# 29mm Minimum Diameter Dual Deploy Go Devil

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#### mtnmanak

##### TRA & NAR L2
TRF Supporter
At some point, I had picked up a Composite Rocketry 29mm Go Devil and it had been sitting in the build pile for a while. (As a side note, I am really confused about the relationship between Rocketry Warehouse, Composite Warehouse and Madcow. Probably a discussion for a different thread.)

We moved recently and I found it in the pile, so I dusted it off and thought about building it out. I looked around the forums and couldn’t find much about building out a 29mm minimum diameter dual deploy rocket, so I decided that is how I want to build this one.

I realized up front I would have to make some modifications and add some parts. The kit comes out of the bag as a pretty standard single deploy 29mm minimum diameter. To make it dual deploy, I am had to research some parts.

First parts were easy. Went to the Composite Warehouse site and ordered a 29mm tube for the payload bay and a 29mm coupler for the ebay. I figure I will just cut a switch band off the 29mm body tube as necessary.

I couldn’t find a 29mm minimum diameter retainer, so I will just build one from scratch.

Next problem was to figure out the parts needed to build out the ebay. Turned out to be difficult to find anyone that sells a 29mm sled/system. A number of altimeters will fit in a 29mm build (RRC2, Stratologger, Easy Mini, etc), but I need a fairly well thought out system to get a computer, battery and some kind of switch into such a small ebay. I saw Apogee had a 29mm ebay kit, so I ordered one. I realized when I got it there was no way it work out of the bag. It didn’t fit in the fiberglass coupler and it was way too long. I thought about modifying it, then decided to CNC parts out of FG that would mimic it. As I was designing that, I ran across a 29mm sled Missile Works makes for the RRC2 series altimeters. Looked perfect! I ordered one (I already have a bunch of RRC2L’s on hand) and it fit very well. Will still need to modify the coupler to fit, but the sled is pretty slick. Built in spot for the RRC2, slot for a 400 maH Li-Ion Battery, spot for a screw switch and slots to install terminal blocks on each end.

https://www.missileworks.com/store/#!/29mm-S-M-A-R-T-Sled-for-RRC2/p/39517483/category=9045099

So, here are all the parts I ended up with.

I measured all the parts and created an initial Rocksim file here:

Initial sims show it ending up around a pound and flying between 1000 feet on some F motors up to 9000 feet on an I200.

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#### dhbarr

##### Amateur Professional
Depending on your dry mass, i224 or i243 should tickle two miles, esp. with the tailcone closure.

#### mtnmanak

##### TRA & NAR L2
TRF Supporter
Depending on your dry mass, i224 or i243 should tickle two miles, esp. with the tailcone closure.
I saw that on my Thrustcurve sims! I don't have any CTI hardware - may have to pick some up when MDRA moves back to Higgs in the fall and I can shoot above 10,000 feet again. That I242 may just come close to 900 MPH with optimal weather conditions

#### mtnmanak

##### TRA & NAR L2
TRF Supporter
I also needed to CNC a couple parts. I plan to use a stepped bulkhead glued to the end of the nosecone coupler with another internal bulkhead glued to that to provide a better connection to the nosecone. They will have a ¼” hole for an eye bolt. The nosecone is very light and this is probably overkill, but I plan to put some kind of tracker in the nosecone – probably one of the small Marco Polo units – so I want to ensure the bulkhead doesn’t rip off. I also want a retainer that I can use with different size 29mm cases. My plan is to CNC a couple 29mm bulkheads for the internal retainer and put a ¼” eye bolt through it to serve double duty as the threaded rod for the motor forward closure and the shock cord connector point in the booster.

The concept of a “shock cord” for this rocket will be a little different, though. The ebay has a cool slot on the bottom running lengthwise for a cord to run through and is held in place by a couple #8 hex nuts that friction fit in when the coupler is tightened around the sled. If that sounds confusing, I will show it in pictures when we get there. I thought about using a short section of cord to run through the ebay and the attaching it to cords in the booster and payload bay, but I think I am going to try a continuous 20’-30’ section of Kevlar cord that attaches to the retainer in the booster and the bulkhead on the nosecone. The ebay will just “float” in the middle. This will cut down on having more hardware in the rocket. Once again, if this sounds confusing as a I describe, I will document it in pictures later in the build.

I CNCed the various bulkheads I needed out of 0.1 “ fiberglass. Note on the photo below - I have been asked before why the cuts have those white "rough edges" along the top. They are not rough edges - it is just some of the adhesive from the double sided tape I use to tack down the pieces to my CNC wasteboard. It just wipes off afterwards.

