Measure once, cut twice: Converting an Aerotech Strong Arm to 38mm & Dual Deploy

It says it right there in the instructions: "Do not modify this rocket." Which is really code for "modify this rocket." I didn't want to, but with such a clear mandate I felt compelled. I refer to an Aerotech Strong Arm kit that I recently purchased, and decided to modify for a 38mm motor mount and dual deployment. Following is a rough chronology of the conversion, including the many mistakes I made because I am impatient and impulsive.

I hope that this posting may serve as both cautionary tale and inspiration for those who enjoy overcoming the results of their own errors. I will first chronicle my mistakes, and then the lessons learned at the end. I do not like building things, because I am very bad at it. However, through successive approximation with the mangling of three Aerotech kits (an Initiator, a Mirage, and now the Strong Arm), I feel like I have risen to "skill level 1."

Hereafter the Aerotech Strong Arm will be referred to as "ASA."

1. The ASA is designed for 29mm motors and single deployment using a motor-based ejection charge. Despite my lack of skills in building even the simplest of rockets, I decided I wanted to convert the ASA to use a 38mm motor and dual deployment using an altimeter. I already have an altimeter (a Telemetrum--awesome device) and a built-out 2.6 inch eBay, so it's not as far fetched as it seems.

2. I purchased four 38mm-in-63mm centering rings and a 38mm LOC body tube from Apogee, as well as a 38mm AeroPack retainer and a 38/120 motor case and closures. I also purchased some 29mm-in-38mm centering rings with the plan of converting the original ASA motor tube into a 29mm motor adapter.

3. I successfully cut the 38mm LOC tube to the same length as the 29mm motor mount that comes with the ASA (mistake--see "lessons learned" below). This should accommodate up to a 38/600 motor. The fact that I accomplished this simple task somewhat competently gives me great joy: I marked the cut, put a couple of wraps of duct tape on either side of the mark, and used a 2x6 to steady the knife while I rotated the tube. I was surprised at how clean the result was. It wasn't clean in the sense of a competent person doing it, but it was a lot better than I hoped for.

4. I realized early on that I was going to have to abandon the Fin Lock system. I planned to shorten the fin tabs, cut up the Fin Lock rings, and epoxy the locks into the appropriate places on the 38mm motor tube. The shortened fins wouldn't actually "lock" of course, because the locking tabs would be lost in shortening--but a suitable application of epoxy should make the bond at least as strong as the Fin Lock, and with my 14oz eBay there were no CG issues according to RockSim. Alas, I had to abandon this approach. In my inevitable impatience, I thought "38 minus 29 is 9, and there are two tabs that are about 9mm long--it's almost as if Aerotech INTENDED this conversion." I also thought I would have the windfall of actually locking the fins into the Fin Lock tabs. Those with a brain already know that 38 minus 29 divided by 2 equals 4.5, which is about how much should be removed from each of the four fins--but I removed the first tab, shortening _each_ fin by about 9mm. So, no lock, and no connection to the motor mount. It gets worse, but you'll have to read on.

5. Having already cut the fins, there was nothing to do but soldier on. I attached the 38-63 centering rings to the motor tube and epoxied them in place. I tested the fit and it worked fine. I was able to insert the fins, which still go through the outer wall, they just don't touch the motor tube. I planned to build channels for the fins out of plastic scraps. Two parallel walls for each fin reaching from the motor tube to the edge of the centering rings and more or less filled with epoxy ought to anchor the fins as well as Fin Lock, right? Well, we'll never know, because in another mistake of impatience I epoxied the motor tube assembly into the body tube before I built the channels. Now I was in a situation where the fins not only didn't reach the motor tube, they had no anchor of any kind once inserted. I toyed with the idea of filling the fin compartment with epoxy, but that was too much of a kludge even for me--so I had to settle on securely gluing the fins to the tube and using rather larger than usual epoxy clay fillets to provide structural support. Yes, the fins will probably shred off the rocket when I put bigger motors in there. Which probably argues for launching it single-deploy initially so I don't throw $400 worth of electronics away in a sky writing exhibition.

