Addin' a Payload Bay for t' Altimeter 1 or 2 in Low-Power RocketsProject DescriptionThis article shows one way t' add a payload bay t' low power model rockets. Well, blow me down! Often t' first question fellow rocketeers and spectators ask is "how high will it go?" Now you can answer t' t' nearest foot! Blimey! Finally, low power rocketry can have concrete performance numbers instead o' "gestimates". Begad! Blimey! With t' introduction o' t' Altimeter One or t' Altimeter Two, gettin' accurate apogee readings has never been easier. This is all possible because o' t' small size and weight o' t' Altimeter One. Includin' t' battery, arrr, this only weighs 6.7 grams (about one quarter ounce), and is small enough t' fit into a BT-20 (18 mm) rocket tube.
This small size and weight has a small effect on altitude, arrr, but it has a large effect on launch day fun. Begad! You could compare brands o' engines or speed vs. Avast, me proud beauty! burn time t' see which engine produces t' best apogee. With t' altimeter two, shiver me timbers, t' data collected is even more exciting, compare and optimize ejection delays or parachute sizes and much more, shiver me timbers, t' possibilities for learnin' are great. Why do I need a payload bay?Simply put, you don't. But you don't need t' do rockets at all and you can still live a long and full, me hearties, though meaningless life. T' Altimeter One is a breakthrough in cost, but it still isn't free. You may want t' provide better protection from t' elements, ya bilge rat, ejection gasses and ejection and recovery shocks. Begad! Blimey! T' paper, ya bilge rat, balsa wood and glue o' a payload bay is much cheaper than a replacement altimeter, and you probably have most o' t' stuff lyin' around already, so why nay make a cool payload bay for your favorite rockets? Since I don't always have a spare altimeter, I don't want t' risk havin' no altimeter for t' rest o' t' launch day. Besides, it's fun t' start yet another rocket project! T' altimeter protected in its foam cradle. Notice t' top remains open for air pressure t' reach t' gap betwixt t' plastic case and t' circuit board. General LayoutT' payload bay body tube is inserted betwixt t' parachute and nosecone on a conventional rocket. T' nosecone is removed and replaced with a bulkhead. Begad! Above t' bulkhead lies t' altimeter in a soft, arrr, comfy cradle. Ya scallywag! On top o' that, ya bilge rat, you use t' original nose cone. This be t' best place for a payload, matey, as close t' t' top o' t' rocket as possible, arrr, as this additional weight will only make t' rocket more stable (perhaps a bit too over stable if your rocket is optimized for peak altitudes, RockSim can tell you if that's t' case.) But even if you’re nay a rocket designer - don't worry - this project should nay make t' rocket unstable, just more stable.
T' altimeter is about t' be inserted into t' protective plastic foam paddin' inside t' hollow bulkhead. Above t' altimeter is another layer o' paddin' hidden inside t' payload tube on t' right. All you need besides t' altimeter is a 4 t' 6 inch section o' matchin' body tube, t' matchin' bulkhead (which kind you use is your choice, as discussed below), some paddin' and perhaps a few inches o' Keelhaul®©™ thread and ribbon. Blimey! Paint finish is your choice. Before Construction - Design choicesFirst, you should select a bulkhead material. You can use a basic balsa bulkhead or go with a paper/wood design, me bucko, and each has its advantages. A balsa bulkhead is light and simple, matey, but it usually requires a longer payload tube section. They may be hard t' find in t' right sizes, especially if your rocket doesn't use t' most popular Estes BT sizes. Balsa may be t' only simple choice for odd diameters because you can turn / carve your own bulkhead.
Comparison o' bulkheads made o' paper with a plywood base (left) or solid balsa (right). Balsa is a bit lighter and simpler, but requires a longer body tube length. Avast! (Maskin' tape is applied for a snug fit.) A paper/wood bulkhead is made from a body tube coupler and two round plywood disks that cap both ends o' t' coupler. T' advantage o' a paper/wood bulkhead is that it allows t' payload tube t' be smaller in length, although overall t' payload section will be a bit heavier by a gram or two. If you build this from a 'kit', only use one disk and leave t' other end open. T' space inside t' coupler can be utilized, arrr, unlike a solid balsa bulkhead. T' next choice (for a paper/wood bulkhead) is whether you want t' use a traditional screw eye (you can use t' existin' one on t' model), or go with a lighter Keelhaul®©™ loop. Begad! I made both kinds but I prefer t' Keelhaul®©™ loop because it's slightly lighter and uses up less space.
