Interchangable motor mounts

[Stymye]

I have almost finished a set of removable Cartridges that house different motor configs for a 4" little joe II
(Yea I admit it's been a excrutiatingly slow project)

I also plan to use them in a 4" Estes Maxi Pershing clone,using the Alien Enterprise reproduction Cone.
(and a beautifull cone it is! )from Ed Miller

the 4 threaded rods fit into a renforced mounting ring inside the Body tube and nuts are screwed on from the aft end with a magnetic nut driver
the coupler size was made from cutting a small section lengthwise from bt 101 till the resulting coupler fit snug inside the Body tube
this is a dry fit pic

from L to R

5 x 24mm
3 x 24mm
1 x29mm

 

[Rocketmaniac]

Originally posted by stymye
the 4 threaded rods fit into a renforced mounting ring inside the Body tube and nuts are screwed on from the aft end with a magnetic nut driver

stymye

Do you have a pic of the re-enforced mounting ring?

 

[Stymye]

sorry I meant to say the nuts are installed from the fore end of the body tube


heres the ring dry fit inside the tube

 

[Stymye]

here is the ring leaning against one of the cartridges

 

[Stones]

Great idea Stymye.
I'm thinking you could also have threaded rods affixed to the reinforced CR and then slide the cartridge over the rods and install the nuts from the aft, having t-nuts installed in the cartridge. This would work nice for those longer airframes where reaching inside, through the front, might not be so easy. I haven't built a clustered bird yet but, I'm guessing with clustered ejection, you wouldn't need a stuffer tube as the multiple charges would be more than enough to get the laundry out...?

 

[SwingWing]

Very nice, great idea. I have a possible future project that I have been debating between 29mm (not very available around here) and clustered 24mm. Now I just may do both!

 

[bsexton]

I have adapted a concept from True Modeling Rocket Kits using their "quick change motor mount system". It consists of a primary motor mount that is permanently installed in the rocket with "quick change adapters" for the various motor configurations. I have used this system in an Estes Fat Boy and Big Daddy so far. I can fly a 3x18mm cluster, a single "D" or a single "E" for these particular rockets. Depending on the airframe you could of course make bigger cluster configurations and/or 29mm motor adapters.

Attached is a picture of my Fat Boy with the primary motor mount installed and a freestanding primary mount for comparison.

 

[bsexton]

A picture of the 3 different motor mounts that can be flown in this rocket (and others that I have adapted).

 

[bsexton]

A picture of the forward end of the primary mount showing the "thrust ring" (smaller centering ring) to prevent the motor mounts from moving forward.

 

[bsexton]

And a final picture of the 3x18mm motor mount installed in my Fat Boy. There is a blind nut installed in the aft centering ring that allows a small screw and washer to contain the motor mount.

 

[cls]

Bruce, Fat Boys' fins are supposed to be glued to the motor mount - from what I have seen it is necessary.

what did you do to reinforce the fins on your Fat Boy?

cool set of MMTs!!! I want to make one like that!

 

[bsexton]

Originally posted by cls
what did you do to reinforce the fins on your Fat Boy?

The fins are still through-the-wall to the primary mount (obviously a little shorter than the original design). To strengthen the fins I covered them with dope and silkspan - lightweight, but still quite strong.

 

[rbeckey]

I made a set of interchangable mounts in a BT 80 coupler for a since deceased 4 inch Crayon rocket. They now reside in a scratch 10 inch saucer design, and will also be used for the reincarnated Crayon and others. Right now I have a 3x 24mm and a 1x 29mm, with plans for a possible 1x 38mm if that ever becomes realistic in light of regulatory status. Also possible would be a 4 or 5x 18mm, but I don't really need that right now.

 

[JBeau]

Hehe, what a great discussion. When I start building the rockets I bought with these larger dimensions, most of this will give me plenty to consider.

However, my Corona is a SLIM rocket. The body tube is 36" BT50, so I'm simply considering my engine options for that rocket right now. 1 engine only, no room for screws and primary/secondary mounts.

1) I don't even own anything other than ABC engines right now, so if I purchase the next sizes up, what does that do width and length wise?

2) Aren't D & E engines the same width and just longer? Would it create big problems if I just use the same MMT and have the engine sticking out the back further?

