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Spacey

Member
Joined
Sep 15, 2021
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Hello Everyone,

I am a first year college STEM student and have seen many builds in the past but this will be my first attempt. I am working on modifying the Estes Doorknob to fly on an H motor in order to earn my Level 1 Cert. on Saturday 9/18 (included build pictures) it's still in the finishing stages.

I am super excited to be apart of the community!!
 

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Hello Everyone,

I am a first year college STEM student and have seen many builds in the past but this will be my first attempt. I am working on modifying the Estes Doorknob to fly on an H motor in order to earn my Level 1 Cert. on Saturday 9/18 (included build pictures) it's still in the finishing stages.

I am super excited to be apart of the community!!
Is it just me or does the 2nd to last photo look like a weird fish...looking straight at ya?
 
Welcome aboard and good luck on the Level 1 flight
What motor did you decide on for your cert flight
 
More pictures.. Primed & waiting to be painted!!
 

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More pictures.. Primed & waiting to be painted!!
I have a Doorknob w/Vanderburn upgrade (plywood fins and centering rings) that is on pause for two reasons and your pics reminded me of one. I also cut the bottom of the nosecone off but now the length of shoulder remaining is quite short. They say it should be about 1 body diameter, but if your cut is like mine, it's about 1/2 the body diameter now. I've been considering trying to glue the lower half back on (with reinforcement) after I add some variable weight to the nose, but I haven't settled on a system for that, which would still be adjustable after I put the shoulder back together. I also thought about attaching the original card stock centering rings on the bottom of the cut nosecone. That doesn't buy me a lot of length though and still makes any variable weight system difficult to manipulate. Now I'm contemplating some kind of wireframe-like nose extension. Kinda like this https://www.thingiverse.com/thing:47015 but made of something more like popsicle sticks/tongue depressors
 
Welcome to the forum. You seem to have some skill, and I have no doubt you will get your L1.

My only suggestion, based on what I've seen, is for future builds, if you move on to bigger rockets and motors: stop using bent-wire eye-bolts, and use one-piece lifting or forged eye-bolts. A little over-energetic pull on the bent-wire eye-bolt can pull it apart just enough to allow the harness to slide off.

Rare, and probably not a concern for you right now. Just something to keep in mind.
 
Hi Spacey,

I ran an open rocket sim on a doorknob with plywood fins and rings with a little nose weight :
1.14 caliber stability
19 oz with an Aerotech H165R loaded
82 MPH off the rod
536 MPH
36 G's yikes !
2108 feet apogee
(don't blink you'll miss it)

Can't wait to see the vid !

Zeta
 
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I have a Doorknob w/Vanderburn upgrade (plywood fins and centering rings) that is on pause for two reasons and your pics reminded me of one. I also cut the bottom of the nosecone off but now the length of shoulder remaining is quite short. They say it should be about 1 body diameter, but if your cut is like mine, it's about 1/2 the body diameter now. I've been considering trying to glue the lower half back on (with reinforcement) after I add some variable weight to the nose, but I haven't settled on a system for that, which would still be adjustable after I put the shoulder back together. I also thought about attaching the original card stock centering rings on the bottom of the cut nosecone. That doesn't buy me a lot of length though and still makes any variable weight system difficult to manipulate. Now I'm contemplating some kind of wireframe-like nose extension. Kinda like this https://www.thingiverse.com/thing:47015 but made of something more like popsicle sticks/tongue depressors

You are absolutely right, After running the sim, I realized my nose cone is way to light. Need to add some type of variable weight to the nose cone due to the HPM. I was thinking derby weights?
 
Welcome to the forum. You seem to have some skill, and I have no doubt you will get your L1.

My only suggestion, based on what I've seen, is for future builds, if you move on to bigger rockets and motors: stop using bent-wire eye-bolts, and use one-piece lifting or forged eye-bolts. A little over-energetic pull on the bent-wire eye-bolt can pull it apart just enough to allow the harness to slide off.

Rare, and probably not a concern for you right now. Just something to keep in mind.

I was unable to find them @ HD, next build I'll have to order online. Thank you!!
 
That's a lot of negative gravity!

?? Would adding weight to the nose cone fix this, I plan on adding just trying to figure out the best way to do that. Was looking at Derby weights from the hobby shop but not 100% sure.
 
I finished the fillets last night, still need another coat of primer then paint but hoping to figure this stability issue out before the launch this Saturday AM! o_O
 

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You are absolutely right, After running the sim, I realized my nose cone is way to light. Need to add some type of variable weight to the nose cone due to the HPM. I was thinking derby weights?

A common way is to cast your own by mixing BB's, lead shot, fishing line weights, etc into epoxy. For a permanent weight, pour it where you want it. Cast it in slugs to stack in a tube, cylinders to slide into all-thread, dowel, smaller tube...
 
?? Would adding weight to the nose cone fix this, I plan on adding just trying to figure out the best way to do that. Was looking at Derby weights from the hobby shop but not 100% sure.
A lot of folks do lead shot mixed with epoxy, but I personally never have any shot laying around. I tend to use nuts/bolts/large washers. You could scuff up some large washers and epoxy them to your nose cone e-bay sled. I would try to stay away from putting the weight at the tip of the nose cone (where you'd normally want to put it) because I think that would exacerbate your short nose cone shoulder. It'll make the nose cone want to pivot back and forth while it's seated in the tube if u know what I mean. If u keep the weight closer to the shoulder, you'll have less of an issue with that.

I you wanted to do something removable you just have to make it removable from the sled, so you could put a stubby bolt or two though the sled and put some washers and a locking but in the other side to hold it in place. Then u could change the number and size of the washers, nuts, bolts etc
 
?? Would adding weight to the nose cone fix this, I plan on adding just trying to figure out the best way to do that. Was looking at Derby weights from the hobby shop but not 100% sure.
If your margin of stability is 1.14, then you don't need nose weight. But I would suggest a lower thrust motor. 36G might tear up a cardboard rocket. How about the H128W? Little longer burn, lower thrust, less G's pulled.
 
Hello Spacey. I think you’ve set yourself quite a challenge for your first rocket. Your build photos look fine but flying and recovering one of these hotrodded Estes models might be a step too far. Are you still planning on going for it tomorrow ? Where are you flying ?
 
You are absolutely right, After running the sim, I realized my nose cone is way to light. Need to add some type of variable weight to the nose cone due to the HPM. I was thinking derby weights?
I use stacked fender washers on a central eye bolt through the bulkhead.... there is a 2.75" that is space efficient for a 3 inch tube.
 
Hello Spacey. I think you’ve set yourself quite a challenge for your first rocket. Your build photos look fine but flying and recovering one of these hotrodded Estes models might be a step too far. Are you still planning on going for it tomorrow ? Where are you flying ?

I still hope to launch tomorrow at the SRA monthly launch. Ive equipped it with tracking on the nose cone sled, and deciding on maybe a smaller motor.
 
Ok, good luck. Motor deploy of recovery device, right ? Not dual deploy or delayed deploy ? What’s the SRA field like ? Have you talked to those folks yet ?
 
Thank you! Yes, It is motor deploy recovery. I have never used their fields, but have spoken to them a couple times as far as their inventory and directions.
 
I ended up using the self adhesive derby weights && attached them to the back of my sled.
 

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