Wildman Motor Eater L3 build

[Neutronium95]

After more than a year of false starts, bad ideas, and changing life circumstances, I finally pulled the trigger on my L3 build. I decided to keep things simple and build a rocket that can comfortably fly on more affordable L2 motors, while also making use of most of my local waiver on a 4 grain M motor. My tentative plan right now is to fly at LDRS, but that's dependent on both getting the rocket built in time and on being able to get a call in waiver.

This is a relatively new kit from Wildman, but there isn't really anything new or exotic about it. It's essentially just a Head End Dual Deploy version of the Extreme Wildman that I chose mostly because I prefer the looks of this design over the Punisher 4. The only change that I'm making to the rocket is the addition of an Aeropack tailcone retainer swiped from my dad's 10 year old half built L3 rocket. Between shifting the motor back, and reducing the base drag, it does put the stability margin right on the edge of what I'd consider acceptable (8% of the rocket length). The final rocket might need a dash of noseweight to make me happy with the stability, but I am hopeful that just swapping in a heavier parachute, and maybe adding some extra data logging electronics could move the CG forward enough.

The kit came a week ago, and I took my time cleaning and weighing the parts before sanding all of the areas to be glued. I did the first bit of actual assembly this evening, attaching the switch band and rear centering ring. Photos will come with better light and more progress tomorrow.

And of course, here's the mandatory picture of the dry fit of the parts right out of the box.

 

[Neutronium95]

Today was quite productive. I got the motor mount assembled and glued into the body.

For this build, I decided to keep things simple and just attach the shock cord to the top of the motor. If I adapt down, I have a 75-54 adapter that has a shock cord anchor built into it that should be sufficient for the weight of this rocket.

I decided to try a new technique for fin attachment. I cut strips of balsa and glued them to the motor mount on either side of each fin. Each trough will get filled with epoxy poured in through the fin slot, and then the fin will just be installed normally. This lets me do fin attachment and internal fillets in one step. I cut the balsa strips a tad too tall, so I had to do a lot of shaving them down with a knife to get the motor mount to fit into the airframe nicely.

Gluing the motor mount in went pretty smoothly. I used the retainer to set the depth into the airframe, in order to make sure that the retainer cap will seat nicely. The only hiccup was a rather large smear of rocketpoxy on the inside of the tube. I wanted all of the glue joints to be nice and neat since I'm not planning on painting this rocket, but I guess my tendency towards ugly rockets can't be overcome.

I also printed out a fin alignment jig. I don't think that it's too necessary, since the tight fin slots force the fins perpendicular to the body pretty well. If all goes well, I'll get the first two fins on tomorrow.

Apologies for the terribly messy work area.

 

[Neutronium95]

Fin attachment went well. Once I figured out the process, things went very smoothly, especially on the last fin. I built a spreadsheet that calculated that I needed about 45 mL of epoxy to fill the channels to the level that I wanted, so I mixed up between 75 and 80 grams of Rocketpoxy. I quickly learned to mix more than was strictly necessary, to avoid needing to try to scrape the dregs into the syringe body. The 60mL syringes also required a bit of sanding on the tips to seat into the fin slots, but other than that worked perfectly for injecting the epoxy into the trough.

Two of the fin slots required a bit of filing to get the fins to fit in nicely. They were also a fraction of an inch too long, which was great, because it gave me a little bit of wiggle room on the motor mount placement.

The fin installation went very smoothly after the epoxy was injected, and a small 3D printed jig worked great to keep everything aligned. I do want to find a better configurable jig, since this one is a little bit floppy at this size. It's rigid enough when the binder clips are applied, but I don't trust it to last for multiple builds.

This picture actually shows one of the slight problems with the kit. The fin tabs were cut to be too long. I decided that the easiest way to deal with that would be to just take a file to the tips of the fins and then bury any resulting ugliness under the fillets. It's kind of annoying, but it gave me a little bit more fin span, which does help with stability. I'm still not sure if I'll need to add nose weight to hit an 8% stability margin when fully loaded.

