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  #21  
Old 02-04-2010, 02:42 PM
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Mark II Mark II is offline
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I'm surprised that no one (not even me) has mentioned Boris Katan yet. He's kind of like the current clustering guru (or Jedi) at the moment. He wrote an interesting article on the subject in Sport Rocketry a couple of issues ago. In it he talked a lot about clustering black powder Ds and Es, but I'm sure he also talked about clustering composite motors, too. I'm not sure if he posts on this forum, but I know that he does on TRF and probably Rocketry Planet as well.

Pratt Hobbies sells a relay ignition add-on that can be used to augment existing launch control systems. You just connect the existing leads to it. No engineering degree or electrician's license needed! Inexpensive, too. You just need to supply your own secondary "at-the-pad" battery. Power from your existing battery closes the relay in the Pratt module out at the pad when you press the launch button on your existing controller, which allows current to flow to the igniters from the battery right next to the pad.

MarkII
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  #22  
Old 02-04-2010, 02:42 PM
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GregGleason GregGleason is offline
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Quote:
Originally Posted by zog139

"I" really do like the new R2D2 ignitors by Quest ! Great product !



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  #23  
Old 02-04-2010, 07:55 PM
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Quote:
Originally Posted by Mark II
-SNIP-Pratt Hobbies sells a relay ignition add-on that can be used to augment existing launch control systems. You just connect the existing leads to it. No engineering degree or electrician's license needed! Inexpensive, too. You just need to supply your own secondary "at-the-pad" battery. Power from your existing battery closes the relay in the Pratt module out at the pad when you press the launch button on your existing controller, which allows current to flow to the igniters from the battery right next to the pad.

MarkII
That's a good heavy-duty system (with a thoughtful notice label on it as well), but I was disappointed to read that it requires a 12 volt launch controller to activate the relay. If I was locked into using 12 volts anyway as the Pad Relay Module requires, I'd just as soon use a launch controller that is hooked directly to a 12 volt car battery and use its high amperage to ensure ignition of clustered motors.
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  #24  
Old 02-05-2010, 04:39 PM
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Quote:
Originally Posted by blackshire
That's a good heavy-duty system (with a thoughtful notice label on it as well), but I was disappointed to read that it requires a 12 volt launch controller to activate the relay. If I was locked into using 12 volts anyway as the Pad Relay Module requires, I'd just as soon use a launch controller that is hooked directly to a 12 volt car battery and use its high amperage to ensure ignition of clustered motors.
I think that the target market for this product are folks who already have a 12v launch system set up at the range and want to tack on a pad-relay system to launch clusters. The module is an inexpensive add-on that provides an existing system with relay capability that is easy and quick to install. All the Pratt Hobbies module does is provide you with the relay and another set of igniter leads/clips, all put together with plug-in convenience. You place the module out at the pad along with a second fully-charged 12v battery to power the cluster of igniters, hook that battery to the module, and then just clip the existing leads from the launch controller to the module as well. The power supply up at the launch control table that is normally used to power the igniter clips out at the pad is used instead to to power the relay in the module. Since you will no doubt be launching other rockets with single motors during the session (on multiple pads as well if it is a club launch), you set up your launch equipment in the same manner that you always do. When the time comes to launch the cluster, you just take the igniter clips from one of the pads and clip them to the module instead. Then you use the set of igniter leads coming out of the module to hook up the igniters in the cluster. In any pad-relay system, either commercially-made or scratch-built, you need to have a second source of power to trip the relay, since it is on a completely separate circuit from the one that will power the cluster of igniters. If you have your system set up to launch single motor rockets already, why not just borrow the juice from that battery to trip the relay when you are ready to launch a cluster? The alternative would be to install and string out leads for a completely separate, dedicated pad-relay system containing its own relay-tripping power supply. In either scenario, you will still need to have a 12v supply out at the pad, but in the second scenario with the dedicated system, you will need to bring along and hook up a third battery to power the relay when the time comes to launch a cluster. The Pratt Hobbies module assumes that you will already have a 12v supply with leads going out to the pad, so it is set up to power the relay off of those leads.

