Apollo CM Crew Hatch

[zrowny]

I've found myself with a lot of free-time now because of everything going on with COVID-19, so I was hoping to finally do a build of Ken West's Apollo Command Module. However, it seems like ecardmodels doesn't have it available right now on their (new?) site, so I figure I'll do the next best thing: design my own 😆! I'm definitely not interested in making a whole Command Module from the ground up, but I've been really inspired to make a detailed version of the Side Crew Hatch ever since seeing Project Egress last year.



The great thing about Project Egress is that the people behind it released CAD and 3D models and basic technical drawings for all the parts into the public domain, which means that anyone with some manufacturing ability (even just a 3D printer) can make their own accurate hatch replica.

Ideally, I'd be able to do that as a scale paper model, maybe at 1/4, which gives a model about 10" (25cm) wide. Obviously I can't physically model every screw, but I'd like to have the major mechanical movements work. I'm starting with all of the moving parts to get a sense of how much mechanical accuracy I can keep at 1/4, or if I have to move up to 1/3 or 1/2.

Hopefully I'll have more to show soon!

[surfduke]

I have one if you want to build it.

[spacecraftcreator]

Have you been able to build it yourself yet and how is it ? This is the first that I have heard of it...

[airdave]

I can get more of Ken's models up (at ecardmodels) in the next few days
starting with the CM, for those who are looking for it.

but designing your own project is also a great idea!!

[zrowny]

I've started with the two (identical) hinges that connect the hatch to the capsule.



They're surprisingly complicated! A six-link mechanism ensures that the sides of the hatch fully clear the capsule:



The hinge is definitely buildable at all at 1/4 scale and the mechanism moves surprisingly smoothly!



For reference, it's about 6cm tall when open. I've simplified the model a lot so that's it built up in layers instead of being true 3D geometry.



As you can see, the "arms" of some of the parts wind up a lot thinner than the ones on the actual hinge, and I don't think it would be practical to have them be built up of like 10 layers each. I'll definitely redesign this, but since it's clear that the hinge works at 1/4 scale, I'll come back to this after prototyping the other moving parts.

[Kevin WS]

Fascinating. Thanks for all design detail and progress shots.

I'm with you on this one!

[Ponytail]

Love to see these kinds of developments!
Nice work.

Following.

[Algebraist]

Fantastic build zrowny and a great thread. Really looking forward to more and appreciate the detailed explanations and pictures.

Regards and take care

Kevin

[zrowny]

Next up is a test build of one of the 15* latches around the perimeter of the hatch that actually lock it into place into hull of the command module.

The hatch normally is operated by a handle which the crewman pumps back and forth. The handle drives a ratchet mechanism which opens or closes the 12* latches around the periphery of the hatch. The latches are so designed that pressure exerted against the hatch serves only to increase the locking pressure of the latches. If the latch gear mechanism should fail, it can be disconnected and the latches opened or closed manually.

A series of linkages connect the gearbox and all of the hatches together in a sort of branching chain. There are a few different variations of latch, for left-handed, right-handed, and multi-connections, depending on how the linkages connect, but the latches are otherwise the same.



Unfortunately, 1/4 scale is definitely too small for this, so this is at 1/2 scale. I think it could definitely be smaller if you were willing to accept some simplification, but I wasn't happy with how that turned out with the hinges so I'm not going to do that here. As is, the paper sadists out there could probably do it at 1/3 scale, but I'm going to be continuing on at 1/2.

* I'm not sure why some NASA documents refer to only 12 latches, since the final design definitely has 15.

[chicharrero]

Simply amazing