Date: Thu, 11 May 95 16:38:29 CST From: Bob Kaplow x5327 To: mjr40@columbia.edu Subject: Re: Newbie on Estes Command Control Here are my chad pad and relay launcher "articles". Both have been posted to rmr before, and published in our newsletter, "The Leading Edge". I hope they help you out ------------------------------------------------------------------------ Standard "Chad Pad" parts list: 1 8' 2x4, preferably treated lumber, unwarped 1 3/8"x3.5 carriage bolt 1 3/8" wing nut 3 3/8" washers 1 3/8" lock washer 4 2.5" galv. deck screws or nails 4 3/8"x12 landscape spikes 1 medium or large flower pot KGB Mini "Chad Pad" and tower parts list: 1 4' 1x2 (I used poplar instead of pine) 1 3/4" or 1" x 36" straight dowel 1 1/4"x2 carriage bolt 1 1/4" wing nut 3 1/4" washers 1 1/4" lock washer 1 1/4" T-nut 4 16# nails 1 small flower pot, ceramic tile, or stainless scrap 4 1.25" screws or nails Chad pad crummy ascii art: (folded for storage) +-------------------------------|-------------------------------+ | | | +-------------------------------|-------------------------------+ +----++-------------------------|--------------------------++---+ | || | || | +----++-------------------------|--------------------------++---+ The original is built from 8' of 2x4, I built a smaller one of 1x2 as well. Take your 2x4 or whatever and cut it almost in half, with one piece about 1" shorter than the other. From the short piece cut a square off each end. Nail or screw the two squares to the now significantly longer piece. Drill a 3/8" (1/4" for the mini version) hole thru the center of the two long pieces, and put a carriage bolt up thru the bottom, with a washer in the middle, and another washer, lock nut, and wing nut on top. With the wing nut loose, the whole thing now closes up as above, or opens in an "X". With it open, drill several holes in the top piece for different sized launch rods. Drill large (3/8" or to fit the 16# nails on the mini version) holes in each of the 4 ends for large landscape spikes to add stability. Blast deflector is a stainless scrap or a flower pot. That's about it! For the 1x2 version, Bunny and I added a 3' dowel with a threaded insert on the bottom. It screwes into the smaller (1/4") carriage bolt, lifting the model up 3' off the ground. Cut the top at a 45 degree angle so the blast deflector sends the exhaust away from the model (I use a scrap ceramic tile here). Perfect for gliders. Add some holes along the top 1x2 for launch rods to keep the glider wings from being blown around in the wind. Finish the whole thing as you choose to protect the wood. Bright colors or Aerotech style hazard colors might be a good choice to prevent people from tripping on it. Rust-o-leum BBQ black is a good choice to withstand repeated rocket exhaust. ------------------------------------------------------------------------ The KGB Aerospace Relay Launcher for HPR By Bob Kaplow - rev 3 Relay launchers are neat because they reduce the length of heavy gauge wire you need to a bare minimum, and reduce the losses from the battery to the ignitor. A relay switches current through the igniter, while a lighter weight control cable is strung between the pad and your controller. Voltage losses due to wire length are minimized, resulting in faster, more reliable ignitions and lighter equipment. This is especially important for ignition of clusters and HPR models with current sucking ignitors. Lightness is a big plus if you have to carry your range gear far to the launch site. The original relay launcher used in NIRA was designed by Ric Gaff for Bunny. Ric's design used two relays and a three wire cable. The first relay does the arming and continuity check remotely, and the second fires the rocket. I did my relay launcher design using only one relay, eliminating the remote continuity check. At 150 feet from the pad, you can't hear the continuity buzzer anyway, so it seemed logical and saved me a relay for another system. My relay is a SPDT (single pole, double throw) device. I originally used the other pole as a buttonless continuity check. As soon as you hook up the igniter, the buzzer tells you all is OK. If that becomes annoying, you can install the optional continuity check button. The Button also eliminates the need for a SPDT relay, so you can use the more common SPST (single pole, single throw) device. My power source is 8 1.2Ah sub-C nicads, the type commonly used in RC car power packs. I've tested the launcher with a 25A automotive fuse in place of an ignitor; it was vaporized instantly. The other demanding test is to fire