L1 Build Thread - Alpha1, Alpha2

[degreaser]

Yeah, yeah - I know... You're saying "Ho Hum, another L1 build thread." Gotta start somewhere right? Hopefully, I'll keep you entertained for a while.

It started out earlier this year when I bought a PML Ariel kit. One of my main interests is electronics and the intent to build and test my own altimeters. As I'm still L-Nada, I'm limited to G motors. Unfortunately, the stock Ariel barely gets off the ground on a G. So I decided to build two rockets, Alpha1 and Alpha2. Alpha1 is a scaled back version of the Ariel, Alpha2 is an extended version of the Ariel. I could certify on Alpha1 (and still may) but my main reason for building it is to obtain flight data so that I may develop a home brew altimeter in single or possibly dual deploy configuration for certification. Alpha1 sims to just under 1000AGL on a G69-Classic which is perfect for my purposes. The 1000AGL ceiling is important for a number of reasons. First it keeps the rocket in Class G uncontrolled airspace and out of FAA's hair. Secondly, it's high enough to provide useful and interesting altimeter data. Alpha2 is designed as a dual deploy rocket. This thread will cover the construction of both rockets.

Why build an altimeter? Because I wouldn't learn anything by buying one. Why buy one when I can build one?

So with these goals in mind and an already purchased Ariel kit, the next thing I did was to toss the instructions and create some RockSim models. The first thing to go was the piston. I opted instead for a baffled zipperless design for both rockets. The baffle will allow engine deployment on the first few flights and altimeter based single deployment on later flights of the Alpha1.

I'm designing the booster section of Alpha1 to use CTI 3 grain 38mm cases and Alpha2 to use up to 6 grain CTI 38mm cases or possibly a 4 grain 54mm case.

Another goal is to try as many new construction techniques as I can. As such, I purchased the Ariel with unslotted phenolic tubes with the intent on fiberglassing them. I purchased additional materials as needed to complete two rockets.

Screen captures and Rocksim files are attached. I'm also creating Rhino3d models as required during the construction.

View attachment alpha2.rkt







View attachment alpha1.rkt

 

[degreaser]

Some notes on my first altimeter. It's based on an 18f4553 PIC processor, a +-50g accelerometer and a mpxa6115 pressure transducer. It has a micro SD Card, 4 pyro channels, dual power capability and a couple of extra memory chips to play with. Communication is performed with USB and audibly via morse code sent via the on-board speaker. Among other things, the altitude, battery voltages and status are reported via morse. The design is a blend of through-hole and surface mount. I used through-hole because I have a large collection of through-hole components I need to use.

Schematic and board design were performed in Eagle, firmware in Microchip MPLAB in C. I have nearly flight ready firmware developed but it's nowhere near ready for controlling deployment charges. Among other things, it includes logging of altimeter data, Kalman filtering of that data, launch/apogee detection.

I used a Parallax breadboard to develop the initial circuitry. Board fabrication was done at batchpcb.com. I ordered two, they shipped four. The SMT devices were soldered using a toaster oven.

This particular design will only fly in Alpha1. The processor is socketed and even though it's a quality socket, I wouldn't trust it in anything greater than a G. I'll have a new design completed within the next few months.

Future designs will be 99% SMT using an 18f87j50 or 18f67j50 processor. I'm thinking of a more modular approach rather than trying to stuff everything on a single board. I have some preliminary designs in Eagle.

 

[degreaser]

On to construction. First some tools.

First is a tube cutter. I had a fairly small Porter-Cable circular saw. I looked through the wood at HD and found a couple pieces that weren't to badly warped. Those were screwed and glued together. I cut the blade clearance slot, drilled and tapped the saw and mounted it to the wood frame. Quick and dirty but it does the job. Sorry, no shots of it in action at the moment.

 

[degreaser]

Next, fiberglassing tools. I've learned everything I know about fiberglassing at https://www.vernk.com. He has a couple of very good pages. Of particular interest was his rocket rotisserie. His design used a number of water cooler pulleys and a fairly hefty motor.

Mine uses a Weber rotisserie motor. To use it, I turned a couple of widgets on my lathe and milled a part that would properly engage with the rotisserie. The other widget has a 5/16" bolt with a couple of skateboard bearings - this end rests in a machining vise when in use. These widgets are sized to snug fit inside a length of 1.5" pvc pipe. The pipe ends are slotted but I've found it unnecessary to use clamps to secure the pipe to the widgets.

