3D Printing Not just another AV Bay

[Ian A Dalton]

I decided to over engineer a fully enclosed 3” AV bay and it's is printing now. I hope it’s the real deal - the last print. The one to the right was a prototype to measure for fit and function. Watch this thread - printing of phase 1 ends on Friday. I still have 2 other components to design and fit then some functional drill guides to create, with ejection rounds (yes, I call them rounds because they are not canisters) coming last... there’s a lot to this.

Ultimately it will hold two Eggtimer Quantums and an Eggfinder, three 'remove before flight' switches, and four integrated ejection charges.

Now, it's fully threaded and I have a GPS unit so I know what you are thinking, 'What is this guy thinking!?!' I went to the dry lake bed and tested the crap out of the prototype and I got 10,000' of range out of this without issue. I'm not too concerned given the rocket sims at 10,000' on a good day - if I want to put that much motor in it. I do btw.

The Rocket will be the Mach 1 Daedalus: https://www.mach1rocketry.com/store/p147/The_Daedalus_.html

 

[dr wogz]

that's a lot of supports!

 

[Wallace]

Support city...Dissolvables are where I'm currently leaning since post processing gets on my nerves more than anything. I find myself avoiding printing anything requiring supports. Pretty sure IDEX is the future for that. I have a machine coming that will at least in theory do exactly that.(that's how irritating I find it). Love the design and layout. Let us know how it pans out...

 

[cwbullet]

Have you though about entering this in the AV bay contest?

 

[Ian A Dalton]

Yes, there are a lot of supports but they only attached the bottom 1/4 along the spine. The rest are there to support the supports I guess. I designed this specifically to minimize supports believe it or not. I printed it at a 45 degree angle to remove the need for supports on the internal structure and because I read somewhere it actually creates a stronger print for stresses. Here is a pictures that show the minimizing of supports. That Shell is designed to break away to keep the internal structure looking good. I did the same thing for the end facing the build plate.

 

[Ian A Dalton]

Have you though about entering this in the AV bay contest?

What is this contest you speak of?

 

[Wallace]

Yes, there are a lot of supports but they only attached the bottom 1/4 along the spine. The rest are there to support the supports I guess. I designed this specifically to minimize supports believe it or not. I printed it at a 45 degree angle to remove the need for supports on the internal structure and because I read somewhere it actually creates a stronger print for stresses. Here is a pictures that show the minimizing of supports. That Shell is designed to break away to keep the internal structure looking good. I did the same thing for the end facing the build plate.

That pic makes it so much easier to grasp. I agree fully, part orientation is absolutely critical. What material is that?

 

[Ian A Dalton]

That pic makes it so much easier to grasp. I agree fully, part orientation is absolutely critical. What material is that?

It’s eSun PETG. I have a very storied PETG past but found this stuff works well enough for my functional prints. I live in Vegas so PETG or ABS is an absolute requirement in my opinion.

 

[dr wogz]

this one:

https://www.rocketryforum.com/threads/10-july-3d-design-contest.151705/

 

[dr wogz]

just a thought:

Sometimes it's beneficial to design & print the object out in 2 or 3 parts & screw it together.

Taking care to align the layers in such a way so that they are perpendicular to the major forces helps with strength. just printing it at 45°wont.

 

[Ian A Dalton]

just a thought:

Sometimes it's beneficial to design & print the object out in 2 or 3 parts & screw it together.

Taking care to align the layers in such a way so that they are perpendicular to the major forces helps with strength. just printing it at 45°wont.

This bay will be totally encased in a FG coupler and bulkheads so I'm not too worried since the stresses will mostly be carried by those other components. You do make a good point overall though and something to think about when I get into my more ambitions creations.

 

[cwbullet]

This design is by far the most advanced model I have seen today. It is well thought out.

 

[Ian A Dalton]

Yay! My 100 hour print was successful. I think this is the final version of the main part of the bay. It's been sanded smooth and I have tested my electronics on it. I think they look great. Now I am printing my wire covers and battery cover. I hope to get all the printing done tomorrow so I can start assembling everything Sunday. I have family coming staying with us tomorrow so we'll see what I actually get to.

 

[Wallace]

Congratulations, looks really good.

 

[Ian A Dalton]

Printing is done. Building is NOW! This is pretty complex...

