Air Starting 5 motors. Any electronics?

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jdbwizzard

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I have been working on my Saturn V. I was wondering if anyone knew of a device that could air start 5 motors and is light weight? At first I was toying with the idea of gap staging but with a distance of 13.5" I don't trust being able to reliably light all the motors. So now I've turned to electronics.
 

blackbrandt

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There's a lot of flight computers that can do this.

RRC3 (from missileworks)
Eggtimer (from Eggtimer Rocketry)
Raven (from Featherweight Electronics)

Don't do airstarts with a basic dumb timer (one with only a g-switch activation). In the event the rocket doesn't go up as high or as fast as you expected before lighting the motors, you run the risk of a sideways ignition. The above altimeters all have some sort of safety check (RRC3, for example, has a time/altitude/velocity check) that aborts airstart if safe conditions are not met.
 

jdbwizzard

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I have review these as options but my concern is being able to handle 5 igniters. The raven looks capable but a little more than I'm willing to spend. My idea is to have 3 tiny lipos. Two connected to two outside motors and one to light central motor. I also have limits on weight I can add so battery size is a big concern. I think I will just build the device but was wondering if there was anything out there or what other have done with clustered air starts. This Saturn V has been a complex problem to tackle.
 

Reinhard

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You can amplify your altimeter with the Whooshtronics Clust-o-matic. It "only" has 4 channels, but two igniters on a channel shouldn't be a problem at all or you can use two of them in parallel, for 8 channels.

Reinhard
 

blackbrandt

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I have review these as options but my concern is being able to handle 5 igniters. The raven looks capable but a little more than I'm willing to spend. My idea is to have 3 tiny lipos. Two connected to two outside motors and one to light central motor. I also have limits on weight I can add so battery size is a big concern. I think I will just build the device but was wondering if there was anything out there or what other have done with clustered air starts. This Saturn V has been a complex problem to tackle.
You might be able to do something with a relay. Hook a relay to the output channel on the altimeter, and then use a pyro battery to light your igniters.
 

FredA

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+1 on the Clust-o-matic. Have used it with great results.
-1 on the relay - worry about inadvertent closure due to shock or take-off/burn-out acceleration - after all, it just has a little spring holding the contacts apart.

I've also build my own version of the Clust-o-matic using opto-isolators. AC-input Opto's with FET outputs give you a nice polarity independent, ground-reference independent, and static immune input.
Usually I like independent output's and batteries for each motor so there are no side effects of series/parallel igniter wiring or shorting on one motor.
 

jdbwizzard

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Yes this I like the design of the Clust-o-matic. Should be easy enough to build one with independent outputs and battery inputs. Thank you for everyones input. Fred do you know the part number of the opto-isolators you used.
 

FredA

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Justin - sorry, it's been a while. Might be able to find the circuit tonight when I'm at the barn.....will look for it and get back to you if I find it.
Failing that, digikey has many to choose from.
 

dlb

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The Marsa54L works, if you question one output, use more than one and time/control each channel to whatever you like...
 

jdbwizzard

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There will be five estes engines. As for igniter I'm hoping to use q2g2 but I need to find 5 more. I have five q2g2 for the first stage but only estes igniters for the second stage as of now.
 

markkoelsch

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What size is this rocket, and what motors? BP, composites, etc?
 

jdbwizzard

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What size is this rocket, and what motors? BP, composites, etc?
The rocket is a modified Estes Saturn V which uses a BT101 (Almost 4") for the main section. All 11 motors will be black powder.5x - D12s in the first stage to 5x - A10 in the second stage to a single A10 for the third stage.
 

StanO

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You can amplify your altimeter with the Whooshtronics Clust-o-matic. It "only" has 4 channels, but two igniters on a channel shouldn't be a problem at all or you can use two of them in parallel, for 8 channels.

Reinhard
From Ausrocketry...https://forum.ausrocketry.com/viewtopic.php?f=60&t=5546

Re: clust-o-matic
Postby PK » Fri Jun 17, 2016 3:17 am
Sorry guys, but I've made the decision to step back (further) from hobby rocketry. This means no more making stuff for folks.
The build thread for the clust-o-matic has the schematics and parts, you should be able to put some together.

PK out...
 

ksaves2

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Control it yourself; if you have some RC equipment, these work great.

https://www.pololu.com/product/2803
Looks interesting. Ostensibly if one had a stock EggTimer altimeter (not a Quantum) it does have a servo option that perhaps one of these Pololu boards might interface with the deployment channels? The EggTimer can be programmed to move a servo
to turn stuff off and on. An outboard board that mirrors apogee and main deployment channels would have to be used to provide the deployment. Now the ET can directly switch current but I don't know if it could handle 5 motors. Yeah, it's a lot of
weight to carry. These boards would be reasonable for a panic button with R/C stuff. Kurt
 

cerving

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Looks interesting. Ostensibly if one had a stock EggTimer altimeter (not a Quantum) it does have a servo option that perhaps one of these Pololu boards might interface with the deployment channels? The EggTimer can be programmed to move a servo
to turn stuff off and on. An outboard board that mirrors apogee and main deployment channels would have to be used to provide the deployment. Now the ET can directly switch current but I don't know if it could handle 5 motors. Yeah, it's a lot of
weight to carry. These boards would be reasonable for a panic button with R/C stuff. Kurt
I haven't tried five ematches with an Eggtimer but I've done four. The TIP120 transistors in the Eggtimer Classic are very durable, the only way you're likely to fry one is by dead-shorting a deployment transistor. I don't know if I'd use the standard Estes igniters for this, but the PSII igniters would probably work, and they light just fine with a 2S LiPo.

Cluster igniters should always be wired in parallel, because if you wire them in series and one of them opens before the others light then the current will be shut off and the remaining igniters won't light. The problem is that three of the four igniters wired in parallel can have no continuity and you have no way of telling. That's what the Clust-O-Matic did... it only allowed the "master" input to see continuity if all of the cluster igniters had continuity. It shouldn't be that difficult to come up with an equivalent circuit to do that; I've had several requests to do that myself, but it's not on my radar.
 

FredA

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I beg to differ - clusters should NEVER be wired in parallel.
Especially if you want them all to light at the same time.
Wiring in parallel will likely fire them in order of resistance.

Given that - this is EXACTLY why I like the Clust-o-matic type solution that has independent circuits for each motor.
Takes all the risk and uncertainty out of the problem.
 
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jderimig

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How about a mini-flash pan? 1 igniter then POOF!

Edit: Then optionally augment each motor nozzle with a short length of quickmatch.
 
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