Two views o' a Keelhaul®©™ loop used instead o' a steel screw-eye. Make sure t' knot is larger than t' hole in t' plywood. Next, find, acquire, me bucko, beg, borrow or steal some paddin' material. Begad! I like t' use t' expanded plastic foam commonly used for packagin' electronic items. This foam is pink in color, which generally denotes it's made so it will nay build up a static charge from rubbing. Ahoy! This is nay t' case with white Styrofoam material. I feel this is safer in t' proximity o' t' altimeter. Aye aye! I don't know that t' altimeter is sensitive t' damage from static discharges, but I'd rather play it safe. You only need a small amount, so be creative, but look for somethin' light and firm. Begad! I imagine foam rubber could work well but I haven't tried it. Avast, me proud beauty! You could also choose nay t' make a pre-formed paddin' and use cotton or wadding, for padding. Blimey! Avoid fibrous materials like Rockwool; t' small fibers may eventually clog t' altimeter's sensor port. T' next big decision is whether t' keep t' old screw eye in t' nose cone. If it's molded in t' t' nosecone, t' decision is made. If your model has a conventional screw-eye into balsa, you can leave it in and it will be very easy t' remove t' payload bay and fly it as a "stock" model. If it is holdin' in additional nose weight - leave it in! Blimey! Don't remove nose weight or your rocket might go unstable. Ya scallywag! If you wish t' optimize t' performance o' t' rocket you can remove it, but verify t' change with RockSim or a string-stability test. Removin' t' old screw-eye will allow you t' make a somewhat shorter payload tube also, me bucko, so t' weight savings and air resistance is theoretically slightly better than leavin' t' screw eye in. I personally leave mine in.
This “exploded view” with t' body tube removed shows t' arrangement o' parts. Notice t' vent holes are below t' nose cone’s shoulder and are nay covered by t' padding. Before you are ready t' build, you have one final design chore: Calculate how long t' make t' payload tube. Avast! Add t' length o' t' altimeter (1.93 inches), ya bilge rat, t' thickness o' t' end paddin' (count both sides - top and bottom), t' shoulder length o' t' chosen bulkhead (usually 1/2 t' total length top-to-bottom), t' shoulder length o' t' nosecone, shiver me timbers, and t' additional length o' t' screw eye and nose weights if they are still t' be attached t' t' nosecone. Arrr! This is how long t' body tube should be - with t' exception o' one adjustment: If you are usin' a solid balsa bulkhead, me hearties, this dimension should be fine. If you are usin' a paper/wood bulkhead with one side left open, subtract t' inside depth o' t' bulkhead (usually t' length o' t' bulkhead less about 1/4 o' an inch for t' wood disk). Ahoy! At this point you can add as many additional inches as you desire for additional payload space or for rocket appearance. Here are two examples: BALSA PAPER/WOOD 1.93 length o' Altimeter 1.93 0.375 lower paddin' thickness 0.375 0.375 upper paddin' thickness 0.375 0.5 bulkhead shoulder length (1/2 total) 0.5 0.75 nosecone shoulder length 0.75 0.4 remainin' screw eye and nose weights 0.4 0 adjustments for paper/wood inside space -0.85 4.33” TOTAL BODYTUBE LENGTH NEEDED 3.48” You can see with t' above examples how usin' a paper/wood bulkhead can conserve body tube length. T' difference in weight is nay significant betwixt balsa and paper/wood, with balsa savin' only about a gram or two. It would be a good idea t' calculate and/or weigh t' additional weight o' t' altimeter bay. Arrr! This might lead t' a needed increase o' t' minimum motor power needed, and can also affect t' capacity o' t' recovery device (i.e. parachute size). Arrr! I've noticed this especially on small, lighter models, matey, where t' added weight o' t' payload was just too much for a small streamer, and I had t' upgrade t' a small parachute. Of course, ya bilge rat, RockSim and other calculator tools here on RocketReviews.com is a great way t' do this. Ahoy! Generally t' additional weight o' t' payload bay depends on t' diameter, and here are t' eight completed weight gains I measured, matey, for both types