The build is going pretty well. The booster just needs external fin fillets, a fillet on the rear centering ring, and to attach the retainer and the rail buttons. Then it's just the avbay. I have a few ideas on how I'll go about that, ranging from just borrowing the sled from an existing rocket to relearning CAD to make a custom printed sled that'll hold my altimeters, a tracker, and maybe a friend's data logger.

Sorry for the lack of pictures, most of the ones for this step featured my ugly mug, and as such aren't fit to print.

 

[jimzcatz]

In deference to Rocketjunkie (Tom Binford TRA 0667) its not a true Motoreater unless it has a minimum of 7 holes in it!!!

 

[Neutronium95]

In deference to Rocketjunkie (Tom Binford TRA 0667) its not a true Motoreater unless it has a minimum of 7 holes in it!!!

I fully agree with you, unfortunately I didn't get the chance to name the kit. I do want to mess around with high power clusters someday.


In other news, I finally got a picture of it in some good light after bonding the fins on. I'm hoping to have time to get the first set of fillets applied this evening. This picture also shows the ugly smear of epoxy that I got on the inside of the tube when installing the motor mount.

I'm really satisfied with the size of this rocket. It's small enough to be easy to transport in my car, and should be light enough to fly well on J and K motors when I don't feel like shelling out the cash for an M motor.

 

[Neutronium95]

I've been making slow progress this past week. Fortunately this is a very simple build, so I've pretty much finished up all of the major structural work, leaving just the avbay and recovery system to go.

The external fin fillets went on alright. I used a spherical fillet tool that I made for a previous build where I couldn't find a fondant tool big enough. It's just a delrin sphere with a length of threaded rod screwed into it.

Laying out the fillet locations and taping them off went smoothly, I put a thin layer of Rocketpoxy dye on the tool to make nice clean marks.

The fillets went on nicely, without any real hassle, besides trying to peel off the tape with gloves on.

Ultimately, the fillets came out fine. I'm not entirely satisfied with how they ended up at the very top and bottom, but that's just an aesthetic issue.

I also glued on the retainer this morning. This view also shows the extra epoxy I added behind the rear centering ring. That was a bit of a mess, but I managed to avoid getting any in a place where it could interfere with the retainer, so I called it a win.

That's pretty much it for major structural work. The next big task will be the avbay. I already have a sled design that will hold my two Stratologgers, but I am tempted to try to design something that can carry a Featherweight GPS and possibly some electronics from a friend as well.

 

[Williamhimka]

My motor eater has a tail one as well. Do tailcones work as thrustplates kinda? Like if you think about it, the retainer body, (not the cone) with the threads is epoxied on. Then your motor goes in. and you put the cone on. Once the cone is on, the threaded body and cone are basically one object now kinda. Since the cone pushes up against the outside of the airframe, would it technically be a thrust plate sorta? Just something to chew on haha…

William

 

[Neutronium95]

I've had a pretty rough few weeks, but I managed to get pretty much everything finished.

I've tried a few new things on this build, chief among them 3D printed parts. I printed the avbay sled, along with a bunch of jigs for drilling holes. One other printed part was a sacrificial piece of plastic that I friction fitted into the avbay coupler wherever I drilled into it, in order to minimize any splintering on the inside surface.

I decided to keep the electronics as simple as possible. A pair of Stratologger CF altimeters with screw switches for deployment, and I'm planning on attaching my Featherweight GPS to the shock cord for tracking, just in case. The screw switches are a neat little part made by an acquaintance on Discord that packs three independent switches onto one board for compactness. I soldered on some twisted pairs of wire, and screwed it onto a printed piece that I glued onto the inside of the avbay.

(I have since wrapped the switch wires in electrical tape to make it less of a rats nest inside the avbay.)

I also found time to drill all of the shear pin holes, and install the 1515 rail buttons.

One thing that I have been slightly concerned about through this build has been stability. When I had pretty much everything together, I measured the mass and CG, and found that the stability was a bit lower than I like, at around 7%. I decided to stay on the safe side and got an extra long eyebolt for the nosecone and put enough fender washers on it to get it to fit well, which came out to more than a pound of noseweight. That bumped the stability up to almost 11% with the M1780 loaded, and more with smaller motors.

