LOC Precision AMRAAM AIM 120C Build Thread

[TimothyAReed]

The purpose of this thread is to document the building of a LOC Precision AMRAAM AIM 120C kit for my Level Two High Power Certification. There does not seem to be a build thread of this rocket already on the forum; I hope to fill that knowledge gap. All input/tips/tricks regarding this build are appreciated. I have a large format 3D printer and a 3018 CNC machine that I plan to use for some of the custom AV-bay pieces, but I will try to make it so that anyone without these can still build this rocket. I also plan to document the prices of everything used in this rocket in an excel spreadsheet to give anyone else an accurate estimate of the costs associated with a level 2 certification.

Building Techniques:
* 90-Minute epoxy for all structural fillets and connections, because this a paper and plywood rocket, the bond will be stronger than the materials used (assuming proper care is taken to prepare the surfaces).
* The epoxy will be measured using a digital scale that is accurate to +- 0.01g allowing for an accurate mixing ratio.
* every part put on this rocket will be weighted and logged using the previously mentioned scale, this will allow for a precise calculation of the center of mass, and allow for me to determine how much the epoxy and paint that is applied affects the weight of the rocket.

NOTE: These photos are what the kit looks like out of the box, I have an extra coupler because I also bought the 4" Ebay (Not included in the photo).

 

[Nytrunner]

You have enough length in that rocket to add a go pro bay looking out horizontally. Just need to figure out the window material, and make sure your fins and bevels are straight to avoid spin

 

[C.O.B.H.C.]

I would suggest putting a longer motor tube in. I put a 28" long motor tube in mine. I also double walled the booster coupler. I didn't use the included baffle system. I did add a LOC Av-bay like you did. I am going to be using a 100 Foot long tether of Atwood Rope Battle Cord (https://atwoodrope.com/collections/battle-cord) in drogue section and 75 feet for main. I'm also going to upgrade the parachute to a 90" X-Form from Top Flight.

 

[TimothyAReed]

Build Log #1 Dec 21, 2019

While I wait for my epoxy to arrive Tuesday, I am going to begin the process of documenting the weight of every part in the kit. The resulting Excel spreadsheet with be posted on Google Docs, where anyone can view it.

Note: I have not weighted the Ebay parts just yet, but when I do, they will be added to the spreadsheet.


Note: This is the link to a View Only version of the spreadsheet
https://docs.google.com/spreadsheets/d/1B6ALUJ4jFSkfKKUay2XwFusFp1vub0LbwkmOSS3vxgU/edit?usp=sharing

 

[TimothyAReed]

I would suggest putting a longer motor tube in. I put a 28" long motor tube in mine. I also double walled the booster coupler. I didn't use the included baffle system. I did add a LOC Av-bay like you did. I am going to be using a 100 Foot long tether of Atwood Rope Battle Cord (https://atwoodrope.com/collections/battle-cord) in drogue section and 75 feet for main. I'm also going to upgrade the parachute to a 90" X-Form from Top Flight.

I have never heard of Battle Cord but will keep that in mind for future projects. I believe cord rated fo 2,650 pounds is a bit overkill for this rocket. For clarification, I only plan on flying this rocket twice; once for a shakedown flight and the second for my certification, after that, I am going to donate it to my ADA unit's battalion headquarters. This is excellent advice for those that plan on flying this kit often while pushing it to its limits. I will definitely look into using those chutes though, it would be a shame to have the rocket come down too hard and break on impact!

 

[TimothyAReed]

Build Log #1.5 Dec 21, 2019

I just finished weighing all of the parts that came with the ebay kit and will begin assembling the ebay tomorrow. I currently have a Missle works RRC2+ for Dual Deploy and an Egg-Finder Mini for GPS tracking. However, I would like another DD altimeter for redundancy and am now thinking of buying an egg-timer wifi switch and a quantum as a backup altimeter. I wanted to ask the peanut gallery about their thoughts/preferences for redundant recovery systems.

I will also try and post a build schedule tomorrow but I am tentatively scheduling a shakedown flight for January 18, 2020, and my level two certification flight for February 8-9 at MDRA or the 22nd at NOVAR.

 

[richP]

I know that I am not in the majority here, but I do like the idea of using similar components for redundant systems; in your case, another RRC2+. My reasoning is, identical systems would perform more predictably and a well vetted altimeter from a reputable company more than likely has all of it's bugs worked out. Extra care does need to be taken in testing and configuring them, so as not to repeat a mistake on both.
I like the idea of a wifi controlled altimeter, but chickened-out at the thought of either adding a dual-battery set-up, or relying on the wifi switch to pass-thru power for the deployment charges; neither of which gave me the warm-and-fuzzies.
Looking forward to your build as I have a soft spot for AMRAAM's. If I remember correctly, they do require a bit of noseweight. Is that the same with this model? And how do you plan on addressing that?

 

[TimothyAReed]

I know that I am not in the majority here, but I do like the idea of using similar components for redundant systems; in your case, another RRC2+. My reasoning is, identical systems would perform more predictably and a well vetted altimeter from a reputable company more than likely has all of it's bugs worked out. Extra care does need to be taken in testing and configuring them, so as not to repeat a mistake on both.
I like the idea of a wifi controlled altimeter, but chickened-out at the thought of either adding a dual-battery set-up, or relying on the wifi switch to pass-thru power for the deployment charges; neither of which gave me the warm-and-fuzzies.
Looking forward to your build as I have a soft spot for AMRAAM's. If I remember correctly, they do require a bit of noseweight. Is that the same with this model? And how do you plan on addressing that?

That's an excellent point for the redundant electronics; In that case, I might buy an RRC3 as my primary altimeter since I have a project in mind that requires an extra event channel. I do have the missile works screw switches that I can use to turn on all the electronics. However, my thought was that this product by egg-timer https://eggtimerrocketry.com/eggtimer-wifi-switch/ would make it easier to turn everything on and off. It also can display the continuity status of the deployment charges remotely, which would help reduce the chance of making a simple mistake.

As far as addressing the nose weight, I have to make the open rocket file today. However, LOC's rockism file of the rocket shows that it has no stability issues due to the canards being a smaller size than scale. I did notice, that there are plenty of inaccuracies on LOC's provided file. For starters, the nose cone weight is overridden to the wrong value! and the sim is showing only two body tubes when there are three, which in turn removes a coupler from the file altogether. I will be creating a more accurate file later and sharing it with you all.

 

[TimothyAReed]

Build Log #2 Dec 22, 2019

I have finished weighing all the parts that came with the kit putting the total part weight at 1,991.3 grams. The previous total weight does not include recovery electronics, batteries, drogue chute, recovery cord, and any epoxy used. I will continue updating the spreadsheet as the build progresses. Today I am going to assemble the Ebay kit and begin working on a layout for it. I am also going to make an updated Openrocket file to check the stability of the rocket.

Here is my tentative build schedule until the first shakedown flight for Jan. 11-12, 2020:

Dec 22 - Assemble Ebay kit and begin planning the layout
Dec 23 - Order another DD altimeter for the Ebay, start designing the layout
Dec 24 - Layout the fincan and print alignment guides, also prepare the surfaces for the epoxy
Dec 25 - Continue Working on the fincan, in-between fillets begin working out how I am going to attach my GPS tracker.
Dec 26 - Continue Working on the fincan, and GPS tracker mounting solution
Dec 27 - Finalize the fincan assembly and prepare to mount it into the body tube.
Dec 28 - Mount Fincan assembly, catch up on anything that was left behind
Dec 29 - Catch up day
Dec 30 - Catch up day
Dec 31- Begin attaching canard fins
Jan 1 - Finish attaching canard fins
Jan 2 - Work on GPS tracker mount
Jan 3 - Finish the GPS tracker mount
Jan 4 - Work on Mounting electronics to the Ebay
Jan 5 - Finish the Ebay
Jan 6 - fit all the parts together and double-check everything
Jan 7-10 - Catch up days
Jan 11-12 Shakedown flight at MDRA

 

[BradMilkomeda]

Wow ambitious schedule. I take it no paint? I need the build another loc kit soon.

Great flight location as hopefully I’ll be able to see the result in person. Good luck!

 

[Jozef]

That's an excellent point for the redundant electronics; In that case, I might buy an RRC3 as my primary altimeter since I have a project in mind that requires an extra event channel. I do have the missile works screw switches that I can use to turn on all the electronics. However, my thought was that this product by egg-timer https://eggtimerrocketry.com/eggtimer-wifi-switch/ would make it easier to turn everything on and off. It also can display the continuity status of the deployment charges remotely, which would help reduce the chance of making a simple mistake.

The continuity test shows connectivity, but it does not guarantee the lighter will fire. Measuring the Ohms through a resistance test is the validation that the lighter is functional. Ask me how I know. Jm Amos provides that instruction in his RRC altimeter manuals.

