Building the [scratch] Pumpnik

If you’re looking for trouble, you might find it in a dollar store.
I dragged a piece of ST-7 tube out of the stash. Cut off three pieces, punched a hole in each of two and two in the third.
I also had a couple of 18 mm balsa blocks about an inch long in my stash. Amazing. I covered one end of each with epoxy and then epoxied that end into two of the tubes.Once that dried I sawed the two ends off flush, coated the end of one cutoff piece with epoxy, and epoxied that into the third tube. (Really, I suppose, the epoxy on the end was needed only on the center tube, but never mind.) Then I glued the three tubes together, holes aligned, with a launch lug in the gap between two of the tubes.

I probably should have put the thrust ring and motor hook in the center tube before gluing them together. Well, as long as they get there.

No, I didn’t put them in the outer tubes too. Yet.

I drilled small holes in the balsa blocks and glued in ends of toothpicks. (Round ones. Yes, I know. Don’t @ me.) These will serve as substitutes, sort of, for a forward centering ring.

As for the pumpkin, I drilled three 3/4″ holes in the bottom. First I had to remove the stem, which was held on top with glue and, I swear, a toothpick. (A round one.)A little knife work, including a slot for flexing the motor hook, and it was suitable for the motor mount. To go in eventually. First I cut four 15″ pieces of 3/16″ dowel, sharpened an end of each, drilled holes in the pumpkin with a drill bit held in the fingers, and dry fit the dowels.(There’s the flat toothpicks you were so concerned about.)

I poked a hole in the top for the launch rod, then used Gorilla Glue (highly viscous, but not yet solidified) to glue the dowels and motor mount in place. I was worried the launch rod hole would get clogged with glue, and, well, it did, but not too badly and I was able to clear it.

Doubtful I’ll paint the dowels before the October 21 launch. After, maybe, if it survives. Will it be stable? Who knows? This design apparently is, though it uses a solid Styrofoam ball and a smaller motor. Likewise the Odd’l Rockets Sputnik. And so are these, but one has fins on the ends of the dowels. The other has no dowels, but also has its motor shoved as far forward as possible. Not something I’d want to try without a plugged motor, unless the motor tube were open at the forward surface which might spoil the look. (Although you could extend it an inch forward, paint it green, and call it the stem. Hm, maybe next time, if this one doesn’t go well.) I think all these except maybe the dowel-less one are designed to spit the motor? Mine’s not, which is why I decided to include the vent tubes.

Anyway. The pumpkin cost me a dollar, the dowels a couple bucks more, and the rest was in my stash. Probably cheaper altogether than the motor it’ll fly on. If it doesn’t survive, oh well.


One thought on “Building the [scratch] Pumpnik

  1. Great work on the Pumpnik! I tried using a styrofoam potato to make a Spudnik, but the irregular (dimpled and dented) top surface deflected the top airflow and wouldn’t give a vertical flight. Close to vertical but not good enough for kit production.

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