Binder Design Excel Plus 54mm Build Thread

It finally came in the mail! I plan on putting this together for my L1 and L2 certification flights. Beautiful design and excellent packaging. I can't wait to assemble it. Between work, kids, and being really careful with my work, it's probably going to take me quite a while to put it all together.

I have a CTI 38mm with an adapter I'll probably use for L1. I'll drop in my CTI 54m casing for L2 with dual deploy. I think I'll omit the electronics and use motor ejection with single deploy for my L1 flight.

Here's the dry fit glamour shot. :-D

mccordmw said:

It finally came in the mail! I plan on putting this together for my L1 and L2 certification flights. Beautiful design and excellent packaging. I can't wait to assemble it. Between work, kids, and being really careful with my work, it's probably going to take me quite a while to put it all together.

I have a CTI 38mm with an adapter I'll probably use for L1. I'll drop in my CTI 54m casing for L2 with dual deploy. I think I'll omit the electronics and use motor ejection with single deploy for my L1 flight.

Here's the dry fit glamour shot. :-D

View attachment 280715

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Sounds like a plan, but go ahead and send the electronics along for the L1 flight just replace the drogue with the main (switch main and drogue locations if possible), then use motor eject as a backup or primary and the altimeter as a backup or primary, then you have redundancy and practice too! My :2: of course!

Another thing you could do is pick up one of John Bean's new Jolly Logic Chute Release Devices. It reefs the parachute. Motor Ejection splits the rocket, then at the designated altitude the device releases its hold on the parachute, and you get the effect of a DD without having to use a 2nd charge.

Had some time this weekend to myself, so I got to starting my build.

First up: Prep all the surfaces.

First, I sanded down the very minor ridges on the nosecone using a 320 grit sanding sponge until it was all glass-smooth. Can't really tell the difference by picture here, so I skipped it.

Next, I filled the body grooves with Elmer's Carpenter's Wood Filler. Excess wood filler was scraped off using a 1" wide metal putty knife. I prefer that to an old credit card. That was finished with a light sand again using the 320 grit sanding sponge. The results (note the shameless plug for the Rocketry magazine :wink: ):



After the surfaces are smooth to the touch, I moved on to reinforcing the edges. All exposed tube edges were strengthened by soaking in 1/4" of cyanoacrylate supeglue. I prefer Loctite Ultra Liquid Control for an easy to handle tip. Edges all look like this:



Next up. rounding off the fins and sealing those edges. Another day...

I'm looking at the motor mount and its eyebolt and thinking...

I was going to attach some kevlar thread to the bolt to have a sturdy system. However, zippering has me worried. I want to use this rocket for both L1 and L2 certifications plus other tests, so I want something that will last even if I have a higher speed deployment.

I think I might ditch the eyebolt on the top of the centering right and go with a 4-point kevlar harness that's "sewn" into the centering ring. Each hold will be sealed off with a dab of JB Weld. The whole harness is a single strand of 1.7 mm braided kevlar with 400 lb breaking strength.

https://www.amazon.com/gp/product/B00746VAU2/?tag=skimlinks_replacement-20

The 4-point system is then joined to a swivel at the top of the booster tube. Since it's a continuous thread, there's only one point to tie off; minimizing points of failure. This layout should mean any pulling in one direction would re-orient the tube and keep torque to a minimum; thereby making this a light, zipper-proof design. The swivel at the top also makes swapping out chutes super easy.

It should be stronger, more stable, and also lighter than a standard eyebolt system. Thoughts?

Are you really looking to shave that much weight off of the rocket? If it were me, I'd build it as strong as possible, get certified, then go for the uberlite rockets. With certification birds, you want them to go up, and down, and be easily recovered so you can get your certification, not sending it into the ionosphere where you may lose it, and have to try again.

I'm not so concerned about weight. This is more about a strong chute system that won't ever zipper. The weight thing is just a bonus I was pointing out.

The off center eyebolt is not the cause of zippering. While your method will shave some weight, it won't do anything to prevent a zipper at high speed deployment. The only true ways of preventing zippers are proper deployment speeds and true anti-zipper design using a coupler and bulkhead at the end of the booster section.

You can minimize the stress on the edge of the tube if you use a nomex sleeve around the harness that extends past the tube. Zipper fears are over-rated IMO. In my whole career of HPR, I've had one zipper. And I knew it was likely because I was using a SU motor with a longer delay than I wanted but that was all the vendor had.

Motor mount assembled. Aeropack retainer installed. Next, I inserted the mount and tacked in the fins with a light bead of JB Weld.
After the fins set, the body tabs were numbered and cut out. I'm currently waiting for the front entering ring to cure before moving on to the internal fillets. Progress!

For the fillets, I'm switching over to Rocket Poxy. It's easier to work with than JB Weld for me at least.