 

[TimothyAReed]

Wow ambitious schedule. I take it no paint? I need the build another loc kit soon.

Great flight location as hopefully I’ll be able to see the result in person. Good luck!

Thanks! I will paint it for the Certification flight, which in February or early March, the shakedown flight is on an H to validate everything. My current work schedule means I can focus the majority of my time on this project during the next two weeks. Plus, once the next semester starts, I want to have this out of the way.

 

[TimothyAReed]

Thanks for the information, I take it you had a personal experience with this subject? I figured it is an excellent option to have, plus I would be able to turn on both altimeters from my phone and get confirmation that they are on. I will be adding a "Remove before flight" strap to remind me to arm the electronics.

 

[Jozef]

Thanks for the information, I take it you had a personal experience with this subject? I figured it is an excellent option to have, plus I would be able to turn on both altimeters from my phone and get confirmation that they are on. I will be adding a "Remove before flight" strap to remind me to arm the electronics.

 

[Jozef]

Yes, I did...once. At URRF 5 in Potter NY. Post mortem showed failed igniter on drogue section. Main did deploy at 240mph. Chute was ripped free. Booster was salvaged and rocket rebuilt. Failed igniter still showed continuity

 

[TimothyAReed]

Yes, I did...once. At URRF 5 in Potter NY. Post mortem showed failed igniter on drogue section. Main did deploy at 240mph. Chute was ripped free. Booster was salvaged and rocket rebuilt. Failed igniter still showed continuity

View attachment 401438

OUCH, I am going to see about using an L2 motor that also has a Bp charge so I can have triple redundancy on the drogue. My condolences for you're rocket.

 

[TimothyAReed]

Build Log #2 Part 2 Dec 22, 2019

I have put together the Ebay kit and realized that it did not come with a stiffer tube, so I am going to have to email LOC about getting a new one... it's not going to be a massive put off on the schedule because I can still mount the electronics. Right now, I am looking at how to install the two 9v batteries required for the Altimeters. My current train of thought is to point both terminals towards the Aft end of the rocket so that the initial acceleration does not force them out of contact.

Note: I am currently thinking about having both batteries terminals facing the aft direction instead of opposite directions.


Note: Pictured below are some Battery holders that I had on hand that I will probably use, They are just a little too small, so they provide excellent pressure on the 9v batteries, a slot will be cut for zip ties to secure the connection further.

 

[TimothyAReed]

Build log #3 Dec 24, 2019

Merry Christmas Eve! Maybe Santa can get me a day of R&R...

This build log was supposed to be posted yesterday, but some stuff came up, and I wasn't able to post. I did, however, stay on schedule and have a pretty solid understanding of how my ebay will be laid out. The West Systems G-Flex 650 epoxy came in the mail today, so I am going to start on the booster section.

Note: The current top layout of the Ebay, the screw switched will be on the other side with the batteries


Note: My 3018 CNC milling the slots for zip ties and wires to pass through the ebay.


Note: The west Systems epoxy I am going to use for the structural components of the rocket. It has a work time of 75 minutes, so it should thoroughly soak into the wood & paper fibers.

 

[blackjack2564]

Good stuff that G-flex

 

[boatgeek]

A couple of notes on electronics in case they’re helpful.

Having a single wifi switch for both altimeters leaves you without full redundancy. If the switch fails, both altimeters go down. A pair of screw switches is easy and reliable.

That said, Egg products have a second switch internal to the unit so that there’s no risk of power to the ematches until the rocket has lifted off and is near apogee. Because of that, it is usually OK to turn on the altimeter during prep. That’s less important for the Quantum or Quark than the Proton since the Qs don’t have an accelerometers that needs to warm up.

Really nice build log and plan on the schedule. I appreciate the number of makeup days you’ve left. It will be really interesting to see how the final dry weight compares to the sum of the components.

 

[TimothyAReed]

A couple of notes on electronics in case they’re helpful.

Having a single wifi switch for both altimeters leaves you without full redundancy. If the switch fails, both altimeters go down. A pair of screw switches is easy and reliable.

That said, Egg products have a second switch internal to the unit so that there’s no risk of power to the ematches until the rocket has lifted off and is near apogee. Because of that, it is usually OK to turn on the altimeter during prep. That’s less important for the Quantum or Quark than the Proton since the Qs don’t have an accelerometers that needs to warm up.

