R2

Recently I finished R2, a scratchbuilt somewhat over-engineered BT60 sized 18mm model, and got in its first two flights at the April 2021 PARA launch. It came out pretty much exactly how I had envisioned, and wound up with a very satisfying second flight after a nearly catastrophic inaugural flight.

R2 finished (one side).

R2 finished (one side).

Construction

R2 began with modeling in OpenRocket, inspired by and based on a BT60 tube and nosecone from a ~26 year old Estes Designer’s box. The design has a payload compartment just for fun, through-the-wall papered fins that interlock with the motor mount rings, redundant Kevlar threads running from the motor mount to the shock cord, conformal angled launch lugs, and a couple other unnecessary touches. I just wanted to build a big, substantive feeling, low power rocket, and experiment with some construction techniques for strength and redundancy. I wasn’t too concerned about weight or overkill features for a rocket intended to fly on C motors at most. Slow, heavy-feeling flights would be just fine (provided stability was good & flights safe).

Modeling R2 in OpenRocket.

Modeling R2 in OpenRocket.

Other than the tubes, nosecone, and parachute, R2 was built up with a mix of 3D printed and CNC cut parts. The boattail was printed on a Wanhao i3+ in ABS for heat resistance, and the launch lugs the same for convenience. The tube coupler is in PLA printed on an Ender 3. Since the coupler isn’t exposed to significant direct heat I’m not too worried about the PLA, but in hindsight I wish I’d done it in ABS as well just to have no doubts about it sitting in a car trunk on a hot day. The fins, centering rings, and bulkheads were cut from 1/16″ balsa using a Cricut Maker. Strength was added by papering the fins with adhesive paper and coating the edges with CA. Rings and bulkheads were beefed up with a PVA glue coating.

Drawing the fin pattern in OpenSCAD.

Drawing the fin pattern in OpenSCAD.

3D printing the boattail.

3D printing the boattail.

All R2's pieces ready for assembly.

All R2’s pieces ready for assembly.

Marking the tube for the fin slots.

Marking the tube for the fin slots.

Gluing together a combo coupler and payload bay bulkhead.

Gluing together a combo coupler and payload bay bulkhead.

R2 fully assembled.

R2 fully assembled.

Finishing

Painting was done with Montana spray paints over a Rustoleum primer sanded down. The Montana paints go on kind of thick & heavy, they’re made for graffiti art, but because of that lend themselves to consistent, smooth, very opaque feeling finishes. The big “R2” lettering was done using vinyl stencils and spray paint while the other details are custom vinyl stickers. The stickers were printed on an inkjet and then they & the stencils cut out with the Cricut. The “SPACECRAFT” icon is a stock art logo I bought as tongue-in-cheek representation of a generic NASA/ESA/whatever. The US, Canadian, and Korean flags were chosen just because they look cool, it doesn’t reflect any actual mission partnership or such.

Really my only disappointments with the rocket came in finishing. One of the stickers on the nosecone smudged a bit in application. I also didn’t think enough about the striping on the payload bay, so there are 10 stripes instead of 8 and they don’t line up exactly with the quartered paint scheme of the body. But overall I think it came out well and looks real cool in the background on video calls.

R2 finished (other side).

R2 finished (other side).

R2 finished (nosecone detail).

R2 finished (nosecone detail).

First Flight—Disaster!

There isn’t anywhere immediately near home to fly anything larger than maybe a 1/2A, so the first R2 launch had to wait until the next PARA meet. I got a good slow motion video of the launch itself, there was a successful parachute ejection, but then disaster: It was a windy day and the rocket drifted into trees immediately behind us.

R2 on the launchpad for its debut.

R2 on the launchpad for its debut.

Ignition!

Ignition! Photo by Mike S.

Up in a tree!

Up in a tree!

Fortunately the club has a telescoping pole with which we were just barely able to reach the rocket. It took some finagling, but eventually we were able to get hands on the rocket. The shock cord stretched a ridiculous amount so it took some effort even beyond that point, but we were eventually able to rip the rocket down.

Getting out the rescue pole.

Getting out the rescue pole.

Hooking the line.

Hooking the line.

Pulling R2 off the tree.

Pulling R2 off the tree.

Second Flight—Success!

Initial damage assessment indicated the parachute was ripped in several places, one shroud line was still in the tree, and a bulkhead was gone. All in all R2 was in reasonable shape but I assumed I wouldn’t be able to fly it again that day. I kept looking at it as the day went on though and really wanted to get in another flight. So between helping Alice launch rockets and other goings-ons, I got to work. The parachute got more or less taped up, lines replaced and retied, the remaining bulkhead reinforced, and so on. It all came together at literally the end of the meet as people started talking about packing up the launch pads. With the very last launch of the day, R2 pulled off a picturesque second flight, up to 365 feet and almost back to my hands.

Staged for second launch.

Staged for second launch.

Wrap

R2 came out great. It looks exactly as I wished, it was a fun build, and it had a perfect second flight with just enough drama beforehand to accentuate the success. I don’t know how much more I’ll fly it and risk R2 getting captured for good by those hungry trees! But it flew well, looks real nice in my office, and was a good little project.

R4 and R6

This past weekend we made our own micro-rocket kits to build & launch in the neighborhood. I’ve been working on a design framework and CAD tools to produce little rockets for which Alice can do a bunch of the construction herself. There’s only a few steps, the fins are self-aligning, etc.. Besides basics like tube and shock cord they’re made of 3D printed and CNC cut parts. Alice chose parameters for her rocket (number & shape of fins, etc.), R6, and we worked together to tune them in a simulator to get the dynamics right. She made a schedule for the morning to get it painted in time to dry before the launch and it came out excellent.

Then we put together a kit, R4, for Brett and I literally ran it over to his house so he could furiously put it together for the planned launch two hours later (the assembled one pictured here is my copy).

Brett’s rocket also came out amazing! It flew as well as it looked too, with a straight ascent, clean streamer deployment, and soft landing. Alice also had a good flight with her new rocket, and it was unfazed by colliding with a fence after drifting a bit.

Model rocketry is a socially acceptable and even popular hobby.

Unfortunately we lost two rockets this day. At the PARA launch we had been gifted two micro-rockets by a guy to whom I had given one of my custom launch pad adapters. One was a little glider that looped around and around beautifully in the changing winds but flew at least a quarter mile away and most likely landed on the rooftops it was last seen over. The other, just barely seen here as a small yellow line at the center of the image, was an excellent scratchbuilt micro-Skywriter, a faithful cardstock mimicry of a classic #2 pencil. It flew incredibly high for the tiny MicroMaxx motor and drifted on the descent into the rocket eating maw of a high tree. An extensive search for the glider turned up nothing, but Alice is keen to check on the pencil next time we go to the field.

R3

R3 in OpenRocket.

The past week has also seen half a dozen launches of R3, my first micro-rocket. It’s an initial experiment with very low power motors amenable to small neighborhood launch sites. Quest MicroMaxx 6mm motors are used, equivalent to 1/8A and with less than a second of burn and no delay before ejection.

Unlike most micro designs I’ve seen so far, the body is a BT5 instead of a T-MM. This gives it a nice, solid look to my eyes more akin to a downscaled typical sport rocket than a straw with fins. R3 was designed in OpenRocket in order to hit a weight target of around 4g unloaded, which seems to be a common ballpark for micro-rockets, and assure stability. The elliptical fins are 1/16″ balsa drawn in Inkscape and cut with a Cricut Maker. An elliptical nosecone, conformal 1/16″ launch lug, and centering rings for the motor mount were modeled in OpenSCAD and 3D printed. The rings are ABS and the other parts PLA. A T-MM tube is used in the motor mount to insulate the rings from the motor, though this is almost certainly unnecessary. A small piece of music wire serves as the engine block. Recovery system is a streamer cut from a Mylar emergency blanket. This however has so far never deployed successfully and remains a work in progress. The finish is a quick spray painting; the masking came out less crisp than I’d prefer, but I like the styling overall.

Nosecone modeling in OpenSCAD.

Cutting the fins.

Assembled motor mount.

On the pad for the inaugural launch.

Having forgotten to taken a picture once built—not at all because we were rushing out the door late for the launch as the spray paint was still drying—I fortunately at the last moment thought to to take a launchpad photo before it started sustaining damage. Recovery system design & packing in such a small rocket will take some more thought. The rocket survived one flutter landing and one ballistic landing on grass, then took a big hit from an asphalt landing after the streamer repeatedly failed to deploy. It was easily repaired though and flew again several times at yesterday’s PARA520 launch. The new, revised streamer still only partially deployed but the rocket had a reasonably soft dirt landing each time. All of the flights have otherwise, even in modest wind, been very straight & true and enjoyable to watch.

Ballistic landing.

Disastrous asphalt landing.

While the streamer will take some more work, overall this is a very satisfying design. It has a nice classic look to it, in a tiny form that we can easily launch from local ballfields. I expect to design and build more micros based on a BT5 like this.

Also very satisfying is the 1/8″ to 1/16″ launch rod adapter I’ve been designing and 3D printing. This lets you fly micros from a standard launcher. Unlike more traditional model rockets wherein a plug keeps the igniter attached for launch, MicroMaxx rockets are typically supported on the rod by the igniter itself. The igniter is set in place and then the rocket slid down the rod on top of it rather than the other way around. To facilitate this for rockets of varying diameter, my adapter design has a little sliding tray with a cup for the igniter. After ~2 iterations it’s trivial to print, attaches and adjusts quickly & smoothly, and provides a stable platform. More on this to come.

Micro launch rod adapter.