Building The Rocket Doctors Recommend Most (Part 2)

I cut the BT-50 tube to length; it’ll go from about a quarter inch behind the forward end of the Fat Brown Bottle (FBB) to about a quarter inch behind the rear end of the Blue Bottle (BB).

Given that I have little confidence I can successfully and securely glue balsa fins to a mystery plastic bottle, especially one that has a paper label on it, I figured this thing probably should have through the wall fins. So I marked three slots and cut them out with a Dremel.

Don’t you hate when people do that?

“With a Dremel”. How did you cut them out with a Dremel? There are only about 17,000 attachments you can chuck into that sucker, right?

I used a Dremel fitted with a… one of those… here. I used these.IMG_2574

Aren’t you glad you asked?

Now, let’s think a little more about those LEDs, shall we?

There’ll be 18 LEDs, 3 at the top and 3 at the bottom of each of the bottles (other than the Skinny Brown Bottle (SBB)). Electrically it’ll just be a 3 x 6 matrix, driven by an Arduino Pro Mini as shown (for an 8 x 8 matrix) here.

I’m embarrassed at how long it took me to realize this, but: The LEDs will be mounted to the outside of the tube, with wires running up to the FBB. That means — among other things — that there can’t be a snug fit to the tube on both ends of any bottle; you can slide the bottle over a bare tube if so, but not one with LEDs and wires on it. The BB is okay, it has a wide mouth — and its lid with the tight hole can go on the tube separately before the LEDs do. The Pink Bismuth Bottle (PBB), on the other hand, is constricted at the top; I already cut off the neck to get a 1″ opening there. That means the bottom of the PBB had to have a larger hole. So I enlarged the rear opening. After considering several tools I ended up using diagonal cutters.IMG_2579

 

Kind of rough but should work.

As for the FBB, it took me even longer to figure out that it’d make things enormously easier if the wide open end were toward the back, not the front. Then I can wire up the LEDs and electronics around the tube — the Arduino and battery will be in the FBB — and put the FBB over everything later. So: I can try to cut out the whole bottom of the FBB, and seriously risk destroying it in the process if I know me, or I can just turn it upside down. I am a coward. Upside down it is.

 

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