Birmingham Rocket Boys Launch System
From LUNARwiki
I'm sure that the system as a whole that I'll be describing will not not fit the needs of many sections. But there are some details of it which could be very useful in any system. Especially the arming warning indicators to be used at each rack and also at HPR junction boxes.
This past winter and spring, I built a new system for the Birmingham Rocket Boys section to use.
The BRB launches are low-key, everyone can fly misfire-alley style using their own launchers. But even so, BRB had a need for a multi-rack launch system for use at regular club launches by those who do not have their own launchers, and also for more specialized launches like demonstration and school launches.
One of the design criteria was to make the equipment easy to transport. Both for easy transport in vehicles, and to not to be too burdensome to hand-carry from vehicles to the launch site such as for school launches and so forth. So, the racks were designed to have parts no longer than 48", and to be made out of light materials. As it turned out, the two racks easily fit with room to spare inside of a cardboard box that an EZ-up type of canopy came in, and the launch panel plus a few other fittings (and blast deflectors) are stored and transported inside of a cardboard filing box. With the launch cables on a couple of wind-up reels.
The main horizontal beam for each rack is four feet of 1 x 1" aluminum tubing. A piece of "U" shaped aluminum of 3/4" inside width was added along the bottom for the electrical wiring to run inside of, including the jacks for the ignition leads. For legs, the racks use 3/4" PVC pipe, with PVC fittings used for allowing the legs to be plugged in. The hardest part was making up a unique joiner to allow the PVC leg assembly to slide inside of the 1 x 1" aluminum tubing, that required the use of 3/4" square aluminum plus some other 1/16" thick "L" aluminum to be added to shim it to 7/8" square to be a good slide fit inside of the 1 x 1 tubing (would have been so nice if 7/8" square aluminum tubing could have been found. I could not use wood for a joiner because inevitably the wood would swell and jam).
Each rack has 5 pads, spaced 11" apart.
The launch panel uses a rotary switch to select which rack is armed. In the 1970's, I saw more than one case when multi-racks were used that way and the wrong rack was selected by accident. So when in 1979 I had modified a 6-pad panel I made in 1973, to use two 4-pad racks, I added indicator lights to the panel and to the racks, to show which was armed. The rack lights were automotive trailer type lights. For the new system this year, I did a similar thing. There are three bright lights on top of the panel, to indicate which of the three racks are selected. Each rack has its own arming light, in this case automotive lights with a cluster of bright LED's, a slim and compact assembly that fits well on each rack. Originally, I had gotten some small strobe lights from All Electronics, but they were not quite as bright as I had expected and were a bit difficult to mount robustly, so I went with the automotive LED lights instead.
But there is more. The panel is set up with two alternating pulse outputs, timed to cycle once per 3/4 second, with one pulse on about 3/8 second and the other pulse on about 3/8 second. That timing cycle seemed good for getting attention audibly and visually, it is easier to notice a sound or light that flashes on and off. Pulse A is used, among other things, to sound a Piezo beeper inside the panel box, to indicate the panel is armed. Pulse B is used, among other things, to sound a mechanical buzzer that is on each rack, sounding the buzzer that is on the rack that is armed, and also to flash the rack's LED arming light. So, the pulsing buzzer sound on a rack, as well as the LED light on the rack which flashes on and off with the same pulse as the rack buzzer, helps to warn everyone which rack is armed (the three bright red lights on top of the launch panel also use Pulse B to indicate which rack is selected). That goes a long long way in reducing the potential for accidentally selecting the wrong rack, which somtimes "stealthily" was a problem in the 1970's when there were no racks that had any visual or audible warning indicator (well, not among the ones I saw at a couple of NARAMs where there were some accidental firings. The last NARAM to use racks for contest flights was 1977). I will make note that at the Southern Thunder launches I attended in 2005 and 2006, hosted by MC2 and HARA, the HPR junction boxes they use do have a bright light that comes on when one of the junction boxes is armed.
The A and B Pulses are also used in the panel to make the green continuity indicator lights flash (using pulse A), and also to make the red pad armed lights flash (using pulse B). The panel uses super-bright LED's for continuity and pad select indicators. They are water-clear, so when on they glow red or green, when off they are clear. The LED's are mounted inside of clear Cliplite holders from All Electronics. That makes them much easier to notice being on than if they were diffused green or red LED's, or inside of green or red colored Cliplite holders. Also, the pulses to make them flash on and off make them easier to notice as being on or not. They work fine even in direct sunlight, I tested for that first to make sure.
