18mm Motor Mount Adapter Question

[Joel E.]

I am interested in learning how to build an 18mm motor mount adapter that can be used in a 24mm motor mount. People have mentioned using this type of adapter in a couple of threads - how are they built? I haven’t built a rocket since when I was into them was a kid. My five year old son and I plan to install the "Estes D and E" 24mm motor mount kit in a Big Bertha kit. It would be nice to have an 18mm adapter so I can fly the smaller engines on windy days. The salesman at the hobby store did not think that Estes has ever sold an engine adapter kit. Please share any thoughts that you have on how this could be done.

PS - Great forum!

 

[rstaff3]

This is simple. A piece of 18mm tubing and two thick 18mm-24mm centering rings, like the ones Apogee sells make a fine adapter. You can add an18mm motor block and/or a motor hook to the 18mm tube if you so desire. Basically you build it just like you are going to glue it in, just skip that step. If the model you are using it in has a motor hook, you might use a third ring at the base of the adaper to catch said hook. If you don't have rings, you can cut them from a spent 24mm casing.

 

[wscarvie]

The only thing I'd add to Dick's comment is that the 18mm engine mount tube should be long enough that you, with the forward 18/24 centering ring glued at the front of the 18mm tube, it sits up against the engine block in the 24mm engine mount. This gives the engine in the adapter something firm to push against.

See attached image. The 18mm engine tube, 18/24 centering rings, and 18mm engine block are all part of the adapter and are glued together. The outer tube and the 24mm engine mount are part of the up-engined Big Bertha.

Make sense?

 

[rstaff3]

A picture is always worth more than words! I personally prefer to have the adapter hang out the back a tad, so the 18mm tube is longer and the 18mm block is further back.

 

[mikeyd]

Here is one I made from a old D motor. I "Peeled" some layers off of the inside of the motor to fit a bt20 inside, with enough sticking out of the back for and motor block, then notched the motor block end to fit past the D mounts motor hook at the top. I then cut a slot in the D motor case so I could put a motor hook in it. Here is a picture of it.

 

[wscarvie]

Hi Dick,

Is this to make it easier to extract the adapter after recovery?

Thanks.

 

[rstaff3]

Yes, it gives something to grab onto. Of course it has to take the impact of landing. If you use a hook, this along with the motor gives you something to grab. For some reason I generally haven't added a hook on my adpaters. I have, however, been known to go nuts with tape and wedge the adapter in.

 

[jflis]

If you don't have parts for this laying around, I could recommend that you look at the FlisKits Engine Mount Kit EMK-18-50 ($1.75).

While it's not mentioned on our components page (which I will fix...), we include an extra centering ring that you can mount at the base of the motor tube (to act like the end of a 24mm motor casing) allowing you to convert this engine mount into an 18mm - 24mm adapter.

jim

 

[Micromeister]

If you have a expended D motor casing the three rings can be cut from it and used with a regular piece of BT-20. I also like to leave about 1/4" of tube sticking out to give you something to grab for removal. I've found one of two of these adaptors are nice to have in the rangebox.

 

[WiK]

Since no-one has noticed.

Welcome to the forum! The biggest wealth of rocketry knowledge on the web (probably!)

If you need to know anything, just ask! And if you have a digital camera, pictures can say a thousand words, so post lots of them and save your fingers!




Phil

 

[jflis]

Originally posted by Micromister
If you have a expended D motor casing the three rings can be cut from it and used with a regular piece of BT-20. I also like to leave about 1/4" of tube sticking out to give you something to grab for removal. I've found one of two of these adaptors are nice to have in the rangebox.

if weight isn't an issue, you can take that expended D motor casing, knock out the nozzle and replace it with a motor block and simply use the whole casing as an adapter. I always keep some of these in my range box for a quick and cheap adapter

 

[Joel E.]

Thank you for the helpful hints - I really appreciate all of the advice. I plan to build the adapter as soon as Jake and I finish the rocket. I plan to post a picture of the rocket when we finish the project!

Joel

 

[jflis]

picture - good

no picture - not good

ungowa timba, post pix

(man, i need some rest... LOL)

 

[astrowolf67]

Originally posted by jflis
if weight isn't an issue, you can take that expended D motor casing, knock out the nozzle and replace it with a motor block and simply use the whole casing as an adapter. I always keep some of these in my range box for a quick and cheap adapter

I was going to suggest this, but Jim beat me to it. This is how I make adapters. Just knock the nozzle out, and any remaining "junk" and glue in an engine block. If any of the "junk" is stubborn and is hard to remove, tape a strip of sand paper to a wooden dowel, and remove it with that. An engine block can be made from a used 18mm motor. Then just friction fit the 18mm motor into the 24mm casing with tape.

The adapters that Estes sold, were not labeled as such. It is actually the 18mm motor mount kit, which contains parts and instructions to make an adapter from some of the kit parts. So, the hobby shop person didn't tell you wrong, he just didn't know.