#### mtnmanak

##### TRA & NAR L2
TRF Supporter
I want to use a switch band, so I cut a ¾” piece off the payload bay tube and cleaned it up / sanded it and body tubes to ensure a tight fit.

Last piece of prep was to trim the coupler tube to the ebay sled. The length was easy, just measured and cut with a hack saw and cleaned up on my bench grinder. However, the sled is designed with a semi-circular notch on one end. I presume this is to ensure everything always lines up properly. I needed to cut that notch in the coupler tube. I traced a rough approximation and ground it down with a Dremel. Once it was close, I used files and sand paper to dial it into the ebay notch. Once it was complete, the ebay fit snugly in the coupler. The ebay is held in place by having the end with the notch be the same size as the coupler tube, so the coupler tube stops against it and the there is a cap on the other end that screws on and holds it all together.

#### mtnmanak

##### TRA & NAR L2
TRF Supporter
Once those parts were complete, I decided to build out the ebay first. Normally, that would be one of the last things I do, but I realize that, if I can’t get the ebay to work, the whole idea of dual deploy is going to be more difficult, at best.

I grabbed some 24 AWG wire and cut off a bunch of lengths for what I would need and proceeded to tin each wire on one end (I will tin the other ends once I figure out the lengths). I used a wire wrap tool to wrap the tinned wires on the terminal blocks and solder them on and then seal with some heat shrink tubing. I used two different color wires to easily tell drogue from main wires.

The LiPo battery has a JST PH connector on it. I didn’t have any female JST pigtails on hand, but I had some female 90 degree plugs, so I soldered a red and black wire to each post in the correct position for this battery. This should allow me to easily disconnect the battery and recharge it without removing it from the sled every time. Finally, I soldered the positive wire from the battery pigtail to the switch and then another positive wire on the other side of the switch that will go to the + port on the RRC2L. I left all the wires long to fit on the sled. I tested everything before installing on the sled to make sure the computer worked and I soldered everything correctly. First time “go”.

I glued the terminal blocks to each sled bulkhead and then installed the RRC2L on the sled with the two included screws. I also installed the screw switch in place with the included screw. I cut all the wires to length and tinned them. Normally, I would use ferrules on any wire that is plugged into the altimeter, but there would no room for them in this build. Once everything was installed, I connected some igniters to the terminal blocks and ran a continuity check. All good.

#### Jmhepworth

##### Well-Known Member
TRF Supporter
Really nice and clean. Well done. A couple of observations (not criticism) that you should feel free to discard. I really like the Missile Works screw switch guides. I don’t know if they would fit or not, but I like them to guide the screw driver and to keep the screw from backing out too far and fall out. I now use them whenever I use a screw switch. The other thing is that I’ve pretty much decided to do away with terminal blocks. In all of my new av bays, I just connect the ematch directly to the altimeter. It eliminates a possible failure point.

#### mtnmanak

##### TRA & NAR L2
TRF Supporter
Really nice and clean. Well done. A couple of observations (not criticism) that you should feel free to discard. I really like the Missile Works screw switch guides. I don’t know if they would fit or not, but I like them to guide the screw driver and to keep the screw from backing out too far and fall out. I now use them whenever I use a screw switch. The other thing is that I’ve pretty much decided to do away with terminal blocks. In all of my new av bays, I just connect the ematch directly to the altimeter. It eliminates a possible failure point.
I hear you on the terminal blocks. On some of my bigger rockets, I have literally blown terminal blocks apart with a big black powder charge. For this build, i decided to stick with the terminal blocks. The charges should be really small, so I am opting for the convenience of the blocks.

Love the MW switch guides, use them all the time. In this build, though, there is about 0.2mm clearance from the switch to the coupler tube and it will be off center from the switch band, so I plan to expose the switch with a hole directly on the body tube. It will also be the vent hole. In fact, no time like the present:

I adhered the switch band on to the coupler tube with 5-min epoxy and then fitted it onto the booster. I measured the exact spot of the switch and drilled a hole through the body tube and coupler. Filed the hole down clean and got it exactly on target for the screw switch:

While I was getting things measured up for the ebay, figured this was a good time to add a 2-56 PEM nut/washer to fasten the coupler to the payload bay. Measured that out, drilled the hole and fastened the PEM and washer in with epoxy.

