PML AMRAAM 4" CPR build

[Jim Hinton]

I like and use the PML 1010 rail guides, but I've had lousy experience with the 1515 guides. They seem too brittle and are prone to crack when railing up. I much prefer the aerodynamic rail buttons instead. The teardrop shape makes them real easy to get on the rail. They are about ideal for long rockets.

Jim

 

[mtnmanak]

Moved some things along yesterday afternoon, got the main tube couplers in and the canards glued in with Aeropoxy and filleted with Rocketpoxy

 

[mtnmanak]

Installed the motor mount and glued the root edges of all the fins in with 5 min epoxy, then filleted all the interior edges with Aeropoxy. Put this aside to cure over night, ready for this morning.

 

[mtnmanak]

This morning, I laid out all the parts where they will go and dry assembled the whole rocket

 

[Hobie1dog]

The switches I have are made by Schurter and you rotate the switch with a screwdriver.

View attachment 434856

Yes, I could see that you use a screwdriver ,But I was asking about the other type that uses an actual key (usually comes with a red lanyard that says "remove before flight")

 

[mtnmanak]

Threw an H motor in (largest motor I had on hand) and all the parachutes, straps, piston parts etc where they were supposed to go to get a rough idea of CG so I could think about rail button placement. I added some weight to the end to simulate an I or J motor. Looks like CG is going to be around 50", so I think the rail buttons will go nicely into the centering ring that sits at around 53". In the pics below, the small piece of tape is the rough CG and the long ring of tape is the centering ring on the trailing edge of the tape. That should provide a nice anchor for the buttons and keep them from interfering with the pistons.

 

[mtnmanak]

Yes, I could see that you use a screwdriver ,But I was asking about the other type that uses an actual key (usually comes with a red lanyard that says "remove before flight")

Ahh, I understand now. I am not sure about those. In the past when I built one rocket to use the pull pin, I followed some advice on other threads on how to do it myself. It didn't turn out so well, 100% because my skill wasn't good enough to make it work well, so I have been going with the rotary switches.

 

[mtnmanak]

Speaking of switches, I need to do some testing with the altimeter and this schurter switch to see which leads are which, but I also need to think about placement. While dry fitting everything, I checked the clearance on the switch if I put it where the directions say to put it. It will be tight. Probably 4-5mm of clearance, which is workable, but tight.

 

[Hobie1dog]

thanks for all the pictures

 

[mtnmanak]

Also, put all the lower buttons/lug on this morning. Going with 1010 buttons, 1515 buttons and the 1515 linear rail lug cut in half (to try it). Noted Jim Hinton's comments above about the 1515 linear lugs being brittle. Will probably add the PML 1010 linear rail lugs later to try them (still have one side open right now ). anchored everything appropriately, going to finish all the internal fillets and epoxying of the internal anchors with Aeropoxy this morning and glue the end centering ring in and set aside to cure for the rest of the day.

 

[mtnmanak]

To do list for today:

- External fillets on the fin section (tonight when internal fillets/end centering ring are mostly cured)
- Switch testing / installation
- Build the pistons / sew & glue all the straps ends to the piston plates/fin section plate.
- Sew shock cord end loops
- Upper rail buttons / linear lug

 

[mtnmanak]

Yes, I could see that you use a screwdriver ,But I was asking about the other type that uses an actual key (usually comes with a red lanyard that says "remove before flight")

I realize you aren't looking for Schurter switches, but if you do use them, I saw Apogee is selling them for about $14 a piece. This place sells them for $5 a piece and sometimes has sales that go down to $2 a piece. If I ever see them go to $2 a piece again, I will probably buy a bunch of them to have in the kit bag.

https://www.goldmine-elec-products.com/prodinfo.asp?number=G23789

 

[heada]

Be wary of cheap knock-off switches. They have been shown to fail MUCH faster than expected. Some have reported failures after only a few cycles.

 

[mtnmanak]

Be wary of cheap knock-off switches. They have been shown to fail MUCH faster than expected. Some have reported failures after only a few cycles.

Good point. These guys claim they are genuine Swiss made Schurter's but I would have no way of verifying that.

 

[Joshua Smith]

FWIW This topic came up very recently on our local mailing list and @JimJarvis50 among others recommended these https://aeroconsystems.com/cart/switches/pcb-screw-switch/ He gave a nice rundown of why and how he uses them. I could copy it in here, but I feel like I'd be doing Jim a disservice if I did so I'll just post the TRF links he provided:
https://www.rocketryforum.com/threads/first-timer-needs-help.119801/#post-1375383https://www.rocketryforum.com/threads/easy-on-off-switch-for-altimeter.140202/#post-1689155

 

[mtnmanak]

FWIW This topic came up very recently on our local mailing list and @JimJarvis50 among others recommended these https://aeroconsystems.com/cart/switches/pcb-screw-switch/ He gave a nice rundown of why and how he uses them. I could copy it in here, but I feel like I'd be doing Jim a disservice if I did so I'll just post the TRF links he provided:
https://www.rocketryforum.com/threads/first-timer-needs-help.119801/#post-1375383https://www.rocketryforum.com/threads/easy-on-off-switch-for-altimeter.140202/#post-1689155

Awesome, thanks. Been looking at all the threads on screw switches as well. The one you listed above looks dirt simple, but the ones from Missile Works look like little circuit boards. Need to see how those work/are wired.

 

[mtnmanak]

I did test the Schurter switch and it works fine. I am going to proceed with it. I read the thread by Jim Jarvis - excellent thread. That is a way more complicated setup than I am doing here and I will definitely look at using the techniques / equipment he recommends in my next build, but for this fairly simple DD build, I think a Schurter is going to be sufficient.