(This doesn't show it too well, but the stack of fender washers is about 2.5" long)

(Simulation with updated masses for everything, altitude is probably optimistic, due to the polished surface finish)

That leaves just a few little details to take care of before I call this done and ready for flight. The avbay bulkheads need to have wires run through them, my terminal blocks should be here tomorrow, so that I can do that. Lastly, I need to fully rig the recovery system and ground test the rocket. I'm planning on doing those at LDRS, since I don't have an appropriate location nearby to do my ground tests, and I'll be borrowing the drogue from a friend at the launch.

Overall, I'm pretty satisfied with the build. There have been a few things that haven't quite gone as I wanted, like the big smear of epoxy from when I installed the motor mount, and the fact that I didn't file down the leading edges of the fins enough to make the fillets around them nice and clean. There are a few other imperfections that could be fixed, but nothing that really affects whether or not it will fly.

 

[RocketScientistAustralia]

I've had a pretty rough few weeks, but I managed to get pretty much everything finished.

I've tried a few new things on this build, chief among them 3D printed parts. I printed the avbay sled, along with a bunch of jigs for drilling holes. One other printed part was a sacrificial piece of plastic that I friction fitted into the avbay coupler wherever I drilled into it, in order to minimize any splintering on the inside surface.

I decided to keep the electronics as simple as possible. A pair of Stratologger CF altimeters with screw switches for deployment, and I'm planning on attaching my Featherweight GPS to the shock cord for tracking, just in case. The screw switches are a neat little part made by an acquaintance on Discord that packs three independent switches onto one board for compactness. I soldered on some twisted pairs of wire, and screwed it onto a printed piece that I glued onto the inside of the avbay.

(I have since wrapped the switch wires in electrical tape to make it less of a rats nest inside the avbay.)

I also found time to drill all of the shear pin holes, and install the 1515 rail buttons.

One thing that I have been slightly concerned about through this build has been stability. When I had pretty much everything together, I measured the mass and CG, and found that the stability was a bit lower than I like, at around 7%. I decided to stay on the safe side and got an extra long eyebolt for the nosecone and put enough fender washers on it to get it to fit well, which came out to more than a pound of noseweight. That bumped the stability up to almost 11% with the M1780 loaded, and more with smaller motors.

(This doesn't show it too well, but the stack of fender washers is about 2.5" long)

(Simulation with updated masses for everything, altitude is probably optimistic, due to the polished surface finish)

That leaves just a few little details to take care of before I call this done and ready for flight. The avbay bulkheads need to have wires run through them, my terminal blocks should be here tomorrow, so that I can do that. Lastly, I need to fully rig the recovery system and ground test the rocket. I'm planning on doing those at LDRS, since I don't have an appropriate location nearby to do my ground tests, and I'll be borrowing the drogue from a friend at the launch.

Overall, I'm pretty satisfied with the build. There have been a few things that haven't quite gone as I wanted, like the big smear of epoxy from when I installed the motor mount, and the fact that I didn't file down the leading edges of the fins enough to make the fillets around them nice and clean. There are a few other imperfections that could be fixed, but nothing that really affects whether or not it will fly.

For your switches, it looks like you've used single core cat5 cable. Solid single cored cables should not be used for rocketry. Break 1 strand and you've got 0.
Stranded servo connector wire is quick and easy and doesn't break as easily.
Good luck with the flight.
Fly high, make us all proud parents. Now go do your homework......

 

[plugger]

For your switches, it looks like you've used single core cat5 cable. Solid single cored cables should not be used for rocketry. Break 1 strand and you've got 0.

Hey Norm, do you use E-matches? Do you rely on them for deployment duties in your hybrids?

 

[RocketScientistAustralia]

Hey Norm, do you use E-matches? Do you rely on them for deployment duties in your hybrids?

Yes. No issues. Like all things electrical, make sure the spec of the match is suitable for the battery being used and flight computer. As a rule of thumb you're trying to get 1watt of energy to the pyro for 1 second. The old ICI igniters had a spec of 1v 1A for 1 sec. and you could fire them with one of those new fangled Alkaline 1.5 V batteries.
Depending on whose e-match you use, some are 3v. Firing off a 3.7 lithium through a controller is probably ok. I do remember seeing some that said the all fire was 7 V. They wouldn't be suitable for single lithium. Although they would probably actually fire, you couldn't guarantee it.

 

[3stoogesrocketry]

Yes. No issues. Like all things electrical, make sure the spec of the match is suitable for the battery being used and flight computer. As a rule of thumb you're trying to get 1watt of energy to the pyro for 1 second. The old ICI igniters had a spec of 1v 1A for 1 sec. and you could fire them with one of those new fangled Alkaline 1.5 V batteries.
Depending on whose e-match you use, some are 3v. Firing off a 3.7 lithium through a controller is probably ok. I do remember seeing some that said the all fire was 7 V. They wouldn't be suitable for single lithium. Although they would probably actually fire, you couldn't guarantee it.

I believe your missing the point. E-matches are solid core wire too so ...

 

[RocketScientistAustralia]

I believe your missing the point. E-matches are solid core wire too so ...

Yes the ematches are solid core and get a single use. Hard wired to their connection point. External to the AV bay once it is assembled.
Internal wiring should be flexible. As it will get moved multiple times.
Pity Andrew couldn't have been clear what his question or point was rather than trying to score a point......

 

[plugger]

Yes the ematches are solid core and get a single use. Hard wired to their connection point. External to the AV bay once it is assembled.
Internal wiring should be flexible. As it will get moved multiple times.
Pity Andrew couldn't have been clear what his question or point was rather than trying to score a point......

I was hoping you'd do your homework, but maybe my expectations are too high

 

[RocketScientistAustralia]

I was hoping you'd do your homework, but maybe my expectations are too high

How did you go with the fins you were going to look at? Did they indeed have stainless leading edges, You forgot to update everyone.

 

[plugger]

How did you go with the fins you were going to look at? Did they indeed have stainless leading edges, You forgot to update everyone.

I don't know what you're referring to Norm, but I've never once incorporated any metal in a fin I've made. I think you're confusing me with someone else.

 

[RocketScientistAustralia]

I don't know what you're referring to Norm, but I've never once incorporated any metal in a fin I've made. I think you're confusing me with someone else.

Weird, I found your original post. Seems to have changed from my memory. https://www.rocketryforum.com/threads/o3400-min-diameter-l3.165546/post-2194636 Been reduced to a good luck message......... Must be my memory. No way you could change a post.....

Here's the original.....from my undoctored email..... Didn't take too much researching. It was not aluminium. It doesn't blue on heating. 316 stainless does and is not magnetic. Titanium can. Anyway don't want to hijack this thread. I'm done.

 

[plugger]

Weird, I found your original post. Seems to have changed from my memory. https://www.rocketryforum.com/threads/o3400-min-diameter-l3.165546/post-2194636 Been reduced to a good luck message......... Must be my memory. No way you could change a post.....

Here's the original.....from my undoctored email..... Didn't take too much researching. I was hoping you'd do your homework, but maybe my expectations are too high. It was not aluminium. It doesn't blue on heating. 316 stainless does and is not magnetic. Titanium can. Anyway don't want to hijack this thread. I'm done.
View attachment 522295

That was Lottering's rocket, not mine Norm.

 

[RocketScientistAustralia]

That was Lottering's rocket, not mine Norm.

The devil is in the detail Andrew. At no point did I say it was yours.