6. Did I mention dual deployment? My first idea was to use my existing eBay. This would leave a one-inch gap in the strakes, but that's more cosmetic than practical. However, after having glued my 12" 38mm motor mount in place, I realized that my existing eBay would hit the forward bulkhead of the MMT before it seated. I should have cut the MMT back for a 38/360 or 38/480, which is as big as I will ever use in this kit anyway unless I'm planning to "retire" it. I should have done that, but I didn't, so I had to punt. My answer was to get another eBay but not to use a spacer. Because of the lack of clearance between the aft end of the eBay, both deployments would have to come out the front of the rocket--and without further modifications that means a Tender Descender or similar. I haven't completed this part of the project yet, but it should work as follows: I add a quick disconnect between the apogee terminal block and the apogee connector on the Telemetrum. I drill another hole in the forward bulkhead and run a long wire for the Tender Descender, to which I also attach a quick disconnect. When I want to launch the ASA, I move my bulkheads and sled as-is to the second eBay coupler, connect the Apogee connector to the Main terminal block, and the Main connector to the long wire mentioned previously. At apogee, the forward charge fires, disgorging the Tender Descend, chute in deployment bag, etc. At main deployment, the Tender Descender fires and the main deploys. It's a great theory, anyway, and more economical than a second altimeter. However, if it fails, I will lose my Telemetrum--so I may end up building out the second eBay with a second, much cheaper altimeter.

7. The 29mm motor adapter was another bit of comedy. I put two 29-38 centering rings on the original 29mm MMT and that worked fine. Then I realized my error: there was no retention in the 38mm MMT. A 38mm motor would be retained under thrust by the aft closure, but the 29mm adapter has no such closure and under thrust would just punch up through the MMT and into the eBay, probably generating a traumatic deployment if not a CATO. I used two solutions, both equally ugly: I pushed one of the very strong 29-63 centering rings down onto the top of the 38mm MMT (as I said, there isn't much space between the front end of the lower body tube and the motor mount). I generously epoxied the ring in place and added an epoxy clay fillet for whatever good that does (I just like making fillets from epoxy clay). I also cut down the 29mm exhaust baffle that came with the ASA, removing the outer ring of material and the top of the baffle, to create a cap for the 29mm MMT adapter that would positively engage the aforementioned 29-63 centering ring when the 29mm MMT adapter was installed. I should also note that the top centering ring of the 38mm motor mount has a screw eye, to which I tied a shock cord. The other end of that shock cord goes to a quick link that connects to the eBay. Even those the eBay should remain in the lower body tube, this little bit of mechanical coupling makes me feel better in case I'm wrong and the engine punches through the rocket and blows the eBay out of the tube. This also allows me to easily convert to single deploy by removing the eBay and inserting a standard coupler.

That's where I stand. I am finishing the rocket right now. My biggest concern is that the fins won't survive under thrust, or will snap off on recovery. The latter I can deal with, I just don't want to lose the Telemetrum. I am contemplating a static drop from 10 feet to see if the fins survive, but sometimes ignorance is bliss. I plan to launch this rocket using a 29mm F40W to test its flight-worthiness and dual deployment strategy. If either fails, I will likely be able to recover the most valuable parts of the rocket.

I promised some lessons:

1. When converting a kit, don't wing it. Think it through and document the steps. Don't glue a damn thing until you have run through the entire build as a table-top exercise or other simulation. I actually considered most of the variables and came up with reasonable solutions, but during the build and operating off the reservation (i.e., the Aerotech instructions) I got ahead of myself and created several situations, at least one of which (the lack of positive through-the-body fin attachment) I can't fix without destroying the rocket.

2. Leave plenty of room for an eBay. It would have been easier and less expensive if I could have done traditional two-compartment dual deployment instead of using a Tender Descender. If I had cut the 38mm MMT to 9" instead of 12" I would have head enough room to install an eBay and a drogue chute in the lower compartment with the main in the upper compartment. A 9" 38mm MMT would support a 38/480 motor which is more than big enough for this little rocket.