3) How far up in engines can I safely go with this rocket? I'm considering adding the Corona-2 when it comes out, so staging might need to be a consideration in how far out the engine sticks (am I gonna have to just buy anoher kit? Hehe)

4) I could insert a perment "block" inside at the point where the largest MMT would nest in the correct position, then use spacers to snug up the smaller engine MMT into the correct position, would friction fit alone be enough to keep these MMTs from popping out the back? Any cool ideas on locking these in from behind effectively?

Jerry

 

[gstarraider]

not quite, the ab&c motors are 18mm (bt-20) and the d&e are 24mm (bt-50) wide. the abc&d motor are the same length and the e motors are longer. if it was me i would put a thrust ring(engine block in the bt-50 tube to handle the length of the e motor and use what i do. i am including a pic of my set up and of the different sizes of motors

 

[gstarraider]

here is how they line up in the rocket

 

[gstarraider]

and one all put together

 

[ben]

These are some nice ideas I might use them in my Phoenix (Estes OOP converting too a 2 stage ) I have a moding thread about it in MPR and I plan on using a 29mm all the way throught (38mm would be nice ) and using an adapter do I can fly it with 24mm in the booster and a 29mm Sustainer or a 29mm all the way through. I was also going to try and fly it with 6 or 7X18mm (8 fit but to tight no room for ring ) I flew it on an Estes E9 and it BARELY got off the pad (Thanx For the motor Bruce ) So I figured the trust in ponds and 7 C's are almost twice the amount of power as an E9 (WWHHHOOO!!!! ) So I have some extra engines I can fly it that way GSTARRAIDER like the 24mm 18mm idea that would be good for smaller Estes kits if you want to "step it up" (who dosen't )

Thanx, Ben

 

[Mad Rocketeer]

When adding up the thrust in a proposed cluster adaptation, don't forget you're also adding weight. Your 7 Cs also weigh a lot more than the E9 does. And it's at the tail of the rocket too, which can adversely affect the stability. Also keep in mind the differences between average thrust and total impulse. Finally, maximum lifting weights come into play, with the possibility that you might get some motors lit and some may fly cold (i.e. unlit dead weight). Figuring this stuff for various configurations and contingencies is the skill part, and if you're on this forum, then you'll probably agree that it's a large part of the fun.

 

[JRThro]

Originally posted by Mad Rocketeer
When adding up the thrust in a proposed cluster adaptation, don't forget you're also adding weight. Your 7 Cs also weigh a lot more than the E9 does. And it's at the tail of the rocket too, which can adversely affect the stability. Also keep in mind the differences between average thrust and total impulse. Finally, maximum lifting weights come into play, with the possibility that you might get some motors lit and some may fly cold (i.e. unlit dead weight). Figuring this stuff for various configurations and contingencies is the skill part, and if you're on this forum, then you'll probably agree that it's a large part of the fun.

Mad,
Thanks for that post. It kept me from having to post the same thing!

So now, let's see just how much weight will be added in changing from a single E9 motor to seven C6 motors.

Going to the NAR website and looking at motor weights and stuff... The E9 motors that they tested weighed between 64.1 and 64.9 grams before firing, while 7 C6 motors will weigh 7 times 24 grams, or 168 grams before firing.

So you're adding about 100 grams in motor weight, subtracting a little bit in centering ring weight, and adding a little weight in motor hooks (if you're using them), so let's just say you're adding 100 grams overall. That's more than 3 ounces of weight being added to the back end of your rocket.

Stability could definitely be affected, adversely.

 

[ben]

I am gonna add a bit more noseweight anyways I already added some to balance for my 2 stage design. It will have a 29mm AND 24mm case so it will have plenty of nose weight for 7 C's (I think)

thanx, Ben

 

[mike_bar]

Originally posted by JRThro
Mad,
Thanks for that post. It kept me from having to post the same thing! [Snip]

Ditto! Nice analysis. Dead weight is dead weight, and adding nose weight just makes it a viscous cycle.

Originally posted by JRThro
The E9 motors that they tested weighed between 64.1 and 64.9 grams before firing, while 7 C6 motors will weigh 7 times 24 grams, or 168 grams before firing. [Snip]

Clustering is fun to do, yet I love the Estes E9 motor... You can't beat a 3-second burn.