Mach 1 Electron BT-55: Dual Deploy Parkflyer Build Thread

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NateB

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Sometimes I struggle to be able to get to club launches. In order to launch larger rockets, I have to have a perfect combination of a club launch occurring, good weather, the weekend off work, and no other family needs that come first. I do have a large park near home which is perfect for smaller rockets.

I have wanted a small dual deploy rocket which I can fly close to home and I like split fin designs. I recently ordered the Mach 1 Electron BT-55. This is an updated version from the original design offered a few years ago with through the wall fins, 5" couplernwith bulkheads, and payload section for dual deploy out of the box. I also added the recovery and retainer options when I ordered the kit for convenience. When the package arrived it included the kit, retainer, streamer for drogue, Top Flight parachute, 2 chute protectors, the necessary lengths of Kevlar cord, swivels, quick links, and eye bolts.

The only remaining hardware needed depends on how you construct your electronics bay and how you decide to attach the coupler to the payload section. I will be using 4-40 threaded rod to make a basic altimeter sled from scraps of G-10. I am also using 2-56 PEM nuts to bolt the coupler to the payload section. This is probably overboard on such a small rocket, but I wanted practice working with them before using them on some planned larger builds. I like my FlightSketch Mini altimeter on small rockets and I have been looking forward to the eventual release of the FlightSketch Sport to add dual deployment. I'll get one when I can, but for now I will use an Eggtimer Quark for this rocket. Last, I have a pair of 0.5g Small Form Charge Wells from Binder Deisgn / Dog House Rocketry.


I thought I had a picture of all the parts before I started, but it appears I don't. As always, the first step when building a fiberglass kit is washing all of the components. I then measure and weigh everything to build an Open Rocket sim as I go.
 

NateB

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Each fiberglass component is scuffed up with sandpaper wherever an epoxy joint will be. The centering rings are laid out clear the slots for the fin tabs and the Kevlar Y harness is carefully placed so it won't interfere with the fin tabs as well and secured with a generous amount of epoxy.

I did not make the centering rings a tight fit against the fin tabs like I would on a larger rocket. I won't be injecting internal fillets or making fin pockets. A simple double dip of epoxy will do for the motors I'll be flying. Small fillets are placed on the opposite sides of each centering ring from where the fin tabs will be.

I used Rocket Poxy for everything except the retainer which used JB weld.
E01.jpg

The mach diamonds on the retainer cap is a nice touch.
E02.jpg

While the motor mount was curing, I used the fin slots on the booster section to mark 3 evenly spaced lines on the coupler for the PEM nuts.
E03.jpg

E04.jpg

The inside of the body tube is so scuffed with sandpaper and I used a dowel rod to apply epoxy for the centering rings. The motor mount is then secured into the body tube and allowed to cure. I also used a dowel rod and reached down from the top of the body tube to ensure there was a good fillet formed on the forward centering ring. It is a little more challenging to reach into places with the smaller diameter tubes.
E05.jpg
 

NateB

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Following along - I have three Mach1 kits waiting for attention…
I've built several of these small fiberglass kits from Mach 1 and I don't want to build cardboard kits anymore.

I've built this rocket as single deploy and it's great on small fields with D12's and E12's. Flown it several times. Nice and stable!

From my sim, it will fly on D, but not high enough to make use of dual deploy. I could easily leave the sled off and put the main in the booster with motor ejection for a quick and easy flight.

I built the similar 3 fin Saberhawk single deploy and it flies great on D and Es as well.
 

waltr

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I've build the Saberhawk and fly it motor deploy, mostly D's. I would like a small DD rocket and this might be the one.
I have flown a number of Eggtimer Quarks in small DD rockets. they work great.

Building FG rockets is nice.
1- can see through the BT for apply epoxy and positioning CR, etc.
2- No grooves to fill or cardboard to tear so easy to get a great finish.
3- tough so hard to break and water proof so the landing in the pond won't hurt it.

Good build tread so far.
 

NateB

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I've build the Saberhawk and fly it motor deploy, mostly D's. I would like a small DD rocket and this might be the one.
I have flown a number of Eggtimer Quarks in small DD rockets. they work great.
It looks like several of the Mach 1 BT-55 sized kits are ready to go for dual deploy now. Pick your favorite one, drop in a Quark and give it a go!
 

NateB

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The next step was attaching the fins. I'm using the Bad Ass Rocketry build guide. I already had one, but if you need one, you can get one when you order a kit too.

Each fin was just rounded slightly using one of the smalle sanding guides from North Coast Rocketry and coarse sandpaper. I rounded the leading edge of the forward fins, the trailing edge of the lower fins, and all of the fin tips. I left the trailing edge of the forward set and the leading edge of the lower set square and rough.
E06.jpg

To attach the fins, I mixed up some Rocketpoxy and let it thicken for about 15 minutes before continuing. Spread some on the root edge, insert the fin into the slot so it presses against the motor mount, remove the fin and repeat with more epoxy. You'll get a good buildup of epoxy around the fin tab that will be plenty strong.
E07.jpg

When I use these guides, I only epoxy one fin at a time, but all 3 fins need to be in the slots and clamped to the guide with binder clips to ensure proper alignment. Make sure to wipe off any excess epoxy with a paper towel dampened with rubbing alcohol. You don't want to glue the guide to the rocket and it's easier to clean up epoxy drips before it cures.

I epoxy 1 at a time to keep things less messy, but Rocket Poxy is pretty thick and wouldn't run too much if you do all 3 at the same time. I'm in no hurry, so the the build time doesn't matter.
E08.jpg

Once all 3 fins on the lower set are cured in place, I move on to the upper set. I repeat the double dipping process 1 fin at a time and using the fin guide with all 3 fins like I did with the lower set. In addition to using the printed.guide, I also used craft sticks and binder clips to ensure the upper and lower fin sets are perfectly aligned. I find the craft sticks or aluminum angle to be necessary for the best fin alignment on split find. Using the 3d printed guide as well is a "belt and suspenders" approach to keeping everything aligned as best as possible.

Let the fins cure, I'm going to use the guide with the fins in place for more marking and drilling before moving on to the external fillets and the rest of the build.
E09.jpg
 
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waltr

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It looks like several of the Mach 1 BT-55 sized kits are ready to go for dual deploy now. Pick your favorite one, drop in a Quark and give it a go!

Looking on the Mach 1 site and see there isn't a bada$$ sled for BT55. Those sleds are very nice but its not too hard to scratch build one.
 

cerving

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What motor retainer is that? I have an Electron sitting in front of me, it's my next build... if I can find some time.
 

mo2872

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My son has the BT55 Electron setup for DD. So far he's sent it on F39's........hits about 1k with that, and you can see all the events happening. Good practice for larger DD.
 

NateB

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So far this build has been straightforward. I wanted to use PEM nuts to attach the coupler to the payload section so I would be more familiar with their use on a couple future builds. I ordered some 2-56 sized PEM nuts (McMaster part number 94648A310, although the fiberglass is thinner than recommended for this part) with a No. 26 drill bit and 3/16" 2-56 button head screws. I also used some longer socket head screws and washers to pull the PEM nuts in place.

I taped the coupler in place and used the drill guide and lines I marked earlier to drill the first hole for the PEM nuts and screws. The hole in the coupler will need to be larger than the hole in the body tube due to the diameter of the PEM nut. The guide has 3 holes spaced between each fin. I'll line the PEM nuts up with the fins so the screw heads don't rub on the rail and drill holes for venting the altimeter bay in between each fin. I'll be drilling the holes and installing the PEM nuts 1 at a time to ensure everything stays aligned even if the drill bits wander some. I started with a pilot hole going through the Payload body tube and the coupler.
E10.jpg

This picture you can see 2 pilot holes for vent holes and 1 pilot hole for the PEM nuts. I wasn't worried about the vent holes lining up as precisely as the holes for the screws.
E11.jpg

The pilot holes on the coupler and body tube need to be enlarged to accommodate the diameter of the PEM nut and the diameter of shaft of the screw.
E12.jpg
 

NateB

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I won't lie, installing the tiny PEM nuts was a pain. This process was also difficult to photograph while I was working on it. The nuts themselves are tiny and the thin fiberglass wall doesn't allow for much hold on to. The nuts I bought are for a thicker material than the Mach 1 tubing. If the flange of the nut is fully seated against the tube, part of it will pull through and prevent the coupler from mating inside the body tube.
E13.jpg

E14.jpg



E15.jpg

I placed the coupler into the body tube and aligned the holes. A longer 2-56 socket head screw and washers is used to pull the PEM nut in place and the body tube in position prevents you from pulling it through too far. Carefully apply epoxy to the flange and tighten the screw. Clean up any epoxy that may have dripped on the screw, threads, and anywhere else you don't want it. I did this one at a time and allowed the PEM nuts to fully cure in place before moving on to the next one. Once all 3 were in, I went back and made a fillet of epoxy around the flanges of each nut.

E16.jpg

I went slow, but everything lines up. I cut a witness mark, but each hole and nut lines up close enough that the orientation of the payload body tube to the coupler doesn't matter.
E17.jpg
 

NateB

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Using the holes on the fin guides one last time, I drilled holes for the rail buttons. Open Rocket calculates the CP at 27.72" which happens to be just above the forward centering ring. As I mentioned in another thread, I like to use a rail button to mark CP if I can. I drilled a hole at the CP for the forward rail button and one just above the rear center ring for the lower rail button. The screws for the rail buttons thread into the fiberglass nicely and are then removed until after painting. E18.jpg
 

crossfire

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I won't lie, installing the tiny PEM nuts was a pain. This process was also difficult to photograph while I was working on it. The nuts themselves are tiny and the thin fiberglass wall doesn't allow for much hold on to. The nuts I bought are for a thicker material than the Mach 1 tubing. If the flange of the nut is fully seated against the tube, part of it will pull through and prevent the coupler from mating inside the body tube.
View attachment 516414