With that done , I tested out using the #8 hex nuts to hold the ebay in place. I placed the ebay on the Kevlar cord and fitted the hex nuts in place. I found it worked best if I actually wrapped the cord around the nut once and placed it in the well – there was plenty of room. This created a lock tight fit when the coupler tube was fastened on.

So, with all the preliminaries out of the way, will tackle the fins tomorrow.

#### crossfire

I would just use twist and tuck method no switch. Eliminate another failure point. In 30 years of HP twist method has never failed me.

#### mtnmanak

##### TRA & NAR L2
TRF Supporter
I would just use twist and tuck method no switch. Eliminate another failure point. In 30 years of HP twist method has never failed me.
I like to use twist and tape, not a fan of tucking the wires back in once armed in case something goes wrong on the pad and then you need to try and fish the wires back out.

For this build, the whole thing is built around this MW sled that has the built in space for the screw switch, so going with it. It is quite cool. Of all the switch types I have used, these screw switches have been 100% reliable.

#### mtnmanak

##### TRA & NAR L2
TRF Supporter
With the confidence that the ebay is going to work, I moved on to the actual rocket build. Began with the fins. I plan to glass the fins tip-to-tip, so this will be a fairly standard minimum diameter build. I measured the fin placement and marked the tube accordingly. I roughed up the tube and the fins along the root edge and the sides of the root edge. I dry fit the fins with the included fin guides and then tacked each one on with 5-minute epoxy. Will let this cure for a while this morning and then get moving on the fillets.

#### mtnmanak

##### TRA & NAR L2
TRF Supporter
I am using JB weld and a fondant tool to shape my fillets, so I coated some paper with some charcoal and used the fondant ball to mark out the lines for the fillets. I taped them off and globbed in some JB Weld. I let the JB weld stiffen up for a couple hours and then smoothed out the fillets with an alcohol dipped ball. After removing the tape, I cleaned up any spillover with alcohol and ensured the ends were shaped and the edges were feathered. I will let this sit for another couple hours, then repeat with the other fillets and allow all of them to cure overnight.

#### mtnmanak

##### TRA & NAR L2
TRF Supporter
While I had some JB Weld mixed up, I used it to bond some ¼” couplers to the end of a few pieces of threaded road. I will use these later on to make extensions for different motor cases.

Also while the fillets are curing, I assembled the bulkhead for the nosecone and epoxied it in place with 5-minute epoxy. I waited about 10 minutes, then turned it over and poured about 20ml of West Systems 105/205 into the nosecone. That coated the bulkhead and bolt. I set that aside to cure overnight.

#### Igotnothing

##### Well-Known Member
Flew my 38mm Go Devil in HED config this weekend. That was the smallest airframe I could get a Eggfinder TRS into the nosecone. Are you going to add a tracker to that 29mm?

#### mtnmanak

##### TRA & NAR L2
TRF Supporter
Flew my 38mm Go Devil in HED config this weekend. That was the smallest airframe I could get a Eggfinder TRS into the nosecone. Are you going to add a tracker to that 29mm?
I am planning to throw the small Marco Polo tracker in the nosecone. I test fit it and it does fit. The nosecone will be completely enclosed for flight and the small MP tracker is rubber coated and ruggedized, so it should be fine to just turn it on and throw it in the nosecone and let 'er rip. I have flown it this way on other rockets and it worked great.

I do use Eggtimer TRS's, but there is no way it is going to fit in this very small build. The MP works, but it is RF only, so it is only good once you get within about 300 yards of the rocket (usually good enough for the clubs I fly at). The ID of the nosecone and NC Coupler is just barely an inch. If anyone knows of a GPS tracker that can fit in a space that small, I would love to take a look.

Maybe I should caveat that. Other issue is cost. This is a small rocket that cost less than $60 and the MP tracker is also cheap. The Altus Metrum TeleGPS is only an inch wide - it may fit, but the idea of putting a$230 tracker in a \$60 rocket seems a little over the top.

#### hball55

##### Well-Known Member
At some point, I had picked up a Composite Rocketry 29mm Go Devil and it had been sitting in the build pile for a while. (As a side note, I am really confused about the relationship between Rocketry Warehouse, Composite Warehouse and Madcow. Probably a discussion for a different thread.)

We moved recently and I found it in the pile, so I dusted it off and thought about building it out. I looked around the forums and couldn’t find much about building out a 29mm minimum diameter dual deploy rocket, so I decided that is how I want to build this one.

I realized up front I would have to make some modifications and add some parts. The kit comes out of the bag as a pretty standard single deploy 29mm minimum diameter. To make it dual deploy, I am had to research some parts.

