Aerotech HV Arcas Build Thread

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JayB

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Hi! I've been lurking a long time while soaking up all kinds of terrific ideas and inspiration. So its about time to return something to the community with a build thread for my newly-purchased Aerotech HV Arcas. I've taken up rocketry again after a long break, and my previous experience is all LPR. I thought the Arcas would provide a good opportunity to move into larger engines, dual deployment and electronics all of which is new ground for me.

So, this build thread may contain examples of what NOT to do. But thats still leading by example, right?

Feedback and ideas more than welcome.

Thanks,
Jay
 
AV Bay part 1:
The objectives for the AV Bay are to support dual-deployment and some "fun" add-ons. I've built and tested an Eggtimer Quantum with a telemetry module, and would also like to fit a small camera (RunCam Split 3 Light) and two LiPo batteries. I also got a pull-pin switch from LabRat Rocketry because having a big 'Remove Before Flight' tag seemed like a cool idea and I'd like the camera to start recording at power-on on the rail.

I'm not contemplating redundancy for the charges or the altimeter at this time. However, I suppose the motor ejection could provide redundancy for the drogue.

I printed up some bulkheads in order to play with placement and fittings - each bulkhead has to mount a charge well and through bulkhead terminals, a u-bolt for attaching recovery and a 1/4" threaded rod to hold the module together. The parts are printed in PET-CF.

My concern is that the bay is really heavy - right now without a sled, electronics or batteries its ~300g. Did I overbuild it? There isn't one thing I can point at as the problem. If I remove the 4 large metal bars tying the U-bolt to the threaded rod I could save some weight, and if I went to an aluminium threaded rod I could save some more. The former introduces some risk if the bulkhead fails badly, the latter might be an option but doesn't gain much.

Also, how do people shock-test thier bays? I attached the forward end to my basesment ceiling with 2' of Kevlar, then attached 10lbs of weight to the aft with another 2' of Kevlar and dropped it a few times. It all held together, but I don't know how valid a test that is.

Thoughts and feedback welcome!
 

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Motor Mount Part 1:

I needed a break from agonizing over the design of the sled in the AV bay so I decided to get into the actual kit. The version I got has replaced the engine hook with a threaded retainer so there is an addendum/errata for the instructions which isn't too hard to follow. You just install the fin-lock rings at a different position on the motor tube.

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Test fitting the fins was interesting. This is my first mid-power kit and locking mechanisms and through-tube fin mounting is new to me. I read in another thread that the fins needed a 'wiggle' to seat properly but that was not the case for me - they required some force to place but not excessive. I did it by seating the forward end of the fin first and then rocking the fin 'down' into the aft ring. As I did so I supported the rear tab with a finger through the motor tube so that nothing flexed. The fin-lock rings are pretty solid though.

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I also filled and sanded the tubes.
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So much tube. So much spiral.
 
I had a lot of trouble getting the fins to snap into place. Almost deformed the tube getting them in place. Was not impressed.
I usually put a motor or motor case in the motor tube when snapping the fins in to help with that particular task. It's not the most fun you'll have in the build, but it does show how strongly they are attached.
 
I appreciate your willingness to do a build thread on a “simple” rocket because even those have their challenge points, and showing them helps others who also want to build the kit. It’s great to have build series for all different kinds of rockets. I’ve flown several AT kits through the years but I still enjoy watching a build series on one, to see if others had the same challenges. Always something to be learned when we share.
 
My concern is that the bay is really heavy - right now without a sled, electronics or batteries its ~300g. Did I overbuild it? There isn't one thing I can point at as the problem. If I remove the 4 large metal bars tying the U-bolt to the threaded rod I could save some weight, and if I went to an aluminum threaded rod I could save some more. The former introduces some risk if the bulkhead fails badly, the latter might be an option but doesn't gain much.
I would replace the steel U bolts and bars with kevlar loops. If you are worried about the bulkhead failing switch to a 1/4" plywood or fiberglass bulkhead.
 
Other options are simply using motor deploy and a Jolly Logic Chute Release. I always practiced the JLCR on a cheap majestic from Hobby Lobby and then it dawned on me I needed to watch the owner's video on how to fold the chute.

Always read the instructions; no matter how many years you have been doing rockets.

Also if you don't trust motor eject then just put an altimeter for apogee only deploy in the stock payload section and put the match wire into a small hole in it [seal it with silicon sealer] and a charge plastic tube from an Aerotech reload for apogee.

Then the JLCR for the main.

I did that with my LOC ISP 3" rocket with an I65 as it is a plugged motor. Just put a Perfect Flight Strato logger in the payload section with a charge into the rocket and used the JLCR for the main.

It got almost 5000 feet even though I had to launch it 20 degrees into the wind based on what the RSO was requiring. On such a long burn motor I could have launched it straight up and it still would have moved into the wind on it's own and got more altitude.
 
Kevlar loops would be as strong as the steel U bolts. You can save some weight going with aluminum all-thread. Get it at McMaster-Carr. I've gone down to #8 or #10 all-thread for smaller rockets.
 
McMaster is great for this stuff but shipping on a 6ft piece of #10-24 aluminum threaded rod is killer. I’m about 220 miles from their Santa Fe Springs warehouse and they want $25.00 S&H.

I’ll often get this kind of stuff from Zoro. They want $10.39, or $1.36 more for a six ft piece, but shipping is only $5.00 unless your order is $50.00 or more. Then shipping is free. Your order will come in a long heavy wall cardboard tube by UPS. If you order more than one piece and their supplier or warehouse only has one, you’ll get one tube from one warehouse and another from a different warehouse.

I am sure Zoro loses their shirt on this, but I’m happy. Think about adding some 6 ft stainless steel launch rods in different sizes like 3/16 or 1/4, or maybe even an 8 ft piece of 1” 8020 aluminum rail to hit the $50 threshold.
 
I got very busy during the holidays and didn't keep up with this, my apologies.

I'll try to catch up with current state:

The motor mount went into the body tube without problem, and the advice from @loopy to use a motor casing inside the mount was very helpful when snapping the fins in place. There was no deformatation of the motor tube this way and I felt a little better about using some force to get the fins in. Another lesson from this step - reorient the motor mount as each fin is put in place as the motor mount will rotate under force within the body tube.

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Once that was done I moved on to the fin can. Marking it utilized a template with notches on either side of the can, and then you connect the notches in order to get your cut lines. If I could do this over again I'd have marked points and then checked them with an angle as its slightly off in places. Or we can blame the beverages.

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Go slow, use a straight edge and a new sharp blade and then make many shallow scoring cuts.

When mounting the panels that you cut out, be sure to put pressure on them until the glue sets up. When gluing mine they had a tendancy to lift up and create a gap between the can and the body panel.


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Nose Cone:

The nose cone had a decent amount of flash. Also as the mold line arced towards the point, there was a gap that needed filling.
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I cleaned it up with a knife and then filled the gap with some Testor's Contour Putty. I (over)filled the gap, then when it dried it was easy enough to sand it down with some 400 and then 1000 grit sandpaper. Based on a quick test against the cone's bukhead I didn't feel great about using anything coarser than this as it sort of tore/fuzzed up the surface.

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We'll see how it looks when its primed and painted but I am hopeful.
 
AV Bay episode 23

Thanks for all of the great advice on the AV Bay. I took alot of the metal out, reduced the u-bolts down small wire clips and some aluminum #8 allthreads are coming to replace the steel ones I used to replace the 1/4" monster that took up the center of version 1.

Its still heavy :( but way better than before ;)

With the removal of the center post things really work better in here. Its mounting an Eggtimer Quantum, Telemetry Module, Runcam Split 3 Lite camera (with a board and UBEC) plus two 300mah batteries and a dual pull-pin switch. The bulkheads have charge wells and the terminals run through the bulkheads.

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I printed it in PET-CF with the bulkheads as single pieces, the sled mostly as a single piece (two small hoops/bands to hold the telemetry board and support the antenna) and the charge wells as two parts each.

The camera is spring-mounted so that the coupler can slide over it and then the camera can nestle into its viewport. The viewport is slightly angled down with a verrrry small protrusion in the switch band. We'll see how it does when it flies but overall I'm excited about it.

I took a lot of inspiration from AV bay designs posted by @Cherrywaves89 - thiers was the first I saw with a spring mount and I also took a lot of other great ideas from thier designs.
 
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AV Bay episode 24

The switch band provides the camera viewport with a small fairing, the port for the switch pin, and additional vent holes for the AV Bay altimeter. The loop around the camera's viewport also serves as an 'index' for orienting the body tubes, which will useful for attachment screws and shear pins later.

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With some careful measurement and then poking around with a pin, I was able to drill holes for attaching the upper body tube to the AV bay bulkhead. I also drilled some holes for shear pins, though I am not sure I'll need them for the lower body tube. The upper screws mate with heat-set inserts in the bulkhead lip.

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Finishing:

I followed as best as I could the instructions for finishing the rocket - front part red, one fin red, rest gloss white, add decals. Sounds easy right? It was. But in retrospect if I could do this again, I'd do it totally differently. Its hard to match a paint color to the decal for the stripes down the side. Did the best I could but its not perfect and it bugs me. Were I to do it over, I'd mask and paint the stripe. For anyone else building it, I'd recommend that rather than using the stripe decal.
Another point against the decal for the stripes, at least in my build, is that I've lengthened the body by ~.75" due to the switch band in the coupler. This throws off the sizing of the decals from the nose downward and made for some tricky joints in the decal line. Don't do what I did, just paint it.

With that, some photos:
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Recovery:

I've set this up as dual-deploy:
Drogue is in the aft section, using a 12" nylon Top Flight chute. The shock cord is the kit's elastic strap, attached to the aft bulkhead of the AV bay and the eye on the kit's motor mount/baffle assembly. I added Nomex protectors for the cord and chute since the ejection charge is coming from the AV bay, not from the motor charge via the baffle.

Main is in the forward section, using the kit's 30" nylon chute. It is connected to the eye of the nose cone, and also uses a Nomex protector. Shock cord is 10' of 1/4" braided Kevlar between the nose cone eye and the forward AV bay bulkhead. The forward body tube is connected to the AV bay with M2 screws. I'm a little worried about zippering and will look at options to avoid that.

If weather cooperates I'll be ground testing ejection charges next weekend. I've played around with the online calculators to get a starting point for charges.

Drogue bay is 2.6"x10", calculators are around 0.3g to get 53 lb force (10psi) on that bulkhead, which will also shear 2 #2 pins which I have made provisions for but also not sure I need. Seems like overkill, I may try two 2" pieces of Scotch tape longitudinally instead.

Main bay is 2.6"x14.5", calcuators are around 0.4g for 53 lb force (10psi) on that bulkhead. I havent made provisions for shear pins for the nose cone and was intending to use two 2" pieces of Scotch tape instead.

Feedback welcome. Thanks.
 
I probably need to re-weigh everything now that its painted up. Then do another round of sims in OpenRocket to make a final decision on the motor for the first flight.

I've got a Aerotech 29/40-120 casing and I bought a G53FJ thinking it would be a good first flight motor. However, with all the weight that SOMEHOW got added to the rocket (who did that?! how did it get there?! ;)) I think its over 2.3lbs and thus below 5:1 TWR with that motor. I also recall the velocity off the rail wasn't great in the initial sims. Another round of sims with final weights will settle that.

If the G53 won't be enough I was going to look at either a G64W or a G76G, but it will depend on the sims. The field I'll likely fly at has restrictions on flights over 2k and depending on the wind direction even a 1k flight could get scrubbed so I'd like to keep it in that range. I also like the longer burn/lower max thrust on the G64 vs the G76 though thats more aesthetics than anything.

If you've got ideas or suggestions for a motor I'm all ears. Thanks!
Jay
 
I have an Aerotech Arcas, added some weight to equal yours in RS and a G64-7 looks like a perfect motor for your flight. Good vel. off the rail, spot on with the delay and an altitude of 1100 ft. The G64 is my favorite MPR motor, I'm sure you will like it also.
 
I have an Aerotech Arcas, added some weight to equal yours in RS and a G64-7 looks like a perfect motor for your flight. Good vel. off the rail, spot on with the delay and an altitude of 1100 ft. The G64 is my favorite MPR motor, I'm sure you will like it also.

Thanks!!

Final weight is 1050g w/o motor. Like me, that rocket used to be much lighter.

From the sims, a G53 will get it off a 8' rail at 56ft/s and on up to 650 feet. Will that work if there isn't much wind?

The G64-7 does look perfect! Sims to just over 1000' on OpenRocket, and I've got enough time for one to arrive before my first opportunity to launch it.
 
56ft/s is good off the rail. Is a 5 sec. delay short enough at 650 ft. I never flew a MPR or HPR rocket ever that low in 27 years. You never know if it comes off the rail less than vertical or weather cocks could be in trouble flying that low.
 
56ft/s is good off the rail. Is a 5 sec. delay short enough at 650 ft. I never flew a MPR or HPR rocket ever that low in 27 years. You never know if it comes off the rail less than vertical or weather cocks could be in trouble flying that low
Thanks, that definitely helped me make my mind up. Just ordered the G64-7.
 
@JayB --

Are you going to use your electronics for apogee ejection ?

-- kjh
Yes, an Eggtimer Quantum for both drogue and main. Drogue @ apogee, main @400 or so.

I was able ground test everything yesterday and it all worked! 0.3 / 0.4g of BP in the 3-d printed charge wells with a bunch of wadding to fill empty space and create containment, blue-taped down with the igniter. I used two 1” pieces of Scotch tape for retaining the nosecone and drogue.

Next up, launching it for real. Hopefully soon!
 
@JayB --

Are you going to use your electronics for apogee ejection ?

-- kjh

Yes, an Eggtimer Quantum for both drogue and main. Drogue @ apogee, main @400 or so.

I was able ground test everything yesterday and it all worked! 0.3 / 0.4g of BP in the 3-d printed charge wells with a bunch of wadding to fill empty space and create containment, blue-taped down with the igniter. I used two 1” pieces of Scotch tape for retaining the nosecone and drogue.

Next up, launching it for real. Hopefully soon!
Good call @JayB !

So the motor delay does not matter unless you want it for backup and if you want the backup motor delay very near apogee ...

It is YOUR Arcas, but I REALLY like the RMS 29/40-120 G64W myself, if your launch site can handle it :)

It is one of my all-time favorite AT motors ( over 100 N at ignition and 119 Ns impulse over 2.1 seconds ).

And I just recently got ahold of an RMS 29/40-120 G76G that I am itching to fly in the right rocket on the right day.

Have fun !

-- kjh
 
Just to finish this off, today’s maiden flight went incredibly well. Fairly high winds, 10-15kts and gusty, but it got 861ft on a G64W. Dual deploy worked perfectly, telemetry worked, and the only downside was forgetting to put an SD card in for the camera :(

Thanks for all of the tips and ideas that people shared on this thread. It definitely helped and we appreciate it.

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