The panel has two different 20 amp circuit breakers in it. One is an automotive self-resetting (thermal break and self-reset) type, recommended by John DeMar. The other is a panel-mount breaker, which pops out if it is triggered and needs to be reset manually. They are wired up to a high current rocker switch that selects one of them, so if one of the breakers went bad, the panel can run off of the other breaker. The panel is designed so that if a breaker is tripped, a continuous buzzer will sound to indicate the selected breaker is out and either needs to be manually reset or should reset itself in a few seconds (if it was the self-reset breaker that tripped).
The racks include their own continuity check capability. I saw those on some racks (I think provided by DARS) used at NARAM-19 in 1977, and was impressed. So I added them to my 2-rack upgrade in 1979 when I modified my 1973 panel from a single 6-pad rack. Back then, they were LED lights, though a bit hard to see sometimes. For the new racks, a Piezo beeper is used instead, since it's easier to go by a sound for continuity rather than a light you have to see. A small pushbutton is mounted at each pad location, to be pressed to find the continuity status. Only one beeper is used for the whole rack, rather than one for each pad, it is not too likely two people would check continuity at the same time. Power for the continuity beeper at the rack is provided by a 9 volt battery, mounted inside of a small plastic case attached to the rack. The plastic case also has the Piezo beeper mounted in it. The 9 volt batteries will last at least a year, so, once a year they need to be changed.
Now, actually the launch system currently has two racks, not three. There might be a third rack made later down the line (and for that matter, the panel itself could be upgraded to run 5 racks someday). Otherwise, the third rack rotary switch position serves double duty for HPR use. Currently, it's simply being used for one HPR pad. Even so, the leads used for the HPR pad have an arming strobe light and a special VERY loud Piezo arming beeper added to it, running off of Pulse B, the same way that the racks use Pulse B to for their light and buzzer to indicate they are armed. There is no question when the HPR pad is armed, the strobe might not be as visible as desired but the loud Piezo beeper (From All Electronics) is two-tone and very loud. Later down the road, probably next spring, the single HPR pad set-up will be upgraded to a HPR Junction box to serve up to five HPR pads. That HPR junction box will then house the existing loud Piezo HPR arming beeper and strobe light (I may try to find a brighter strobe to use, though the loud Piezo beeper tends to make a visual warning superfluous).
7-conductor cable is used to run from the panel to each rack (and to HPR). That is sufficient for the 5 pads, ground, and "B" pulse to the arming indicators (sound and light). To connect the cabling between the panel and racks, 8-pin Molex connectors are used (the last two pins are doubled up for the ground wire). You can find the Molex connectors on page 257 of the Allied Electronics catalog. Here's a pdf file of ttat page: Media:terminals_alliedelectronics_catalog.pdf
Male plugs are used at both ends of the cable. The launch panel has a female flush-mount socket in it for each of the three rack locations, while each rack has a female plug that is attached to a 3 foot length of cable coming from the rack (there was not enough space in the rack to use a flush-mount socket).
Photos
From the January launch, a foam and plastic mock-up of the panel is on the left, new panel box in the middle, and old 1973 launch panel on the right side. I was surprised to find Bud still made the very same box in 2006 that they made in 1973, and like the idea of a panel with plenty of internal space and very easy access.
From the March launch, old 1973 panel at left, modified from 6 pads in 1979 to two 4-pad racks . At right, the new panel (yellow). In the background, an interim temporary 3-pad "R&D" rack made out of 3/4" PVC.
From the "Birmingham Blast Off" launch in April - a photo of one of the racks. The blast deflectors are 6 x 6" bathroom type of "field tile".
From the May launch, a close-up of key details of the rack. The small rectangular yellow box with an A" on it contains the 9 volt battery and Piezo beeper used for the rack continuity testing. To the left of that, the arming buzzer. To the right of pad 3, the red translucent housing for the automotive LED arming light. At each pad, small red button for continuity testing, and the RCA jacks and plugs for the ignition leads.
Also from the May launch, a view of the panel in the foreground and rack in the background.
And finally, a photo from a recent demo launch, held at a local golf club.
- George Gassaway