First parts were easy. Went to the Composite Warehouse site and ordered a 29mm tube for the payload bay and a 29mm coupler for the ebay. I figure I will just cut a switch band off the 29mm body tube as necessary.

I couldn’t find a 29mm minimum diameter retainer, so I will just build one from scratch.

Next problem was to figure out the parts needed to build out the ebay. Turned out to be difficult to find anyone that sells a 29mm sled/system. A number of altimeters will fit in a 29mm build (RRC2, Stratologger, Easy Mini, etc), but I need a fairly well thought out system to get a computer, battery and some kind of switch into such a small ebay. I saw Apogee had a 29mm ebay kit, so I ordered one. I realized when I got it there was no way it work out of the bag. It didn’t fit in the fiberglass coupler and it was way too long. I thought about modifying it, then decided to CNC parts out of FG that would mimic it. As I was designing that, I ran across a 29mm sled Missile Works makes for the RRC2 series altimeters. Looked perfect! I ordered one (I already have a bunch of RRC2L’s on hand) and it fit very well. Will still need to modify the coupler to fit, but the sled is pretty slick. Built in spot for the RRC2, slot for a 400 maH Li-Ion Battery, spot for a screw switch and slots to install terminal blocks on each end.

https://www.missileworks.com/store/#!/29mm-S-M-A-R-T-Sled-for-RRC2/p/39517483/category=9045099

So, here are all the parts I ended up with.

View attachment 460782

View attachment 460783

I measured all the parts and created an initial Rocksim file here:

Initial sims show it ending up around a pound and flying between 1000 feet on some F motors up to 9000 feet on an I200.
If you ever find that there’s something like the altimeter sleds that don’t work, check out Landru at Additive Aerospace, I believe it is he that supplies the 3D printed sleds, etc. that Missile Works sells. Early on it was Landru that I purchased 3D printed sleds and camera shrouds from.

#### mtnmanak

##### TRA & NAR L2
TRF Supporter
If you ever find that there’s something like the altimeter sleds that don’t work, check out Landru at Additive Aerospace, I believe it is he that supplies the 3D printed sleds, etc. that Missile Works sells. Early on it was Landru that I purchased 3D printed sleds and camera shrouds from.
Absolutely - love the Additive Aerospace sleds - have a bunch of them in each size and just got a new order of camera shrouds from them earlier this week.

Oddly, they don't have anything on their site in 29mm. 38mm is as small as they go. Also, they make it a point on their site to point you to MW site if you want to use a MW altimeter, even though their sleds work just fine for all MW altimeters. I think they must have an agreement with MW to not cannibalize the business MW works does selling RRC specific sleds.

I am sure they could custom make a small sled if asked, but am also confident they would point me over to MW site if I told them it would be for an RRC2L.

Either way, technically I am using one of their sleds on this build

Here is a cool compact build I did using one of their sleds on a 3" Darkstar. It has a Strattologger CF on one side and a Raven 4 on the other.

#### mtnmanak

##### TRA & NAR L2
TRF Supporter
Alright, alright alright!

On to glassing the fins. I let the fillets cure overnight and then cut out pieces of 1 ounce FG cloth for the tip-to-tip glassing. I roughed up the entire fin can area and fillets with 100 grit and glassed each fin section with West Systems 105/205. When a section was “green” I trimmed the edges with a razor blade and glassed the next section. Once all sections are complete, I will set aside to cure overnight.

#### 0011001100

##### A Person
If anyone knows of a GPS tracker that can fit in a space that small, I would love to take a look.
Eggfinder Mini TX will fit. I've got a one that I plan on putting in a 29mm short nose cone and have test fit it and it works. It is tight with the 300mAh battery I am using but you can go smaller on the battery.

#### mtnmanak

##### TRA & NAR L2
TRF Supporter
Eggfinder Mini TX will fit. I've got a one that I plan on putting in a 29mm short nose cone and have test fit it and it works. It is tight with the 300mAh battery I am using but you can go smaller on the battery.
Awesome, I do have some Minis on hand, going to try them out. Assuming they fit (also lengthwise, the antenna may be big for this build), I will need to figure out a way to secure it so it doesn't get smashed in there.

#### mtnmanak

##### TRA & NAR L2
TRF Supporter
While waiting for the glass to cure, got a PEM nut and washer in the nosecone & coupler. Will allow me to keep the bay closed during flight and open it up to insert tracker. Need to fish a Egggtimer Mini out of whatever box I hid them in and see if one fits...