Anyway back to the OP issue. I still stand by the statement that the internal wiring to the screw switches should be flexible. Not solid core. In fact all wiring internal to an AV bay (where possible) should be flexible stranded. This has been covered in multiple other AV bay questions. Solid cored wire work hardens when flexed, gives no prior indication before failure that it is about to go. Unless you HAVE to use it for some reason(and I cannot think what that reason would be), you only give yourself an additional point of failure that will take out a whole flight computer(if that's what it's connected to).
Norm

 

[Neutronium95]

I did a test flight on a L1720 yesterday. After several attempts to get the igniter to work, the motor finally lit. The flight was picture perfect, with a straight boost, and a final altitude of about 11,700 feet. Recovery was also great, with the drogue and main deploying right on cue. It landed a mile down range, and suffered no damage. This takes a lot of stress out of the L3 flight, since the L1720 got it going almost as fast as the M1780 will.

 

[Neutronium95]

Well that wasn't supposed to happen.

The motor failed at the forward seal disk, and might have had a too short liner. It does look like the rocket will be salvageable by cutting the tube just below the burn through area and splicing on a new piece of tube with a coupler. The fin that came off did so pretty cleanly, so I should just be able to put epoxy on the root edge and inside the slot and reattach it.

I would like to send a big thank you to the people at Aerotech and Tim at Wildman for taking care of the warranty replacement on the field, since I borrowed the hardware from a friend.

I'll be aiming to make a second attempt at XPRS or BALLS. I'm hoping to make it to both this year, but those plans still aren't certain.

 

[crossfire]

Well that wasn't supposed to happen.

The motor failed at the forward seal disk, and might have had a too short liner. It does look like the rocket will be salvageable by cutting the tube just below the burn through area and splicing on a new piece of tube with a coupler. The fin that came off did so pretty cleanly, so I should just be able to put epoxy on the root edge and inside the slot and reattach it.

I would like to send a big thank you to the people at Aerotech and Tim at Wildman for taking care of the warranty replacement on the field, since I borrowed the hardware from a friend.

I'll be aiming to make a second attempt at XPRS or BALLS. I'm hoping to make it to both this year, but those plans still aren't certain.

Sorry to see that. It might be better just to build a new kit looks like the whole rocket took a lot of heat. What motor was it? Warranty replacement at the field that was nice.

 

[rfjustin]

Well that wasn't supposed to happen.

The motor failed at the forward seal disk, and might have had a too short liner. It does look like the rocket will be salvageable by cutting the tube just below the burn through area and splicing on a new piece of tube with a coupler. The fin that came off did so pretty cleanly, so I should just be able to put epoxy on the root edge and inside the slot and reattach it.

I would like to send a big thank you to the people at Aerotech and Tim at Wildman for taking care of the warranty replacement on the field, since I borrowed the hardware from a friend.

I'll be aiming to make a second attempt at XPRS or BALLS. I'm hoping to make it to both this year, but those plans still aren't certain.

Sorry to see that happen... curious to understand more about the short liner. Was that input from Tim or AT?

Did you get o-ring compression when putting the motor together?

IMO build a new booster, that thing is fubar

 

[T34zac]

I did a test flight on a L1720 yesterday. After several attempts to get the igniter to work, the motor finally lit. The flight was picture perfect, with a straight boost, and a final altitude of about 11,700 feet. Recovery was also great, with the drogue and main deploying right on cue. It landed a mile down range, and suffered no damage. This takes a lot of stress out of the L3 flight, since the L1720 got it going almost as fast as the M1780 will.

@Neutron95 L1720 flight.

 

[T34zac]

Well that wasn't supposed to happen.

The motor failed at the forward seal disk, and might have had a too short liner. It does look like the rocket will be salvageable by cutting the tube just below the burn through area and splicing on a new piece of tube with a coupler. The fin that came off did so pretty cleanly, so I should just be able to put epoxy on the root edge and inside the slot and reattach it.

I would like to send a big thank you to the people at Aerotech and Tim at Wildman for taking care of the warranty replacement on the field, since I borrowed the hardware from a friend.

I'll be aiming to make a second attempt at XPRS or BALLS. I'm hoping to make it to both this year, but those plans still aren't certain.

First bit of the burn looked good.



Didn't last much longer though

 

[plugger]

Well that wasn't supposed to happen.