Really nice build log and plan on the schedule. I appreciate the number of makeup days you’ve left. It will be really interesting to see how the final dry weight compares to the sum of the components.

That for the feedback! I decided to go with two screw switches since I already have them on hand. I was not aware Eggtimers had that second internal switch, so thats good to know.

 

[TimothyAReed]

Build Log #4 Dec 24, 2019

Made good progress on the fincan, and have been enjoying the kits' part quality. Tomorrow will be double-checking the fin alignment, then tacking on the fins and Aft centering ring in place with CA before the epoxy goes on. Not sure how I am going to mount the GPS tracker just yet, but it will probably have to do with cutting off the bottom of the nosecone and replacing it with a bulkhead with an inner tube to house the GPS. I also have a neat Idea for the ground station but won't disclose any more information until it is complete.

Note: Custom 3D printed alignment jig for the centering rings. The idea is to tighten it around the tube and press the ring against it to align the ring. Notice the guidelines drawn on the side of the tube; this is so that I can visually line up the two aft centering rings.


Note: My mini-scale maxes out at 200G (the trade-off for +- 0.01g accuracy). will need to keep track of the amount of epoxy added along with parts being glued on to get the total fincan weight. I will be purchasing a larger scale in the future.


Note: The current progress, the fins and aft centering ring have yet to be glued on, I am waiting to check the alignment tomorrow morning before I do anything that cannot be undone!


Note: Obligatory picture of me next to the airframe, I am 6' for reference. The fins are not attached to this photo, just friction fitted into the slots.

 

[jd2cylman]

Just for reference, I use MW RRC3's and RRC2+'s in several rockets (like 6... ). I set the RRC2+ for +1 second at apogee. Always works great for me. Just my $.02

 

[TimothyAReed]

Just for reference, I use MW RRC3's and RRC2+'s in several rockets (like 6... ). I set the RRC2+ for +1 second at apogee. Always works great for me. Just my $.02

Thanks! what altitude do you set for the main deploy channel on the larger rockets? I was thing 1,000ft for the RRC3 and 800 for the RRC2+

 

[jd2cylman]

Thanks! what altitude do you set for the main deploy channel on the larger rockets? I was thing 1,000ft for the RRC3 and 800 for the RRC2+

Yep. The RRC2+ has a limited selection of altitudes: 300', 500', 800', and 1000'. So, the RRC3 always gets set 100' above the RRC2+. So if the RRC2+ is set at 800, the RRC3 gets set at 900' or 1000'. Smaller rockets (say 4" OD) get set to 500' and the RRC3 to 600'. The RRC2+ is always the back up. Unless I've got two in the bay...
Which also works just fine. The usual blah, blah, blah YMMV...

 

[boatgeek]

Thanks! what altitude do you set for the main deploy channel on the larger rockets? I was thing 1,000ft for the RRC3 and 800 for the RRC2+

I like to set the primary at apogee for the drogue and 600-700 for the main. The backup is a second after apogee and 500 respectively. I wouldn’t set the main lower until you have experience with how quickly the main inflates. Some people like to have the main higher if they have a big field to have a better chance of seeing the rocket under main and/or getting a fix on the tracker.

 

[TimothyAReed]

Build Log #5 Dec 25, 2019

First of all, I apologize for the late postings; I intend to do a build update at the end of the day. There were a few Christmas related shenanigans that kept me busy and away from the keyboard. The way things are looking the fincan should be ready to mount tomorrow. I am thinking that making a few modifications to the nose cone is the best Idea and will be working on that in between filleting today. Without further ado here are yesterdays build photos:

Note: Alignment jig 3D printed to help ensure the fins are parallel with the centerline of the rocket.


Note: The fincan with all its fins tacked on and waiting for epoxy


Note: The first application of epoxy fillets. Notice how the Aft centering ring is NOT epoxied or tacked on at all. After finishing the fin fillets, that centering ring will be removed so that the internal fin-to-tube fillets can be completed.


Note: The epoxy weight tracker so that the total weight of the fincan is known.

 

[Tim51]

Great build so far. Just one point - you might want to change that curled eyebolt for an upset forged one.

 

[ECayemberg]

Fantastic job on this build! Great job!

 

[TimothyAReed]

Fantastic job on this build! Great job!

Thanks!

Great build so far. Just one point - you might want to change that curled eyebolt for an upset forged one.

I might have already epoxied it to the centering ring... I do have two forged eye bolts and will be using those on the primary chute side as those should come under more stress than the drogue side of the recovery system.