Disposable Motor Adapter - DMA

[kramer714]

At one point I had 3 motor adapters from 29mm to 38mm, packing up my range box, I'm now down to one. I started thinking about it, yeah there was that launch were someone borrowed one for his Level 1 attempt...I never remember getting it back. Shame on me for being helpful... I decided to make a disposable motor adapter, return it, don't return it, no worries. Cost about $0.60 to make.

Simple three part design,

• Top Hat - goes on at the nozzle end transfers the thrust
• Spacer Ring - goes around the aft closure for the Aeropack, Snap Ring, metal plate, or mirror clips to hold onto.
• Upper Ring - keeps the motor from flopping side to side

Simple assembly,

1. Slide the Top Hat over the motor, tape around the motor case to keep the motor in place
2. Slide the Upper Ring over the motor somewhere on the forward side so it still is inside the motor tube on the rocket, tape both sides (for a short motor just push the upper ring against the top hat and use one piece of tape to hold them both in place.
3. Put the motor in the rocket, drop the Spacer Ring in place, use the retainer to hold in place

Yeah, motors get hot, but in the 1-2 seconds the motor burns there isn't enough time for the 3d printed parts to soften and fail.

I did make the inner diameter a bit bigger than needed, I am WAY to lazy to peel off the stickers on the outside of disposable motor.

- one fault with this, now I have to remember who borrowed my tape.

Mike K

 

[kramer714]

STL Files, use at your own risk..... I made these with PETG, I wouldn't use PLA

 

[fyrwrxz]

Kramer-sell these. brilliant! I'd be up for a 29/38 set to mess around with. Agreed the other adapters take up too much room, mostly left on the bench then your screwed if the vendor is out of your motor or conditions keep you lower. Happened to me this past LDRS. I'd pay labour, mat'l, your time and shipping. pm me. This is what I love about us. Steely-eyed Missile Men rule! Shame about losing your other adapter. Straight smoke and good chutes!

 

[kramer714]

Kramer-sell these. brilliant! I'd be up for a 29/38 set to mess around with. Agreed the other adapters take up too much room, mostly left on the bench then your screwed if the vendor is out of your motor or conditions keep you lower. Happened to me this past LDRS. I'd pay labour, mat'l, your time and shipping. pm me. This is what I love about us. Steely-eyed Missile Men rule! Shame about losing your other adapter. Straight smoke and good chutes!

Going to Rocstock? Stop by I will give you a set. BYOT (bring your own tape)

 

[fyrwrxz]

Going to Rocstock? Stop by I will give you a set. BYOT (bring your own tape)

Oh buddy! Only going Sat as I'm still sicker than a dog with a sinus infection. Wife only letting me go with my son for recovery. Nothing big or high. Packing car today (slowly). I'll bring you a rocket goody. Thx! -dave-

 

[cwbullet]

I have a similar design. They can get stuck on the motor because of shrinkage with heating/melting.

 

[Buckeye]

Me likey. 100%. Commercial motor adapters are way too big and pricey than needed.

 

[wsume99]

I have a similar design. They can get stuck on the motor because of shrinkage with heating/melting.

I have had similar issues with MMTs in 3D printed fin cans. I resolved the issue by adding a section of cardboard MMT to insulate the casing from the printed parts.

I have not printed any adapters but if I did I would try enlarging the ID of the adapter so that a ring of tape can be added to keep the casing away from the adapter. That might solve the problem.

 

[kramer714]

I have a similar design. They can get stuck on the motor because of shrinkage with heating/melting.

Spacer Ring - The one part that absoultly will get toasted is the spacer ring, that is one reason why I made it seperate, even if melted it will pop off using a screwdiver against the aft closure.

Pry Slot - I thought about making a slot to help pry them off if needed, but i think the gap I have should work. If not plan B would be just to add a pry slot.

Sizing - The actual size for a 29mm case from Aerotech is 28.57 mm. I have no idea what their tolerance is, since they anodize the threads the anodize tolerance cant be too bad. I get 28.62 measuring a old Rouse Tech case (harbor freight micrometers....). The parts I made measure out to be 29.0 mm ID (measured using a caliper, didnt use the telscope gage and micrometer). I do have my printer calibrated for shrinkage for PETG.

Annealing I anneal structural things for the day job but, didnt want to bother with these. Im figuring on single use, if it wasnt for 'certification issues, modifying a motor, you could epoxy them to a DMS motor. ( ADDED - the post printing stability can change depending on the brand of filament and printing temps, I use Overture PETG, Initial printing temperature 230, printing temperature 240, bed temp 80 - i print on blue painters tape for rocket stuff, semi enclosed chamber, chamber temps usually around 50-60)

Tape bad - parchemnt paper good - If the issue is aneling, adding tape will actully make it worse, shrink fitting onto the 'formable tape', if there is an issue of melting / sticking a piece of parchment paper works best. Again I dont think it is an issue, and for DMS non issue (disposable adapter)

The Test - I have a motor case with a ring on it sitting in a 170F degree oven. I have done some testing of how hot motor cases get (unless you ve something stranve, the L2300 KBA gets hot at the delay grain for example) or if you have a cracked liner / c slot) and 150F is about it except around the aft closure from the pad. Funny thing, the motor cases I instrumented actually got hotter sitting on the table in June in Luceren California than they did flying (M motors). I would be more concerned with them anenealing / shrinking when left in the car. (ADDED - test results, 30 minutes in 170F convection oven, ring spins on the motor case like a journal bearing smooth no 'catching' measured at 28.90)

Fin Cans - I do make one piece 3d printed fin cans too, two types, ones that fit directly on motor cases (RATT hybrids) and ones that fit over fiberglass body tubes. The variation of diamter and 'roundness' of the fiberglass is way worse than the motor tubes. For these I mold in three ridges on the ID to allow for some fiberglass flex and annealing (car trunk), and CTE changes between the PETG and fiberglass. Plus if I find a really tight one I can shave down one of the ridges.

YMMV

 

[John Kemker]

I might try making some with ABS-Like resin and see how they do.

 

[Zyzzyva1000]

Might I just add that this is awesome! I just printed a set in ABS with 100% infill, sure seems sturdy (and still very light weight). Will have to print some more to have on hand, but just tried it on a 29 180 case and it fit into a 38 MMT perfectly and with the spacer ring the aero pack retaining ring held everything down perfectly. I will still probably tape the pieces on, but the friction fit was pretty good, I can't imagine anything moving. This is a great design!

 

[mrwalsh85]

Me likey. 100%. Commercial motor adapters are way too big and pricey than needed.

I made my own 38-29 "aft closure style" adapter using a scrap piece of aluminum kicking around the shop. Took about 10 minutes on the lathe. Forward end of the motor will be built up tape

 

[DigBaddy]

If one doesn't want disposable, I designed these clamshell adapters (similar to the Estes ones). Posted in the design thread as well. Printed in PETG, they should last a while and they work with many retainers.

https://www.thingiverse.com/thing:5971997