3. When designing a motor adapter, plan for retention in both directions. I got into the habit early of using AeroPack retainers for the primary MMT, but I did not give thought (having no experience in this area) to the adapter. If I had launched using F40Ws as I described above, the 29mm motor adapter probably would have punched through the 38mm MMT and pushed out the eBay under thrust.

4. Measure twice, cut once. This seems like something someone else should have figured out (irony intended). Most of the challenges in this conversion were the result of my own mistakes, which were the result of impatience. The biggest example is the fins, which have no positive connection to the MMT because I cut the fin tabs too short. I will probably not stop being impatient, but I am trying hard to be more careful about measurements and visualizing the whole build before I start cutting and gluing.

5. Have fun. Despite my poor technique, ignorance, and repeated errors caused my own impatience, I've had a lot of fun building this kit. The strakes even came out well, which I was dreading (AeroTech provides nicely pre-formed fins and other parts, but for some reason they give you what look like rigid plastic window seals that you have to cut out to form the strakes). Creating and overcoming problems has been a blast (figuratively speaking)--and I hope the launch will not be a blast (literally speaking)!

That's some discription. You don't happen to have a relative that farms in Texas do you?

Tis a shame you so much trouble. I have several AT kits I have converted to DD plus a couple to 38mm

Used all the stock items. Just sanded out the supplied CR's cut down fin tabs & epoxied into place.

Flown on 6grain 38 motors and all have survived with flying colors!

Jim: You don't have trouble because you're competent. I'm not, so I have to take small victories when I can find them! Other than the centering rings, what you describe is what I planned to do, but when I glued the MMT assembly into the body tube that put paid to that idea.

If by Texas you mean Maine, I do have such a relative. But if by Texas you actually mean Texas, I don't.

The Strong Arm modification has so far surpassed my wildest dreams. I am not sure my concept for the altimeter bay (using a Blue Tube coupler without a spacing ring) is the best, though. It will require drilling holes through the body tube for static ports and switches--not a huge deal but that will depend on the bay and the tubes being properly aligned throughout the flight. I guess that means I'll be installing some shear pins or maybe even rivets.

The bay I'm designing is fixed (but not permanently) to the fin section. The drogue charge fires from the forward end of the bay, and the main charge (the Tender Descender) fires from a long wire attached to the forward end of the bay. I've toyed with the idea of mounting my Telemetrum in a free-floating bay that ejects with the drogue and Tender Descender. The issue of parting the main (Tender Descender) deployment charge wire is worse because two parts may be twisting in opposite directions, but I can't imagine it will be much worse.

The nagging feeling in the back of my mind is that I'm making this more complex than it needs to be. Single deployment is not an option, but is there some obvious solution I'm missing?

Have you decided on the Tender Descender? Did you investigate the ARRD from Rattworks or the Defy Gravity Tether? I haven't figured out how I could use a Cable Cutter on my 28 lb. project. Are there other options?
Thanks for the help,
Matt

Matt: I did use the Tender Descender, did not look at alternatives mostly because I wanted to single-source things from Apogee. The TD worked well in two static ground tests, but I haven't had a flight test yet for reasons I'll describe below!

I am impressed by your ability to keep pressing on despite setbacks.

I have to say that your thread reminds me of a few things.

1. Walk before you run
2. I appreciate the reminder that purchasing a kit for 38mm motors was extremely wise.
3. I know you have invested time money and a little bit of your soul into this build but I would be extremely concerned about flying this with only fillets between the fine and body tube. The plastic on AT fins isn't the most epoxy friendly and I would worry about having them come off under power.
4. If you use an aeropac 38-29 mm adapter you will be ok. Do not use the at cardboard one as you noticed.
5. Archetype makes a cable cutter that would help solve your eBay issue. If I were you I'd reconsider electronics on this bird and keep it to MPR where your fins have a chance to stay on. If you choose the cable cutter you need to promise to read the directions and test it.
6. Seriously man. Buy a 38mm paper and ply kit from Madcow or LOC from apogee and do it right!

Just my two cents. Take them or leave them. At this point you have sunk a couple hundred dollars into a rocket that might not make it past the RSO table. Why risk a potential dangerous flight? Not trying to beat you up but I would be worried about safety here.

I look forward to this thread!

My modified Aerotech Strong Arm (hereafter ASA) was a fun project. I modified the rocket from 29mm to 38mm motors (with a 29mm adapter) and for single-compartment dual-deployment using an Altus Metrum Telemetrum and a Tender Descender.

The construction phase exercised my innovative capabilities and brought many of my basic rocket-building skills to near-competence. I made several mistakes (described previously), including cutting the fin roots too short to mate with the motor tube, and then gluing the fin can in place before I had implemented my solution to the "short fin root" problem. In the final analysis, the fins turned out to be plenty strong even though they were not mated to the motor tube.

Having built three kits in rapid succession, the ASA came out very well indeed--especially considering how far I deviated from the original design.

For those who care, here is a brief description of the ASA: I used a 38mm motor mount tube with three plywood centering rings. I cut the motor tube to 11" but could have (and should have) gone shorter and used dual-compartment instead of single-compartment dual deployment.

I chose to substitute a 2.6in Blue Tube eBay from Apogee for the normal coupler. The eBay was anchored to both body tube sections by plastic rivets--four in the lower section and three in the upper section. In place of a fourth rivet in the upper section was a 1/4" static port which also provided access to the socket for the pull-pin safety key. I used a normally closed Radio Shack power jack as the switch for the altimeter--the corresponding plug, when inserted, breaks the circuit. Of course I drilled the plug and inserted a "Remove Before Flight" tag

The forward bulkhead of the eBay was crowded, because it included a charge cup for the apogee charge, terminal blocks for apogee and main charges, and a plastic guide (the barrel of a BIC pen) for the Telemetrum's antenna (which is far too long to fit inside the eBay). Also, the center eye bolt and the thread rods, washers, and nuts. For the latter, I used regular 1/4" nuts instead of the wing nuts in the eBay kit, and used 3/8" plastic bushings as a standoff between the flat washer, lock washer, and nut. Quick-disconnect couplings were on the internal face of the forward bulkhead for the apogee and main charges.

They don't seem to make a commercial deployment bag for 30-36" nylon chutes in 2.6" body tubes, so I tack-stitched a Nomex blanket in approximately the right places to make a simple deployment bag.

The Tender Descender (TD) connected the nose cone and drogue chute with the main chute and the main body of the rocket. I chose to connect the tethered link (and hence the body of the TD itself) to the main recovery harness--so if my drogue and/or nose cone got lost, I wouldn't lose the TD. This put all the eggs in one basket, but based on simulations it was the right choice to recover the biggest part of my investment [though I relied too much on simulations--see below]. The wiring for the TD was knotted to the quick links at the TD end and at the eBay end of the main recovery harness, and from there connected to the eBay terminal block and a separate "free" terminal block/barrier strip I used to make more positive connections between the main ejection lead and the TD igniter.

I performed two static ground tests of the apogee and main deployment. 1g of FFFF black power was more than enough to separate the nose cone and push the TD, wrapped main chute, and harness out of the main body of the rocket with decent force. The TD charge also worked well. I abused the harness to the extent I could without damaging the rocket to make sure no wires would pull free during violent flight events.

The recovery assembly was tight, meaning there wasn't much space between the eBay and nose cone shoulder for all these harnesses, wires, chutes, and gadgets. Using the "4-5x rocket length" theory of recovery harnesses, split between the nose and main body, just wasn't going to work. The total length of the two halves of the harness was about 2.5x the rocket's length.

For the initial fight RockSim predicted about 900 feet from an F40 motor. An alarm should have gone off here, because the Aerotech Initiator that I bought for my daughter only goes to about 1200 feet on an F40. It turns out that although I carefully modified the RockSim file for the ASA to reflect my design changes, the "mass override" was turned on--meaning no matter what I changed, the mass of the rocket was always coming out around 20 ounces. Being the impatient, impulsive person I am, I didn't think about the fact that the altitude of the rocket was staying fairly constant even as I was adding a lot of weight to the design.

My feeling is that RockSim ought to not allow you to make ANY changes other than engine selection as long as "mass override" is enabled. But in the end it was my own fault that I didn't catch this--and it turned out to be pivotal in the event.

Launch day was breezier than I would have liked with winds around 15 knots from the southwest. I went as far as I could into the southwest corner of my launching area, did a countdown, and launched the rocket.

The rocket was slow coming off the pad, but not terribly slow (an 88" Mirage modified for DD on a G71 was terribly slow). It weather-cocked about 5 degrees, rose into the air, nosed over, and proceeded to fall straight to earth without any kind of deployment whatsoever. We actually felt the "thump" as it hit the ground about 100 feet upwind of the launch point.

The rocket was buried a good 12" into the ground and the forward body tube was accordioned. The rocket was a loss, but the Blue Tube eBay and a sled that I had recently redesigned for greater impact resistance survived almost unharmed. The power socket for the Telemetrum was pulled slightly off the board by the impact, but I was able to re-seat it and the Telemetrum worked normally (sending back to Bdale for a once-over, though).

I still had a radio link with the Telemetrum so I did another static test with the otherwise untouched recovery system. Both charges worked fine on the ground (firing the main charge reset the Telemetrum, but I'm going to chock that up to the loose power socket on the altimeter board). Also, on reviewing the flight data I had _not_ lost tracking. The Telemetrum recorded a flight up and a flight down, but no recovery events.

So what happened?

First of all, my altitude projections were based on a 20oz airframe. The actual weight of the rocket with the eBay, chutes, Kevlar harness, wiring, altimeter, battery, and Tender Descender, was MUCH heavier than 20oz. Trying to simulate my altitude, I came out with a loaded weight of somewhere around 60oz. The final altitude of the flight was only 67 meters or a bit over 200 feet.

Still, the Telemetrum was functioning at apogee and during the descent. So why didn't at least the apogee charge fire?

I sent the flight data to Keith of Altus Metrum and it turns out that the Telemetrum won't arm recovery events unless the flight tops 100 meters:

TeleMetrum inhibits the motor burn-out detection until the flight reaches 100m. I'm afraid the reason for that test is now lost in the mists of time though -- it was part of the original TeleMini Kalman filter implementation, and I'm betting it has something to do with avoiding false motor burn-out detection early in the boost phase due to a noise sensor.

I think I can safely remove that check for TeleMetrum boards where the accelerometer will ensure that a noisy baro sensor doesn't cause problems.

-keith

Click to expand...

So the ASA is a loss, but building, testing, launching, and troubleshooting were still a lot of fun. I've learned a lot of great lessons which I'm sure will prevent any further mishaps (NOT!).

Jason: All points well taken. We all have different styles of learning, and mine has always been "leap before you look." That's why Pike liked Kirk, right? ;-)

I will say that the fins not only didn't come off in flight, they were one of the few pieces of the airframe other than the Blue Tube eBay that were NOT deformed or destroyed by the impact of my very expensive dirt dart. But like you I was not comfortable with that setup, and I would never bring that kit to an event or anyone else's field.

I am lucky that I have a field of my own to fly in, so my RSO will always give me a pass. The field itself is barely "legal" for a high-power range, but barely still counts--and in any event my family owns all the property around the field for a quite a distance in any direction. So I am willing to take some chances here that I would not take in someone else's field.

