Towers B/C

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Tesel
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Re: Towers B/C

Post by Tesel » March 2nd, 2017, 10:09 am

HandsFreeCookieDunk wrote:Does anyone here have any recommendations for gluing techniques? After examining my joints, it seems like they are definitely weaker than the balsa itself. I'm currently using the widely accepted method of picking up small drops between two pins and placing them at the edge of the joint, but it seems like this just isn't giving me the strength I need.
Part of the problem may be the style of joints you are using. Are you using butt joints for the ladders, to provide superior compressive strength? Lap joints for your bracings, to maximize the tension forces? Also, what type of glue are you using?
Balsa man will be able to answer more, but there are multiple additional considerations that would be helpful to know. The strength of joints depends on a lot of things, not just the amount of glue.
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Re: Towers B/C

Post by HandsFreeCookieDunk » March 2nd, 2017, 10:11 am

Tesel wrote:
HandsFreeCookieDunk wrote:Does anyone here have any recommendations for gluing techniques? After examining my joints, it seems like they are definitely weaker than the balsa itself. I'm currently using the widely accepted method of picking up small drops between two pins and placing them at the edge of the joint, but it seems like this just isn't giving me the strength I need.
Part of the problem may be the style of joints you are using. Are you using butt joints for the ladders, to provide superior compressive strength? Lap joints for your bracings, to maximize the tension forces? Also, what type of glue are you using?
Balsa man will be able to answer more, but there are multiple additional considerations that would be helpful to know. The strength of joints depends on a lot of things, not just the amount of glue.
The joints in question are lap joints for tension members, joining 1/8 leg to 1/16 bracing member with CA.

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Re: Towers B/C

Post by Tesel » March 2nd, 2017, 10:26 am

HandsFreeCookieDunk wrote:
Tesel wrote:
HandsFreeCookieDunk wrote:Does anyone here have any recommendations for gluing techniques? After examining my joints, it seems like they are definitely weaker than the balsa itself. I'm currently using the widely accepted method of picking up small drops between two pins and placing them at the edge of the joint, but it seems like this just isn't giving me the strength I need.
Part of the problem may be the style of joints you are using. Are you using butt joints for the ladders, to provide superior compressive strength? Lap joints for your bracings, to maximize the tension forces? Also, what type of glue are you using?
Balsa man will be able to answer more, but there are multiple additional considerations that would be helpful to know. The strength of joints depends on a lot of things, not just the amount of glue.
The joints in question are lap joints for tension members, joining 1/8 leg to 1/16 bracing member with CA.
I think I understand your problem. If you put too much glue on the joints for the ladders, they interfere with the joints for the bracings as the CA glue seeps into the wood. It makes it impossible to get a good seal and joint. You would need to sand off the top layer to get a better joint.
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Re: Towers B/C

Post by Balsa Man » March 2nd, 2017, 10:47 am

Tesel wrote:
HandsFreeCookieDunk wrote:
Tesel wrote:
Part of the problem may be the style of joints you are using. Are you using butt joints for the ladders, to provide superior compressive strength? Lap joints for your bracings, to maximize the tension forces? Also, what type of glue are you using?
Balsa man will be able to answer more, but there are multiple additional considerations that would be helpful to know. The strength of joints depends on a lot of things, not just the amount of glue.
The joints in question are lap joints for tension members, joining 1/8 leg to 1/16 bracing member with CA.
I think I understand your problem. If you put too much glue on the joints for the ladders, they interfere with the joints for the bracings as the CA glue seeps into the wood. It makes it impossible to get a good seal and joint. You would need to sand off the top layer to get a better joint.
Hmmm.... I'm inclined to think the problem is a combination of wood density and glue technique. What density (36" stick weight) of 1/16 are you using? If you're in the 0.2, 0.3, 0.4 range, the weakness is in the wood, not the glue; as discussed in an earlier post, under tension, thin layer of the wood will shear off. If you use 1/16 x 1/32 at twice the density (same stick weight), you'll have a significantly stronger joint under tension loading. The other factor is technique. The thin glue, 2 pin applicator approach for the butt joints for ladders is fine. There should be no excess glue from this. Virtually no glue is needed for the ladders; just enough to hold them in-place (so seepage from ladder joints is not/should not be an issue; sanding won't help, if there is a bit of thin CA soaked in, will only strengthen the joint). But to get the Xs/tension members to hold, you want to make sure there is a glue layer across the full contact zone of the 1/16. Best way I know to do that is a microtip applicator, using medium CA; you can run a thin glue line on/across the contact line. Using thin CA/2 pin applicator and wicking into the joint will likely not get a glue layer across the contact area, so joint will be weaker than with a line of medium CA
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Re: Towers B/C

