first mid power, Darkstar mini build

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RKeller

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My wife just bought me the darkstar mini kit with the dual deploy kit for my birthday. she's pretty awesome:D. This is my first mid power rocket. I'd like to get your advice on which motor retainer to use, launch lugs, and any other tips you have. I'm thinking I'll start off without the DD and just use the engine to deploy the chute. that will give me plenty of time to plan out the electronics. I'm thinking maybe eggtimer and eggfinder but I don't know if it will all fit.
 
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Rex R

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I've built two 'minis' (wild childs)...the Aero pack retainer(29p) works well. I would advise not using 'paper' lugs, had one get ripped apart(the lug, the rocket is otherwise fine) when it bound up on the rod(think the rod had a bend in it). used 5/16" thinwall brass tube for the second mini. if you follow the instructions (online) you should be fine. you do want to run flight simulations before your first flight as these birds coast longer than you might expect. a 15" top flight chute is a good choice(I would suggest neon green or hot pink). don't try using ordinary sand paper though...fiberglass is tougher than it is, use wet/dry black and at that expect to run through a fair amount(if you plan to paint yours you can stop at 400 grit).
Rex
 

nute

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I would recommend using Rail Buttons instead of launch lugs. For mid power, especially F motors, 1/4" lugs will work, but it's more than likely that eventually you'll want to fly Gs and Hs in this rocket (especially with the DD option). For these motors rod whip will be a problem, and some clubs might even insist you use rails. As far as motor retainer, Estes brand is very cheap and gets the job done, but with such a small diameter the OD of the retainer will stick out from the outside of the rocket. Thus, I think the more expensive slimline or Aeropack is your best bet. What epoxy are you planning on using? I used Rocketpoxy on my Shapeshifter Mini and that survived a lawndart and chute-less landing with just a couple scratches.

Nate
 

RKeller

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Thanks for the advice, I was just reading about using rail buttons. the local club meets aug 16th-17th. I will bring the kit along and get their recommendation. and thanks for the links for the motor retainers. I had seen the estes ones and liked them but didn't think they may be wider than the 38mm tube. I have access to a machine shop so I may make my own if I can get some dimensions of other ones. I haven't decided which epoxy to use, haven't even researched that yet.
 

cbrarick

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Railbuttons (1010) are the only way to go.
Make sure you get the RA29P and use a little JB weld. Put on the retainer first and build the rocket aft to forward.
The chute that comes with it it just right for it.

For your first foray in DD, set it up as motor eject, with the altimeter set to do both main and apogee. just pop the nose cone off with no chute, to see if you got it right. Then switch the chute and you're golden

You really need a tracker for large G's and bigger motors. I've had several people try to do L1 without trackers, none found their rocket without the tracker.
 

RKeller

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what's the best way to install the rail buttons? can you get threaded inserts in tube? or just tap the fiberglass and epoxy them in?
 

ksm2001

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Welcome to the forum :handshake:

Tap the fiberglass to fit the size of threads of the rail buttons. There isn't much wall thickness but using a fine threaded screw will work fine. I managed to tap mine in the centering rings. Here is my thread if it helps but built mine much like CJ's 3" Darkstar found at the top of the high power thread.

Keep us posted and ask questions if in doubt.
 

RKeller

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oh duh, centering rings would give plenty of thread. any reason not to drill and tap through the MMT? seems like it should be fine as long as the screw doesn't protrude into the tube. I've read through your build, very nice.
 

FlyBoy

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Don't be afraid to try the foam is and fly it method of assembly, I used it on my Mini Darkstar and have flown on H motors no problem. On rail buttons you can always epoxy a couple of small pieces of G-12 to the rocket to build out some spots to mount the rail buttons.
 
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ksm2001

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Not sure I would want to drill through the motor mount. You should have enough strength with the treads in the body tube. I used some wide centering rings which made it easy to drill and tap. On other builds I epoxied a piece of plywood to the motor mount where I wanted the rail button screws to go and sanded to the contour of the centering ring. Just have to be careful so it doesn't get in the way of the fins.
 

blackjack2564

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We just drill a hole with 1/8 bit and let the screw self tap. Done this on many rockets up to 4in and 20 lbs flying on M motors. It will hold just fine on a mini.

Don't over think this build. it's all been figured out and works.

I'd be much more worried about finding it when flown on H motors and above. I've flown mine on I's to over 6,000 ft. Motor eject and just a tracker.
 
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FlyBoy

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So I have been doing extra work for nothing, man I hate that. I don't have any problem finding my mini flown on H motors and I don't use trackers, of course I fly at Lucerne and it is hard to lose something on a dry lakebed.
 

RKeller

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the fit of the coupler is really loose. I can wrap 1 and 1/2 turns of blue masking tape and it still fits into the body tube and the 8" DD tube. is this normal? the fit of the nose cone is nice and tight.
013.jpg
 

ksm2001

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The fit using masking tape is fine. Depending on the run of coupler tubing the outside diameter on one might be snug the other a bit loose. Mine needs a bit of masking tape also to be safe from drag separation.
 

RKeller

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those are slick. and cheap too. thanks for the tip!
 

RKeller

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what is the difference in the motor mounts? RA29P is what I need to get but what are the L, L2, hybrid and such?
 