You will see some mono plugs as well. These are for my charge wells. I am taking a 10mm centrifuge vial and connecting it to a small terminal block that is soldered to a male mono plug. That contraption slides into a printed shell and that shell threads into the bay. The threading keeps the shell in place to keep the male plug in contact with the female end that's epoxied inside the bay.

I like this because I don't have to manage any charge wires. I simply close the bay and twist in my charges. Done - easy - clean. The Shells will have gaskets to keep the ejection gases out of the bay as well.

 

[Wschmiedlin]

Will you be sharing the design? It would be nice to have a good starting point for my current project.

 

[OverTheTop]

Nice looking model. Here are some things to consider:

• Be careful with the mono plugs. They rely on the sideforce from the contact on the center pin to ground the outer barrel . Use with extreme caution.
• On a similar note, make sure that none of the ejection gases can get back into the electronics. BP residue is quite corrosive.
• Having a plastic tube around the antenna can affect the tuning. The non-air dielectric alters the electrical length. I don't have a feel for how much your design would slide the frequency of the antenna unfortunately. It might be reasonably OK by the sound of it.

 

[Ian A Dalton]

• Be careful with the mono plugs. They rely on the sideforce from the contact on the center pin to ground the outer barrel . Use with extreme caution.

• On a similar note, make sure that none of the ejection gases can get back into the electronics. BP residue is quite corrosive.

Thanks for the warning. I’ve done some testing and made sure the movement of everything is minimized. I guess the bigger concern would be around G forces. I’ll do more tests. The plugs feel pretty dang snug on their own. Maybe an RCA style will be better in the future.

Having a plastic tube around the antenna can affect the tuning. The non-air dielectric alters the electrical length. I don't have a feel for how much your design would slide the frequency of the antenna unfortunately. It might be reasonably OK by the sound of it.

So... I have ground tested this already with my prototype and I get decent range - as high as the rocket will fly. I'm not too concerned. It's a big rocket as is and I don't know if tracking is absolutely necessary. I like to have it because... why not?

 

[Ian A Dalton]

All electronics are in the bay! It was several hours of work to solder everything, test , secure in place, and test again. Several pictures are below to show what it all looks like. Next I need to design and print some drill guides for the bulkheads and switch band.

 

[Wschmiedlin]

Very clean!

 

[Ian A Dalton]

...aaaaand done. I'll upload my STL files in the next day or two. Now I just need to build the rocket. Deets:

• Diameter: 3"
• Length: 9"
• Empty weight: 803g
• Full loaded weight: 938g
• Total print time for all used components: 125 hours
• Print Filament PETG
  • Bed: 90c
  • Nozzle: 245c
  • Speed: 50mms
• Altimeters: 2 x Eggtimer Quantums
• Tracking: Eggfinder TX

Notable features (I think so anyway):

• Fully 3D printed with the exception FG coupler, eyebolts and rods, electronics
• No visible charge wires and a general lack of wire management needed overall
• Charges are loaded in a self contained shell
• Allows for all electronics to be loaded and bay closed before they are armed via a pull pin

 

[Ian A Dalton]

Nice looking model. Here are some things to consider:

• Be careful with the mono plugs. They rely on the sideforce from the contact on the center pin to ground the outer barrel . Use with extreme caution.

I have been doing a lot of research on this. I actually lost sleep over it, so I did A LOT of research. It appears mono plugs were pretty standard practice for switches back in the day. Then people started to get the issues you discussed and abandoned them. I can understand why this is bad bad bad. Basically, any loss of continuity between the battery and the altimeter will cause the altimeter to fail and it won't start up again when the rocket is mid-flight. Even if that loss was fractions of a second. But for an ejection charge the application is different and I am not worried here is why:

1. The center pin has two contacts on it. If one did lose contact, the other will hopefully keep it.
2. In my tests of the Eggtimer Quantum, the charge continuity check is only when the altimeter is armed. Once the altimeter is armed, the ejection charge can loose and establish connectivity without impacting what the altimeter is going to do. In other words, the altimeter is going to send the signal to ignite regardless of whats happening with the ejection charge wires. I have an email out to Cris to confirm my assumptions.
3. The load on the contacts should be at their minimum when the charge needs to go of. If there is enough force working on the connection to separate contacts, the rocket is going way too fast for an effective recovery and I'll probably shred the parachute as is.
4. Even if the charge wire did lose contact it will most likely be momentary (like factions of a second). The Quantum can send the ignite signal for up to 9 seconds. I'm doubtful both contacts will be out of contact for anything close to that long.
5. there are two altimeter so both charges have to fail this way.

• On a similar note, make sure that none of the ejection gases can get back into the electronics. BP residue is quite corrosive.

Everything hole and connection is sealed with a gasket of some type. I'm pretty confident everything will be fine.

I think my reasoning is sound for all of this. I REALLY appreciate the word of caution.

 

[Ian A Dalton]

Oh, and if anyone is interested - here is my Daedalus build thread where this will be used. https://www.rocketryforum.com/threads/mach1-3-daedalus-build-thread.153702/

 

[tollyman]

I really really like what you did with the ejection charges and the mono plugs. I've never seen that before. I might try to do something similar but with an ejection well and some 3mm bullet connectors. I've been skeptical about putting lol the ejection charges on the Av bay because more than likely you will have one parachute that has to be pulled out by the momentum of the rocket instead of being pushed out by the ejection charges.

Also do you think that the 3D prints will be able to hold up over time? I am using pyrodex so I'm afraid that I can't use the 10mm centrifuge tubes because I need more pressure to guarantee full combustion. What type of powder are you using?

 

[Ian A Dalton]

I might try to do something similar but with an ejection well and some 3mm bullet connectors.

Are you thinking you will just push charge into the connector? I'd be really interested to see what you do. I went with mono jack because I wanted to thread the charge canister and I needed something I could twist.

I've been skeptical about putting lol the ejection charges on the Av bay because more than likely you will have one parachute that has to be pulled out by the momentum of the rocket instead of being pushed out by the ejection charges.

I will alway keep motor deploy for the drug if I can. I use it as a backup so I set the delay long (if I can). You could make motor be primary and the charges secondary.

Also do you think that the 3D prints will be able to hold up over time?

Well, I don't know. I think so. I used a strong heat tolerant filament that is not too brittle. If a print fails I can always print another one.

What type of powder are you using?

I have been using pyrodex but this new AV bay changes that. I cannot find FFFFg powder anywhere in my town so I need to buy it online. I found a place online that will send it to me for $50 shipped. People may scoff at that price but if it lasts a life time like everyone says it will, what is $50 over the rest of the years I am in the hobby?

 

[tollyman]

After giving some thought I will probably use either an xt60 or xt30 for ease of use. The system would b similar to yours where the charge will slot down into the av bay most of the way but then instead of screwing in from the back it will have some way to hold it down from the top but still allowing the charge to go of. I'm making some designed now. I like this whole idea but I don't know If I will have time to implement it as my lunch date is September 14th.

One thing I thought of for using the 10mm centerfuge tubes, what if you need an ejection charge greater than what they can hold? That's kinda he position I'm at now.

 

[Ian A Dalton]

Go XT30 because of size. But dang those are hard connections to break. I’d spend too much time fighting with it to remove the vial. Why not go with an RCA connection? You want something that is reliable but easy to remove.

As for what if I need more powder? I’d just print my own centrifuge vial that’s the right size and go with that.

 

[tollyman]

I think I would have the an aluminum or copper pipe as the carrier and a 3d printed part as the ejection charge. Still working on the design. I don't trust all plastic parts so I want the 3d part to be replacable and the metal will be for strength.

 

[Ian A Dalton]

I don't trust all plastic parts so I want the 3d part to be replacable and the metal will be for strength.

I wanted to let you know I ground tested this bay. The centrifuge vials load inside the 3D printed charge shell then that contraption is screwed into the bay it’s self.

I first tested one centrifuge vial alone, with no charge shell, and the whole thing just blew up into pieces like a fire cracker.

Then I put a vial into a shell and only the top came off (like expected) when ignited. The centrifuge vial and shell showed zero signs of stressing.

Then I put it all into the the AV bay and did my deployment tests. Everything worked perfectly with no issues.

I am willing to say a centrifuge vial inside an 3D printed shell is sufficient to ensure a controlled explosion without impacting the structural integrity of the shell.

Hope this helps, or at very least is informative!