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Help with LOC MMA-2

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Mr Rocket

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I am working on my L1, and recently got a Loc-Precision MMA-2, 38-29mm Motor Adapter. Included with the parts is a 3/4" length of 38mm motor tube. There is no mention of the part in the instructions. I assume it is to be glued to the aft end of the adapter to act as a thrust ring. However, 3/4" makes the adapter stick too far out to use the motor retainer that I installed. I am thinking that I should cut this down to 1/8" to 1/4" long. Does this make sense, or do I have this all wrong?
 

David Schwantz

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Here are a couple pics of mine. I used LOC parts but just ordered them alone, not the MMA kit. Hope this helps.
 

David Schwantz

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Here are a couple pics of mine. I used LOC parts but just ordered them alone, not the MMA kit. Hope this helps.
 

kuririn

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There is an MMA-2 adapter in my LOC Cyclotron kit. The 38mm ring measures 1/2" wide on mine. And yes, it is an aft thrust ring. I suppose you could cut it down. My only concern is that the narrower you make it, the more you compromise the structural integrity.
 

Mr Rocket

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I ended up modifying the adapter.
  • I cut the thrust ring down to only 1/4" so it is approximately the same thickness as the thrust ring on the 29mm Hobby Motor
  • I recessed the motor tube 1/4" so that the 29mm motors will not project further out the back than the 38's
IMG_3700.JPG IMG_3699.JPG IMG_3701.JPG
 

Mr Rocket

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Here it is test mounted into the rocket with the RouseTech 29/40-120.

IMG_3698.JPG
 

David Schwantz

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Looking at your thrust ring in the pic, it shows that it is NOT in contact with the rear bulkhed. Can you tighten the bolts more and suck the motor down tighter to the bulkhead? If you look at mine, I made spacers on the 3" bulkhead that I used as the thrust ring. I did not want to crush the 38mmt when I tightened the bolts.
 

David Schwantz

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Also if I may say, the screw for your rail button could be a flat head instead. Gary pointed this out to me before my cert flight. So I counter sunk them and changed to flat heads, he also said it was best for them to rotate as to not get hung up on the rail.
 

Mr Rocket

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There is an MMA-2 adapter in my LOC Cyclotron kit. The 38mm ring measures 1/2" wide on mine. And yes, it is an aft thrust ring. I suppose you could cut it down. My only concern is that the narrower you make it, the more you compromise the structural integrity.
Thanks for the reply.

The thrust ring included with mine was just shy of 3/4". That would have been WAY too thick for my application. I think that they just include a short length of tube, and let you cut it to the desired length IF you want to use it. It is not even mentioned in the instructions.

Considering that I have read about many people making tape thrust rings, and I have a full 1/4" epoxy x almost 5" circumference, and the force is applied in shear, I am not worried too much about compromising the structural integrity.
 

Mr Rocket

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Looking at your thrust ring in the pic, it shows that it is NOT in contact with the rear bulkhed. Can you tighten the bolts more and suck the motor down tighter to the bulkhead? If you look at mine, I made spacers on the 3" bulkhead that I used as the thrust ring. I did not want to crush the 38mmt when I tightened the bolts.
No matter how tight I make the bolts, the thrust ring will never get pulled tight against the bulkhead because it is applying its force directly to the motor mount which projects about 1/2" beyond the bulkhead. Both the motor mount (which is Loc heavy duty tubing) and the thrust ring were reinforced with thin CA. I do not plan on cranking down on the bolts enough to crush that. It should only need to be a partial turn past finger tight to be effective. Also, the SS plate has some spring in it.
 

David Schwantz

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Gotcha, the tube that I am seeing as part of the new adapter is actually part of the MMT.
 
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