3-Cubed
- Thread starter Alan R
- Start date
Help Support The Rocketry Forum:
- Joined
- Aug 27, 2011
- Messages
- 7,355
- Reaction score
- 2,300
Not hard at all.
couple of ways, the "Mathematical/Scientific way" and the "Eyeball" Method"
In either case, you are making a three sided pyramid rather than a true cone.
The First way.
Measure the diameter/width of one of your rocket body sides (presumably they should all be the same.)
Select the Angle you want for the Apex. Call it Theta
Make an Isosceles triangle. Use 1/2 the width of the body side for the base, 1/2 your selected angle for the apex, and Tangent function
reminder here, I always get them mixed up
Sine, Cosine, Tangent, explained and with Examples and practice identifying opposite, adjacent sides and hypotenuse
This page explains the sine, cosine, tangent ratio, gives on an overview of their range of values and provides many practice problems on identifying the sides that are opposite and adjacent to a given angle.
www.mathwarehouse.com
to get the height (adjacent),
tangent Theta= opposite/adjacent = (1/2 your body side width)/height.
solving for height
Height = (1/2 your body tube side width)/tangent Theta
This gives you measurements of a triangle that makes up 1/2 (right or left side) of each of your three pyramid facets.
Draw it out on paper (in fact, use cheap paper, old notes already written on one side that you are going to throw away, whatever), and cut it out and compare it to your actual model. Depending on the angle you pick, you may find it too stubby or too long. You can pick a new Theta until you get what you want.
The Second way.
Measure the diameter width of one of your rocket body sides.
Draw a horizontal line in the mid line (right to left) near (or at) the bottom of a sheet of paper, the length of this measurement.
Mark the middle of this line.
Use a right angle (I like to use those throw away cardstock advertisements you get in the mail) to draw a vertical line from your first line midline all the way to the top of the page.
Pick a point on this line and draw in pencil lines from that point to the right and left lateral edges of your first line. What point doesn't really matter, I'd say start with a point the length of your width line.
Eyeball it. If it looks too stubby, try a new point a bit higher. If it is too long, go down a bit.
One you get a "facet" side you are happy with, next step depends on your construction materials.
If you go with Balsa, use either of the above to make a card stock template from the facet pattern you have selected above.
I don't use balsa, so I am not sure what GRAIN orientation to use. What I would recommend would be a two ply method, use 1/16" balsa (you can go thicker) to cut three triangles with the grain PARALLEL to the long axis of your template and three with the grain ORTHOGONAL to the long axis of the temple. Glue one of each together with wood glue, use a hotel key card or other squeegee to make sure you get full coverage over the surface of one of the sides but as little glue as possible remaining ON the fin, mate the fins together, stick them in a fold of parchment paper or wax paper, and shove them in an OLD throw away book, maybe with some weights on it, overnight.
Once they are dry, sand a bevel (about 60 degrees, won't be exact because you are not making a "tube" but a pyramid, but 60 degree will probably be close enough for government work) toward the INSIDE face of the LATERAL margins of the facets, and glue them together
If you are going with cardstock or mating board, you can either use the template above and trace three triangles, lateral edge to lateral edge to lateral edge, and then add on overlap on the last lateral edge to give you a glue tab to tuck inside.
OR, if you went with the Mathematical/Scientific method, and especially if you have a 360 degree protractor, you can measure out three "Thetas", draw the lateral margins the calculated length of the hypotenuse using Geometry sin function OR math (Square the 1/2 base edge length, square the height, add them, and take the square root), and draw them directly on your card stock or matting board (the stuff they use to highlight pictures that are too small for the frame). If you have a preference for which "side" you want to face the outside of the facet, draw your pattern on the "non" face side. Use a ball point pen drawing a "heavy" line on the lateral edges of the triangle, or the back side of the knife, to "score" (deeply impress but NOT cut) the edges. This will make the folds easy.
To make "shoulder", measure the "inside" diameter" of your rocket "sides", go a bit smaller (say a mm or 2), and cut a cardboard shoulder to fit inside your triangular tube. Stick in halfway, eyeball the corner cutouts you will need and fold these inwards. Rest your nose pyramid on top until you get the fit you want. Lightly tack (medium CA?) the shoulder tabs onto the pyramid with it perfectly positioned and masking taped to the body (be careful NOT to put so much glue on you glue the shoulder into the body!)