I'm still so sloppy with epoxy. Need more practice with it.

Last night, I had some free time, so I knocked out the internal fillets, and made sure all the rings and fins had solid epoxy connections to the motor mount. Fillets were done with Rocket Poxy. Here's the end result.



I've read a lot on tips and techniques for doing fillets, but one thing that still gets me is the actual application of epoxy to the surface. I use a craft popsicle sticks, but it's a pain to cleanly get the epoxy on the surface without putting down too much or having strings of epoxy drag all over the place and mess up the pretty look. I'm not worried about the internal part. That was just good practice. But I want to be much more careful when doing the external fillets.

Besides masking the area to keep it clean, how do people prefer to put down epoxy? Stick? Load it in a syringe? Gloved finger? I plan on masking the areas and using a cut down pvc tube wetted with isopropanol to drag out the fillets. CWF and sanding will hopefully make it all pretty-like. (In my head, I'm skilled at this. )

Next up; epoxy the motor mount into the airframe. Maybe tonight if I have time. This weekend is supposed to get to almost 70 degrees, so I'd like to get to a stage where I can do some priming. It was in the 20s and colder the last few days. Bleah.

Beautiful job on the beveling.

mccordmw said:

I've read a lot on tips and techniques for doing fillets, but one thing that still gets me is the actual application of epoxy to the surface. I use a craft popsicle sticks, but it's a pain to cleanly get the epoxy on the surface without putting down too much or having strings of epoxy drag all over the place and mess up the pretty look. I'm not worried about the internal part. That was just good practice. But I want to be much more careful when doing the external fillets.

Besides masking the area to keep it clean, how do people prefer to put down epoxy? Stick? Load it in a syringe? Gloved finger? I plan on masking the areas and using a cut down pvc tube wetted with isopropanol to drag out the fillets. CWF and sanding will hopefully make it all pretty-like. (In my head, I'm skilled at this. )

Click to expand...

As far as putting it down I simply pour it. Often with a bit of help from the coffee stirrer I used to mix it. The 30m epoxy + microbeads or Proline 4500 that I've use for fillets is still (barely) pourable when I apply it, not runny but it will still self-level given a few minutes. I first mask off both the body tube and fins where I want the fillet to stop (which is first determined by marking up the end of the PVC pipe I use with a sharpie then drag it along the joint to transfer some ink to the tube & fin), then I pour on the epoxy and shape/smooth it with the pipe (which was wiped with alcohol first). Some of the epoxy will squeeze out of the joint onto the tape, and if you let it sit too long it might flow back into the joint, so I make sure to remove the tape before this happens. Similarly I tape underneath the area I'm gluing (a bit past the end of the fins on the body tube), some of the glue that is shaped past the end of the fin will flow below the fin so I can just remove the tape to catch it rather than having to wipe anything off the tube itself.

Getting the area just above and just below the fins looking good has been the trickiest part for me, I've been very happy with the long run down the fin itself. Generally I'll go back with my finger and try to manually shape the ends once the epoxy is becoming less workable so that it won't flow on its own anymore.

Fin can is all dry and ready to re-insert into the body. Before inserting, I checked over all the construction to make sure there are no gaps in the epoxy. That's when I noticed that the front centering ring had shifted a little while the epoxy was curing. The front ring is tilted 2 degrees. That's not much, but will it affect the stability of the flight by causing the thrust of the motor to not be perfectly in line with the body?

This doodle is exaggerated to show what I mean...


A 2 degree tilt in the front ring will cause the front of the tube to not be perfectly centered, thereby tilting the whole motor mount and moving the thrust out of alignment. The question is, how critical is a 2 degree ring tilt. Math time! Oh man...trig. I haven't done that in decades. I had to Google the formula:

height = hypotenuse * sin(angle)

To show the extreme case, take the 4" centering ring and tilt it 45 degrees. Calculating the height, we get 2.8" (which would be awful). I'm bad at building, but not THAT bad.



So if my ring is tilted about 2 degrees, we have a new height of h= 4" * sin(88 degrees) = 3.99 inches. So I'm off center by one one hundredth of an inch.

Ok, I feel better now hashing this out on paper. If I was even off by 10 degrees, I'd still be within 7/100 of an inch.

So if I'm off by 10 degrees, the top of the mount is off by 0.07 inches which creates a new triangle from the top of the motor to the nozzle. I can use that to calculate how far off it throws the thrust from perfect alignment.

angle = tan^-1 (2 * height / motor length)
angle = 0.332 degrees off center thrust

Pfft. I'm not worried any more.

Rocket stuff is hard, man.

... but fun.

Use the tilted mmt in your favor. Line it up with one fin and remember which fin it is, then use this unexpected force vector in the x direction to counter any forces due to wind.

mccordmw said:

Pfft. I'm not worried any more.

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Yeah, you won't see any effect from it because if one side is tilted up, the other side is tilted down an equal amount. Thus self centering it.

Bottom rail guide is in. I deviated from the instructions on this. Before inserting the completed fin can, I drilled a hole 1 cm forward of the bottom centering ring and hardened the hole with CA. The bottom rail guide was inserted in here with a tiny drop of Rocket Poxy to hold the guide to the body. On the inside of the tube, I used a larger drop of Rocket Poxy to hold the screw to the body. The extra epoxy on the inside makes me feel safer.

I could have gone by the instructions and installed the guides after the fin can was put in, but then I couldn't get to the bottom one for internal reinforcement. I could add more epoxy to the outside for security, but I just don't like that aesthetic. I like crisp edges from the rail guide to the body. I'll do the same to the top rail guide later.

Once the bottom rail guide is done curing, I'll put in the fin can and upload all the pics.

Mark,

Been following along here and wanted to know how you went about rounding the fins?

Had a nice amount of time this weekend to work on my build and go through the pictures. As I mentioned, I put in the delrin rail buttons before inserting the fin can. The rear rail hole was drilled 1 cm forward of where the rear centering ring will be when the fin can is inserted. The forward rail hole was drilled as close to the CG as possible. That put it around 2.5" down from the top of the body tube. However, that would put it through a coupler, so that won't work. I moved the drill spot down to 4" from the front. Holes were drilled and reinforced with thin CA. After insertion, a #10 nut was threaded on to the screw and permanently attached with epoxy.

Pic of the front rail button screw with epoxy. Note, the drips you see are the thin CA I used to harder the ends of the body tube. I put it all on too thick, so it ran and had to be sanded down a little to get the couplers to fit. Next time, I'm going to use a wood lacquer that brushes on, soaks in, and hardens like a rock. Should give me cleaner results. I'll save the pricier CA to harden screw holes.



The drogue shock cord was tied off to the eyebolt and pulled back through the motor mount to keep it clear of the epoxy.

Epoxy was spread in a 3/4" wide band on the inside of the body tube where the top of the fin slots ended. That should give enough smear to affix the front centering ring well while building up a nice fillet on the top of it. The fin can was inserted just enough for the front centering ring to clear the bottom 2" of the tube. Then a 1/2" wide band of epoxy was spread along the bottom inside to give a good attachment point and fillet to the bottom centering ring. A thin bead of epoxy was spread along the thrust plate edge that will meet the body tube, and the whole thing was slid back in. I use zip ties to hold the tube together tightly for a good seal. I prefer that over rubber bands or string since the epoxy doesn't want to stick well to the zips. Makes for easy removal if I got sloppy with the epoxy.



After the fin can cured overnight, I re-inserted the numbered tabs that I cut out earlier. Those were simply glued back in place with a small drop of phenolic wood glue. No pics.

The front centering ring had a good fillet build up, so I didn't have to go back and add more.



Next up was the external fin fillets. This is where I need the most practice to get good results. The whole area was lightly sanded with 80 grit paper to allow good epoxy hold. I used a 3/4" PVC pipe and a pencil to scribe the lines where the epoxy should go and masked it all off with painter's tape. I made a mistake here. I didn't think of the fact that the width of the pencil won't let me get down far enough to scribe a line right where the PVC touches the tube. That means I masked off too high. And when I drag the PVC across the epoxy to build a smooth fillet, there's overspill at the edges that builds a small ridgeline. I had to go back with isopropanol wetted glove fingers to smooth that out. Took a lot of fiddling, but it worked out ok. Next time, I'll use my sandpaper-wrapped PVC to scratch a line to show me where to mask. Learning is fun!

This pic shows the extra epoxy bead line at the margins of where I had masked. Had to go back over it with a finger to smooth it out.



For the fillets, I used Rocket Poxy. After mixing, it was spread out thin to let air bubbles pop and let sit for 15 minutes to thicken a little. That gave me the perfect consistency for spreading the fillets. It was like toothpaste; fluid enough to self-level a little and get rid of edges, but not so thin that it dripped or ran.
Masking tape was removed about 5 minutes after each fillet pair was done. The set was left to harden a couple hours before rotating the rocket and working on the next fillets.

Hard to tell in these pics, but they came out nice and smooth with good, gradual transitions from body to fin. Fillets also wrapped around the front and back of each fin, so the whole thing just melts into the body nice and smooth.

The end result. Not completely perfect, but it should smooth out really nice after CWF and sanding rounds.




Next up is sanding and CWF to get smooth fillets. Hopefully, I'll have time this week to get to that.

calambert said:

Mark,

Been following along here and wanted to know how you went about rounding the fins?

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I have a couple simple tricks.

