Clusters

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ben

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how do you make shure all the engines fire in acluster? About how many amps/volts does each motor take to ignite?
 
Ben,

The nickle tour for answers to this question are:

1) Check your igniters to make sure they are all good (continuity check on each would be good)

2) All igniters should be about the same size/shape

3) *carefully* install them (take extra care)

4) Conect the igniters in PARALLEL, NOT in series. You can do this by twisting the leads or using a multi-clip whip

5) Use a strong 12V DC power source. I recommend a car battery (it's all i ever use)

ALso, a search on TRF uncovers these interesting threads:

How to properly ignite a 3 motor cluster

7 Motor Cluster ignition questions

first cluster

cluster question

how do you launch a cluster?

Hope this helps

jim
 
Jim's suggestions are right on the money, as you might expect.

I've launched my scratch 2-motor cluster rocket twice now. On the first flight, only one motor ignited, but both ignited on the second flight.

I used a fellow club member's launch controller that hooks to a car battery (my minivan's battery worked great). I spread the leads of each igniter apart to try to prevent shorting of the leads, and I think I broke one of the igniters on the first flight, since it looked like it still had pyrogen on it after the flight. I did not check continuity of the igniter after the flight. For each flight, I twisted the leads of the two igniters together and clipped the launch controller's clips to the twisted leads.

First flight was very umimpressive (50 feet up, ejection after it hit the ground), but the second flight was cool! LOTS more tracking smoke than I'm used to, and a nice high flight on two Quest motors, B6-4's I think. It was cool.

From everything I've read, using a big high-current battery is the only way to go with clusters, so I plan to use nothing but car batteries or something very similar whenever I fly a clustered model.

Because, well, I want all the motors to light, and when they do, it's really cool.

Did I mention that cluster flights are cool? They really are.
 
All those comments by Jim are right on the mark, and those threads are good ones too.

About all I can add: you do everything that you can to assure a successful ignition, and most of the time it will work. Part of the time you will just miss on one or two of the motors. I don't know if it is possible to be 100 percent certain of perfect cluster ignitions.

One last point: to protect your rocket AFTER ignition, you should select two or three of your motors to have the desired delay charge for best recovery deployment, and put those motors in mounts that allow the ejection charges to vent forward through the rocket for deployment. Odds are, at least one of those motors will be ignited and you will have a good recovery deploy. Any other motors can be mounted in plugged MMTs or their ejection charges can simply be vented overboard.
 
Originally posted by powderburner
Any other motors can be mounted in plugged MMTs or their ejection charges can simply be vented overboard.
powderburner,

If you use a motor with an ejection charge in a plugged motor tube, aren't you just asking to have the motor eject out the back, or even worse, have the motor tube rupture, when the ejection charge goes off?
 
A plugged MMT is exactly what you want to use if you do want to eject extra motor casings.

Yes, there is some chance that you can rupture the MMT ..... if you load the motor in the standard way with tape wraps and motor retaining hardware. If, however, you WANT the motor to leave (Astron Streak), you only add enough tape wrap (or paper shim) to lightly hold the motor in the mount while it is sitting on the pad.

For a mega-cluster adventure you really only need one or two of the motors to deploy the recovery gear. Make that two or three motors for redundancy/safety. The rest are all dead weight during landing, often to the point where they add a significant weight and can damage any fin that touches down first. All those other motors can be ejected in mid-air using their own ejection charges or using the booster blow-through gas. If you are sqeamish about peppering the ground with motor casings, add a little streamer to each (it's a really cool effect to see a bunch of these raining down).

I think that in order to have any serious risk of rupturing the MMT you would have to use a plugged front end at the same time you use a retaining clip.....and why would you?
 
Originally posted by powderburner

I think that in order to have any serious risk of rupturing the MMT you would have to use a plugged front end at the same time you use a retaining clip.....and why would you?
Um... because I don't know what I'm doing and haven't thought things through very carefully? :D
 
There are some cool, OLD model rocket designs that seem to have been forgotten. They use motor mounts where the motor is intentionally loose, and moves around at ejection to activate the recovery mode.

Without going way off thread, let me just say that I think everyone ought to be required to build at least one old Astron Sprite. The motor in this old design shifted aft at ejection but was still retained in the rocket. The new c.g. results in an unstable rocket, which tumbles back down to the ground.

I guess my point is this: the motor does not have to be anchored in place to work, sometimes you DO want them to eject.

If you do this for a NAR contest the ejected motors are required to have a recovery device. Back in olden times you could use BT30 for MMTs and wrap a streamer around the motor case before slipping it into the mount. And a bright streamer helps you find the burned motors after they land, so you don't trash someone's property with rocket debris.
 
thanks for all the good advice I can now successfully launch my 15 engines on my scratchbuilt Vostock.
 
Originally posted by powderburner


Without going way off thread, let me just say that I think everyone ought to be required to build at least one old Astron Sprite. The motor in this old design shifted aft at ejection but was still retained in the rocket. The new c.g. results in an unstable rocket, which tumbles back down to the ground.


Heck, build the FlisKits Tumbleweed

:D
 
Originally posted by powderburner

One last point: to protect your rocket AFTER ignition, you should select two or three of your motors to have the desired delay charge for best recovery deployment, and put those motors in mounts that allow the ejection charges to vent forward through the rocket for deployment. Odds are, at least one of those motors will be ignited and you will have a good recovery deploy. Any other motors can be mounted in plugged MMTs or their ejection charges can simply be vented overboard.

Another bit of cheap insurance: stuff a small amount (~1" square) of wadding into the front end of each motor. There have been cases when a motor which failed to light on the pad got lit at the wrong end by the ejection charge of another motor. Not a pretty sight.


Bill
 
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