Once you get it perfect, you can insert a short segment of dowel that easily fits into the central "hole" in the shoulder into the nose cone. Put a screw eye into it for shock cord attachment. This I would glue in place using Gorilla Polyurethane glue, with the nose cone pointed DOWN while it dries. You may want to put masking tape or some other method to seal the "free" edge if you went the folded origami route, polyurethane glue has a knack for leaking out tiny cracks and then foaming into big ugly globs.
Anyhoo, probably more than you wanted to read, hope this helps.
Wow. You outdid yourself there. Thank you for your interest and help. Some of that will be useful.
I was just going to do some measuring and then a few trial and error attempts. The tricky part - trying to include the shoulder into the NC pattern as a single piece. A little more complicated, but doable.
Probably head back to Blocklayer and see what they've got. Start with something from there. I love their patterns.
- Joined
- Aug 27, 2011
- Messages
- 7,355
- Reaction score
- 2,300
COMPLETED Gyskelion Build Thread--Non-Competition Helicopter
Okay, here goes. Gyskelion is a three rotor helicopter. Up front for safety purposes (especially given the drought and recent fires) please note this is an ENGINE EJECT rocket, so caution is REQUIRED when firing this puppy in drought ravaged areas (or any dry grass or timber.):y...
www.rocketryforum.com
See post 55
Interesting thread.
Time to just say it now.. I'm getting really frustrated. The body sides are not equal length and it's giving me lots of headaches with the NC. Inside lengths are 77mm, 70mm, 68mm
Not sure where I'm going: deal with it, re-do the body fold, or just take a long break from frustration.
Last option most likely at this point.
- Joined
- Aug 27, 2011
- Messages
- 7,355
- Reaction score
- 2,300
Enemy of good is better, enemy of better is perfect.
If the dimensions of the sides aren’t equal, your nose pyramid is going to be a bit eccentric. If you have enough finnage and velocity, it won’t make much difference. Look at the Nimbus
You need isosceles triangles, not equilateral triangles. My preference is for taller skinnier triangles, but not sure it matters.
All three triangles need to have the same length SIDES, they do NOT have to have the same length BASE.
Build the pyramid first, then build a shoulder that fits into the body, THEN figure out how to mate them up.
When I started this I honestly thought it would just fold together in a few hours.
I confess that this project has been one of the longest, most frustrating builds I've ever done.
Thank you for the tip. I can see that you're correct. I think the way to do that is get out the compass again and make a new NC pattern.
Air is still bad outside here today so nice time to tackle the problem.
- Joined
- Aug 27, 2011
- Messages
- 7,355
- Reaction score
- 2,300
Lol, it gets easier after your first 100 tries!
Use the OUTSIDE diameter of your tube edges for the pyramid base dimensions. Use the INSIDE diameter of the tube dimensions minus a couple mm for the shoulder.
Oh i know that much. I kept trying to make a nice equalateral nc and it just never jibed. plus I was trying to make it so it would fold together in one piece including the shoulder. Now I'm just going to glue the shoulder piece in to the point after i get it all figured out.
I had lots of downtime at the last launch so I played with this. Got a nice origami nose cone finally just using cardstock.
I rolled a launch lug from a coffee filter (hey, i was camping.. didnt have lots to work with). First flight, D12-5. it hung on the rod. I cut the lug into 2 short pieces, used some quick epoxy and tried again couple hours later.
Second flight, I decided a bit bigger motor would help also. AT-E20. ... just like a disaster video... off the rod and end over end. Most likely the heavy motor causing a CG error.
No serious damage. It's going to get about an ounce of clay into the nose and that should stabilize things much better.
220 Grams with the D12 motor and streamer.
Just like @BABAR said there.. I used a compass to make equal sides, but different length bases and got a working NC with built in-shoulder. all one piece. Used an estes mount on the nc for the shock line.
I rolled a launch lug from a coffee filter (hey, i was camping.. didnt have lots to work with). First flight, D12-5. it hung on the rod. I cut the lug into 2 short pieces, used some quick epoxy and tried again couple hours later.
Second flight, I decided a bit bigger motor would help also. AT-E20. ... just like a disaster video... off the rod and end over end. Most likely the heavy motor causing a CG error.
No serious damage. It's going to get about an ounce of clay into the nose and that should stabilize things much better.
220 Grams with the D12 motor and streamer.
- Joined
- Aug 27, 2011
- Messages
- 7,355
- Reaction score
- 2,300