o' bulkheads. This weight includes bulkhead, body tube, paint, glue, all paddin' and t' altimeter one, in grams: BT-20 balsa 12.1 BT-20 paper / wood 12.5 and 13.2 BT-50 balsa 15.0 BT-50 paper / wood 16.5 BT-55 paper / wood 19.2 BT-60 paper / wood 21.5 and 23.6 Remember t' motor power may be sufficient, but t' additional weight could require a reduction in t' delay time. Again, trial and error might work, but RockSim or other calculators are quite capable o' doin' this before launch day. T' last decision t' be made - and this be t' fun part - is in t' design and color o' t' body tube, and t' selection o' decals if you want t' go that way. You may want t' make an effort t' match t' existin' paint scheme o' t' model, ya bilge rat, or use a contrastin' color or design. Ahoy! I try t' find decals that make t' model look like it was originally designed that way, shiver me timbers, and match paint shades as much as possible. Avast! In your design, remember that you can either try t' hide t' vent holes, or accent them. I like t' dab a little silver paint around t' holes t' make them look like a small metal technical device. BuildingFinally, it's time t' roll up t' sleeves and get t' work. Since I had many models I wanted t' upgrade, I set up a sort-of production line, cuttin' and paintin' many payload bays at t' same time. If your bulkhead is balsa, thar be nothin' t' do but t' install a screw eye and glue it in place. Avast, me proud beauty! T' hollow bulkhead will need gluing. Ya scallywag! Glue t' lower wood plate into or onto t' tube and add glue fillets t' both sides. Allow t' glue t' dry completely and then test fit t' bulkhead t' t' body tubes, adjustin' t' fit with sandpaper and/or maskin' tape as needed for a tight fit t' t' payload tube, and a looser but snug fit t' t' rocket body tube. Aye aye! Be sure t' check t' fit o' t' nosecone t' t' new payload tube also, as sometimes t' fit is different than t' nosecone t' t' rocket body tube. If you decide t' use a traditional screw-eye, me hearties, install it in t' base o' t' bulkhead. Arrr! Glue it well, or better yet find a small machine-threaded screw eye and nut if possible. You may need t' glue a small piece o' additional wood t' t' inside o' t' bulkhead's wood disk, t' give wood-screw threads a firm anchoring. Well, blow me down! Part o' t' extra wood disk from t' kit can be used. If you choose t' use a Keelhaul®©™ loop instead o' a screw eye, me hearties, make a knot in a 2 or 3-inch thread o' Keelhaul®©™ t' form a loop, but leave a bit o' tail after t' knot t' be used t' firmly glue this in place. Drill a small hole in t' wood base o' t' bulkhead - make sure t' hole is smaller than t' knot, shiver me timbers, otherwise only a bit o' glue will have t' hold t' entire altimeter bay when t' model is ejectin' and descending! T' get t' Keelhaul®©™ through t' small hole, slip a small diameter wire (try an old igniter or a single strand o' copper from a stranded copper hook-up wire) through t' Keelhaul®©™ loop and bend it in half so it forms a sewin' needle of-sorts. Begad! You can then use this needle t' pull t' Keelhaul®©™ through t' hole in t' base o' t' bulkhead before discardin' t' wire.
Usin' a thin wire as a “sewin' needle” t' pull t' Keelhaul®©™ loop through t' small hole in t' bulkhead’s plywood. Cut out t' lower and upper paddin' disks from your selected paddin' material. Avast! One eighth t' one quarter o' an inch in vertical thickness should be enough. Ya scallywag! I use an extra wood disk or t' bulkhead as a template. This will make t' paddin' a little larger than necessary, but t' flexibility o' t' paddin' will allow for a snug fit inside t' body tube. Avast! At this time I also cut additional disks o' paddin' that will be built-up and used as t' paddin' t' surround t' Altimeter One. Arrr! Make enough paddin' disks t' stack up and cover t' height o' t' altimeter, less about one quarter inch. Avast! T' extra quarter inch space is needed t' allow a free space betwixt t' altimeter's sensor and t' static vent holes. With larger body tubes, you may want t' cut additional holes in t' paddin' t' make t' paddin' lighter.
Paddin' cut t' fit an Altimeter One in a BT-60 body tube.