MarkII
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  #25  
Old 02-05-2010, 08:52 PM
Green Dragon Green Dragon is offline
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Actually it is not needed for a second battery to power the relay .

Our own relay launcher runs off of the same pad battery - just a simpel circuit to divert some juice back tot he controlelr to close the relay, the long distance does not matter if enough to still lock it up .

if not enough, always the huge capacitor driven 'master blaster' type - those will light anythign short of dirt , and maybe dirt, too

( personally I use a homemade control, uses on rechargable 9 v nicad, that will fire anythign I am liekly to fly on my own, including copper heads - anythign larger I would fly at a club launch and they have the good setup

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  #26  
Old 02-05-2010, 09:45 PM
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Quote:
Originally Posted by Green Dragon
Actually it is not needed for a second battery to power the relay .
Well, as you can see my knowledge of pad-relay launch systems is rather scant. I just assumed that any juice that was bled off of the pad battery to power the relay had the effect of reducing the amount of power that could be delivered to the igniters, and so that was to be avoided. I kind of thought that keeping the power losses to an absolute minimum was the whole point of a pad-relay system.

Regardless of that, in the example of the specific product that we were discussing, existing pad leads and the launch control power supply are connected to the unit and are used to trip the relay, allowing the pad battery to deliver all of its power to the igniters. That is why the module is constructed to use a 12v battery for operation of the relay. At least that's what I have gleaned from the description on the Pratt Hobbies web site. This may not be the only way to set up a pad-relay power system, but I gather that the Pratt module is designed like that in order to facilitate quick and painless connection and disconnection from the standard system at the range as needed. It is certainly reasonably priced and it appears to be so easy, a Neanderthal like me can use it.

MarkII
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  #27  
Old 02-05-2010, 11:20 PM
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I can see where Pratt Hobbies' relay module would be useful at group launches or contests where long leads are run from the LCO's (Launch Control Officer's) firing console out to the launchers (especially if rack launchers are used), as the voltage drop even with a 12 volt firing console power supply might make reliable cluster ignition problematic.

I'd like to see a relay firing system (I may build one, one of these days) that could be triggered by an Estes Electron Beam or Quest Launch Controller and would use a gel cell relay battery. I once saw a commercial (intended for car repair shops) battery booster that was built onto a small hand truck for portability. Something like that would be perfect for a portable "all-in-one" launch controller/launch pad that would include a relay firing system. It could have holes for 1/8," 3/16," and 1/4" launch rods drilled into the hand truck frame, and it would be laid down flat to serve as the launch pad, with the rolled-up firing leads with the hand-held launch controller being unrolled from their receptacle on the hand truck.
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Last edited by blackshire : 02-05-2010 at 11:31 PM. Reason: This ol' hoss done forgot somethin'.
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  #28  
Old 02-06-2010, 10:38 PM
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John Brohm John Brohm is offline
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Quote:
Originally Posted by Mark II
Well, as you can see my knowledge of pad-relay launch systems is rather scant. I just assumed that any juice that was bled off of the pad battery to power the relay had the effect of reducing the amount of power that could be delivered to the igniters, and so that was to be avoided. I kind of thought that keeping the power losses to an absolute minimum was the whole point of a pad-relay system.

...


Hi MarkII;

Well as a design principle that's usually the case, although relay-based launch systems tend to be sourced by high capacity batteries and the losses would typically not matter.

Our club has two systems, one that we use for our competition launches, and one that we use for sport launches. I'll make a few remarks about each, and since I intend to show some pictures, I'll spread this over two posts.

The Competition System is a relay based system, and one of its design principles is a complete separation of control and ignition power. The ignition battery is located at the field relay unit, and when the relay contacts for a particular pad are closed, basically the 12VDC source is switched across the igniter. Since we use an auto battery for the ignition source, quite a bit of current gets dumped, and it really has no problem with clusters.

The pad power in this system is used only for firing igniters; relay control power and continuity check power is all sourced from the control battery in the LCO Box.