I'm not exactly a rocketry neophyte, though 2012/2013 mark the end of a 30-year hiatus for me. My move toward dual deployment was triggered by the rocket-eating trees snatching several attempts I made to "walk" using simple MPR rockets and simple recovery systems. I am again lucky that I was able to cut down the trees and get my rockets back--but DD seemed an obvious way to ensure more, better outcomes. "Seemed" being the operative word--it's pretty clear from my experience with the Telemetrum and MPR kits in general that the idea of using dual deployment on MPR kits just hasn't occurred to most manufacturers and flyers. The two DD flights I've attempted have resulted in an in-flight reset of the altimeter, apparently due to RFI from the drogue ejection charge ignition signal, and a complete failure due to the Telemetrum not even arming until it passes 100 meters.

Having said all that, there is no rationalization I can offer for my decision to modify the ASA for 38mm motors. I could go for level 1 using 29mm motors. I had all the hardware for 29mm motors. Going to 38mm motors was a lot of additional expense and offered a very limited motor range for my self-described field and altitude limitations. So as I start over today, I'm not going to try to modify a kit for a bigger engine. Lesson learned, and a lot more fun than thinking it through ahead of time ;-)

I've learned more through making mistakes than from anything else. As long as I keep making NEW mistakes, and don't do anything dangerous, I don't mind.

See I jumped to conclusions and had a vision of this frankenrocket going up with $400 of electronics and hardware in it with a 5 grain I motor for a Level-1 certification "just to see if it would work". I was more concerned with safety and had no idea that you actually had already pushed the button on it! My apologies as you did have good intent to be safe just you forgot about some thrust to weight math but hey it happens.

I totally understand that learning by doing is an excellent way to figure stuff out. I am a believer in dual deploy and use it whenever I have a chance as it really affords you a greater chance to get your "investment" back. It is a bit more challenging for MPR but I would still encourage you to check out the Archetype Cable cutter - that really is a good solution for MPR in my opinion - simple, light and effective. The telemetrum stuff is extremely cool and I'd want to play with it too.

To make lemonade though: You have some excellent 38mm hardware, a telemetrum and a tender descender and a bunch of useful experience. Find some 38mm rocket kit that flicks your bic or build your own scratcher using HPR components. After the challenges you faced modifying a MPR you'll be on easy street.

Thanks for the tale and apologies for my tirade. I think that I have been reading too many stories of people putting too much motor in their rocket or saucer and causing an inevitable shred that made me cringe. This is all fun and games until someone gets hurt - a little common sense goes a LONG way to preventing that.

I look forward to your next build thread!

Sully said:

View attachment 132610

I've learned more through making mistakes than from anything else. As long as I keep making NEW mistakes, and don't do anything dangerous, I don't mind.

Click to expand...

.....can I get an AMEN?!?!

Amen-a!

Jason: No problem from this end--I took your words to heart before you wrote them and agreed 100% when I read them--and for anyone else in my position reading the thread they provide a valuable reminder.

One point I may not have made clearly enough is that I relied too much on RockSim to do the math for me. I bought a nice digital scale to weigh my rockets and components, but I didn't use it. I just kept adding things to RockSim and it kept predicting a 900+/- foot flight. I suspended my own intuition and judgement in favor of output from a program I really don't know how to use very well. As they say, GIGO.

The Telemetrum is a wonderful device that so far has not worked for me. I have the following complaints about the Telemetrum:

* It does not fail safe--power interruptions or RFI during flight will cause a reset that effectively means you are flying without electronics or tracking.
* It does not arm below 100m [this may be fixed soon]
* In idle mode there is no audible or visible indication of power or arming status

By admission of its builders, it's very sensitive to RFI--and I've already mentioned the issue with not arming until it reaches 100m. That latter says to me that no one ever considered using a Telemetrum for flights under 100m, but it's worth pointing out to new Telemetrum users that if your rocket is under-powered or for whatever reason ends up going horizontal and stays under 100m, no deployment events will occur [Keith Packard indicated that they'll probably do away with the 100m arming altitude since that is evidently an artifact from the baro-only Telemini development process].

