Night Launch rocket - Aft Access

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tollyman

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I am in the process of building a high power rocket called sensory overload for TRA Minnesota Night launch in September. My plan is to have LED strips run the entire length of the rocket which means the bodytube is going to be in one piece and will pop the nosecone for parachute deployment. I will be having a coupler section bolted inside the rocket to house all the electronics. To get power to the LED strips, bolts will be acting as conductors to allow power to pass through the body tube. I have a circuit to control the LED strips but the issue is being able to connect everything together.

I really dont want to have 4ft long wires extending to the top of the body tube so i can connect the battery before sliding in my coupler section. I was planning on having the entire fin can of the rocket be removable, so there will be no external fillets. I will be putting in a makeshift "thrust ring" where the top centring ring will contact to transfer thrust. Thrust ring will most likely be epoxied and bolted just for extra measure.

What are your suggestions for preventing the fin can from "falling out" since there shouldnt be any ejection forces on it i was thinking a few bolts through the body tube would be sufficient just to prevent it from sliding out. I have never really built a rocket without external fillets so im not sure if the thrust ring will be sufficient enough for this project. Im open to suggestions

For reference the rocket is 5ft long cardboard tube, 6" diameter, flying on a J450, and have a dry mass of around 7kg. The thrust ring and coupler/av bay are fiberglass
 

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I cannot open ork files, but a thrust ring must transfer force to the body tube. Normally done at the rear so you can screw it to the rear CR. But since you want it to be at the forward CR you must make sure that #1 it stays on and #2 it stays aligned. Can you run carbon rods from the fin can, glued to the inside of the body tube, to a mating carbon tube glued to the inside of the boost section? Drill matching holes in the thrust ring, this will keep it aligned. On the upper section, drill through assembled tube and rod, and then tap the carbon rod for a 4-40 or 6-32 button head screw to run through outer card board tube. This should lock everything in place.
 
After reading what I wrote, can you junk the thrust ring idea and just use two identical CRs at the joint? This way you can make the CRs together so they are exactly the same.The joint then just becomes 2 body tube sections butting together and all the force is transmitted from 1 CR to the other. And still use the rod idea?
 
Build short fin can up into a coupler.
Build electronics coupler with center tube, have bottom CR removable for access to battery's, or have access doors thru side of body.
Connect fin can to upper body with plastic rivets.
Untitled.gif
Can mount all your light permanently without long wires.
Can still use motor ejection for backup to altimeter.
With a 6 in tube you will have lots of room to work.
 
Build short fin can up into a coupler.
Build electronics coupler with center tube, have bottom CR removable for access to battery's, or have access doors thru side of body.
Connect fin can to upper body with plastic rivets.
View attachment 410546
Can mount all your light permanently without long wires.
Can still use motor ejection for backup to altimeter.
With a 6 in tube you will have lots of room to work.

Unfortunatly this does not work with how i want my LED strips to be on the rocket. They will extend all the way down the the bottom of the rocket and the hassle of having connectors to extend the LED strips isnt worth it. I would have liked to do a hatch in the side to make it easy to connect but the entire external of the rocket will be covered with LED strips
 
After reading what I wrote, can you junk the thrust ring idea and just use two identical CRs at the joint? This way you can make the CRs together so they are exactly the same.The joint then just becomes 2 body tube sections butting together and all the force is transmitted from 1 CR to the other. And still use the rod idea?

I think i follow what you are saying here but im not sure it goes with what i had in mind. The fins, motor mount tube and centering rings are all epoxied together. Fin slots are already cut in the tube and the entire fin assembly slides into the rocket and stops when it reaches the end of the fin slots. I am suggesting a thrust ring (not a plate) from fiberglass coupler that gets bolted/epoxied in place so that when the fin assembly is inserted the top centering ring will be touching the thrust ring and the fin tabs will be touching the end of the fin slots.
 
You could have threaded rods come down through all the centering rings and hold it together with nuts on the bottom. Then up at the top just have 2 centering rings butted together to transfer the thrust, like the other guy said.
 
Ok, here ya go. I am doing one right now with a removable thrust plate. Bottom CR has lightning holes in it. Thrust plate screws to it, 54mm flanged retainer still to go on thrust plate. Bottom edge of rocket body extends past CR and thrust plate sits inside of that. Just make one of the lightning holes big enough for your switch or how ever you need to access your lighting.
 

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I think i follow what you are saying here but im not sure it goes with what i had in mind. The fins, motor mount tube and centering rings are all epoxied together. Fin slots are already cut in the tube and the entire fin assembly slides into the rocket and stops when it reaches the end of the fin slots. I am suggesting a thrust ring (not a plate) from fiberglass coupler that gets bolted/epoxied in place so that when the fin assembly is inserted the top centering ring will be touching the thrust ring and the fin tabs will be touching the end of the fin slots.

So is it that you want the whole fin can to be removable? Is that how you want to access your lighting?
 
If you want a hatch in the side, just cut out the cardboard, I use a razor saw by Zona. Very, very thin blade. The cardboard will hold its shape. Use an uncut portion as a pattern to make a frame work to go around the hatch. Then glue a lip around the inside of the cut out that you will be able to screw the hatch to.
 

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So build the rocket normally with the ebay at the top with a removable cap for access, or hatches. With a pass thru tube if you want motor ejection.Maybe.gif
 
I appreciate the ideas and discussion and here is my progress so far. I have 3D printed the "nosecone" and attached my light to the top. The fin can is epoxied together but will not be epoxied into the rocket. The LED strips are attached with two 3D printed "clamps". The idea was that the sticky backing of the strips would hold them to the rocket but i was dead wrong. So i decided wrapping the entire thing in packaging tape to make sure nothing comes apart during flight. The whole thing is powered by a 3s (12.6V) 8Ah lipo battery with approx 30-45 minutes of battery life. I created a custom PCB to control the LED strips. Still have to figure out how im going to mount everything but thats for a later day.
 

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