The next two images are of foam donuts which are used to provide a friction mount between the pipe and the airframe sections. I also use motor mounts inside the airframe sections during glassing to ensure that they stay round. I cut the center of the foam donut with an apple coring tool (found in kitchen).

 

[degreaser]

More tools. A mini-roller, plastic plates, tongue depressors, salsa containers, etc. And drop cloths to protect everything. Not shown are latex/nitril gloves, two on each hand.

The next set of images show how it all goes together.

 

[degreaser]

On to the actual glassing. I used US Composites 735 3:1 epoxy and three wraps of 4oz cloth. Vern suggests drawing a straight line across the length of the tube to be used as an alignment aid. It works great when I remember to draw the line. I usually remembered after having applied the first bit of resin. It took three sessions to get all of the tubes glassed.

I tried Vern's suggestion of spraying a bit of 3M adhesive on the trailing end of the glass cloth. I found that I have a tendency to apply too much and as a result, the cloth doesn't set properly in the resin. I only used that technique in the first glassing session.

The second image shows how I trimmed the ends using a hose clamp as a guide. The technique works very well. I used a Dremel fiber reinforced cutoff blade.

The third image is the collection of glassed airframe tubes for both Alpha1 and Alpha2. There are also a couple of spare segments.

I hadn't done glassing since high school and was a bit intimidated but it turns out it's not at all difficult. It's all in the prep.

 

[degreaser]

When applying the resin, I used one of the bondo squeegies to remove the excess resin. This left the texture of the cloth visible on the surface. Somewhere on the web I found mention of using microballoons and resin to fill the texture. The site suggested this as an alternative to sanding the surface smooth as doing so removes fiberglass cloth and weakens the structure.

I bought a quart of phenolic microballoons from West Marine and proceeded to apply a 50:50 mixture of resin/microballoons to the surface. It has the appearance and texture of chocolate pudding.

The final image in this post is of the tubes sanded to 150 grit. There are only a couple of remaining defects that need to be addressed and they can likely be sanded out. After I've slotted the two booster sections, I'll sand everything to 400 grit. The two shiny tubes are the spares.

 

[degreaser]

This arrived last Wednesday from Wildman Betcha can't guess what's inside.

 

[degreaser]

Here are the baffles. I've made two. I got the idea from this posting.

https://www.rocketryforum.com/showthread.php?t=1901&highlight=baffle

 

[degreaser]

And here are the completed baffles.

 

[degreaser]

Now, how to cut the fin slots. I've seen lots of different techniques, box designs etc. I tried to make a box out of some really cruddy wood I got from HD but two weeks after I made it, it was incredibly warped. Firewood.

So I decided to use the tools I already have. I have a small metal shop with a lathe and mill. It was simply a matter of making jigs to hold the tube while the slots were milled.

I decided to make a variation of the rocket rotisserie, except in this case the rotisserie would be attached to a rotary table. The table is capable of very precise motion.

I started off by turning down two chunks of 4x4 lumber into two slugs that snugly fit into the interior of the tubes. The slugs have a length of 1/2" all-thread running through the middle.

 

[degreaser]

Here's the fin slotting jig mounted on the milling table. The rotary table is on the left. The right end of the all-thread is held by a short piece of 2x.25 stock bolted onto a machining angle.

 

[degreaser]

I used a 123 block, feeler gauges and a dial indicator to square the tube and jig to the table. Then I used an edge finder to locate the edges of the tube. Once that was done, finding the center was easy.

The Alpha2 booster tube is on the jig at the moment. I'm using two different G10 fin thicknesses. .1" for the Alpha2 and .062" for the Alpha1. I only have a 3/32 router bit at the moment. The 1/16" bit should be here next week. So I started with the Alpha2.

 

[degreaser]

I started the machining process by drilling the vent and epoxy injection holes. I also drilled pilot holes for the PML linear rail lug mounting screws.

I secured the tube through a vent hole to the jig slug with 3x 6-32 SHCS. That was to prevent any slipping during the cutting of the fin slots.

The resulting slots are a bit snug as the router bit was .093 and the fins are .1". A bit of sand paper should give it a perfect fit. I'll work on Alpha1 when the router bit arrives.

 

[degreaser]

So that's it for now. With the exception of the altimeter, most of this work has been performed over the past 1.5 months or so. Unlike last summer, I'll definitely be ready by the time Black Rock dries out next summer.

One more picture. I was scratching my head last night trying to figure out how to secure an altimeter bay in a PML nose cone. Then it occurred to me after cutting the base off of a nose cone - a centering ring fits perfectly on the *backside* of the coupler section of the nose cone. A centering ring made of fiberglass or machined aluminum would work very well and provide a very secure base for mounting the av bay.