The best piece of advice I can offer to anyone building with the Telemetrum _especially_ in a tight electronics bay like a 2.6" is to make sure your ejection leads are twisted and kept as far away from the antenna as possible. Even modest RFI (like that generated by the ejection signals flowing through a copper wire) will generate voltages on the board that it is not designed to handle, and it will shut down. An in-flight reset like that means you not only don't get any further deployment events, but you will lose tracking as well. In their defense, Altus Metrum in written and video instructions make it clear that RFI is a threat--but even after reading and watching all of that I didn't realize how much of a threat it was. You have to go to what I consider extraordinary measures to protect the Telemetrum against RFI.

That said, I will continue to use the Telemetrum and do whatever I can to support the folks at Altus Metrum.

Thanks for the detailed recap. This was especially interesting for me since I am contemplating doing my first dual deploy build soon and I hope to avoid some of the problems you had.

If I modify a motor tube size I will definitely get a 4th grader to double check my arithmetic before I cut anything. :grin:

Nathan: As worthy of ridicule as the "fin slip" was, the fins survived a free fall from 67m of an aerodynamic projectile weighing +/- 4 pounds, whereas most of the rest of the airframe and components did not. The gs incurred in that impact far exceed anything the fins would have ever experienced from any motor I could have jammed into or adapted to the rocket (except maybe a warp drive, and that as I understand it, is inertia free) ;-)

Do you know if Telemetrium folks have done any testing to see if ferrite beads will help suppress the RFI problems?

I've had some correspondence with Bdale Garbee and Keith Packard of Altus Metrum, and they have not mentioned ferrite beads as a method of RFI mitigation--but I'm guessing that any shielding/suppression technique would help, including beads, tight twists, shielded wire channels, etc. The issue of course is weight, but considering the cost of the Telemetrum, you should assume anything that can fail will fail--including RFI pulses, g-induced movement (including switch closure), etc., and engineer accordingly.

What the Altus Metrum folks consistently recommend, and what I did, is to make sure the ejection leads are tightly twisted and kept away from the antenna. To make sure they stay twisted, I used some small-diameter shrink wrap tubing. I also routed the leads as far to one side of the TeleMetrum's antenna as feasible in a cramped 2.56" electronics bay and made sure they were positively retained.

The TeleMetrum is a conceptually awesome device (the MegaMetrum promises to be even more so), but my opinion is that it is not very robust. An end user really shouldn't have to worry about these issues. On the flip side, I would suffer the loss of several rockets and even a TeleMetrum or two in order to gain the experience necessary to use this board to its potential.

Just a final note: I was able to salvage my motor mount from the Strong ARM, as well as everything else except the body tubes, nose cone (which is still buried in my field), and fins.

Why couldn't I salvage the fins? Because I couldn't remove them. Even though they were not connected to the motor mount, two of the four fins broke before the epoxy fillets let go. I don't know for sure of course, but I would say that even though the fin attachment was my biggest screw-up in this project (well, second biggest--launching a 4 pound rocket with an F40 was the biggest), the fins most likely would have survive any MPR shot and quite likely most HPR shots as well.

The video of the fatal but entertaining plunge of my Aerotech Strong ARM: https://www.youtube.com/watch?v=ubLDtTFGRsM

Nice video. Now it looks like you are going to need to build some more rockets. If that Aerotech Initiator came straight down with no chute and still got lost in the woods, you might also need to find a bigger field!

I built one Aerotech kit last winter (a Mustang) but I don't plan on building any more of them because I don't like the snap-on plastic fins. There isn't much to building a rocket, and shaping and finishing wood fins is one of the few construction steps that actually requires a bit of craftsmanship.

The field is about 800 x 1500, but we launched on the extreme upwind corner of the field because the wind was fairly high. That's a good plan until the recovery system fails. The rocket body came down in the trees, the nose cone (under a 30" chute) drifted about a half mile into another set of trees. Sometimes ya can't win ;-)

In truth, I'm very lucky the Strong Arm came down where it did... A few more feet in 3 of 4 directions and it to would have come down in the trees.