Semroc MX Goblin Build Thread

[sod4]

Got my MX Goblin kit in from ERockets today. I'll do primary construction and capture pictures starting tomorrow. It looks like a good little kit, though going by the MX Mars Lander kit, ERockets has got this MMX thing figured out!



The obligatory layout shot:

 

[sod4]

Step one is to fully assemble the motor mount.

First I marked each end of the tube at 1/8inch (or close enough, I have a decimal ruler). This is where the centering rings will eventually be glued on.



Next I tied a double overhand knot in the shock cord as per instructions.




A bit of glue is inserted into the motor tube at one end.



Then the shock cord is fed through the motor tube, knot first, with the thrust ring following after. The shock cord is supposed to be trapped between the motor mount and the thrust ring.



The thrust ring is inserted until flush and the shock cord is pulled until the knot is resting against the thrust ring. I've never built a mount and shock cord attachment like this but it seems like a simple way to get a shock cord that will *never* detach with the ejection charge of these small motors.



Final step in the motor mount is to glue on the centering rings. mine were cut a bit small on the inner surface (better than being too loose!) so I had to sand a bit. I probably should have gotten a dowel out of the scrap box and made a sanding jig like bradycros does but crumpled up sandpaper did the job *ok*.



Finally I slid the centering rings onto the motor mount. It was so tight I likely could have forgone glue with the thrust of these small motors but I put a bead around the front of the front and the rear of the rear to fix them in place.



And that brings us to the end of step one! Next Fins!

 

[sod4]

Next step in instructions is to remove the fins from the sprue and prep. The next step after that is the motor mount. I went ahead and attached all of the fins before moving on to the motor mount.

Here's the fin stock removed from the sprue. I couldn't tell exactly what kind of wood it was. Maybe a hard balsa? In any case, the laser cuts turned out great.



After sanding the fins I premarked a line on the motor tube for the launch lugs. Because I knew I was going to cut down the lug and attach it as two separate pieces, I need this line later to ensure alignment.



I then attached each fin using medium CA as per the instructions. I had a little more success with the alignment jig this time, though I only used both of them for the first fin. The other three fins were attached with a single jig.



And here's the fins complete with the jig removed.



So! Fins complete, motor mount and nose cone next!

 

[sod4]

At this point I couldn't resist a size comparison with my BT5 goblin. The MX Goblin is *tiny*!



To get the motor mount to fit in the body tube I had to sand down the centering rings.



A smidge of TitebondII was then applied to the business end of the body tube and the motor mount inserted. I apologize to Semroc here because I generally disregard motor mount insertion guidelines and like it flush with the bottom of the body tube.



The shock cord was then glued into the nosecone by first poking the aft end of the nose cone with the pointy dowel provided, inserting the shock cord into the resulting hole, applying glue, and then following up with the pointy dowel to pin everything in place. The remainder of the dowel was then cut away.



I then sealed the nose cone by soaking it with thin CA. (I'm not sure how well this picture shows this)



And after a sanding with 800, the nosecone feels smooth to the touch. (Again, not sure if this will be apparent in the photo)



Next post, launch lugs!

 

[sod4]

Remember that line from post #3? It's still barely visible after hitting the body tube with some 800 grit.



I cut down the launch lug into roughly 1/4 inch sections and glued two of them at fore and aft positions along the aforementioned line.



And here's the final. I'll probably update this with better focus in a bit.



It is super cold in Alabama at the moment so I don't know when I'll be able to get paint on. I plan to go launch later this afternoon, weather permitting. I'll try and get video but this thing will likely be even more of a teleporter than the Mars Lander. The MX ML is 8.6g dry and this is only 3.2(!)g dry.

 

[SCooke123]

Nice work!

 

[kitbasher99]

Just an FYI. The fins are Basswood.

 

[user 13]

Nice build!

Thanks for sharing it.

What colors do you think you will use?

It looks like it will be a good flyer! Should get some altitude!

 

[sod4]

I'm thinking blue of some sort. I almost always use the rustoleum 2x so maybe seaside blue?



Needs to be something lighter to show the decals well.

I'll probably mask the ring instead of using the decal.

 

[Antares JS]

I'm thinking blue of some sort. I almost always use the rustoleum 2x so maybe seaside blue?

View attachment 442577

Needs to be something lighter to show the decals well.

I'll probably mask the ring instead of using the decal.

I would advise you to consider that that color might disappear against the sky. There's a reason most of my micro rockets are red, orange, and/or yellow.