1. Color the edges of the fins with pencil lead or a charcoal stick. That will let you easily see what material you're removing.
2. Clamp the fin to a sawhorse to give a stable platform. Alternatively, I'll put the fin on a pallet and kneel on it. The fin just needs to be nice and still.
3. I use a palm sander with 180 grit sandpaper for plywood. It removes material in a nice and controlled speed while leaving it smooth enough to prime later.
4. Hold the palm sander at 45 degrees and sand one edge until you've removed half of the colored end.
5. Optional, until you've learned to do it by eye, recolor the new edge.
6. Hold the palm sander at 22 degrees and again sand one edge until you've removed half of the newly colored end.
7. Quickly do one pass over the whole thing to smooth out the angle transitions.
8. Flip and repeat for a nice, rounded fin.

Pics!



I've done primary bevels, micro bevels, and back bevels so much with knife sharpening, that I did these fins just by eye with no coloring anything else special.

Hope that helps.

Thanks Mark...Very Helpful. One other question. What is the distance from where the bevel starts, to the edge of the fin? Looking at the pictures I'm guessing about 3/8"?

Measured it this morning. 3/8" is really close.

mccordmw said:

Measured it this morning. 3/8" is really close.

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Great! Thanks.

I've got the fillets and sanding out of the way. I'll post pics soon. I'm looking at shear pins for the lower airframe on drogue deployment and then the upper airframe for main deployment.

I'm planning on a L1 cert using a CTI 38mm I285 classic motor. I'd prefer a sparky for the neat look, but I'll avoid the fire concerns that some launches have. The OR flight plot shows me that at motor burnout, I have a max deceleration of -70 m/s2. So...

Force = m * a

I measured the nosecone + upper airframe + avionics to be 659g. I might increase it once I get the new Quantum Eggtimer, but this is a start.

F = 659g * 70m/s2 = 46.1 Newtons = 10.5 pounds of force pulling apart my rocket on burnout. 2 x #2-56 nylon shear pins can hold about 60 pounds, so I'll go with that.

The nosecone and upper bay weigh even less, so I'll secure that with a single #2-56 shear pin.

Once assembled, I'll test ejection using BP amounts suggested by the NASSA calculator at https://www.rimworld.com/nassarocketry/indextools.html

Lower airframe: 4" x 34"
Desired pressure: 10psi
Suggested FFFFg BP: 2.2g
Shear pin limit: 3

Upper airframe: 4" x 17"
Desired pressure: 10psi
Suggested FFFFg BP: 1.1g
Shear pin limit: 3

So 2.2 and 1.1g BP should be enough to generate 10 PSI for separation and can break up to 3 shear pins.

Once everything is assembled, epoxied, and painted I'll re-weigh to get the most accurate masses and adjust pins+BP accordingly. The current figured should be pretty close, though. Let me know if my figures are wonky.

I should note that for my L2 cert, I'll pull out the 38-54 adapter and fly with a CTI K160 longburn. Sims to about 7000 ft. At burnout, deceleration is a mild 33 m/s2, so I'm good to use the same pin count and BP amounts here too.

mccordmw said:

I should note that for my L2 cert, I'll pull out the 38-54 adapter and fly with a CTI K160 longburn.

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That will be really nice. L2 in style.

Avionics bay shell done. Edges of the tubes were hardened with thin CA. Each 12" coupler was marked 2" in. The switch band was smeared lightly with RocketPoxy, and the couplers were inserted to the 2"marks. I used a Popsicle stick on the inside of the bay to spread out any epoxy that oozed inside.



Given that bolts are secured through the bay bulkheads, I'm not sure how critical it is to epoxy the plywood together. Nevertheless, I smeared a small amount of epoxy between layers, clamped for a few hours, and then epoxied the eyebolts in place. Here they are inverted to show the epoxy on the nuts. Also, a small amount of epoxy was used to close the eyebolts. Probably not needed.



For ease of use, I'll probably attach the shock cords to the bay via quick links and swivels.

Waiting on my Eggtimer Quantum to solder that together and build an electronics sled.

Once that's done, it's a long, impatient wait for 70 degree weather to prime and paint.

I got my shock cords and links set up. The goals were:

- allow easy switch-out/replacement
- use swivels to prevent twisting
- avoid excessive cord length to reduce the chance of tangles during ejection
- have enough length to keep the sections from bonking into each other (thought that one was obvious :-D )

I have a minimum of about 1-2' of clearance between sections while they hang under a chute. Should I use longer shock cords? I have enough on hand to double all the lengths, but that seems like overkill. Here's a diagram of how I put it together. I figured it would be more educational that a picture of tangled cords.

If you're really worried about zippering, get a Giant Leap Fireball.

mccordmw said:

Given that bolts are secured through the bay bulkheads, I'm not sure how critical it is to epoxy the plywood together.

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It does make it much stronger and it keeps the caps aligned better because the milled holes for the hardware are a free fit.