Post by HandsFreeCookieDunk » March 2nd, 2017, 7:22 pm

You know, I think we can all say that thanks to Balsa Man, all of us know more about towers than we knew we wanted to know. But in all the discussions we've had about what makes a good tower and in looking at the forces that go into it, I've noticed that it seems as though the actual geometry of the tower doesn't matter all that much as long as it's symmetrical. Normally the trope you hear in these building events is "Always use triangles!", but they never really came into play.

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Re: Towers B/C

Post by musicalwhang » March 2nd, 2017, 7:33 pm

https://drive.google.com/file/d/0B1BYt2 ... sp=sharing
Hello, so I built this partially complete tower weighing in at about 7.3 grams and I am curious as to how I should connect these two sides together without constructing a jig. How can I accurately get these two sides in place and finish this tower?

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Re: Towers B/C

Post by dhdarren » March 2nd, 2017, 8:21 pm

musical_whang wrote:https://drive.google.com/file/d/0B1BYt2 ... sp=sharing
Hello, so I built this partially complete tower weighing in at about 7.3 grams and I am curious as to how I should connect these two sides together without constructing a jig. How can I accurately get these two sides in place and finish this tower?
I've been in this situation before, and here's what I did:

Just as you have those blueprint drawings as shown in the picture, use it for these two sides of the tower. But instead of having just sticks, you need to stand them the two sides over the drawing, so that you have the two tower sides sticking up vertically on the side of its legs. Use tape to secure one to the drawing, but don't tape it down too tight, because you'll need a little bit of wiggle room for it to move. Then, cut TWO sets of ladders that will be used to connect the sides. When you have them cut out, tape the other side down in the same manner, then glue in the ladders on the side that is elevated, sanding accordingly to make smooth fits. It is important that you do the top side first because if you do the bottom first, the top may not be at the correct spacing between the two sides. By doing the top first, the bottom will be at the correct spacing set by the tape, and the top will be at the spacing as per the ladder lengths. When you have those glued, you can either glue in the bottom ladders with the sides still taped down, or take it off if the other parts of the ladder get in the way of your hands. After all the ladders are attached, you can take it off and add all of the X bracing.

This worked alright for me, and I got a score of 1360 using this method (no bonus), so really wasn't awful, but it probably can't fully replace a jig; I did notice a very slight deviation from 90 degrees at the corners of the tower, so it might have had a negative effect, but it was definitely close to perfect. This is just what I did, and I'm sure there's other better ways to do it. If anybody else has other methods, I'd be very interested :)
2015:
R | S
Bridge: 1 | 8
AirTraj: 5 | 26
WS: 12 | 9
Scrambler: 6 | 17
DP: 7 | X

2016:
Bridge: 2 | 15
AirTraj: 2 | 6
WS: 3 | 11
DP: 4 | 15
GeoMap: 4 | 25

2017:
Heli: 1 | 1
Hover: 1 | 4
Towers: 2 | 15
DP: 1 | 6
Wind: 2 | 8
2018:
R | S
Heli:
Hover:
Towers:
DP:
Eco:
MV:[/b]

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Re: Towers B/C

Post by Balsa Man » March 3rd, 2017, 7:36 am

HandsFreeCookieDunk wrote:You know, I think we can all say that thanks to Balsa Man, all of us know more about towers than we knew we wanted to know. But in all the discussions we've had about what makes a good tower and in looking at the forces that go into it, I've noticed that it seems as though the actual geometry of the tower doesn't matter all that much as long as it's symmetrical. Normally the trope you hear in these building events is "Always use triangles!", but they never really came into play.
Good observation; symmetry is critical for a….high performance tower (or any other structure). Remember that engineering is about approximations that work. If all 4 legs are exactly the same length, lean in at exactly the same angle, are all symmetrical to the vertical centerline, we can assume the load is equally distributed, and (closely) approximate the forces under load, and with testing and calculation, identify sticks that are as light as possible to carry our “design loads.” This analysis, the basis for design and wood selection that we’ve been discussing is a “static” analysis- a perfect structure that doesn’t move. You learn about the relationships and principles we’ve been using in ‘statics’ engineering courses. Its fairly simple and straightforward once you understand it. The more precisely you build, the closer to an ideal, static structure you get, and the closer to ‘the limits’ (of the strength and weight of wood and strength of joints) you can get.
But we all know that any real tower never gets ‘perfect.’ Little variations exist; a slight bow in a leg stick (even though with bracing in-place, its held very close to straight, a slight difference in leg length, either top or bottom leg ends slightly off….design angle, so the load going through the leg is not perfectly axial (i.e., some amount of bending is being induced under load).