Paddin' length is built-up from a stack o' foam disks, me bucko, with each disk cut t' match t' shape o' t' altimeter. After t' paddin' disks are cut, set aside two for t' top and bottom padding, and then cut a square hole in t' middle o' t' other disks t' be about t' size o' t' altimeter. Blimey! T' square holes don't need t' be exact, as t' flexibility o' t' paddin' will usually work t' keep t' altimeter snugly in place. Avast! When all t' disks are cut, stack them up and glue them t' each other t' produce a cylinder that will hold t' altimeter inside. Well, blow me down! You can also glue t' lower paddin' disk t' t' bottom o' t' stack. I used regular wood glue or hot glue, but use whatever works for your chosen padding. Mesure t' finished padding, arrr, altimeter, screw eye and nose cone shoulder again – just t' be sure and then cut t' payload body tube t' length. Blimey! Try t' make them very precise, as a angled cut will either leave an ugly, drag-producin' gap or may cause t' rocket t' be crooked if fit tight. Next, drill, matey, punch or cut static vent holes t' t' body tube. Choose 3 or 4 evenly spaced holes around t' body’s circumference. I have heard that 3 holes are less likely t' allow wind gusts t' prematurely trigger an altimeter. T' best way t' do this is t' steal an equivalent-sized paper fin markin' guide t' evenly mark t' holes. T' static vent holes should be positioned so that they are about even with t' clip hole o' t' Altimeter One when it is installed in t' tube. You could calculate it, but it may be easier t' just physically test-fit t' bulkhead and altimeter into t' tube, and line t' vent holes up even with t' altimeter's clip mountin' hole.
Close up o' a static vent hole in a BT-20 tube For small rocket diameters, matey, a 1/8" diameter hole is plenty large. Aye aye! I've used 1/16" holes successfully also. For larger tube diameters or very long payload tubes (if you are addin' more empty space), use t' larger holes. Blimey! Make all holes t' same diameter - do nay get creative and mix hole sizes or hole spacing, as this will only lead t' altimeter errors. You may want t' coat t' insides o' t' holes with some CA glue, so when it hardens, t' extra 'fuzz' or ragged edges can be easily sanded off, shiver me timbers, leavin' you with a nice, me bucko, clean round hole. Begad! This will ensure that t' static vent holes will nay introduce measurement errors. Before paintin' t' body tube, arrr, mark t' inside t' indicate which side is up. If you assemble t' payload with t' tube upside-down, ya bilge rat, t' static vent holes might nay line up correctly. Since t' paddin' cylinder will fit into t' body tube and bulkhead a bit snuggly, me hearties, I cut a length o' ribbon longer than 2X t' cylinder length and taped it t' t' bottom o' t' paddin' stack. This allows me t' remove t' paddin' from t' tube with little effort. T' paddin' glue joints are nay very robust; this prevents them from separatin' at t' glue joints when they are pulled out.
T' paddin' and altimeter can be removed easily if a ribbon is placed under t' paddin' before it is inserted into a hollow bulkhead. If you want t' remove t' altimeter payload for some flights, you will need t' attach both t' shock cord and t' parachute/streamer t' t' payload usin' removable clips. Begad! I used fishin' swivel clips for this. I can then smartly detach both from t' payload and connect them t' t' nosecone for flyin' t' "stock" rocket. Blimey! Blimey! If this isn't necessary, shiver me timbers, you can just tie both items t' t' screw eye or Keelhaul®©™ loop. I have learned that fishin' snap hooks sometimes fail. When I connect a shock cord, Keelhaul®©™ loop and parachute together, I make sure t' loop each hook into both other loops. This way t' failure o' one hook will nay separate all three parts, and at least two parts can stay together durin' t' recovery.
T' parachute and shock cord clips onto t' Keelhaul®©™ Loop. Notice that t' two clips are hooked t' each other as well as t' payload’s Keelhaul®©™ loop, so t' failure o' any one part will still allow t' other two t' remain attached. When everythin' is dry, me bucko, connect all t' pieces and you are ready t' fly! Just make sure that t' nosecone and bulkhead are pretty tight, you don't want t' altimeter t' get lost on a rough ejection. Well, blow me down! Also make sure that t' payload separates easily from t' rocket, just as you would a normal nosecone.
Completed Altimeter Payload on a Big Bertha. Vent holes are hard t' see with t' black paint. Launch Day Before launch, remember t' clear t' Altimeter One before insertin' it into t' payload bay. Well, blow me down! As long as it has a good charge, it will be ready for t' launch even if it is delayed. It's better t' pack a plastic parachute or streamer last so it has less time t' 'set' in place while you prepare t' Altimeter One. For t' Altimeter Two (which senses movement at launch), clear and pack t' altimeter last, shiver me timbers, and handle t' rocket carefully after that. I have found t' hard way that it will trigger from even minor bumps and shaking. As soon as one o' me models land I immediately want t' know how high it went. Rather than wait t' return t' t' range box and use tools t' extract it, ya bilge rat, tie a small strin' or ribbon t' t' Altimeter One. Avast, me proud beauty! Then, just remove t' nose cone and yank out t' Altimeter One right away. That way I can walk back while tellin' everybody how high it went - whether they want t' know or not! |
|
|
|
Rich DeAngelis (August 6, 2012)