 

[Joshua Smith]

I did test the Schurter switch and it works fine. I am going to proceed with it. I read the thread by Jim Jarvis - excellent thread. That is a way more complicated setup than I am doing here and I will definitely look at using the techniques / equipment he recommends in my next build, but for this fairly simple DD build, I think a Schurter is going to be sufficient.

Yeah, Jim is often going for 10x the altitude of us mortals Or, he's doing awesome stuff like active roll control etc

 

[mtnmanak]

Yeah, Jim is often going for 10x the altitude of us mortals Or, he's doing awesome stuff like active roll control etc

Ha, yeah - the two clubs I normally fly at only have 5000' waivers, so I do not plan to regularly fly this one high or fast. The closest club with a high waiver is 3-4 hours away, so I generally only make that trek a couple times a year for an event of some kind.

Not to mention heada's anecdote above about disintegrating on a J1999. It certainly sounds like these quantum tubes have their limits. So far, this is a great rocket and a fun build, but will be keeping it squarely in low altitude.

 

[Joshua Smith]

Ha, yeah - the two clubs I normally fly at only have 5000' waivers, so I do not plan to regularly fly this one high or fast. The closest club with a high waiver is 3-4 hours away, so I generally only make that trek a couple times a year for an event of some kind.

Not to mention heada's anecdote above about disintegrating on a J1999. It certainly sounds like these quantum tubes have their limits. So far, this is a great rocket and a fun build, but will be keeping it squarely in low altitude.

Yeah, so far I'm a big fan of my Striker and Bull Puppy, tho they only have 1 flight among them total LOL

 

[mtnmanak]

Fin section is complete

 

[mtnmanak]

All the shock cords have loops sewn in now. Swivel sewn into middle loop on one for main chute.

 

[jd2cylman]

I wouldn’t bother with the 1515 buttons. You’ll never get enough weight or thrust in this rocket to stress the 1010’s. I’ve seen 6” WM rockets launch on 1010’s. Just my $0.02...

 

[mtnmanak]

I wouldn’t bother with the 1515 buttons. You’ll never get enough weight or thrust in this rocket to stress the 1010’s. I’ve seen 6” WM rockets launch on 1010’s. Just my $0.02...

Good point and, frankly, not too worried about this working well on 1010's, but the club I fly with the most is somewhat small, I guess, and they usually put out 5 1010 rails and 2 1515 rails. Generally, the 1010s are usually full and the 1515s are usually empty. If nothing else, besides being able to get in when the 1010s are full, it just seems like the nice thing to do to be able to use the 1515 rail and keep the 1010 rails open for someone else. At the end of the day, for the want of a few minutes to install the 1515 buttons, it isn't a big deal to have both.

 

[jd2cylman]

Good point.

 

[manixFan]

The switches I have are made by Schurter and you rotate the switch with a screwdriver. Very secure in that they stay in the position you place them in and have very little chance of switching off. Pic below. I can't remember where I got these - got them on a sale at some point in the past. It looks like Apogee sells them now, but there may be a cheaper source somewhere.

Been a while since I played with them, I need to do some testing to remember which posts to use and which ones to cut off.

Also need to think about where I am going to install these. They are much deeper than the slide switches, so will need to place carefully without interfering with the altimeter plate.

I have always put the switch on the actual mounting plate itself and then accessed through a hole that goes through both he airframe and inner CPR mount. It requires careful measuring but I found it to be a lot easier than one mounted to the CPR itself.


Tony

 

[mtnmanak]

I was working on getting the D-rings and straps for the pistons and fin section done and I was looking at this design for the fin can and it doesn't look like a great idea to me.

Why have this method of gluing a strap back on itself through a slot vs. using an eye bolt or U-bolt? Seems like a possible point of failure for a glued strap vs. the mechanical certainty of bolt solution. Can anyone that has built this rocket give me some insight as to why the glued strap solution is preferable over a bolted solution?

Also, this solution will not allow the use of an engine ejection charge as a backup to the DD system since the plate is glued on to the top of the fins section.

 

[manixFan]

I was working on getting the D-rings and straps for the pistons and fin section done and I was looking at this design for the fin can and it doesn't look like a great idea to me.

Why have this method of gluing a strap back on itself through a slot vs. using an eye bolt or U-bolt? Seems like a possible point of failure for a glued strap vs. the mechanical certainty of bolt solution. Can anyone that has built this rocket give me some insight as to why the glued strap solution is preferable over a bolted solution?

Also, this solution will not allow the use of an engine ejection charge as a backup to the DD system since the plate is glued on to the top of the fins section.
...<graphics snipped>...

This is the step I recommended against in my list - don't glue the strap, either knot or sew a loop. The epoxy bond is not very strong when used with the strap. On some of my later builds that used the piston I substituted a quick link for the D-ring. I actually had one of the d rings break so I quit using them.

I've never used motor backup so that's never been an issue for me. That style of recovery setup is referred to as ''zipper less' because you can't zipper the fin can. But if you doubled up the bulkhead (or fiberglassed it) for strength I suppose you could drill holes to allow the ejection charge to pass through. Maybe others will have better ideas on that.


Tony

 

[mtnmanak]

I was thinking just a simple coupler centering ring with an eye bolt drilled in it. Basically, the same config you would use for a standard single deployment / motor eject rocket.

Like in the fin section of this LOC IV. Seems like it would be simpler, more secure and more versatile. Need to think about it and see if I can find a reason I would go with the strap at all vs. an eye bolt.

In the case of the AMRAAM fin section, the ring would be right near the top of the coupler tube. Should be almost zero chance of a zipper.

 

[mtnmanak]

Basically, as simple as this: