BT60 Cluster?

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paulm

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I would like to put three c motors in a BT60 body. I can't find any centering rings or devices for mounting the tubes. So, before I engineer an overly complicated solution to an exceedingly simple problem, I would like to ask what others have done or would recommend. Any suggestions, please?
 

dhbarr

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https://www.unclemikesrocketshack.com/Motor_Mounts_Accs/Dual_Triple_MM.html ?

Edit: misread bt60 as bt80. I'd have to check the math, but I think those would slide right in with maybe a wrap or two of thin paper. Small balsa plugs to keep the gas in, et viola!

Edit2: I also somehow got the idea 24mm motors were involved. Maybe I should stop 'helping', as my solution appears to be for a different problem than you're having :D
 
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BDB

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Check out Fliskits: https://www.fliskits.com/products/01prod_fs.htm. It looks like the conventional 3x18 mm motor mount for BT60 is currently not available, but the canted mount is. I just built a 3x24 mm canted motor mount for BT70 this weekend. It's pretty cool, and Jim's instructions are easy to follow.
 
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hcmbanjo

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Three BT-20 tubes in a BT-60 doesn't leave much room for centering rings.
You could always go old school and use some tissue/glue putty.
Check out steps 3 and 4 in the old Estes Ranger plans:
https://www.spacemodeling.org/jimz/estes/k-06.pdf

I've used it in the past. The trick is to tear up the tissue pieces very small before mixing with the glue.
It makes for a smother packing filler.

Or, a three engine cluster using a single plywood ring on top.
https://modelrocketbuilding.blogspo...0-04:00&max-results=20&start=20&by-date=false
Scroll down to posts 2 through 7.
 
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EXPjawa

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As Estes did with the old Astron Ranger & Cobra models, you just glue three 18mm motor tubes together, slide them into the BT60 tube and plug the gaps. The last one I did, I trimmed segments of a BT60 centering ring to fit between the tubes. I figured it would be lighter than filling the space with tissue & glue, but its was just easier anyway.
 

gdjsky01

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Right. Like Chris says, you can just glue the three tubes together and once installed use the old school tissue and white glue to fill the gaps.
3x18mm in a BT60 would IIRC leaves no room for classic Centering Rings. Though some people have laser cut wood 'caps' that would go on either end to seal the gaps...
Tissue and glue works just as well. Soak little pieces of tissue in white glue... ball it up like putty... push it into the gaps with a dowel or toothpick.

You don't need much. Weight is trivial since the vast majority is the three motors. Once in there... it is not coming out.
 
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Mugs914

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I just finished a three 18mm cluster BT-60 job and used the tissue and glue method. Its easier than it sounds (less messy than it sounds, too!) and is actually pretty light. Give it a shot...
 

Tramper Al

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I built the Semroc Ranger and it includes a single centering ring to 3-cluster the BT-60. Due to the eRockets search procedures, I'm sorry I can't easily tell if it is sold separately. On the old Semroc plans pdf, it was called RA-2060X3.
 

Micromeister

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As others have mentioned 3- BT-20's are glued together and slide well into a BT-60. plain old tissue paper soaked in white glue makes a sealing putty between the gaps and at the center. Be sure to make these tissue plugs at least 3/8" deep. The thicker the heavier;)

Having built many 3 motor clusters in BT-60 bodies I NEVER use centering rings they are just WAY to fragile after cutting.

My best method for securing the 3- BT-20 motor tubes is to add a 1/8" wide x 2" strips on each tube, between the stacked tubes. This gap between tubes allows for both external and internal friction tape application motor retension and/or if used, gives the three motor hooks a little more space to move.
 
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Mugs914

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My best method for securing the 3- BT-20 motor tubes is to add a 1/8" wide x 2" strips on each tube, between the stacked tubes. This gap between tubes allows for both external and internal friction tape application motor retension and/or if used, gives the three motor hooks a little more space to move.
Great idea. Do they still fit well in a BT-60 with the spacers? I know there is a tiny bit of slop in a BT-60 when the mount tubes are glued directly to one another, I imagine the 1/8 between mount tubes would fill that nicely.
 

Woody's Workshop

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For a view of cluster engine mount assembly instructions,
"GO HERE", (Thanks to Randy at eRockets for keeping it alive) to view the Ranger.
"GO HERE", to view the Scrambler. There also RocSim files to download of each.
At the bottom of the page is a pdf file for the instructions.
I'd link the instruction page, but for some reason something happened and can't simply open a pdf no longer. I have to download it and save it to look at it. (Could use some help with this issue)
I've used myself without the centering ring, wrapped the 3 engine tubes with masking tape for a snug fit.
And used a plywood centering ring at the ejection end of the tube. You can get a good bead of glue around that to hold the trust of 3 c's on a heavy lift.
 

walterb

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There was a Custom rocket that had three bt 20 in a 60. My wife did it so I'm not sure how it went but I don't recall rings. It had the three 20s with a short tube with fins and then more 60 at the top for the recovery and like a big bertha nose.
 

Trident

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Here's how I did my clone of an Astron Cobra. I used a section of 4-40 threaded shaft, which uses a 4-40 bolt and washer to hold the 3 motors in place. Nice and clean for display -- no hooks or bolts showing. Mount anchoring was old school -- tissue/glue wads.

The top side holds the shock cord anchor, a stainless steel fishing leader from Walmart. Elastic shock cord ties to it near top of body tube.




 
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Micromeister

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Great idea. Do they still fit well in a BT-60 with the spacers? I know there is a tiny bit of slop in a BT-60 when the mount tubes are glued directly to one another, I imagine the 1/8 between mount tubes would fill that nicely.
Yes I should have mentioned the 1/8" wide strips are Standard file folder or 67lb cardstock DOH! with 2 spacers per joint that leaves plenty of room to slide the Clustered MMT into the BT-60 body snuggly.

And ditto Trident on the 4-40 stainless center Machine screw motor and shockcord anchor hardware. On larger BT-80 clusters I use threaded inserts between 3 and 4 motor clusters with a 10-24 Stainless Steel Trush Head MS with Stainless finderwasher retainer. Some other then D12 clusters can use 1/4" inserts and round head machine screws with flat washer.

A bit to big a mount for most models smaller then BT-80 but another option.

687_65th B-day Rocket-a1_BT-80 4-D12 Cluster Body_10-30-13.jpg
 
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T-Rex

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Just did a quick build in OpenRocket. Here is the template for the centering rings for 3x18 in a BT60 tube....
As others have said, there isn't a lot of room in there....

3x18_BT60.jpgView attachment 3x18_BT60.pdf
 

paulm

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Thanks for all ideas guys! My motor tubes will be exposed similar to the Loc Viper. So, the three tubes will be glued together, but I will use the tape to snug them up in the body tube. I will also use the screw in retainer with the threaded sleeve - much nicer looking than the all thread and nut!

Thanks again
 
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