#### 0011001100

##### A Person
Awesome, I do have some Minis on hand, going to try them out. Assuming they fit (also lengthwise, the antenna may be big for this build), I will need to figure out a way to secure it so it doesn't get smashed in there.
I'm literally wrapping mine in foam and have done this before. A sled would fit as long as you don't have a threaded rod through the center as it won't fit.

#### mtnmanak

##### TRA & NAR L2
TRF Supporter
Great idea on the foam, as soon as I can find my minis, I will give that a try. I know I also have some anti-static foam around here somewhere...

This may finally be the rocket that makes me get organized so I can find things!

(I am not holding my breath though )

#### mtnmanak

##### TRA & NAR L2
TRF Supporter
Wanted to get one more thing in tonight so it can cure by tomorrow. The retainer is two bulkheads with an eye bolt through them secured with a nylon insert nut and JB Weld. I made sure to attach the Kevlar first, then put a bit of 5-minute epoxy inside the tube where the retainer would go. This is just to tack the retainer in and seal it to the tube. I used the longest case I plan to fly (an Aerotech 29/360) to ensure the retainer was in the exact right spot. I let the epoxy cure for an hour to ensure it was hard enough to remove the case, then used a syringe and tube to pour about 40ml of West Systems 105/205 on top of the retainer. Since there will be no ejection charge from the motor, all the force I need to care about is forward thrust. A 40ml epoxy plug above the retainer should take care of that. It also truly locks in the eyebolt. I set this assembly to cure over night.

#### Buckeye

##### Well-Known Member
TRF Supporter
I like this sled. I always wondered how to secure a sled with shock cord running through it and no threaded rods.

I do cringe when I see honking big motor retention hardware in a min diameter rocket. Violates the spirit, imo. I am going with this shock cord mount and friction fit on my current build. Nothing but knots:

#### mtnmanak

##### TRA & NAR L2
TRF Supporter
I do cringe when I see honking big motor retention hardware in a min diameter rocket. Violates the spirit, imo. I am going with this shock cord mount and friction fit on my current build. Nothing but knots:

Great idea - If I had seen this post before I epoxied in the retainer, I may have gone this route, but too late now. The eye-bolt and bulkheads may be overkill for a 29mm build, but at least I know it won't come out!

#### mtnmanak

##### TRA & NAR L2
TRF Supporter
With that done, the rocket build is essentially complete. I guided all the components onto the shock cord in the proper order:

• Ebay cap
• Coupler
• 2 #8 hex nuts
Then tied the cord off to the nosecone and secured the knot with some epoxy.

I placed the ebay on the Kevlar cord and fitted the hex nuts in place.

I tied a swivel between the ebay and the nosecone and attached an 18” parachute. This is the whole assembly:

Before finishing the fin can and clear coating, I wanted to test the deployment. I built some charge wells with the small cardboard tubes and ground tested. The charges need to be very small. The booster separates with as little as 0.2 grams of FFFFg and then I made the friction fit on the nosecone tight enough to require 0.4 grams of FFFFG. I want to ensure the drogue charge doesn’t separate the nosecone at apogee.

#### mtnmanak

##### TRA & NAR L2
TRF Supporter
With ground testing out of the way, I thoroughly sanded the fin can with 80 grit to smooth it out and get rid of some egregious drips from the glassing process. I bondo’ed the fillets and ends and will let that cure for a few hours. With some luck from the weather, I may be able to get all the finishing done today.

#### mtnmanak

##### TRA & NAR L2
TRF Supporter
With the help of Duplicolor Engine primer, paint and clearcoat, I was able to get the rocket completed today. Love Duplicolor - you only need to wait 10 min between coats and layers. Makes it so much easier.

I bondo’ed the fillets and ends and let that cure. After sanding out the bondo, everything was pretty smooth. I wet sanded the whole fin can, taped off the end and shot it with Duplicolor primer. I primed and wet sanded with 800 grit until everything was smooth, then shot it with Duplicolor Engine Black. After the last coat of black, I gave it about 15 min to cure, then gave the whole rocket 3 coats of Duplicolor Engine Gloss Clear.

The rocket came with decals, but I kind of like the slick and clean look of this without them. I think I am going to keep them off for now.

End weight is 506 grams/ 1.12 pounds. I plan to fly it with fly-away rail guides, so no lugs/buttons needed.

#### Buckeye

##### Well-Known Member
TRF Supporter
Nice work on the fillets.