Launch Lab Rocketry - Bullet Bobby

[NateB]

I just bought the Bullet Bobby kit from Launch Lab Rocketry for my son as he has discovered a classic game which inspired the design of this rocket. It is a short and stubby kit that should be fun to launch in the park and land close to the pad. This kit comes with everything you need except glue and paint. It has nice instructions and there were even a few pieces of candy in the box.



I started by weighing everything and building a sim file for Open Rocket. I'm only going to stray from the instructions to use mini rail buttons instead of the included lug and I will also paint a little thin epoxy on the outside of the nose cone. This technique was noted in the instructions for my Thor. I do not know if it is needed for strength on the 3D printed parts, but it did make filling and painting the grooves from the printing much, much easier. The added weight of the epoxy is small, but will be helpful on this design.

 

[DuctTapeandRocketFuel]

Looks like a fun build. Take plenty of pictures as you build it.

 

[NateB]

The motor mount is built in the standard way with wood glue filets around the joint between the motor mount tube and the centering rings. On this kit, note the forward centering ring has a slot cut for the shock cord and the center ring has a notch cut out for the engine hook. The thrust ring sits flush with the motor mount on top of the engine hook.

 

[NateB]

These steps can be skipped and aren't part of the instructions for the kit.

I filled the spirals with Bondo Putty and scraped the excess away. I looks like I cut my finger in the process, but it's just the Bondo. This isn't one of my favorite steps, I'm sloppy about it, and I prefer building with fiberglass anyway. I'll lightly sand the body tube before I attach the fins.






I also mixed up a small amount of thin epoxy and painted a light layer on top of the nosecone to fill the gaps from 3D printing and provide a nice, smooth surface for finishing. Once fully cured, it will still need some sanding before priming.

 

[SCooke123]

Looks good so far!!

 

[messedupryan]

I also mixed up a small amount of thin epoxy and painted a light layer on top of the nosecone to fill the gaps from 3D printing and provide a nice, smooth surface for finishing. Once fully cured, it will still need some sanding before priming.

That looks so good!

 

[NateB]

Next steps, tie the shock cord to the motor mount, secure the knot with a little glue, and thread the shock cord through the slot on the centering ring.



Place a bead of glue on the inside of the body tube where the centering rings will meet. Slide the motor mount assembly in place and then add another filet of glue on the exposed forward and rear centering rings. This is easy with large body tube.

 

[FlyBy01]

Nice build, I just ordered one myself.

 

[Sooner Boomer]

Next steps, tie the shock cord to the motor mount, secure the knot with a little glue, and thread the shock cord through the slot on the centering ring.

View attachment 455968

Place a bead of glue on the inside of the body tube where the centering rings will meet. Slide the motor mount assembly in place and then add another filet of glue on the exposed forward and rear centering rings. This is easy with large body tube.
View attachment 455969

All that glue on the centering ring is going to cause a "pucker" when it dries. I've seen it many times with large diameter rockets like the Fat Boy and Big Daddy. Here, it's *very* noticible in the aft centering ring, less so in the forward one. Notice the "hump" of the body tube along the fin/body line.



This is only a problem with carrier-evaporation curing glues. Because they shrink when they cure(dry), they draw together. Epoxies and other catalyzer-cured glues don't shrink, and don't cause this problem.

 

[NateB]

Fins are on today. First the location was marked using the included tube marking guide.


I also marked the fins where they will sit against the rear of the body tube.



Just like the instructions state, place a bead of wood glue on the fin, place the fin in position, and quickly remove. Let the glue set up for a couple of minutes and place the fin back into position and carefully align it. Hold in position for 30 seconds or until the glue holds the fin in place. Repeat, being careful not to knock the other fins out of alignment.



I eyeballed alignment. I like the fin guides from Badass Rocketry, but don't have one in this size. Not perfect, but close enough.

 

[NateB]

All that glue on the centering ring is going to cause a "pucker" when it dries. I've seen it many times with large diameter rockets like the Fat Boy and Big Daddy.

Noted. I don't see any bulging this time, but I can see how it might happen in some cases.

 

[Daddyisabar]

A little diluted wood filler or bondo, sand and it will come right out. Next time don't use so much wood glue at once.

 

[Daddyisabar]

You can always use a small drop of CA at each end of the root edge of the fin to quickly set in place. Rough up the tube before gluing. Then nice fiilet with trim glue. Bullet Bobby's fins will break off. Superglue them back on and load up another D21 and rip off the pad. Bullet Bobby, THE MAGIC MAN, now you see him, (press the launch button,) now you don't! The crowd will love it!

 

[NateB]

Bullet Bobby's fins will break off. Superglue them back on and load up another D21 and rip off the pad.

That reminds me. I should have said to make sure you trace a fin to make a template before you build the rocket. I think if you fly this one frequently, you'll need to make a replacement fin sooner than later.

 

[Daddyisabar]

That reminds me. I should have said to make sure you trace a fin to make a template before you build the rocket. I think if you fly this one frequently, you'll need to make a replacement fin sooner than later.