a length of thermalite using the internal core wire. The whole piece virtually explodes instantly. I really need to use a heavier duty relay. The ones supplied by Ric were only rated at 5 amps. I'm obviously way over that. Radio Shack has a heavy duty 30 amp, 12 volt SPST relay for car stereo applications that should work fine. If you don't need real high current, try the GE 9V (7.2v nom) rechargable battery. One of them can vaporize the leads on Solar ignitors; two in series will fire coppertails. My system is built into a plastic project box, 2x4x6 that contains all components including the nicad batteries. If you are going to use an external battery or the GE rechargable 9V, you can use a smaller box. Use a high current rated connector for the external power cable. I used a dual banana jack for the output, so I can connect NIRA or NARAM launch system clips to the output, and can stack multiple connectors. There is also an RC jack that serves as both charge and launch cable connector. My launch cable is 150' long. Make yours as long as you need for the motors you intend to fly often. At the other end of the cable is a 35mm film can. We've been using plastic 35mm film cans for launch controllers for about 10 years now. Mine contains a mini pushbutton switch and a mini phono jack for a removable interlock. The contacts are shorted on the phono plug to create the safety key. Run your wire through the bottom of the film can, and don't forget to tie a knot in the wire for strain relief. Ric's original launcher contained a spring loaded switch for a safety key, but the safety code requires a removable interlock. Construction was pretty easy. Drill holes in the plastic box for the banana jack, cable/charging jack and optionally, for the continuity check button. I used hot melt glue to attach the relay, piezo buzzer and my Ni-cads. My Ni-cad cells were a very tight fit. You can use a holder if yours are looser. All connections were point to point wired, except the connections to the banana jack. Those are attached to terminal lugs bolted into place. The larger 30 amp relay has spade lugs, so you wouldn't need to solder those connections if you went with the larger relay. Before NARAM-36 I discovered a nifty feature of this system. I was designing a relay box to be triggered by a normal launch system. I ended up with the same circuit, except the connections to the NARAM system were to the GROUND and FIRE pins. The normal remote cable connects to the CHARGE and FIRE pins. With the addition of an extra RC plug with bent paper clips soldered to their ends, I had a double duty relay box. Build yourself a reliable, rugged relay launcher today! Parts List: Most parts (except 35mm film can) can be found at any good electronics store or your local Radio Shack. Main Box: --------- 12 volt 5 amp (or larger) SPDT relay 12 volt piezo buzzer 9-12 volt Nicad or Gel Cell battery Dual banana jack Dual banana plug Micro clips RC charging jack, panel mounted, three conductor (J2) Project box big enough for battery, relay, buzzer and other parts Heavy gauge (18 or better) wire for all connections Small push button for continuity check (SW2) (optional) Power jack, cable, and clips if using external battery Remote Controller: ------------------ Plastic 35 mm film can Two conductor stranded wire of desired length RC charge plug (P2) 3.5mm phono plug (P1) 3.5mm phono jack (J1) (for Safety Key) Small pushbutton launch switch (SW1) Charge cord: (optional for internal battery only) ------------ RC charge plug (P2) Two conductor stranded wire to connect to your charger (Editors Note: if you substitute components for J2 and P2, use only non-shorting polarized plugs and jacks. Accidentally shorting the Fire and Charge leads will cause the relay to close and ignite the rocket while you are at the pad. You also don't want to short the battery through the launch controller.) In use I do NOT connect or disconnect the remote cable while there is a rocket on the pad. That is what the safety key is for. Crude ASCII schematic: [download the original if you want better] Relay Launcher NC +-------[buzz]----------O | \ / SW2 \ COM /(momentary) O------------< / (optional) / | NO / +-----------------------O | | Fire 12V 5-30A relay | >---------------+ SPDT Charge | | >-------+ | | | Banana _ _) Jack J2 ___ Battery _) _ 9-12V _) ___ _) | | Ground | | >-------+---------------------------------------< Launch Controller / SW1 Fire +------> >--------------/ --------------> | P1 shorted J1 P2 |safety key safety jack Charge +------> >------------------------------->