One of the features of this system is its ability to support an HPR pad. The field relay unit houses the appliances and circuitry for 5 pads, and the HPR pad is to be controlled by a remote box (we call it the Pad 6 Away Box); the idea is that the HPR pad should be even further away from the LCO and the specatator line for safety reasons, and in our case, it's located 100' away (our club flies with a G impulse limit, so when we say HPR in our context, it's relative).

Well this system was an inherited system and when it came to us, the Pad 6 Control Box was MIA. Since we were getting to the point where we had some flyers that wanted to use that 6th pad capability, the club asked me to design and build a replacement Pad 6 controller. With a little reverse engineering and the schematics for the Field box, I was able to come up with the Pad 6 Away box that you see here. A couple of upgrades to th design were included; those would be the printed circuit boards that capture the continuity check circuit (both local and remote) as well as the Pad Active display board (the big 1' multi-die LED).

It all works very fine, and the concept of isolating control and ignition power is elegant. If I have a complaint at all it's that the control power ends up be extended quite far, although as a practical matter the loss in the control cabling is only a few tenths of a volt.
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  #29  
Old 02-06-2010, 10:45 PM
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John: I significantly shortened my original post here because you provided much more relevant information than I did.

Black Shire - My guess is that a significant portion, if not the majority, of clusters are flown at organized sanctioned launches, so a product like the Pratt Hobbies module that can be easily connected to and disconnected from the club's system as needed would no doubt find at least a few buyers.

MarkII
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Last edited by Mark II : 02-06-2010 at 11:05 PM.
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  #30  
Old 02-06-2010, 11:07 PM
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Quote:
Originally Posted by Mark II
Well, as you can see my knowledge of pad-relay launch systems is rather scant. I just assumed that any juice that was bled off of the pad battery to power the relay had the effect of reducing the amount of power that could be delivered to the igniters, and so that was to be avoided. I kind of thought that keeping the power losses to an absolute minimum was the whole point of a pad-relay system.

...



Our second system, the Sport Launch system, also has a separation of control and ignition power, but not as strictly implemented as in the case of our Competition System. In the Sport Launch system, control power is used to pick the pad relays and to source the LCO continuity indication, but Ignition power out at the pad is used to source power for the Pad Active indicators as well as the local continuity indications. In this system, since only one pad can be active at any on time (unlike the competition system, where all pads can be active), the current drain on the ignition battery is only 10s of milliamps, as it's being used to drive LEDs. This approach makes the implementation of a couple of the design features a little more practical in the pad rack, and the impact to ignition power is neglible when high capacity sources are deployed.

Our Sport Launch system is very old, its origins spawned somehow from the genesis of the club. From a control perspective, it functioned like a great big Electron Beam; the ignition power was located at the LCO box (which like an Electron Beam mainly consisted of a key switch, a launch switch, and a continuity indicator). Power was taken from an auto battery, passed through the switches in the LCO box, and then off through a 50' small gauge mulit-core cable to feed the individual pads. If our Equipment Master didn't make a point of keeping the battery charged, APCP engines in particular were at times difficult to ignite.

Our Equipment Master complained about this one day, and asked I would be willling to upgrade the Sport System to an all relay capability. I told him I would be happy to, so long as he was happy charging two batteries instead of one.

Away went the old LCO box, to be replaced by the unit you see below, and the pad rack was taken apart, upgraded with control relays, heavy duty wiring, local auto continuity indicators (solved the unpreferred problem of asking the LCO to check continuity while people were still at the pad!), and a very large and highly visible multi-die LED indicator at each pad location to provide a Pad Active indication. The system also incorporates a safety timer disconnect, so if the LCO inadvertently leaves the key switch in, the LCO box times out after a couple of minutes and the unit has to be recycled in order to ARM it.

What I found was that maintaining a pure isolation between control and ignition power would have added a little more cost and complexity to this particular implementation, and since the bleed on the ignition power was a few LEDs, the impact, as mentioned earlier, was negligible. So in this system we have a separation between LCO Box and Pad Rack power, a minor but practical compromise as compared to the design of the Competition System.
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