3" Punisher - L2 build

[wsume99]

Not planning to do an exhaustive build thread because there are already a lot of build threads for wildman fiberglass rockets and the process is similar. So I'll mainly be asking specific questions where I'd like some advice from the community.

My first question is about recovery harness attachment to the MMT. Most builds, including the original CJ build thread, show the Kevlar strap being glued on opposite sides of the MMT, basically 180° apart. This makes complete sense to me however I am not sure that's what I want to do. I marked the fin locations on the MMT and left 1/2" of free space on either side of each fin for the internal fillets to adhere to. That leaves about 1-1/8" between each fin for me to glue on the 1" wide kevlar strap. I have a pic of the layout below. I don't see how I'm going to make 180° work. Only issue I can come up with is the sustainer might not hang completely vertical in descent. Not sure that's anything to be worried about. Anyone see a problem with the harness attachment points only being 120° apart?

 

[Flyfalcons]

I am building a P3 now. I epoxied a single strip of 1" kevlar to the motor mount. The strip goes the length of the body tube and has a loop on the end to attach the full length harness. This has worked well on my heavier 4" Drago. Note that there is an overhand knot tied to the end of the harness on the motor mount - this serves as a mechanical stop in the unlikely event the epoxy fails.

 

[GaryT]

On the smaller kits I do a one piece of 1/4" Tubular Kevlar, if it can fit I'll make a small knotch in the CR against the MM tube and tie a knot on the underside and epoxy that. I let it extend about a foot out the top of the BT. Just be sure to sand/smooth the edge of that BT, that piece of Kevlar rubs against the BT's side pretty heavily on its way down from high flight. On bigger kits I'll do the 180 with the loop coming out the top.

 

[Speaknoevil]

Not planning to do an exhaustive build thread because there are already a lot of build threads for wildman fiberglass rockets and the process is similar. So I'll mainly be asking specific questions where I'd like some advice from the community.

My first question is about recovery harness attachment to the MMT. Most builds, including the original CJ build thread, show the Kevlar strap being glued on opposite sides of the MMT, basically 180° apart. This makes complete sense to me however I am not sure that's what I want to do. I marked the fin locations on the MMT and left 1/2" of free space on either side of each fin for the internal fillets to adhere to. That leaves about 1-1/8" between each fin for me to glue on the 1" wide kevlar strap. I have a pic of the layout below. I don't see how I'm going to make 180° work. Only issue I can come up with is the sustainer might not hang completely vertical in descent. Not sure that's anything to be worried about. Anyone see a problem with the harness attachment points only being 120° apart?
View attachment 411211

I have done exactly this with the wide "ribbon" kevlar. Like you said, makes it easier to place fins.

 

[wsume99]

Thanks for the replies guys. Got some good ideas here. I already knocked the sharp edges off of all the corners before I washed the parts. I'll go back and make sure the ID at the top of the body tube is smooth. I'll add a knot at the bottom of the kevlar strap as a backup as well. That's a simple backup.

 

[crossfire]

I have used the single attachment of 1" strap onto the MMT many times. Most of the time I go with a loop sewed on one end. Sewed loop has never failed me.

 

[wsume99]

Made some good progress. The sustainer is assembled and I'm working on the av bay now. I have a question about the shear pins. I'm planning to use three #2-56 nylon screws as shear pins to hold the coupler onto the nosecone. In CJ's Punisher 3 thread he uses a 7/64" drill bit for #2-56 shear pins. I'm confused by this because 7/64" is way oversized for that size shear pin. This is my first rocket with shear pins so I was assuming I'd just drill and tap the hole like any other threaded hole. Is that correct or am I mistaken? Looking for any pointers on shear pin installation.

 

[crossfire]

Made some good progress. The sustainer is assembled and I'm working on the av bay now. I have a question about the shear pins. I'm planning to use three #2-56 nylon screws as shear pins to hold the coupler onto the nosecone. In CJ's Punisher 3 thread he uses a 7/64" drill bit for #2-56 shear pins. I'm confused by this because 7/64" is way oversized for that size shear pin. This is my first rocket with shear pins so I was assuming I'd just drill and tap the hole like any other threaded hole. Is that correct or am I mistaken? Looking for any pointers on shear pin installation.

I would say 2 shear pins are plenty. You might want to ground test charges.

 

[QBrandt]

Made some good progress. The sustainer is assembled and I'm working on the av bay now. I have a question about the shear pins. I'm planning to use three #2-56 nylon screws as shear pins to hold the coupler onto the nosecone. In CJ's Punisher 3 thread he uses a 7/64" drill bit for #2-56 shear pins. I'm confused by this because 7/64" is way oversized for that size shear pin. This is my first rocket with shear pins so I was assuming I'd just drill and tap the hole like any other threaded hole. Is that correct or am I mistaken? Looking for any pointers on shear pin installation.

