The Goblin: 3in Diameter Model Rocket - Galactic Series

Update: 09/12/2005 - I have added rail buttons, just in case you needed them.

A classic reborn—with a personal milestone.

My journey with the 3in Goblin started as a tribute to the Estes Goblin I flew as a kid. I wanted something familiar but capable—something that could handle serious motors while still nodding to its roots. This version does just that. It’s built for high-power launches, but can outperform with mid-power setups at Class 1 fields. I actually earned my L1 High Power Certification with this rocket's predecessor because it struck the perfect balance: compact, reliable, and just aggressive enough to make a statement. It’s more than a build—it’s a milestone.

This is a builder's kit, which means that you should be familiar enough with rocket modeling and building that instructions aren't necessary, so I don't provide them.  I will include some tips for certain parts that might not be intuitive.  If you have any questions, please don't hesitate to contact me.

I have also included an OpenRocket simulation file.  The values in the sim are approximations and you should adjust dimensions and mass to your build.  They are attached under “Other Files” below the model files. 

The Parts:

There aren't a lot of parts to this rocket, but they are bigger.  You should still be able to print this model within a 256mm cube.

• Fincan - The fincan is mostly one piece, with only the coupler as a separate piece so you don't have to fool around with fin alignment guides and inner fillets. 
• Coupler - This coupler was separated from the fincan to make printing more accessible to human-sized printers. 
• Motor Retainer - This retainer simply screws into the back end of the fincan, securing your motor in place
• Nosecone - Comes in two pieces to fit more printers.  The two pieces socket together.
• Nosecone Avionics Sled - This sled screws into the bottom of the nosecone.  It will allow you to store your altimeters and GPS trackers.  It allows access to the interior of the nosecone so weight can be adjusted for a perfect balance

And that's it!

Building Notes:

I have done my best to provide cutaway images of the nosecone and fincan, but sometimes, words help pictures.

• For the nosecone assembly - This walls are 3mm thick, so this is a stout rocket.  Still, you should take some time to prep the nosecone.  I typically will laminate the interior with epoxy.  You can also reinforce the walls and the joint with fiberglass if you plan to run HPR motors.
   
• AV Sled - This sled is blank so you can mount any combination of electronics on it.  It features two port holes for venting and to run e-matches into the body tube, if you plan to do electronic deployment.  It also has a ¼-20 threaded hole in the bottom to attach your eyebolt.  
   
• I use 12mm tubular nylon shock cord.  The shock cord channel in the fincan is 13mm x 3mm.  10-15ft of cord should be plenty.  The cord will be sandwiched in between the motor mount tube and fincan. Use plenty of epoxy.
   
• Be sure to scratch up any mating surfaces where you will apply epoxy.  Oh yeah, use epoxy.
   
• The retaining cap can sometime be a little tight when first screwing it in.  I suggest putting some lubrication on the threads and working them back and forth until everything is seated.
   
• The motor mount tube should end flush with the aft of the fincan to allow the thrust ring for the motor or motor adapter to seat between the fincan and retainer.  
   
• I use and design around LOC/Precision tubes.  Estes tubes will not work and its a gamble with regular mailing tubes.  Always Ready Rocketry's BlueTube 2.0 will work and are a great choice.  You are free to scale down to fit, but when you do, other things might not work.  For ease of building, go to https://locprecision.com/ and get your body and motor tubes.  You can also pick up the other parts you're going to need like hardware, parachutes, and shock cords.
   
• Final Note:  It seems silly to say but remember that this is a 3D printed rocket.  I have worked very hard to balance strength and weight.  If you decide to do something really crazy, be sure to consider reinforcing the nosecone/fincan with composites.  I hate breaking rockets, but if you do, don't be sad.  Just print another one and be crazy again!
   

Safety Police Disclaimer:  

Rocketry is a safe and rewarding hobby.  With knowledge and experience, you can experience the excitement of yeeting a rocket thousands of feet into the sky.  There is nothing else like it.  

Having said that, you are responsible for the rockets you fly.  If you build and fly one of these rockets, you should understand the NAR Safety Code and the potential risks involved with launching any rocket, especially these.  They were not designed to be toys.  They are real rockets that can potentially go very high and carry significant energy.  This rocket is intended to be built and flown by experienced rocketeers who understand the risks and can mitigate potential issues through experience.  By printing and flying this model, you do so at your own risk.  You are solely liable for any unexpected results, and you agree to hold me and any manufacturer harmless from any liability.  I recommend you join NAR or Tripoli, join a club, and ask lots of questions.  Launching a rocket as an NAR/TRA member at a sanctioned event provides you with insurance you don't get at the park.  If you show up with one of my rockets, you're gonna make a friend! Money-back guaranteed :) 

</end of Safety Rant>

This model took a lot of time, and I hope that you have a lot of fun with it.  If you have any questions, please reach out to me here or on The Rocketry Forum under @frogglicker.

If you enjoy this model and kit, I would love for you to post a Make (with pictures and videos) as well as a Like.  I also have a BuyMeACoffee page, and a donation would be appreciated if you can.