A real tower under load is … a dynamic situation/system. If you watch very closely, at some load, little movements occur. In towers that are not precisely built, these distortions come in with relatively little load; overall twisting of the structure starts, and failure happens quickly. If you’ve ever taken a tower that only has ladder bracing in place, put a plate on top so you can put a little down pressure on, you’ve seen how it is easy to ….rotate the plate, or ‘translate’ the plate (moving side to side without rotation), and the whole structure either twists or leans. But what happens when X (or Z) braces are put in? The whole structure…stiffens dramatically- the bracing stops (up to some loading level) twisting/leaning. These X or Z braces form…..triangles. So, yes, triangles come into play, and they are critical to dynamic structural rigidity.
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Re: Towers B/C

Post by Balsa Man » March 3rd, 2017, 2:23 pm

dhdarren wrote:
musical_whang wrote:https://drive.google.com/file/d/0B1BYt2 ... sp=sharing
Hello, so I built this partially complete tower weighing in at about 7.3 grams and I am curious as to how I should connect these two sides together without constructing a jig. How can I accurately get these two sides in place and finish this tower?
I've been in this situation before, and here's what I did:

Just as you have those blueprint drawings as shown in the picture, use it for these two sides of the tower. But instead of having just sticks, you need to stand them the two sides over the drawing, so that you have the two tower sides sticking up vertically on the side of its legs. Use tape to secure one to the drawing, but don't tape it down too tight, because you'll need a little bit of wiggle room for it to move. Then, cut TWO sets of ladders that will be used to connect the sides. When you have them cut out, tape the other side down in the same manner, then glue in the ladders on the side that is elevated, sanding accordingly to make smooth fits. It is important that you do the top side first because if you do the bottom first, the top may not be at the correct spacing between the two sides. By doing the top first, the bottom will be at the correct spacing set by the tape, and the top will be at the spacing as per the ladder lengths. When you have those glued, you can either glue in the bottom ladders with the sides still taped down, or take it off if the other parts of the ladder get in the way of your hands. After all the ladders are attached, you can take it off and add all of the X bracing.

This worked alright for me, and I got a score of 1360 using this method (no bonus), so really wasn't awful, but it probably can't fully replace a jig; I did notice a very slight deviation from 90 degrees at the corners of the tower, so it might have had a negative effect, but it was definitely close to perfect. This is just what I did, and I'm sure there's other better ways to do it. If anybody else has other methods, I'd be very interested :)
That's certainly a reasonable way to handle the situation. The biggest potential drawback is that without a jig, it is very difficult to get all 4 leg bottom ends in the same plane, and get the overall tower truly vertical.. If only 3 of the leg ends are in the same plane, two of the legs end up up carrying significantly more than 50% of the load, and break prematurely.. Even if you get all 4 legs in the same plane, if the tower is not very close to vertical (if its leaning to one side.....by a millimeter or two, again, two legs get significantly more than 50% of the load, and you get premature failure. With careful sanding and measuring, you can get it 'trued-up', but its work.....
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Re: Towers B/C

Post by Random Human » March 3rd, 2017, 8:09 pm

musical_whang wrote:https://drive.google.com/file/d/0B1BYt2 ... sp=sharing
Hello, so I built this partially complete tower weighing in at about 7.3 grams and I am curious as to how I should connect these two sides together without constructing a jig. How can I accurately get these two sides in place and finish this tower?
Musical_Whang here is a great video explaining the purpose of trusses, pretty much what Balsa Man said but in an actual video
https://www.youtube.com/watch?v=Uv0G4OwRWCw
Hope this helps!
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