More to come...

 

[degreaser]

I'm contemplating the fin cans. Here's a Rhino sketch of a fin alignment jig. I'll likely machine the jig out of 6061 1x.75 stock.

I'm wondering about epoxy injection. I'm planning to use 30 minute Devcon but I'm not sure if it should be thinned with DN. Any suggestions? Where's a good place to get syringes? What size?

 

[cbrarick]

Where's a good place to get syringes? What size?

Get them from Walmart, they have a 10 cc oral syringe.

 

[degreaser]

Get them from Walmart, they have a 10 cc oral syringe.

Great idea! The Walmart near me doesn't carry them but they provided the phone number of a local pharmacy that does. $1 each.

 

[Rocketman248]

I actually prefer the ones that Wildman sells. Both will work, but the Wildman syringes are a better quality.

 

[degreaser]

I saw those at West Marine but it looks like Wildman has a better price. They appear to be around 15cc capacity. Do you clean and reuse yours or toss them after one use?

 

[blackjack2564]

Clean with denatured alcohol.
I got one I've been using for 3 yrs.
So worn the numbers are gone!

Nice build.

 

[degreaser]

Thanks!

I ordered a 12 pack and a gallon of denatured alcohol from West Marine. That should last the duration I think

 

[degreaser]

I have a start on the fin alignment jig and have the rough machining done. I started with two 14" lengths of 6061 1x.75 bar stock. I clamped it to the milling table using a set of v-blocks. Machining was done with a 3/4" roughing endmill. I took off .500". The surface finish isn't too bad so I'll likely just leave it as-is rather than doing a finishing pass.

Tomorrow night I'll trim the blanks, machine to length, cut the .025" clearance slots and drill/tap the mounting holes.

 

[degreaser]

I only got about half of what I wanted to do tonite done. The way things were going I figured it was best to quit while I was ahead.

The jig is milled to length. I'll finish it up tomorrow.

 

[degreaser]

Progress. Milled, drilled and tapped.

I'm contemplating how to use the jig. I may use the rotary table to set the angle much like I did when I was milling the fin slots. Thinking along those lines I added a length of drill rod to allow the jig to be securely fastened to the mill spindle and precisely positioned.

This jig should handle up to a 75mm motor mount tube and a flat fin with a root chord of around 10".

 

[degreaser]

I raided the wood pile and cut another 6 chunks of 4x4 for additional slugs, 2 each for the 38mm, 54mm and coupler tubes.

I've turned two of them down for the 54mm tubes. I'm just about ready to mount the fins but I first need to cut a shorter length of drill rod. The one on the jig is longer than I'd like.

These techniques will work up to about a 4" or 5" body tube. Larger than that, I'll have to come up with other techniques.

Football, then fin mounting later

 

[degreaser]

Fins!

They are tacked on with a thin bead of 5 minute Devcon. I'll start to build up the fin can tomorrow and get started on the other booster.

 

[degreaser]

I've started working on the interior fin can fillets. I'm using some milled fiber that I got from West Marine and 30min Devcon. I mixed up 4 grams each of fiber, resin and hardener per session, using about 2/3 of the mix. It mixed to mayonnaise consistency. I smoothed the fillet with a short length of 3/4" Delrin rod producing a 3/8" radius fillet. I'm using 3/8" for the fins and 1/4" radius for the centering rings. I pulled the tape off after about 20 or 30 minutes into the cure.

I'm using JB Weld on the rear centering ring. I'm going to use a HAMR retainer and JB Weld is the epoxy of choice per PML.

 

[JDcluster]

It looks like you have allot of nice toys....I mean tools to play with.

You do know that you will need a L1 to buy & fly that G 185, right? It's a nice motor for that border line flight. I flew one in my 4" Stump based on the Binder Design Thug.


Good Luck

JD

 

[degreaser]

It looks like you have allot of nice toys....I mean tools to play with.

You do know that you will need a L1 to buy & fly that G 185, right? It's a nice motor for that border line flight. I flew one in my 4" Stump based on the Binder Design Thug.

I like tools Think Tim Allen and Binford.

You have to be L1 to purchase H and I, not G. A G is a mid-power, not high power motor.

[Edit] Ah shoot. You're correct. Motors of 80N average thrust or greater are considered HPR motors regardless of total impulse. I always thought it was based solely on total impulse. I should RTFM..... A G69-Classic will get it done too. Another Wildman order is coming.....

:bangpan: