradually over 4 or 5 cm of the rod. Last weekend we tested multiple booms that have carried full load in the past just to see what the max would be, and they consistently broke between 18 and 21 KG

For Div C, I'd recommend going to 3/32 x 1/16"
I agree with Dan, for Div C, in our experience even the higher density 1/16 x 1/16" bass sticks are not strong enough to reliably hold the entire load. 1/16 x 1/16 maple would probably be strong enough, but those sticks are about twice the mass of bass wood, so we tend to prefer larger dimensional bass for more contact surface area.

I don't believe there is a single "correct" answer for the tension rods. Over the past 2 years, we have used 3/16 x 1/32, 3/32 x 1/16, and 1/8 x 1/16 all with various levels of success. It depends on your specific design and how much non-pure tension loading is going on.

Don't forget to carefully measure the weight of each stick you are using. While bass wood doesn't have the huge density range that balsa does, there is still a big range - probably 50-60% variation. Make sure you use a balanced set of tension members and keep good records for each build.

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Re: Boomilever B/C

Post by scioly2345 » March 5th, 2020, 7:25 am

michiganmarc wrote:
March 5th, 2020, 5:40 am
dholdgreve wrote:
March 5th, 2020, 5:11 am
BigBootyBason wrote:
March 4th, 2020, 7:42 am
if one were to use 1/16 x 1/16 bass for tension from a 24" stick. What weight would be ideal for a 24" stick
1/16" square WILL hold full load on Div B designs... Gets a little sketchy on Div C designs. We buy our 1/16" squares in 48" lengths ranging from 1.07 to 1.57 grams. Even the very lightest holds with our design, which utilizes 2 tension rods. The key is to keep the rods perfectly straight and create a design that distributes the load gradually over 4 or 5 cm of the rod. Last weekend we tested multiple booms that have carried full load in the past just to see what the max would be, and they consistently broke between 18 and 21 KG

For Div C, I'd recommend going to 3/32 x 1/16"
I agree with Dan, for Div C, in our experience even the higher density 1/16 x 1/16" bass sticks are not strong enough to reliably hold the entire load. 1/16 x 1/16 maple would probably be strong enough, but those sticks are about twice the mass of bass wood, so we tend to prefer larger dimensional bass for more contact surface area.

I don't believe there is a single "correct" answer for the tension rods. Over the past 2 years, we have used 3/16 x 1/32, 3/32 x 1/16, and 1/8 x 1/16 all with various levels of success. It depends on your specific design and how much non-pure tension loading is going on.

Don't forget to carefully measure the weight of each stick you are using. While bass wood doesn't have the huge density range that balsa does, there is still a big range - probably 50-60% variation. Make sure you use a balanced set of tension members and keep good records for each build.
Despite the debate of 1/16 square v. 3/32 square v. 1/32x3/16 v. 1/16x1/8 (what I use), wouldn’t a rectangle size (despite the obvious heavier mass) just be more efficient because the flat side gives a larger surface area to connect tension to compression on the distal end? Last season the most frustrating breaks I’ve had are at the base or hook area, but this season the most frustrating breaks are at the distal end, the tension popping off because I didn’t laminate it enough. Even for states I’m scared to go down to a 1/32 by 1/8 size, but I might try out 3/16 by 1/32, which I suspect the masses for those will be the same as 1/16 by 1/8, if not SLIGHTLY different, either heavier or lighter. Not sure. I might just stick to my normal size since states is in a week and I don’t have much time to experiment.
Last edited by scioly2345 on March 5th, 2020, 11:45 am, edited 1 time in total.
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2020 events - Boomilever, Disease Detectives, Write It Do It, Wright Stuff
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