DizWolf

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what is the difference in the motor mounts? RA29P is what I need to get but what are the L, L2, hybrid and such?
Different sizes for paper tubes. As for motors, there's plenty of fun to be had in single use, but you're going to run into hazmat shipping on G's. The 29/40-120 is a good case with TONS of loads for it, many with no hazmat. the 120, 180, 240 and 360 are all great motors as well. I shoulda pulled them all out at the launch for you to check out....sorry didn't think of it. All depends on how high you wanna go. Windless day with no crops? I'd do an I200 :). Chris went single deploy well over a mile at URRF and put it on the field with one. For the DD, I'd absolutely recommend an RRC2+. If you do decide to track it, I'd say rig up something in the NC with a removable bulkhead (wood plate and set screws) or order a really long coupler.
 

RKeller

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Started the build...
Parts minus the DD extension and coupler
002.jpg
Using automotive 80 grit sand paper to rough up all surfaces that will see epoxy
005.jpg
used a chainsaw sharpening file to notch the centering ring for the shock cord. the motor tube is plenty long so I wrapped the shock cord around the tube and glued it in place with 30 min bob smith epoxy. you can see in the pic that the fins will not hit the cord.
007.jpg

now I have to wait for my motor mount to show up...
 

RKeller

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but while I wait I messed with the fins. these are pretty thin and I didn't feel like making an even thinner knife edge on them. I set my little disc sander to 45 degrees and beveled the edges
003.jpg004.jpg008.jpg009.jpg
I noticed other builds don't bevel the edges between the fins. any reason for this?
 

RKeller

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as soon as I epoxy on the shock cord I see others are doing a loop with both ends epoxied to the MMT. what's your thoughts on this? obviously if you tie a knot at the end of the cord loop you have a redundant shock cord mount. I could easily file a grove on the OD of the centering ring and epoxy the other end down... worth it?
 

blackjack2564

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I noticed other builds don't bevel the edges between the fins. any reason for this?

Yes....

on larger versions with split fins, the square edge between them is what gives you the 'whistle' when air moves across the fins.Blunt edge causes turbulence & the whistle. If you bevel that edge... no sound.

Think of split fins as one that has been sliced then separated . Nothing gained by beveling that joint/edge.
 

blackjack2564

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as soon as I epoxy on the shock cord I see others are doing a loop with both ends epoxied to the MMT. what's your thoughts on this? obviously if you tie a knot at the end of the cord loop you have a redundant shock cord mount. I could easily file a grove on the OD of the centering ring and epoxy the other end down... worth it?


If you are using Kevlar, there is no need on a rocket this small.

On bigger projects you glue a Y-harness to the motor mount [Kevlar] then attach your shock cord to that. In many cases that will be tubular nylon which has some "give" to it. Helps relieve stress of chute shock opening.

If cord is mounted to only one side of MM, the rocket will recover tilted to one side. Y-harness helps rocket fall "centered" on cord, which is a plus on heavier, larger rockets.
 

RKeller

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motor mount and rail buttons came today from wildman;) I want to leave the back side open so I can see how the fins look and run some thin epoxy down as internal fillets if needed. I taped the motor tube so the mount was a nice fit then taped the od of the mount so it matched the ID of the body tube. then applied epoxy up in the tube about .5 to 1 inch in front of where the centering ring will be, pushed and twisted the mount into the epoxy and wrapped tape around the mount and body tube to center them. I made sure to leave a gap so the motor mount nut doesn't hit the body.
001.jpg002.jpg003.jpg005.jpg
 

RecoRocket

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A standard trick for me with TTW fins, is that when you build the MMT, you make sure you can remove the back CR. I use a wire or a Kevlar thread to make a little handle I can use to remove it. Then, attach the front of the MMT in the BT, with the rear ring in place.

When the front has set up, pull the rear ring off. This allows internal filet of the fins to the motor mount (and maybe a t-nut for the lower rail button!). When all is done inside, actually attach the rear CR! (then the aeropack retainer, but only after painting!)
 

RKeller

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I was going to use the rear CR but I figured if I used the retainer it would also help me get the length right. it worked well.

I roughed up a square nut and glued it in the tube with JB weld for the rear rail button.
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I drilled and tapped the front centering ring for the other.
005.jpg
today I printed some fin guides on card stock to help get the angles right.
001.jpg
I used a microjet to lay a bead of 15 min epoxy through the fin slot on the MMT for each fin. once I was happy with the alignment I let the rear fins set up.
008.jpg007.jpg
Then I repeated the same process for the front and used the straightest Popsicle sticks I could find and small harbor freight clams to align the front fins with the rear. so far so good :)010.jpg
 
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RecoRocket

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Did I read this right? You left off the rear CR to allow for the retainer? As an RSO, I would not allow you to fly.

Overbuilding is common in MPR/L1 (you could probably drive over my L1 cert rocket and it would still fly), but leaving off the rear CR would show you don't understand the purpose of the rear CR....
 
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RKeller

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no, the rear CR will go in. I didn't use it to align the MMT. I used the motor retainer so I could center and position the MMT where I wanted it. the rear CR is a little loose so I didn't want to rely on it for centering the MMT. it will be epoxied in place soon.
 

DizWolf

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Pretty sure he intents to install the rear CR. However, I don't see the need for one.
 
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