Modular Rocket

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Jim-K
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Modular Rocket

Postby Jim-K » Sat Nov 16, 2019 12:08 am

With the summer warming up and no flying until April/May, I have started to tinker with a modular rocket design. My aim is to make different sections that can be stuck together to mix and match different motors, recovery, staging etc.

So far, I have 3D printed some ends and tried our a few prototype sections. It all seems to work, but once I set forth with a particular interface, its going to be hard to change. Happy to listen to opinions on features to add or remove.

The basic structure is based upon BT-70 & 80 tubes. This gives plenty of room to fit stuff into the airframe later. 3D printed ends are bonded in with some balsa stringers running longitudinally and a bit of PU foam.

Here are some illustrations:

4710C058-C921-4B47-BCDA-FD6615A9BCCE.jpeg

A53B007C-C347-4CB4-977B-D64605BDF540.jpeg


I built a short section - about 120mm long - to check the longitudinal strength. About 2kN, which should be sufficient for anything I am likely to put in the back end.

2F856838-D77A-4445-BFAE-5EA7B160CB60.jpeg


The features so far are:
- Each section joined by 6 off M1.6 fasteners.
- Four pairs of balsa stringers to assist with longitudinal load.
- Two longitudinal tubes to assist with running communications.
- Radial hard points. Initially closed, but can be fitted with an M2 ‘helicoil’ as necessary.

First up I will build a tail section, a mid section with parachute and a nose section. Fly it with a 24 mm diameter E or F category, and see how we go.

316C85F5-AD01-497A-9B8B-11DD85DB0C4A.jpeg
316C85F5-AD01-497A-9B8B-11DD85DB0C4A.jpeg (22.88 KiB) Viewed 1809 times


Ideally there will be time for bigger, faster, higher etc later.

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SpaceManMat
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Re: Modular Rocket

Postby SpaceManMat » Sat Nov 16, 2019 7:48 am

Neat idea. It will be interesting to see how this comes together.
QRS: 124
AMRS: 32 L2 RSO
Highest Altitude: 13,647 feet
Fastest Flight: Mach 1.55
Largest Motor: CTI 1115J530 IM
Current Project: X Wing

strud
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Re: Modular Rocket

Postby strud » Sat Nov 16, 2019 11:54 am

I like modular approaches, reuse saves time and reduces risk in new projects.... theoretically.

M1.6 fasteners, wow didn't know they existed!

Jim-K
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Re: Modular Rocket

Postby Jim-K » Wed Jan 08, 2020 11:34 pm

Starting at the top for no particular reason, I have a nose cone assembly.

This assembly is just going to pop off the top with the ejection charge on the end of the motor. The typical nose cone (this one was from Apogee) will do this without modification, but the inner BT-70 does not suit the BT-80 nose cone. I also have plans to use the same nose cone with more sophisticated rockets later. I also just like tinkering.

The 3D printed rings (from 3D Hubs in FDM PLA) came out slightly 'woolly', but the tolerances seem good and they slip together with the tubes neatly. First off, I have bonded in the washers and nuts. This seemed to work best if the joint is torqued up gently so that the nuts and washers are compressed into the rings, though clearly you need to be careful with the epoxy adhesive.

Nut End Ring.JPG
Nut End Ring.JPG (87.47 KiB) Viewed 1196 times


Bolt End Ring.JPG
Bolt End Ring.JPG (86.04 KiB) Viewed 1196 times


Next I bonded on the BT-70 and 80 tubes (these are identical lengths) followed by the balsa stringers. I also trimmed out the sides to allow access to the bolts, though I could probably have done this later.

Short Section - Unbonded.JPG


Sticking the two parts together was trickier and time bounded with the PU foam and epoxy curing before my eyes. I will try to get some photos next time. The epoxy went on the end rings. The PU foam in between the two balsa stringers (in the trial parts, the PU foamed up and bonded the inner and outer tubes together).

Short Section - Bonded.JPG
Short Section - Bonded.JPG (47.26 KiB) Viewed 1196 times


The nose cone has a similar structure with a BT-70 running about 50% of its length. It also has 1/8 inch aluminum tubes running to the end of the BT-70 to allow communications for later systems. But I didn't take any photographs.

Nose Cone.JPG


The next post will be about the central section. This will contain the parachute, maybe some other things. I might also think about painting the external surface.

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SpaceManMat
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Re: Modular Rocket

Postby SpaceManMat » Thu Jan 09, 2020 11:50 am

Looks pretty nice. Kind of wish I had added a place to put nuts in the cockpit for my X Wing, but I didn't because I wanted to make sure it never fell out because there will be no access to the underside.
QRS: 124
AMRS: 32 L2 RSO
Highest Altitude: 13,647 feet
Fastest Flight: Mach 1.55
Largest Motor: CTI 1115J530 IM
Current Project: X Wing

Jim-K
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Joined: Mon Nov 04, 2019 9:53 pm

Re: Modular Rocket

Postby Jim-K » Tue Jul 28, 2020 12:36 am

Been a while, but I have been tinkering in the background. The mid section turned out trickier than I thought - though I may be over thinking things. I have a nose and a tail done.

Tail

Tricky thing was the transition between 24 mm and 56/66 mm diameter zones. I opted for some strategically placed centering rings, epoxy and crossing my fingers. I don’t see any issue with the load transfer into and out of the 24 mm motor mount and have filled a section between the 24 and 56 mm tubes with rigid PU foam.

066AE2A2-01E6-4B50-A287-03AB60B48ECE.jpeg
066AE2A2-01E6-4B50-A287-03AB60B48ECE.jpeg (47.71 KiB) Viewed 51 times


The small aluminium tube will carry signal wires if I fancy trying an air start. Here it is again with the tail cone fitted.

079ED6CF-8B53-4886-B504-A3F1FF77D21F.jpeg
079ED6CF-8B53-4886-B504-A3F1FF77D21F.jpeg (43.13 KiB) Viewed 51 times


I should have taken some more photos of the fin fitting. They are laminated balsa fitted into slots in the 66 mm diameter tube, butting against the inner 56mm tube. Cutting the slots was weeks of preparation turning my dremal into a router table and making a tool to hold the tail cone. The actual slot cutting took about 5 minutes.

The aim with the forward swept fins is to protect them on impact (with chute deployed).

The painting was also tricky - a craft that I will need to persevere at. The point of the project, however, is to make interchangeable parts. I can always swap the offending parts out if I needed to.

Hope to get it flying this year, or maybe the next.

51BB4C65-EC3B-4CD9-822C-9D8588DB3788.jpeg
51BB4C65-EC3B-4CD9-822C-9D8588DB3788.jpeg (79.72 KiB) Viewed 51 times


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