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Re: Towers B/C

Posted: April 17th, 2017, 6:42 am
by Alex-RCHS
Hey guys. This may be the wrong place to ask this, but what is the importance of using a jig?

Re: Towers B/C

Posted: April 17th, 2017, 8:20 am
by Unome
Alex-RCHS wrote:Hey guys. This may be the wrong place to ask this, but what is the importance of using a jig?
Primarily uniformity; building freehand means that you're more likely to end up with some pieces slightly (or greater than slightly) offset, which could significantly weaken the structure. If you look around at competitions, a lot of the structures which look a little distorted were probably built either without a jig or with a poorly designed jig (e.g. basically just placing it on a flat surface and hoping it works), which means that the load is distributed unevenly; the structure will break at the point of weakest load, so an even distribution is important.

Re: Towers B/C

Posted: April 17th, 2017, 8:40 am
by Balsa Man
Unome wrote:
Alex-RCHS wrote:Hey guys. This may be the wrong place to ask this, but what is the importance of using a jig?
Primarily uniformity; building freehand means that you're more likely to end up with some pieces slightly (or greater than slightly) offset, which could significantly weaken the structure. If you look around at competitions, a lot of the structures which look a little distorted were probably built either without a jig or with a poorly designed jig (e.g. basically just placing it on a flat surface and hoping it works), which means that the load is distributed unevenly; the structure will break at the point of weakest load, so an even distribution is important.
All true, and important. Where a good jig helps the most is in....development; as you work to get the weight down; increasing strength/density of parts that break prematurely, cutting down on density/strength of parts that don't break. If every build is the same shape, then you can make adjustments in wood density/strength and know if it works or not. If the shape is even a little bit different, you have no idea whether the adjustments worked or didn't, because the forces on pieces are different. By controlling the 'shape variable', you can actually see/adjust other variables.

If you go back and read through the pages of the tower forum, there is a lot of detailed discussion on why, and how to build/use a good jig, and all other important aspects of dessign and construction.

Re: Towers B/C

Posted: April 18th, 2017, 8:13 pm
by GhostPants_
Balsa Man, I believe BS test results were in the range of 25-28 grams and our tower was actually 1/11 bracing interval.

Re: Towers B/C

Posted: April 19th, 2017, 3:41 am
by Balsa Man
GhostPants_ wrote:Balsa Man, I believe BS test results were in the range of 25-28 grams and our tower was actually 1/11 bracing interval.
Thanks, again, for the feedback. Very fine engineering, btw, getting to full load and then breaking; perfect.

Quick followup set of questions; can't quite tell from the video- the Xs are lap jointed on the outsides of the legs, yes? So that means they are very slightly bowed (either both Xs in a set, or one of the Xs), yes? Did you glue where the Xs cross each other?

That BS range is, btw, pretty typical for 1.2gr sticks. The upper end we found for 1.2s seems to be around 33-34; found 1 1.22 at 36.7.

Re: Towers B/C

Posted: April 19th, 2017, 4:38 pm
by GhostPants_
Yes, X's are glued to the outside of the legs and are slightly bowed and we did glue in the middle of the X.

Re: Towers B/C

Posted: April 19th, 2017, 6:03 pm
by Balsa Man
GhostPants_ wrote:Yes, X's are glued to the outside of the legs and are slightly bowed and we did glue in the middle of the X.
Thanks

Re: Towers B/C

Posted: April 19th, 2017, 7:13 pm
by musicalwhang
Hi all!
States is on Saturday for me and I'm very excited to compete this year. I'm hoping the tower I built for the competition can get a high efficiency.
For the legs, I used 1/8 x 1/8 wood at about 1.2 gr/36". The BS was ~28.5 grams. For my ladders and tension members, I used a combination of .3 gram and .4 gram 1/16 x 1/16 wood. The legs are braced at a 1/5th interval and the lower 3 ladders are lap joints and top 3 are butt joints. Overall, the tower weighs 6.2 grams and I didn't go for the bonus
Attached below are the pics of the tower. I was wondering if anyone had any tips for loading the tower and my possible efficiency. Also, where do you think this tower will break first? Any weaknesses in the design?
Thank you all!
https://drive.google.com/file/d/0ByNusF ... sp=sharing
https://drive.google.com/file/d/0ByNusF ... sp=sharing

Re: Towers B/C

Posted: April 19th, 2017, 7:29 pm
by MIScioly
musical_whang wrote:Hi all!
States is on Saturday for me and I'm very excited to compete this year. I'm hoping the tower I built for the competition can get a high efficiency.
For the legs, I used 1/8 x 1/8 wood at about 1.2 gr/36". The BS was ~28.5 grams. For my ladders and tension members, I used a combination of .3 gram and .4 gram 1/16 x 1/16 wood. The legs are braced at a 1/5th interval and the lower 3 ladders are lap joints and top 3 are butt joints. Overall, the tower weighs 6.2 grams and I didn't go for the bonus
Attached below are the pics of the tower. I was wondering if anyone had any tips for loading the tower and my possible efficiency. Also, where do you think this tower will break first? Any weaknesses in the design?
Thank you all!
https://drive.google.com/file/d/0ByNusF ... sp=sharing
https://drive.google.com/file/d/0ByNusF ... sp=sharing
I'm not an expert on towers by any means, but you should definitely be proud of that build, especially being in division B! I think your tower could hold it all probably, but again, I'm not an expert. It looks very well built.

Re: Towers B/C

Posted: April 19th, 2017, 7:41 pm
by musicalwhang
MIScioly wrote:
musical_whang wrote:Hi all!
States is on Saturday for me and I'm very excited to compete this year. I'm hoping the tower I built for the competition can get a high efficiency.
For the legs, I used 1/8 x 1/8 wood at about 1.2 gr/36". The BS was ~28.5 grams. For my ladders and tension members, I used a combination of .3 gram and .4 gram 1/16 x 1/16 wood. The legs are braced at a 1/5th interval and the lower 3 ladders are lap joints and top 3 are butt joints. Overall, the tower weighs 6.2 grams and I didn't go for the bonus
Attached below are the pics of the tower. I was wondering if anyone had any tips for loading the tower and my possible efficiency. Also, where do you think this tower will break first? Any weaknesses in the design?
Thank you all!
https://drive.google.com/file/d/0ByNusF ... sp=sharing
https://drive.google.com/file/d/0ByNusF ... sp=sharing
I'm not an expert on towers by any means, but you should definitely be proud of that build, especially being in division B! I think your tower could hold it all probably, but again, I'm not an expert. It looks very well built.
Thank you! I spent a lot of time on this forum and even more building the tower