bandman444
Well-Known Member
Introduction:
Nine years ago (2014), I earned my Level 3 certification on a 5x upscale Madcow Rocketry Squat. Since witnessing my first Squat fly at LDRS 29 (infamously), I've been enamored by their goofy aspect ratio. Over the last 15 years, I've built big ones, little ones, grass-covered ones, and carbon fiber ones. And I just love them! We can all relate to our desire to take our favorite design and dream of making it bigger. My hope is that this thread act as a place for curious rocketeers to ask tons of questions and learn as much as possible about building and flying the largest rockets our hobby offers. Ask away!
Introducing the build log for my LDRS 41 and BALLS 31 project:
Specs:
This project started last year when a friend joked online about me rebuilding my L3 for its 10-year anniversary. After a big family move from AZ to WA, I thought I might finally have the space to rebuild. I spent countless hours in CAD testing out designs for the fin construction and the nosecone design. After 6 months of thinking about it, it became time to give it a go. But rebuilding my L3 as is didn't feel like that much fun for some reason, so why not bigger? My L3 was 20", so this time, let's go for 24"!
After LDRS was announced last year, I knew that I would aim to fly this project at Bong. This presented some unique challenges and opportunities. The main challenge was to keep to the Complex N motor limit for commercial motors. I wanted to do EX, but the 10,240N-sec limit with no clusters would make that extremely tricky at best. So, commercial motors up to 20,480N-sec it is. How heavy could this thing be?
Pre-build mass budget: <200 pounds (dry)
- Fins: 30 pounds
- Body Tube: 40 pounds
- Recovery: 20 pounds
- Motor Mount: 20 pounds
- Paint: 5 pounds
- Nosecone: 50 pounds
Total: 165 pounds
This gave me roughly 35 pounds of wiggle room for the inevitable mass growth. Based on my CAD predictions, I suspected that most of the unknown mass would be in the nosecone construction, and therefore, the added mass moves the CG farther forward.
Documenting the Process:
One of my main goals for this project was to document my thought process, my design process, and my build process. I want this thread to serve as an example of one way to build a project like this. Everyone has their own ways of doing things, and their own personal (and professional) experiences. A lot of my construction ideas come from an amalgam of other projects I've seen, my own rocketry experience, and my woodworking/mechanical background. I want to always learn new techniques and try something new, but with many of the techniques I showcase for this build, I test them out on a much smaller scale before trying it here. No project this scale can have assured success, but you can test and calculate the scenarios that are the most risky and use your experience to do the best you can. Always solicit advice from others you trust. Especially with projects of this scale, remember to test safely and fly safely.
So let's dive into the design! Off to OpenRocket
OpenRocket is king for playing with a rocket concept. This gave me easy tools to scale up the model and mess with the overall vehicle layout. I can mess with the materials and thicknesses to start getting a very rough idea for weights and where I will need to balance this thing. I can, of course, play around with motor combinations, but at this point, that is more for fun than progress. But once I started getting the size of the rocket where I wanted it, it was time to CAD! Note: because this is a short and squat rocket, the use of the imaginary drag cone is needed to more accurately portray the vehicle's actual CP.
I use Fusion 360 as my CAD package. Its ability to export .dxf files of sketch planes and .stl files of solid objects fulfill my needs. I started with a rough 3D model that basically reflects the OML (outer mold line, meaning the outside shape) of the project. Here I can gently tweak dimensions, adjust sizes, and overall get a feel for the scale of the project. For a long time, this image was the face of the project. It was the inspiration as well as the nightmare.
The most time-consuming step was the detailed CAD design. I rarely find it valuable to model every nut and bolt, but depending on the concept, nuts and bolts were painstakingly added to convey design intent and visual concepts.
In CAD, I can develop and understand various requirements for the rocket and how they interact with one another. For instance, the fins for this project NEED to be removable to allow for storage and transport. The body is huge, the fins are huge. Even with my trailer, this rocket won't fit in the trailer with its launch pad if it has the fins on.
I thought it would look nice to not have too much exposed hardware around the fins, and the riveted solution from my L3 Squat build I found not to be as secure as I would have liked. I really liked the internal channel using angle aluminum extrusion. So I doubled down on that and bolted 8" pieces of angle aluminum to the forward and aft centerings. (4 total pieces per fin, 12 total amongst the 3 fins)
The two centering rings were cut out of 3/4" plywood on my Maslow CNC machine (a pretty cool machine for cutting wood with low accuracy, speed, and cost). I went ahead and made the center hole ready to take a Pro150 ~6.33" motor tube and then six 98mm holes for motor tubes if I choose to install them in the future. (Let's pretend they are just "lightening holes" for now)
Video of Maslow CNC machine in action!
Body Tube:
The body tube is the most straightforward part of this build. The tube is 24" concrete form from a local store.
The concrete form is just basic cardboard, and I've learned from other projects that if you just start applying fiberglass, the tube soaks up so much epoxy that your fiberglass gets dry. To combat this, I apply a coat of epoxy directly to the body tube before
fiberglass, let it cure, and then apply fiberglass.
Because these tubes are designed to have a good internal finish and not a smooth exterior, the grooves need to be sanded down prior to adding fiberglass. So the raised spiral was sanded down, and then I can start on the fiberglass layers.
The fiberglass is more to protect the rocket during transport than actually needed for flight, so a single layer of 6oz glass with US Composites epoxy is all I did. (I use different colors of epoxy to denote which batch it is from)
A little bit of trimming and sanding later, and the body tube was complete.
Nine years ago (2014), I earned my Level 3 certification on a 5x upscale Madcow Rocketry Squat. Since witnessing my first Squat fly at LDRS 29 (infamously), I've been enamored by their goofy aspect ratio. Over the last 15 years, I've built big ones, little ones, grass-covered ones, and carbon fiber ones. And I just love them! We can all relate to our desire to take our favorite design and dream of making it bigger. My hope is that this thread act as a place for curious rocketeers to ask tons of questions and learn as much as possible about building and flying the largest rockets our hobby offers. Ask away!
Introducing the build log for my LDRS 41 and BALLS 31 project:
Project SaSQUATch
Specs:
- Diameter: 24 inches (610mm)
- Height: 14.5 feet (4.4m)
- Dry Weight: 180 pounds (82kg)
- Motor mounts: 1x Pro150, 6x 98mm
- Recovery: 1x 28 ft diameter C-9 parachute or 1x QS-550 toroidal tandem reserve chute
This project started last year when a friend joked online about me rebuilding my L3 for its 10-year anniversary. After a big family move from AZ to WA, I thought I might finally have the space to rebuild. I spent countless hours in CAD testing out designs for the fin construction and the nosecone design. After 6 months of thinking about it, it became time to give it a go. But rebuilding my L3 as is didn't feel like that much fun for some reason, so why not bigger? My L3 was 20", so this time, let's go for 24"!
After LDRS was announced last year, I knew that I would aim to fly this project at Bong. This presented some unique challenges and opportunities. The main challenge was to keep to the Complex N motor limit for commercial motors. I wanted to do EX, but the 10,240N-sec limit with no clusters would make that extremely tricky at best. So, commercial motors up to 20,480N-sec it is. How heavy could this thing be?
Pre-build mass budget: <200 pounds (dry)
- Fins: 30 pounds
- Body Tube: 40 pounds
- Recovery: 20 pounds
- Motor Mount: 20 pounds
- Paint: 5 pounds
- Nosecone: 50 pounds
Total: 165 pounds
This gave me roughly 35 pounds of wiggle room for the inevitable mass growth. Based on my CAD predictions, I suspected that most of the unknown mass would be in the nosecone construction, and therefore, the added mass moves the CG farther forward.
Documenting the Process:
One of my main goals for this project was to document my thought process, my design process, and my build process. I want this thread to serve as an example of one way to build a project like this. Everyone has their own ways of doing things, and their own personal (and professional) experiences. A lot of my construction ideas come from an amalgam of other projects I've seen, my own rocketry experience, and my woodworking/mechanical background. I want to always learn new techniques and try something new, but with many of the techniques I showcase for this build, I test them out on a much smaller scale before trying it here. No project this scale can have assured success, but you can test and calculate the scenarios that are the most risky and use your experience to do the best you can. Always solicit advice from others you trust. Especially with projects of this scale, remember to test safely and fly safely.
So let's dive into the design! Off to OpenRocket
OpenRocket is king for playing with a rocket concept. This gave me easy tools to scale up the model and mess with the overall vehicle layout. I can mess with the materials and thicknesses to start getting a very rough idea for weights and where I will need to balance this thing. I can, of course, play around with motor combinations, but at this point, that is more for fun than progress. But once I started getting the size of the rocket where I wanted it, it was time to CAD! Note: because this is a short and squat rocket, the use of the imaginary drag cone is needed to more accurately portray the vehicle's actual CP.
I use Fusion 360 as my CAD package. Its ability to export .dxf files of sketch planes and .stl files of solid objects fulfill my needs. I started with a rough 3D model that basically reflects the OML (outer mold line, meaning the outside shape) of the project. Here I can gently tweak dimensions, adjust sizes, and overall get a feel for the scale of the project. For a long time, this image was the face of the project. It was the inspiration as well as the nightmare.
The most time-consuming step was the detailed CAD design. I rarely find it valuable to model every nut and bolt, but depending on the concept, nuts and bolts were painstakingly added to convey design intent and visual concepts.
In CAD, I can develop and understand various requirements for the rocket and how they interact with one another. For instance, the fins for this project NEED to be removable to allow for storage and transport. The body is huge, the fins are huge. Even with my trailer, this rocket won't fit in the trailer with its launch pad if it has the fins on.
I thought it would look nice to not have too much exposed hardware around the fins, and the riveted solution from my L3 Squat build I found not to be as secure as I would have liked. I really liked the internal channel using angle aluminum extrusion. So I doubled down on that and bolted 8" pieces of angle aluminum to the forward and aft centerings. (4 total pieces per fin, 12 total amongst the 3 fins)
The two centering rings were cut out of 3/4" plywood on my Maslow CNC machine (a pretty cool machine for cutting wood with low accuracy, speed, and cost). I went ahead and made the center hole ready to take a Pro150 ~6.33" motor tube and then six 98mm holes for motor tubes if I choose to install them in the future. (Let's pretend they are just "lightening holes" for now)
Video of Maslow CNC machine in action!
Body Tube:
The body tube is the most straightforward part of this build. The tube is 24" concrete form from a local store.
The concrete form is just basic cardboard, and I've learned from other projects that if you just start applying fiberglass, the tube soaks up so much epoxy that your fiberglass gets dry. To combat this, I apply a coat of epoxy directly to the body tube before
fiberglass, let it cure, and then apply fiberglass.
Because these tubes are designed to have a good internal finish and not a smooth exterior, the grooves need to be sanded down prior to adding fiberglass. So the raised spiral was sanded down, and then I can start on the fiberglass layers.
The fiberglass is more to protect the rocket during transport than actually needed for flight, so a single layer of 6oz glass with US Composites epoxy is all I did. (I use different colors of epoxy to denote which batch it is from)
A little bit of trimming and sanding later, and the body tube was complete.
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