Bullet Bobby has a tendency to land in parking lot breaking a fin. A spare is always a good idea. Another good idea (the RSO might not think so) would be to do a naked CHAD stage D12 0 booster motor beneath a C6 5. That heavy printed nose cone should be enough weight up front. If that works go for an E12 0 booster! Bullet Bobby can take the abuse!

 

[Sooner Boomer]

A little diluted wood filler or bondo, sand and it will come right out. Next time don't use so much wood glue at once.

Oh, yeah, it's fixable. Not and end-of-the-world problem. Just don't be surprised whrn it happens, and know why.

 

[BEC]

Ryan Winslow (@Flyfalcons) brought Bullet Bobby to our little club launch last Saturday. He turned in a very nice flight on a B6-2 (small, rough site).

 

[BABAR]

Any problems with chute deployment? The compartment is really wide put really short. Wondering if a plug or plunger or piston style separation between motor mount and forward compartment may help?

 

[kuririn]

Any problems with chute deployment? The compartment is really wide put really short. Wondering if a plug or plunger or piston style separation between motor mount and forward compartment may help?

If I may interject,
lots of room in the nose cone for the laundry and clay weight underneath.

 

[cwbullet]

Great kit!!!! I order one and it came very quick and well packed.

 

[BABAR]

If I may interject,
lots of room in the nose cone for the laundry and clay weight underneath.
View attachment 457023

INTERESTING!

@NateB , can you show a pic of how the shock cord is attached to the nose cone?

Not trying to derail this thread. I built something like a Fat Boy with a BT-80 cone that looks like this, but my cone has a shoulder and a cap, so I don’t HAVE all that extra room, and the broad width and minimal length of the body tube makes it hard to get a good seal of wadding between the motor mount and the chute.

I just might drill a couple dowels into the front of the cone, cut off the base of the shoulder, attach the cord to the dowels and some gorilla glue, and take advantage of all that currently wasted space.

thanks!

 

[rbeckey]

I have had mixed results getting a chute to deploy from inside the NC. Even tying the shrouds off closer to the tube didn't work out all the time. Maybe just poor luck. I'll be interested to see if this model has an issue.

 

[DigBaddy]

I've also acquired one of these. My wife wants to build it; with assistance as she's new to this. But, she wanted this kit to exist and sure enough it does

INTERESTING!

@NateB , can you show a pic of how the shock cord is attached to the nose cone?

Not trying to derail this thread. I built something like a Fat Boy with a BT-80 cone that looks like this, but my cone has a shoulder and a cap, so I don’t HAVE all that extra room, and the broad width and minimal length of the body tube makes it hard to get a good seal of wadding between the motor mount and the chute.

I just might drill a couple dowels into the front of the cone, cut off the base of the shoulder, attach the cord to the dowels and some gorilla glue, and take advantage of all that currently wasted space.

thanks!

Could cut off the base of the shoulder and do a bulkhead inside the cone like a lot of folks do (myself included) on the Big Daddy. I've got a scratch build in the queue that's going to go this route again but BT60-based and stubby,

 

[kuririn]

If you load the bulk of the kevlar shock cord between the chute and the nose cone the mechanical action of it splaying out at ejection should pull the chute out. Also attaching the chute 1/3rd of the way down the cord instead of directly to the nose cone eye should also help
I have the shroud lines around the chute for storage, but for flight I put them inside the nylon then fold it up.
Close up of the shock cord tied off to the nose cone eye and the loop tied on the kevlar with the chute and a snap swivel attached.


Per instructions half of the nose cone clay is taped to the nose cone pending maiden flight. More may have to be added later.

 

[CalebJ]

I also mixed up a small amount of thin epoxy and painted a light layer on top of the nosecone to fill the gaps from 3D printing and provide a nice, smooth surface for finishing. Once fully cured, it will still need some sanding before priming.

View attachment 455719

What epoxy are you using to paint onto the nose cone?

 

[BABAR]

If you load the bulk of the kevlar shock cord between the chute and the nose cone the mechanical action of it splaying out at ejection should pull the chute out. Also attaching the chute 1/3rd of the way down the cord instead of directly to the nose cone eye should also help
I have the shroud lines around the chute for storage, but for flight I put them inside the nylon then fold it up.
Close up of the shock cord tied off to the nose cone eye and the loop tied on the kevlar with the chute and a snap swivel attached.
View attachment 457059

Per instructions half of the nose cone clay is taped to the nose cone pending maiden flight. More may have to be added later.

so the attachment is a molded hook on the edge of the shoulder?

 

[kuririn]

so the attachment is a molded hook on the edge of the shoulder?

More like a half circle with an eye.

 

[BEC]

Any problems with chute deployment? The compartment is really wide put really short. Wondering if a plug or plunger or piston style separation between motor mount and forward compartment may help?

He only flew it once, but it worked perfectly. That the 'chute is nylon will help over the usual plastic in a model this size. That flight is just after 22:00 on this video that Ryan did:

 

[NateB]

What epoxy are you using to paint onto the nose cone?

I used US Composites Epoxy with the 635 Thin Resin.

 

[shawn_rocket]

Ordered. Can't wait to build it. Looks awesome! Ryan said in his review..."the aerodynamics of a trash can lid..."! 'Bout fell of my chair!