Madcow DX3-XL balcony build

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Aug 28, 2021
Reaction score
I've been planning this project for maybe a year now. This phase, just before I start is always the most challenging for me. Once I do start, the flow comes and I get deep into the project. My design has been signed off by my Taps for the L3 build, so here we are getting ready to document it!

Because I forget to document, I built an outline to make sure I capture some thoughts and photos at each of these phases. In my documentation, they will be in this order, but here, I'll probably do more of a free flow. Let me know if you think of an extra one you'd like to see.

Parts & Tools​


Washing Didn't take pictures of the bath


Coupler ✓
Bay ✓
Payload ✓
Booster ✓
Motor mount ✓


PEM Nuts

Avionics Bay​

Sled model
Wiring diagram
Vent holes

Motor Mount​

Centering ring fit
Y Harness
Motor retention


Internal Filets
External Filets


Shear pins
Rail guides


Last edited:
The build space. We're in an apartment, so this is the space I get for the hobby. As long as I keep it clean and organized, it is completely doable. I've built the majority of my rockets from this space.

The only real limiting factor is space for painting. I tried getting a paint tent, but because I'm right by the community pool space, I didn't feel comfortable with all the fumes that were going out over the balcony.

For my last project, I drove out to a sparsely used park and painted there. It was serviceable, but I'd like for this one to be pristine.


  • IMG_4436.jpg
    5 MB · Views: 0
I feel like I see often see builds where everything goes to plan and I don't ever have that happen.

I planned on using an Aeropack retainer RA75P and had it in the parts box for a while. When I went to test fit it, no joy. I sanded for a good bit with 80 grit, but didn't get it to fit. I was a bit wary of sanding too far down and not having something even, so I scrapped that plan and went to look for a flange 75mm retainer. They are actually sold out most places right now but Composite Warehouse had one and hooked me up. Turning the focus to centering rings for now while I wait for the retainer.


Sanded and measured against the instructions for the kit with a refreshing beverage to accompany the process.

Let's get everything marked up so I don't miss it later. I really like the Estes marking guide. One of the best non-essential tools I've purchased.

In my mechanic days, I remember a buddy telling me that it was fairly easy to get buy a helicopter that was partially built for cheap. It's rewarding to put all the pieces together, but the electronics at the end take forever and there is not much visible progress. I think of this stage as that in reverse. I feel like there is so much consideration and deliberation, prepping the parts that it is slow going. Once I get the motor mount in and the fins start to go on, it'll be looking like a real rocket.
I feel like I see often see builds where everything goes to plan and I don't ever have that happen.

You are soooo sooooo mistaken. You [we] only get to see what people want us to see. We never get to see the pain and suffering that we all know happens on lots of builds, to at least some extent. Nothing ever goes to plan, trust me. I have been building HPR's since 1993 and while my builds usually go pretty darn well, I still struggle with some things and always get bitten a little bit somewhere.

Keep plugging away and eyes on the prize.

Good idea finding a local park. That is far more common than you might realize. I have seen people painting home furnishings while out on bike rides before; on the prairie paths and at the local schools. There are lots of renters these days and its pretty common for people that have hobbies that their living accommodations clash with a bit. We all pay taxes so using a little of the outdoors we pay for, I think is A-OK. Obviously within reason but even still. If a group of people can have half their car torn apart in the Autozone parking lot, then you should be able to do a little rattle can magic at the park or in a parking lot somewhere.
Lot's of updates and too many pictures. I've gotten behind.

For the nose cone, I wanted to secure it with shear pins. With my last rocket, I secured the nose tip to the bulkhead with a threaded rod and capped it with the eye bolt. With that setup, I was able to have the shear pins inside the cone, but for this one I just placed the bulkhead back a bit. I was initially going to use PEM nuts, but my TAPs called it overkill, so the nose becomes pretty simple.
IMG_4449 2.jpegIMG_4450 2.jpeg

I have a good supply of West systems epoxy, so I use that for most applications, sometimes substituting JB weld if I only need a touch. Adding in the silica creates some texture, so once I get to the fin fillets, I'm going to use the proline 4500.
Disaster strikes That whole flange mount attempt? Didn't quite work out.


I had a 3 stack of centering rings and was intending to tap threads into it to secure the bolts. Used the casing to center the flange and felt pretty good about the fit. Drilled through all 12 holes and still looking good.

So where did I go wrong? I didn't secure the 3 together before I started drilling.

The holes were not centered or consistent when I started my tap, which led to me stripping the fiberglass from several holes. No problem, I'll just fill them with epoxy, redrill and retap once I get them secured to the motor mount. Let me go ahead and add that now. Just poor quality all around. The rings were not tightly secured, not flush with the end and worst, I wouldn't have been able to do my internal fillets without drilling into the body.

Well, where do we go from here? Could I have salvaged it? Probably. I wanted to focus my effort in getting it the way I wanted though. Got a new 3"x24" airframe for the motor mount from wildman and now the original retainer will fit! Sanding, measuring, test fitting done, we're going to move on to motor mount v2.

Forward centering ring prep for recovery harness.
Last edited: