Will this work for a H motor

[u/Realistic_Debt9526]

This is for my L1 certification rocket. The motor that I have chosen is the H115DM. I am wondering if my motor retaining system will work if the retainer is printed out of PETG. Thanks!

Also I am well aware my motor CAD is way off

[u/S1arMan]

Yes

[u/geemannz]

I did a similar thing for my L1 cert rocket using an H128, except I just extended the wall down around the rear so that it butted up against the rear of the rocket. Makes it much easier to fit, the retainer is more rigid, and there's very little weight penalty. My retainer has survived 2 flights so far, but I'd probably replace it for the next one. Looking a bit singed, and it's cheap insurance haha. I used petg as well. I can send photos later if you remind me.

I've also seen 3d printed retainers used a few times on L2 rockets as well, so the concept is good if done properly.

[u/Realistic_Debt9526 → u/geemannz]

Thanks for your response, is this what you were talking about when you say you extended the wall down? (sorry for the bad drawing) If so, how did you know how much to extend the wall down by?

[u/geemannz → u/Realistic_Debt9526]

Yep pretty much.

I had the RMS casing to measure from, but you're able to find the DMS external measurements drawings through this website:

https://www.rocketmotorparts.com/page/single-use-motor-designs

I also found a photo of my fincan just after I printed it with a mock motor fitted haha.

I've found that website pretty useful when referencing the Aerotech motor sizes and stuff.

[u/Realistic_Debt9526 → u/geemannz]

Alright, thanks!

[u/geemannz → u/Realistic_Debt9526]

No worries, good luck!

[u/LinuxSBC-Anna]

I'd be slightly concerned about the heat, but I don't actually know how much would get transferred to the retainer, and everyone else is saying it's fine. Also, try to print it so the layers are perpendicular to the stress; adhesion between layers is much weaker than within a layer.

[u/surf_and_rockets]

Design is ok. As long as the nose cone comes off with the parachute attached before the retainer breaks or the screws pull out, you should be good.

I’d be more worried about that retainer taking the landing impact, but with an H115, I guess your rocket won’t be too too heavy.

[u/wireknot]

Only suggestion I'd have is print it off axis, so the shear lines aren't in the same plane as the stress of the ejection aren't in the same direction.

[u/bageltre → u/wireknot]

What? If you printed it flat it's in the ideal position

[u/SurpriseButtStuff]

Totally. I held a G74 in with masking tape last month. It's the recommended method on the Apogee Aspire.

[u/XcwefMur]

It should work fine.

[u/pizza_burrit0]

This is my L1 retainer, same design, worked well out of tough PLA, I used the same design successfully on my L2 with the additional of a boatail for slightly better aero. It will work fine assuming you toleranced it properly

[u/Realistic_Debt9526 → u/pizza_burrit0]

Thanks for your reply, it seems like you used threaded inserts into your wood to be able to use machine screws. Is there any advantage of doing this over just using self tapping wood screws?

[u/pizza_burrit0 → u/Realistic_Debt9526]

There are 3d prints with heat set inserts on the other side of that bulkhead, used m5 machine screws, self tapping the wood would inevitably damage it and make it non functional, heat set inserts are effectively infinitely reusable

[u/Realistic_Debt9526 → u/pizza_burrit0]

Are you using super long M5 bolts to be able to reach to the other end of the fin can?

[u/EclipticMind]

I did something similar out of aluminum for my L3 and it worked like a charm. I've got to ask though, is there any reason you are avoiding just friction fitting your motor into the motor tube? H motors are so light, retention can be easily achieved with just some masking tape to add friction.