Don't need to thread shear pin holes, often makes them difficult to put in and take out. Sizing so a screw can slide in makes your life easier.
Generally want it to be a little tight of a fit, so they don't fall out. (Rule of thumb: Use your thumb. Should be able to press in.) If you drill a little too big, can either rotate the tube a little bit to clamp the pins, or put a little tape over them.

 

[wsume99]

I would say 2 shear pins are plenty. You might want to ground test charges.

Are you suggesting to drill three holes but only use 2 pins? Or at least experiment with two pins.

 

[wsume99]

Don't need to thread shear pin holes, often makes them difficult to put in and take out. Sizing so a screw can slide in makes your life easier.
Generally want it to be a little tight of a fit, so they don't fall out. (Rule of thumb: Use your thumb. Should be able to press in.) If you drill a little too big, can either rotate the tube a little bit to clamp the pins, or put a little tape over them.

I guess I fear if the hole is too large they'd fall out in flight or on descent. I never considered taping them in place. I would prefer to not have tape on the outside of the rocket but that would likely keep them in place.

 

[Speaknoevil]

Made some good progress. The sustainer is assembled and I'm working on the av bay now. I have a question about the shear pins. I'm planning to use three #2-56 nylon screws as shear pins to hold the coupler onto the nosecone. In CJ's Punisher 3 thread he uses a 7/64" drill bit for #2-56 shear pins. I'm confused by this because 7/64" is way oversized for that size shear pin. This is my first rocket with shear pins so I was assuming I'd just drill and tap the hole like any other threaded hole. Is that correct or am I mistaken? Looking for any pointers on shear pin installation.

Get some numbered drill bits. IIRC, 43 is good for #2 nylon screws and 31 for #4 nylon.

 

[Nytrunner]

Made some good progress. The sustainer is assembled and I'm working on the av bay now. I have a question about the shear pins. I'm planning to use three #2-56 nylon screws as shear pins to hold the coupler onto the nosecone. In CJ's Punisher 3 thread he uses a 7/64" drill bit for #2-56 shear pins. I'm confused by this because 7/64" is way oversized for that size shear pin. This is my first rocket with shear pins so I was assuming I'd just drill and tap the hole like any other threaded hole. Is that correct or am I mistaken? Looking for any pointers on shear pin installation.

Just google the drill size for 2-56 threaded tap and then order one from somewhere.

Apogee even sells the tap and drill sets for 2-56 and 4-40

 

[GaryT]

Basically reiterating what others have said, No need to tap the hole, make the SP fit so you can get them it in and out without tools, put the 2 parts together drill the hole and put the pin in, do the same on the next holes, be sure to mark the inside of the BT so both pieces go back the same way each time aligning the holes properly, take my word on it with 3 or more SP's the BT will have to go back the same way for them to align again lol

 

[Flyfalcons]

This is how I set up the head end deploy on my P3.

 

[Handeman]

I've been using alignment pins on my joints. Put the two part together and drill a 3/16 hole centered on the joint. Then glue a piece of wood or composite dowel in the hold. Sand flush with the out side surface. This will ensure your two part always align exactly the same.

Then drill your low clearance holes for your shear pins. The alignment pins keep things lined up and even though you have small clearances, the pins will go in easily every time.

 

[wsume99]

Made some decent progress. The sustainer assembly is compete. I've painted it and the nosecone. I just received some decals from stickershock so I'll be installing those once the paint cures a few more days.

Now I'm focusing on the avionics bay. The plan is to have dual deployment with full redundancy plus tracking. To accomplish this I'm using an Eggtimer TRS for the primary + GPS and an Eggtimer Classic and WiFi switch for the backup side. I'm planning to use the finger tech robotics switches to interrupt the connection between the battery and the electronics. I just finished assembling the eggtimer classic last night and now I'm starting to think about wiring. Here's a couple questions I'm looking for feedback on...

1) Eggtimer suggests using twisted pairs from Ethernet cables for testing. Is this also acceptable for wiring in the AV bay? Anyone have experience or other recommendations to share?

2) At a minimum, wouldn't I need some connector for the lipo battery? It would need to be removed for charging. I'm thinking a premade JST connector and pigtail to mate with the battery connector and terminate with solder joints onto the altimeter would be good here.

3) The Eggtimer Classic doesn't have screw terminals. I do have the locking connector kit but haven't installed them. Eggtimer recommends not using them for power or ignition circuits. I assume the best option for connecting charges then is to install screw terminals and then solder a wire between the altimeter and the screw terminal? I've seen all kinds of variations here. For the TRS I'd just wire the ignitor directly to the screw terminals on the altimeter.

 

[Glasspack]

Ryan you kept saying rubbing alcohol in your last video but your can says Denatured...….. All of my experience is that they are NOT the same.
Is your can filled with rubbing Alcohol? I could be very wrong......but I was curious …….?

 

[wsume99]

Been plugging away on assembling all my Eggtimer hardware. The Classic and WiFi switch are done. I started the TRS next and had to stop at the step where you validate that the Tx is working because I hadn't assembled the Rx. Today I finally got the receiver put together and tested the TRS. I've confirmed the Tx is working so I can finish the assembly.

I 3D printed my own case for the LCD receiver. I added switches for POWER and BACKLIGHT along with an external SELECT pushbutton. The printed case came out ok with the exception of the B in the BKLT text. The two little pieces inside the B didn't stick to the build plate. I don't feel like printing a second one right now so I'm good with it as is. I may end up making another design of the case to make the battery easier to access. For now I'm satisfied with the design.

 

[wsume99]

Need some more advice. I have all my electronics assembled now and I'm laying out the AV bay. I installed the fixed antenna on the TRS but I'm wondering if I should have just gone with the RP-SMA connector instead. The board + antenna is too long to fit inside the coupler. I see three options:

1) Keep as much of the antenna inside the AV bay. Drill a clearance hole in the bulkplate and allow approx 1/4" of the antenna to protrude past the outer surface. This would protect the antenna but it would be inside the AV bay and running parallel to the 1/4" all thread. I'm pretty sure this goes against the recommended installation.

2) Keep as much of the antenna outside of the AV bay possible. I'd mount the TRS as far aft as possible which would allow approx 65mm of the antenna to extend outside the AV bay. I think this would be preferred for better reception but I'm concerned about the antenna being in the way of the recovery gear. With a 54/2800 case I only have about 6" of room between the motor and the AV bay. If I could mount the antenna against the ID of the body tube that would be ideal but I'd need to bend the antenna to do so. I'm under the assumption that bending the antenna is not recommended.

3) Remove the stick antenna and install a RP-SMA connector. This would allow me to mount the antenna anywhere I wanted and the external antenna seems to be more rugged than the stick antenna.

So I'm looking for recommendations on the way to go. I'm leaning towards #3 but maybe there is a better option?

 

[wsume99]

Mostly finished the AV bay build. Still have to install the wiring but I've got everything laid out and it all fits. Here's what I've got inside the coupler:

• Eggtimer TRS
• Eggtimer Classic
• Eggtimer WiFi switch
• Two 500mAh 2s Lipo batteries
• Two Fingertech robotics screw switches

Everything fits with the exception of the antenna on the TRS. I mounted the TRS as far forward in the bay as I could with the antenna pointed aft. I printed a shroud to protect the exposed end of the antenna. It all works well. I have just the single piece of 1/4" all thread running down the centerline. I'm trying to decide wether to use blue loctite on the coupling nut or to cross drill and install a spring pin. Obviously I don't want it to come apart. I need to see how small of a spring pin my local hardware store has. That will probably be the deciding factor.

I 3D printed the bulkplates only for mocking up the position of everything. I'm now printing some templates so I can transfer the hole locations to the FG bulkplates. The batteries weren't fastened down with zip ties but each one will be held into the pocket on the sled with two. They're completely constrained on all sides so they're not going anywhere. The screw switches were not installed either because I stripped my 1.3 mm hex wrench and am waiting for the replacement to arrive. They mount inside the sled at the corners and are mounted so the screw is facing outwards. I can access them thru the vent holes in the band. Now I can finally paint the vent band.

 

[wsume99]

Drew up a cartoonish wiring schematic to make sure I was hooking everything up correctly. Decided to jumper the switch inputs on the eggtimer classic and just power it on/off via the wifi switch. Batteries will be disconnected from the electronics until the rocket is on the pad. Arming of energetics will be done remotely.

 

[wsume99]

After more research and thinking I decided to change the wiring. I moved the switch onto the positive lead of the deployment power feed. This will permit me to power everything up at my setup area and get it all connected and checked out. Then when I'm on the pad I close the switches to connect the charges. Finally I will still arm everything remotely. I feel pretty good about this setup.

 

[jd2cylman]

Ryan you kept saying rubbing alcohol in your last video but your can says Denatured...….. All of my experience is that they are NOT the same.
Is your can filled with rubbing Alcohol? I could be very wrong......but I was curious …….?

I only use Denatured Alcohol...

 

[g.pitts]

After more research and thinking I decided to change the wiring. I moved the switch onto the positive lead of the deployment power feed. This will permit me to power everything up at my setup area and get it all connected and checked out. Then when I'm on the pad I close the switches to connect the charges. Finally I will still arm everything remotely. I feel pretty good about this setup.
View attachment 419107

This is precisely the implementation I'm going to be using for my L2 certification flight (later this month, fingers crossed!). The difference is I'm using Omron limit switches with a "Remove Before Flight" flag and rod rather than the switches you're using. My rationale was that I did not want any brief disturbance of voltage due to G-force or vibration impacting these limit switches to reset the altimeters. Worst-case, it simply disturbs the charge power at a (hopefully) non-critical time.

 

[wsume99]

My rationale was that I did not want any brief disturbance of voltage due to G-force or vibration impacting these limit switches to reset the altimeters. Worst-case, it simply disturbs the charge power at a (hopefully) non-critical time.

That's good to hear because it was the primary reason why I did it too. I think it's also more convenient to get prepped but more importantly it prevents any switch issues from resetting the altimeter.