Building Two Mega DRM At Same Time

sodmeister said:

I did just that ,even though the ply cores were warped ,after using 30 min. epoxy to laminate the skins I placed sheets of wax paper between the fin sets, placed between sheets of 1/4" thick glass plate and placed two bags of lead shot on top (50 pounds total) and the fins came out perfect.

I was very sure however ,that the Balsa skins did not shift off possition from the ply cores (as i cut the Balsa skins the same shape & size as the cores ,leaving a 1/16" all around) when I was stacking them together and placing the weight on top.

A little sanding on all edges(I also gave the leading edges a bit of a bevel) and a coat of 20 min finish epoxy and Bob`s your uncle.


Paul T

Click to expand...

The whole skins shifting thing is what made me just lay it on the whole sheet of balsa and trim down to the core. I could see the load causing the cut to shape as the directions say ending up off the mark and then what do you do? cut and paste, bondo, epoxy with micro baboon???

I do like the .25 or .50 sheet of glass idea!!! heavy as all get out on its own.

Hi All,



How do you like my classy chemical storage:tongue: The cans that this A+B came in were each in a plastic bag and for good reason. They were hard to open, clumsy, and hard to pour!
So a quick trip to the Kitchen store and two flip top glass bottles. As you can see they are easy to tell apart and the thick chem pours very well into the 1 oz. cups and then into the 3 oz. cup for mixing.



I have no pics of mix as I wanted to get it where it belongs quickly, But it does really take a minute or two for the reaction to get going.



The first pour was 2 oz. of total chem 1+1 and this filled the void and just began to come through the lightning holes.

Very nicely done!


Later!

--Coop

Hi All,



Well the pix are out of order but... This is a shot of both fin cans done and another project about to get some foam, it is BT-20 x 2 with NC filled with foam and then a tapered transition.



At this point I thought it might be good to add the rail guides, :bangpan: so as you can see just through the wall + washer and nut. This is some good tube, it was not just going to roll over for the carbide cutter in my Dremel. I like to let the tool do the work and not push or force the bit beyond keeping it in place and cutting, but this was good stuff under that plastic coating.:grin:



This pic shows the foam intruding and the rail guide.



The second pour above the CR I used less Chem, but also the lack of containment of heat or something gives less volume??



This is the left overs from the pour into the skinny tube, I just let it puke out for about a min. then when it was not expanding as fast I put the transition in and held it. I could have corked it earlier but I did not want to miss shape the BT-20, just add some support to it.

This foam is cool stuff, mixed it pours and flows nicely until it just starts to get the reaction started. Pouring down the BT-20 was no problem and hitting the lightning holes was easy.

Hi All,

Sunny in Maine, but gray on rockets. Sanded up the BT so that it was good and micro fuzzy with 150 grit and wiped down with Denatured Alcohol. Sprayed all over with primer and then sanded all over with 320 grit and wiped down and filled small boo-boos with Spot putty. Cured and re-sanded spots. Second rocket is in rotation as well Spray, Sand, Fix, Sand, Spray....

Both BTs look good after first prime and sand with 320 grit, but the surface does have a slight ruddyness. The only thing that is sharp and deep after first sand was the very small spiral. I will see if the next 320 grit sanding is enough.

I must say that most of the rockets I have built have been smaller than 4"(mostly 66 mm), wow this size rocket takes up a lot of paint in a hurry! The MDRM BT and Fins takes almost 3/4 of a 9 oz. can of primer. Granted it is cheep Ace Hardware off-off brand(it is just primer) so no fancy nozzle or 2X paint. 4 cans = $9. Your milage may vary.:lol:

Hi All,

Now the fin fillets



Masking off the fillets



Fillets with 60 min. epoxy and micro cell for the peanut butter consistency.

Scott (or anybody): how much weight does the foam add compared to epoxying internal fillets? I haven't started my MDRM with the 38mm MM yet, but I am wondering if stability will be an issue with bigger motors. I'd like to try foaming a fin can, but if it adds enough weight that I have to add nose weight... Well at some point it'll be heavy enough that I will lose the unfair advantage that the bigger MM will give me in a drag race. :wink:

Hi Sully,

The fin can took about 3.5 oz. total, 1.5 A and 1.5. BUT you will have less room between MMT and BT, so you may have the first pour fill more space toward the Aft solid CR. A+B is heavier than water so I probably added 3+ oz. to the aft end.

And I just finished the fin filets with 60 min. epoxy and micro baboon. Used tape to mask and it made nice looking filets.


Just went back and looked at fillets and the last ones I did look REALLY good I am pleased, I used good old twin tube 6o min. epoxy and mixed in some micro baboon and got it good and thick, and just when I had it good and thick I gave it a little push of epoxy again, mixed it in and went to work. It came out glass smooth.

SAC of MMMSClub said:

And I just finished the fin filets with 60 min. epoxy and micro baboon.

Click to expand...

Thanks, I may give the foam a try. By the way, where do you get the micro baboon? And is he small enough to go down into the airframe to do internal fillets or retie the shock cord?

Sully said:

Thanks, I may give the foam a try. By the way, where do you get the micro baboon? And is he small enough to go down into the airframe to do internal fillets or retie the shock cord?

Click to expand...

Yes, yes he is but the Baboon union scale is out of my budget range, so he is relegated to epoxy thickening duty only.

I got used to working with 5 min. epoxy when I worked in the _______ shop and like it. I mix it 50/50 per directions and most of my pours are in the 5 to 10 gram total chem amount.

For the internals I just poured it down the fin/BT joint and rolled and tilted the rocket to let is flow around the joints till it kicked. It took two pours per a chamber.

This is the first time I have uses a filler and 60 min. epoxy for a fin fillet exterior and I am very pleased.

Before I would mix 5 min and pour it and tilt and roll to get the fillet how i wanted it.

Hi All,

Well it is bleepen cold in the NE so no painting till the cold snap breaks and the electric heater can keep the garage warmish.

So I wanted to work on some nose cones and the two that came with the MDRM. I am foaming them and adding anchor point in the 66mm ones and adding a 3" electronics bay in the 4" NCs

that came with the MDRM, The nose cones will most likely out last the rocket so why not do the mod from the start.



Here we have all the usual suspects .25 all thread, .25x2" washers, .25 nuts, and a torch, i can wash the oil off the washers and nuts, but torch will burn off the oil on the all thread.



I like to leave some of the shoulder of the NC, but this one needed some trimming to allow the washer in. The two 66mm NCs will just get all thread and washer and nuts and foam.



As you can see the washer comes to a stop just over half way down the NC.



Now the inside space of the NC on this rocket is huge, it is an elongated NC with much of the NC being over 3" in dia. before it tapers down to the rounded point. If anyone has a research project to do on a 4" rocket and wants a NC to fill with hardware this is a good one. IMHO The MDRM nose cones will get a .25 all thread centered and two 8-32 all thread rods that are with the E-bay. Washers will be spaced down the .25 all thread to hold it in the foam. The other thing you can do is to wash the inside of the NC with degreaser and hit it with some 36 grit to scar it up so that epoxy or foam will stick better.


The two NCs that came in the MDRM kits are good and solid and will be even more solid shortly. As you can see I left some sholder when cutting out the bottom. I have seen the tail end of the NC just cut off but I think this way gives just a little more for the foam to grab onto.

sodmeister said:

I did just that ,even though the ply cores were warped ,after using 30 min. epoxy to laminate the skins I placed sheets of wax paper between the fin sets, placed between sheets of 1/4" thick glass plate and placed two bags of lead shot on top (50 pounds total) and the fins came out perfect.

I was very sure however ,that the Balsa skins did not shift off possition from the ply cores (as i cut the Balsa skins the same shape & size as the cores ,leaving a 1/16" all around) when I was stacking them together and placing the weight on top.

A little sanding on all edges(I also gave the leading edges a bit of a bevel) and a coat of 20 min finish epoxy and Bob`s your uncle.


Paul T

Click to expand...

I'm thinking about building this kit and was wondering if this warping of the fins is common? What causes it?

AfterBurners said:

I'm thinking about building this kit and was wondering if this warping of the fins is common? What causes it?

Click to expand...

The glue I used is Tight Bond ii so I think it has to do with the water content in the glue.

This changes the size of the wood, causing one side of the sheet to expand. As the actual glue cure is a slow process the wood can change shape.

The epoxy cures by chemical reaction not evaporation, so if the wood soaks in anything it is a bonding factor.

I think that .25 plywood would have been more abuse resistant, cat cuddled up to one and over it went and the balsa dents easily!!

SAC of MMMSClub said:

The glue I used is Tight Bond ii so I think it has to do with the water content in the glue.

This changes the size of the wood, causing one side of the sheet to expand. As the actual glue cure is a slow process the wood can change shape.

The epoxy cures by chemical reaction not evaporation, so if the wood soaks in anything it is a bonding factor.

I think that .25 plywood would have been more abuse resistant, cat cuddled up to one and over it went and the balsa dents easily!!

Click to expand...

Yeah balsa does ding pretty easy. Over all it looks like a nice kit and well made. Parts looks pretty. How big of a chute do they give? How many shroud lines is one it? Just curious because Ihave some extra chutes I can use if it's not what I expect.

Measurement of the one I'd opened is a 28" flat 'chute: seems a little optimistic that a 'chute that small is going to safely bring down a moderately built one of these. Considering upgrade options on-budget as we speak.


Later!

--Coop

SAC of MMMSClub said:

Hi All,

View attachment 112442

How do you like my classy chemical storage:tongue: The cans that this A+B came in were each in a plastic bag and for good reason. They were hard to open, clumsy, and hard to pour!
So a quick trip to the Kitchen store and two flip top glass bottles. As you can see they are easy to tell apart and the thick chem pours very well into the 1 oz. cups and then into the 3 oz. cup for mixing.

Click to expand...

How do you find the shelf life using the bottles? My A/B foam is in the original plastic bottles and I know all about the lids crusting up and being really hard to open!

Krusty

AfterBurners said:

Yeah balsa does ding pretty easy. Over all it looks like a nice kit and well made. Parts looks pretty. How big of a chute do they give? How many shroud lines is one it? Just curious because Ihave some extra chutes I can use if it's not what I expect.

Click to expand...

I'm thinking of swapping the balsa for 1.5mm lite ply. That's super durable

Krusty

Nice Build thread!

I just started building mine and laminated the ply wood fins and balsa with West Systems epoxy and weighed them down with MDF board and some weight. They came out straight.

As a few have mentioned the balsa is easy to ding. My Estes Mega Mosquito had a hole punched through the balsa fin when it landed on the frozen stubble field (Canadian prairie winters when theirs no snow at the time).

So on these fins I thought I'd try epoxy, 1.5 oz fiberglass cloth, and release fabric. This was the first time I tried the release fabric, when removed leaves a smooth surface and only needs a light sanding before priming. I'm very impressed with the results and how easy the release fabric is to use, strengthens the surface and only used 10ml of epoxy for each fin with the fiberglass.

Ken

Hi All,

sorry so long away, the nose cones are foamed and paint is on and sanded and on and sanded. Drying and waiting for final sand and paint. About to order pink kitty max
from StickerShock. Next to secure the motor retention to MMT and paint tail end.





So here are a couple of shots of them just chilling and paint curing.

Things are looking very nice, glad you came back as i almost forgot about this build.

I hope to get mine painted soon ,but there is quite a queue at the moment !


Paul T

Hi All,

Sorry so long away from this build, paint has just not been that cooperative, nor the weather!

So here is the Estes stock motor retainers secured with JB Weld. I used the stock ones to see how they hold up.

The MMT and inside of the retainer got a stern talk with the 60 grit paper.

Retainer on the traditional red one.

Retainer with good smearing of JB Weld.

Given a good twist while sliding it into place to give the epoxy a good smear.

Any excess that went inside the MMT was removed with a gloved finger.

The tail end of the rocket is still primer gray as I have been working on painting the fins and body first to get some good coats on and do the paint,sand,paint,sand,paint fun and then give the tail end a quick blast.

Scott

I finally got mine finished today ,and got 3 coats of gloss clear.Just need to JB the retainer as well as I installed rail buttons in.

Have fun with those HUGE decals,you will be tested .....but they look great once applied :wink:


Take care

Paul T

I have to say that Estes did themselves good on this kit. I did modify mine to a 38mm MMT, put an eye bolt in the upper CR, replaced the shock cord with tubular nylon and attached rail buttons. I did not add any nose weight, nor did I glass any portion of it. Instead of using the water slide decals, I ordered a set from Mark and put some vinyl on instead. That long-windedness aside, she flew awesome!! Thanks to TRF's Jeff Gotatowsky for the fantastic pics:

https://www.flickr.com/photos/jeffgortatowsky/8998556057/in/set-72157634029090327

https://www.flickr.com/photos/jeffgortatowsky/8998557475/in/set-72157634029090327

kelltym88 said:

I have to say that Estes did themselves good on this kit. I did modify mine to a 38mm MMT, put an eye bolt in the upper CR, replaced the shock cord with tubular nylon and attached rail buttons. I did not add any nose weight, nor did I glass any portion of it. Instead of using the water slide decals, I ordered a set from Mark and put some vinyl on instead. That long-windedness aside, she flew awesome!! Thanks to TRF's Jeff Gotatowsky for the fantastic pics:

https://www.flickr.com/photos/jeffgortatowsky/8998556057/in/set-72157634029090327

https://www.flickr.com/photos/jeffgortatowsky/8998557475/in/set-72157634029090327

Click to expand...

Tim, I`m flying mine on CTI 29mm reloads ,starting with bigger Fs (to get rid of my stock to make room for new loads in Gs and Hs) and then work on my G reloads and then mild H loads.

I was wondering if i would need nose weight or not ,as it sounds like I built mine pretty much like yours.

Paul t