The motor failed at the forward seal disk, and might have had a too short liner. It does look like the rocket will be salvageable by cutting the tube just below the burn through area and splicing on a new piece of tube with a coupler. The fin that came off did so pretty cleanly, so I should just be able to put epoxy on the root edge and inside the slot and reattach it.

I would like to send a big thank you to the people at Aerotech and Tim at Wildman for taking care of the warranty replacement on the field, since I borrowed the hardware from a friend.

I'll be aiming to make a second attempt at XPRS or BALLS. I'm hoping to make it to both this year, but those plans still aren't certain.

Really sorry to see this occur, but glad to hear you'll be making another attempt soon!

 

[RocketScientistAustralia]

Well that wasn't supposed to happen.

The motor failed at the forward seal disk, and might have had a too short liner. It does look like the rocket will be salvageable by cutting the tube just below the burn through area and splicing on a new piece of tube with a coupler. The fin that came off did so pretty cleanly, so I should just be able to put epoxy on the root edge and inside the slot and reattach it.

I would like to send a big thank you to the people at Aerotech and Tim at Wildman for taking care of the warranty replacement on the field, since I borrowed the hardware from a friend.

I'll be aiming to make a second attempt at XPRS or BALLS. I'm hoping to make it to both this year, but those plans still aren't certain.

Good luck with your next launch.
Norm

 

[Neutronium95]

So with a few days since the failed flight, I thought that I'd look at what worked, what didn't, some lessons learned, and what to do next.

What worked:

• Pretty much everything. The rocket was relatively simple to prep, and flew perfectly on an L motor that got it going almost as fast as the planned cert motor.
• The 72" Top Flight main parachute was a big standout. It packed significantly smaller than the Rocketman 7 foot parachute that I was initially planning on using, and it gave me only a slightly faster descent rate.
• The screw switch block made for a nice compact solution for mounting 3 switches.

What didn't:

• The avionics wiring was a bit of a mess. I think that it was mostly due to the long switch wires I used.
• The Featherweight GPS cut out on the pad. I had a friend's RDF beacon on the flight, so I went ahead, but future projects should have a better tracker mounting solution, and I should also get more experience with the system.
• The 1/4" kevlar that I used for the main parachute shock cord snapped when the parachute was yanked out at high speed. I'm not sure if this matters, because if it was stronger then the parachute might have shredded instead.

Lessons learned:

• Check the feel of the aft closure as you screw it down. I missed that the liner was too short, but that evening I did catch a short liner when assembling a M1500 for @bandman444
• The glue pockets for attaching and filleting the fins worked really nicely. I think that I'll be using this method on a lot of my future builds.
• I need to get better at wiring my avionics. Future plans include connectors between the avbay sled and bulkheads/switches, so that it can be easily disassembled without needing long wires that get in the way.

I'm not quite certain what I'll do next. I think that the fin can and avbay can be salvaged. The body tube burned through about 8" above the forward centering ring, so I can cut it off just below the burn and glue in a coupler to attach a new section of tube to. The nosecone got crunched a few inches below the tip. I might replace the whole nose, or cut it off below the crunched section and get a friend to make a larger nose tip on his lathe.

I also have some other ideas for possible L3 projects. I already have most of the parts for a 98mm minimum diameter rocket, and it might actually be cheaper, since I just need fins for it. I know that TAPs have been pretty cool on extreme cert rockets, but they'd hopefully be fine with me doing a L3 cert on a minimum diameter rocket adapted down to the M1297 that I got to replace the failed motor.

 

[plugger]

I also have some other ideas for possible L3 projects. I already have most of the parts for a 98mm minimum diameter rocket, and it might actually be cheaper, since I just need fins for it. I know that TAPs have been pretty cool on extreme cert rockets, but they'd hopefully be fine with me doing a L3 cert on a minimum diameter rocket adapted down to the M1297 that I got to replace the failed motor.

I did my L3 on a MD airframe and there weren't any issues with that from a TAP perspective. You've demonstrated you ability to build to handle that sort of flight, so why not go for it if that's what you want to do!

 

[Neutronium95]

@UPscaler got some great video of the test flight, and put it in his first LDRS video.