Contact Lens Case Front-End Weight

DigBaddy

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Had this idea for a while and finally made it happen. Needed a way to easily add 20g of weight to the front of my upscale Nike-X for slightly heavier motors (G/H) to make the stability margin a bit more favorable. It's got a payload bay, so there's no laundry near the shoulder of the nose cone. We have an excess supply of Target contact lens cases from buying bottles of multipurpose solution and besides being useful for small amounts of epoxy, I found a way to use them for some easy add weight.

Need to also add this to the nosecone bulkhead of my 29mm Big Daddy...

1. Cut the case in half, trim off edges.
2. Scuff inside of bottom of the case and the top of the lid/cover with sandpaper.
3. Epoxy and/or use a screw to attach lid to nosecone base. This piece weights ~2g.
4. Fill bottom of case with slurry of copper/lead shot and epoxy, let set.
5. To add weight, simply thread the bottom of the case into the lid attached to the nosecone.
6. Make a few more of various weights if needed.

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BigMacDaddy

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That is cool -- I have been thinking about incorporating a removable / adjustable weight for some of my 3D printed nose cones.

My one thought about your implementation is why not figure out how to put that weight higher up in the nose cone? I would think you'd be able to use less weight and more effectively shift CG if your weight was close to the tip of the nose cone. I know it would not be as easy to get to it and screw in part but if you can figure out how to screw this into front couple of inches of nose it might be even better.

Actually, as I write this I realized that I should just make the front portion of my 3D printed nose cones replaceable with different weights incorporated inside them.
 

DigBaddy

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That is cool -- I have been thinking about incorporating a removable / adjustable weight for some of my 3D printed nose cones.

My one thought about your implementation is why not figure out how to put that weight higher up in the nose cone? I would think you'd be able to use less weight and more effectively shift CG if your weight was close to the tip of the nose cone. I know it would not be as easy to get to it and screw in part but if you can figure out how to screw this into front couple of inches of nose it might be even better.

Actually, as I write this I realized that I should just make the front portion of my 3D printed nose cones replaceable with different weights incorporated inside them.

Yeah, getting it further forward is a challenge with this design/solution. The Nike-X is pretty long, so the effect is still pretty good with the weight on the rear of the NC. Any longer rocket will see similar results. My 29mm Big Daddy has a bulkhead up in the NC a ways, so also not perfect, but better than on the rear of the NC. If I'm shoving a G or H into a Big Daddy, a bit more weight to get the proper CG isn't a horrible thing :)
 

DigBaddy

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Actually, as I write this I realized that I should just make the front portion of my 3D printed nose cones replaceable with different weights incorporated inside them.

I just had an idea, add some female pipe thread in the nose, say 1/2" or 3/8" and then you can cut and cap some PVC pipe and fill it with weight. Cut a screwdriver slot into the PVC cap and then thread it in place. Or, just print those weight carriers with the thread and a philips screwdriver impression already in it :)
 

tjkopena

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For my daughter's build of an ASP Stretch Stubby we wanted to be able to fly it with any combo of body segments. For the smallest configuration (just the tail + nosecone) it needed ballast, and simulation indicated any reasonable amount of ballast needed to be at the very tip of the nose. The ballast also needed to be adjustable as making multiple nosecones of different weights didn't fit our intended spirit of mixing & matching the same components each flight. We also didn't have time to make different variants---this was getting done kind of last minute in the days before a launch. Otherwise I probably would have designed a whole nosecone to print with an integral compartment or other attachment mechanism.

Instead, I happened to have on hand a test print of a ring w/ a threaded hole, and a matching plug, and made a compartment in a few minutes:
  1. Cut the bottom off a plastic Estes nosecone matching the kit's balsa nosecone;
  2. Epoxied the threaded ring inside near the tip w/ just enough space for some weights;
  3. Screwed and epoxied the eye bolt into the plug.

Tada!---a little compartment with a chunky screw cap for securing different quantities of weights at the very tip of the nosecone. As a bonus, the body segments are easy to swap in & out once the plug is unscrewed.

The ring & plug are just simple test parts designed w/ Tinkercad's basic thread tool (maybe with a bigger diameter than default, I don't remember).

Biggest issue is that I can't really get my fingers in enough to unscrew the plug and have to use pliers to grasp the eyebolt, but that's minor. With more lead time you could certainly design and print a whole nosecone designed from the start with a compartment like this, ideally incorporating something to make the unscrewing easier.

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The completed Stretch Stubby, with a tail section, 3 optional body segments, and the nosecone.

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View of the threaded ring inside the nosecone, the biggest weight the compartment is intended to fit, and the plug.
 
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DigBaddy

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For my daughter's build of an ASP Stretch Stubby we wanted to be able to fly it with any combo of body segments. For the smallest configuration (just the tail + nosecone) it needed ballast, and simulation indicated any reasonable amount of ballast needed to be at the very tip of the nose. The ballast also needed to be adjustable as making multiple nosecones of different weights didn't fit our intended spirit of mixing & matching the same components each flight. We also didn't have time to make different variants---this was getting done kind of last minute in the days before a launch. Otherwise I probably would have designed a whole nosecone to print with an integral compartment or other attachment mechanism.

Instead, I happened to have on hand a test print of a ring w/ a threaded hole, and a matching plug, and made a compartment in a few minutes:
  1. Cut the bottom off a plastic Estes nosecone matching the kit's balsa nosecone;
  2. Epoxied the threaded ring inside near the tip w/ just enough space for some weights;
  3. Screwed and epoxied the eye bolt into the plug.

Tada!---a little compartment with a chunky screw cap for securing different quantities of weights at the very tip of the nosecone. As a bonus, the body segments are easy to swap in & out once the plug is unscrewed.

The ring & plug are just simple test parts designed w/ Tinkercad's basic thread tool (maybe with a bigger diameter than default, I don't remember).

Biggest issue is that I can't really get my fingers in enough to unscrew the plug and have to use pliers to grasp the eyebolt, but that's minor. With more lead time you could certainly design and print a whole nosecone designed from the start with a compartment like this, ideally incorporating something to make the unscrewing easier.

View attachment 513172
The completed Stretch Stubby, with a tail section, 3 optional body segments, and the nosecone.

View attachment 513173
View of the threaded ring inside the nosecone, the biggest weight the compartment is intended to fit, and the plug.

That's a great setup! Thanks for posting that. Love the potential options with what you made. May need to copy that :)
 

tjkopena

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You could potentially combine the two setups and avoid any printing/make it quick: If it's big enough, cut the bottom off a nosecone and epoxy the receiving half of the contact case up as far as it will go inside. Depending on the size/weight of the rocket and strength of those cases, you could run an eyebolt through the positive side of the case (maybe epoxy a nut to the interior) and there's your cord anchor. To make a bigger compartment, cut the top off the receiving half so you're epoxying in just the threads and the weights can go all the way up, maybe w/ some foam to hold them in place if you're not filling the compartment.
 

BigMacDaddy

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I have also found that I can use a pair of long needle-nose pliers or flat tweezers to screw / unscrew recessed items...
 

BigMacDaddy

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I am eventually going to make a Big Daddy clone (slightly larger to make use of a tube that had some whiskey inside). I was gonna need to print the nose cone in two parts anyway so decided to try out a quarter-turn locking setup that would let me replace / change nose cone weight. I wonder if I load the weight in the nose and just pack some foam or paper towel or something around it / below it if the weight would stay in place without needing to glue it in.

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