(For the first time ever, my ADHD @$$ is starting a new thread instead of hijacking one.)

Tim posted this pic of his 24mm to BT-70(?) motor mount.



The first time I ever saw a coupler used as part of a motor mount was probably the old Estes Saturn V system which used BT-60 as a sleeve for interchangeable 1x24mm and 3x18mm mounts (and required the custom BT-63 tube to receive it).



During my BAR-dom, I have built many motor mounts, but have always avoided the use of sleeves (ie, couplers) around the mounts relying on the rings themselves to provide the seal as well as load structure of the mounts. For example, this 29mm-BT70 mount has only the fore and aft rings.


So, why do folks use the sleeves? What do you like about them? How do they improve the mount? Is it just a paradigm left over from the old Estes catalog? Or is there something else?

Doug

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YORF member #11

I've done them both ways. When I built my Centuri Saturn V, they didn't have 24mm motors and the kit was for 3x18mm only, so I made my first interchangeable mount after reading that it could be done in the Estes catalog. I didn't use a coupler with it. I used flimsy cardboard centering rings so I had to permeate the corrugations with glue to make sure the ring was strong enough to be retained at ejection.

The recent ones we've made have couplers/sleeves because......just because.

I had couplers on hand. I had scrap cardboard for centering rings on hand. I didn't have to go out to the shop and cut plywood for the non-sleeved type. Maybe that's why I did it. Maybe it's because I liked the slick clean look of the Centuri Power System mounts.

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I love sanding.

I did the same thing with my Semroc Saturn 1B. Using a BT-70 and couplers. I had them on hand at the time so thta's what I used.

Attached Thumbnails

 

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Tony Vincent
NAR # 45082 L1
CMASS, MMMSC Member

I think it's "dealer's choice".

Using a tube will reinforce the rings if they are prone to flex, but will add more weight.

If the centering rings are stiff enough, then the tube is unnecessary.

On my MPR/HPR project, I opted to use rings only.

Greg

I wonder if the use of stage couplers on such motor mounts began as Estes' way of burning through an oversized inventory of couplers? I once read that their SPEV ("Spare Parts Elimination Vehicle") kit was the result of a company inventory audit that showed that they had up to a 50-year supply (at their then-current sales rates) of some rocket parts.

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Black Shire--Draft horse in human form, model rocketeer, occasional mystic, and writer, see:
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NAR #54895 SR

I'm going to do this for my Saturn V, but I'm wanting to do a 5 engine cluster. 4x18mm for the outboards and a 24mm for the core. I'd love to be able to switch those out for a 29mm or a 38mm so I can level 1 with this one. I hope that will allow me for few different flying options

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She said, "Don't make me release the flying monkeys!"

Too late, I'm here......

Estes originally used the centering rings/coupler arrangement on all of their models that required an engine mount (i.e. BT-50 and up). This structure gave the strength necessary for the G forces the model would experience. It was the flimsy diecut cardstock centering rings that Estes used during the early years that mandated the use of the coupler in the mount. In later years Estes went to a heavy centering ring and adopted the mount design that Doug favors. However, the largest Estes tube to use this type of mount was, as far as I recall, the BT-55. I don't think Estes ever made the heavy ring in a '60' size or larger, so they stayed with their original design for larger models such as the Big Bertha, at least for a while. I know that they never used the coupler for an engine mount in their really big models such as the Maxi Brutes (unless you include the Saturn V in that group) but they did provide heavier cardstock rings in those kits.

Joe

That raises two interesting questions, Joe. Kits with BT-50 body tubes such as the Astron Farside and (if memory serves) the 18 mm motor Honest John used the "flat rings 'n stage coupler" motor mounts, as did many of the Design Of the Month winners in the early years.

[1] However, did the Alpha ever use this earlier type of motor mount? All of the ones I've ever seen (which go back to 1969, and this kit first appeared in 1966) have had the thick spiral-wound CR-2050 Centering Rings that are standard today. The model rocket guide in the 1969 Estes catalog (the "yellow pages section"), which features the Alpha, also shows the modern motor mount in the exploded view drawing of the Alpha.

[2] Did later production runs of the Farside, Honest John, and other Estes kits with the older-type motor mount have their motor mounts updated to the newer design?

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Black Shire--Draft horse in human form, model rocketeer, occasional mystic, and writer, see:
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All of my book proceeds go to the Northcote Heavy Horse Centre www.northcotehorses.com.
NAR #54895 SR

No. I had an Alpha from the very first run of the kits (purchased in spring, 1967). It had, as I recall, the AR2050 rings, just as you described.

Having never owned any Centuri kits back in the day, I didn't see that type of mount until after I became a BAR.

I believe that the "coupler and rings" type of mount was more of a Centuri thing. None of the Estes kits that I had used that style.

MarkII

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SAM # 0011

Thank you for confirming this--I suspected it, but I wasn't sure.My brother Richard's Centuri Nike-Smoke had the "flat rings 'n stage coupler" motor mount. My father's 1968-vintage Estes Big Bertha also had this type of motor mount, but I don't know of any other Estes kits besides the Astron Farside and (I think) the 18 mm Honest John that used it.

The Estes Model Rocketry Manual (see: http://www.ninfinger.org/rockets/no...a/estesmrm.html ) that first appeared in the 1969 Estes Catalog (see: http://www.ninfinger.org/rockets/no...a/69estcat.html ) shows the "flat rings 'n stage coupler" motor mount on page 52 of the catalog (see: http://www.ninfinger.org/rockets/no...a/69estp52.html ). However, the only motor mount of this type that is shown is one for BT-60 size rockets, so BT-55 and smaller kits may all have been using spiral-wound motor tube centering rings by that time.

__________________
Black Shire--Draft horse in human form, model rocketeer, occasional mystic, and writer, see:
http://www.lulu.com/content/paperba...an-form/8075185
http://www.lulu.com/product/cd/what...of-2%29/6122050
http://www.lulu.com/product/cd/what...of-2%29/6126511
All of my book proceeds go to the Northcote Heavy Horse Centre www.northcotehorses.com.
NAR #54895 SR