View attachment 516415



View attachment 516416

I placed the coupler into the body tube and aligned the holes. A longer 2-56 socket head screw and washers is used to pull the PEM nut in place and the body tube in position prevents you from pulling it through too far. Carefully apply epoxy to the flange and tighten the screw. Clean up any epoxy that may have dripped on the screw, threads, and anywhere else you don't want it. I did this one at a time and allowed the PEM nuts to fully cure in place before moving on to the next one. Once all 3 were in, I went back and made a fillet of epoxy around the flanges of each nut.

View attachment 516418

I went slow, but everything lines up. I cut a witness mark, but each hole and nut lines up close enough that the orientation of the payload body tube to the coupler doesn't matter.
View attachment 516420
Would plastic rivets work well?
 

NateB

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Using a pencil, paper, and the ball fondant tool makes marking the area for external fillets quick and easy. Mark the lines, mask the area you don't want epoxy, and make sure the body tube and fin surfaces are sanded for a good bond.
E19.jpg

I have the best results mixing some Rocket Poxy and allowing it to rest for 15 minutes before pouring it on the area for the fillet. Let it sit and level out for 15 more minutes, then shape with the fondant tool dipped in rubbing alcohol. Let the shaped fillets rest a few more minutes and then pull the tape. Clean up any drips or areas that need attention with an alcohol dampened paper towel or your finger dipped in alcohol. Careful work now prevents tedious sanding later. I like to do one set at a time and wait at least 4 hours before starting on the next set.

E20.jpg

E21.jpg

While the fillets were curing, I drilled some holes and added a loop of Kevlar cord to the nosecone.

E22.jpg
 

NateB

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I would like to try the Flight Sketch Sport when it is available, but I had a Quark for another build and decided to use it for now. I was able to assemble the Quark one afternoon at work when I knew we were staying inside for poor weather. After soldering the kit, it was tested and everything appears to be working.

E23.jpg

The sled was pieced together from some other parts laying around. Nothing fancy here, just G10, threaded rod, aluminum tubing, and small hardware. Not pictured is a small screw switch from Fingertech which uses a 3/32 allen wrench to turn.

E24.jpg

Sled is ready, but a work in progress. It is a little awkward to reach through the vent hole to access the switch. A wifi switch might be worth it, but I'll see as I fly it more. For now, the Quark is held in by foam tape until I decide how I want to keep it. The battery has tape and will have some zip ties for flight.

E25.jpg

Each vent hole was enlarged to allow for the 3/32 allen wrench. Wires get tucked into place and everything fits in the small coupler.

E26.jpg

I ground tested charges before starting to paint. 0.3g of 4fg worked great on both sides. I didn't drill any holes for shear pins on the payload side. I'm planning on using tape. It I get an early main deployment, I'll add a toothpick or something similar.
 

NateB

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This thread is getting caught up to my build. After ground testing ejection charges, I started finishing this rocket. My plan for this is to be a routine flyer in my local park. The field is grass with some soccer fields, open grass, and some sidewalks. There isn't much to damage the rocket on landing unless it comes down on the parking lot or sidewalk. I like the paint scheme on the Mach 1 website with solid navy blue and silver decals. I'm aiming for a good finish, but not taking the time for a perfect polish finish.

First layer of 2x Primer and sanded.
E27.jpg

After 1st coat of blue on and sanded.

E28.jpg

2nd coat of blue on, you can still see some blemishes. The primary color is Rustoleum Enamel which didn't fill as well as 2x does. I should have filled in some spots with Bondo after the 1st layer of primer and sprayed a 3rd layer for a smoother finish.

E29.jpg
E30.jpg

3rd layer of color down and I will be adding the decals and clear coat soon.

E31.jpg
 

NateB

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With 2 coats of primer, 3 coats of Navy Blue and 4 coats of clear, I wrapped up this build today. Rail buttons installed and the final measurements were taken for my sim file. The prepped rocket with no motor but all recovery and a Flight Sketch mini has a CG at 20.75" and weighs 14oz.

I'm happy with how it turned out. There's a little orange peel on the clear coat, but not enough that I wanted to sand it down and keep painting. I'd like to fly this frequently, so it will get some wear soon.

E33.jpg


ThurstCurve estimates 937' on an E-28 which should be good for a maiden flight.
 

NateB

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I was hoping for a launch tomorrow, but I don't have the right motors. I thought for sure I had a pack of E18 and E28, but no luck. It could fly on a D, so maybe I'll take the electronics out and let her go with motor deploy.
 

waltr

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The tiny eye nut and bolts for the coupler bulkheads came with the kit. I didn't have to track those down anywhere.
Yes, they are available from Mach 1.
 

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