HPR Cluster Idea... What To Do When Some Start, And Others Don't

[K'Tesh]

I'm not a doctor, nor do I play one on TV...

Ok... So, I'm not a whizkid on electronics, but one thing I seem to keep seeing is problems with clustered HPR launches going bad when one or more of the motors fail to light. Now, presuming that once one lights, and the others are having a momentary delay in firing off, the speed that the rocket leaves the pad can yank the leads off the igniters, and disaster ensues.

So, what about this idea? The launch pad director pushes the button, and that sends a signal (via wires, or a reliable wireless system) to onboard electronics that send the juice to the motors... If the rocket leaves the pad, the power will continue flowing to the late starting motors... UNLESS sensors detect aberrant flight performance, at which the power stops, and preloaded emergency procedures go into effect (blow it apart or blow it up). Basically, in my mind, this is some kind of variation of an airstart. However, the rocket doesn't need to be in motion for the start.

Can it be done? Has it been done? Can I somehow get some credit for the idea if it hasn't?

 

[Bat-mite]

I don't know, as clustering is not my thing. But, I can tell you this: while you may get credit, you will not get royalties. You cannot patent an idea, only the execution of an idea. If one could patent an idea, then there would only be one brand of car, one brand of refrigerator, etc. Unless you come up with the specifications for the device, then all you could ever get is an attaboy.

 

[rstaff3]

I'm not a doctor, nor do I play one on TV...

Ok... So, I'm not a whizkid on electronics, but one thing I seem to keep seeing is problems with HPR launches going bad when one or more of the motors fail to light. Now, presuming that once one lights, and the others are having a momentary delay in firing off, the speed that the rocket leaves the pad can yank the leads off the igniters, and disaster ensues.

So, what about this idea? The launch pad director pushes the button, and that sends a signal (via wires, or a reliable wireless system) to onboard electronics that send the juice to the motors... If the rocket leaves the pad, the power will continue flowing to the late starting motors... UNLESS sensors detect aberrant flight performance, at which the power stops, and preloaded emergency procedures go into effect (blow it apart or blow it up). Basically, in my mind, this is some kind of variation of an airstart. However, the rocket doesn't need to be in motion for the start.

Can it be done? Has it been done? Can I somehow get some credit for the idea if it hasn't?

Sounds a lot like airstarts to me. You light the central motor that, hopefully, is enough to give a safe and satisfying flight. Electronics detect launch and light the airstarts. Here's an example of the smaller motors going off before the main...no bueno.



edit: I read too fast and didn't notice the comment on airstarts, so yeah your idea is different. I don't know if there is any benefit having the main ignition controlled by an on-board computer, but it might be useful to have the computer verify all airstarts have continuity before firing them. The other part of the original idea is how to terminate an errant flight. IMO more thought needs to be put into that part. For instance, it is not clear that there is always a benefit to terminating a flight mid burn. Just quick thoughts...just slightly less quick than my first comment. It will be interesting to hear from more experienced folks and especially those who have built flight computers.

 

[cavecentral]

Like airstarts, low current igniters would be needed.

 

[Tonimus]

I could imagine this could be done pretty simply with an onboard self-latching relay. I've airstarted 6-29mm motors with one small lipo. Wasn't an issue. Use your launcher to trip the self latching relay and the relay and power supply is carried off on the rocket.

 

[blackjack2564]

The old G-whiz units would light outer ring motors [#] as soon as it sensed motion from the pad lit motor.
If central motor did not light, then nothing else would.

Simple use of a G switch, firing from on board system with separate pyro battery.

#[if set to do so]

However in reality....properly prepped cluster motors. [ thermite, BKNO3, Pyrodex pellets etc.] used as igniters with extra long pad leads...I use 10ft..allow that extra time for ignition while moving up rail.

Using CTI motors with e-match and their pre-installed pellet makes clusters a no-brainer. Cloning this by using a pellet in AT motors with an E-match will get same results.

It's really more about proper clustering technique, than cooking up electronics which come with another skill set need.
First and foremost ya need a good mentor with experience.
Your idea is intriguing, but simple tried and true methods do exist.



This can be done with many modern altimeters, by the way, already to program to fire pyro channels, any way you wish. That is after main motor is lit, which should always be capable of safe flight on it's own.

A missleworks WRC [wireless control]can be used to launch from inside rocket and many altimeters can do the rest.

 

[cerving]

Once a motor ignites, not much you can do about it. If you have a 4-motor cluster and only one lights, you're in for a rough flight. By the time you detect that the other three motors haven't lit, it's way too late, even if you have an on-board battery to keep the other three igniters alive. Chances are that the other three ain't gonna light at that point, regardless of what you do.

That's why your best bet for clusters is to use identical motors and igniters, preferably either well-dipped igniters or CTI motors with the BP pellet for ignition. Smokies, Whites, and variants thereof tend to light easiest; colored motors (red, green, pink, etc.) and longburns tend to take longer to light.

BTW, somebody used to make a cluster controller that was originally for airstarted clusters, but also could be used for single stage clusters. If you didn't get good continuity on all selected channels, it didn't show continuity. That helps prevent a failed launch if you have a bad igniter, but not if they're all good but one or more doesn't light the motor.

 

[Charles_McG]

I think Jim's idea (essentially a 0 altitude airstart) is to address the failure mode of slow igniters getting pulled out during ascent. But is that really a common failure mode? Is it more common that igniters pop, but fail to light the motor?

Unstable flight abort by deployment is a separate idea. I have no idea if it's a good one - plenty of experience with unstable flights, mind you a but only in little rockets.

 

[K'Tesh]

I think Jim's idea (essentially a 0 altitude airstart) is to address the failure mode of slow igniters getting pulled out during ascent. But is that really a common failure mode? Is it more common that igniters pop, but fail to light the motor?

Unstable flight abort by deployment is a separate idea. I have no idea if it's a good one - plenty of experience with unstable flights, mind you a but only in little rockets.

How many of them pop, but just as, or just after they are yanked out, thus failing to light the motor?

 

[cerving]

How many of them pop, but just as, or just after they are yanked out, thus failing to light the motor?

If you have a HPR cluster, it's a good idea to have a long igniter whip that's elevated to about half the height of the rail, so that the rocket can rise without the igniters getting pulled out if they're not lit yet. That gives them a few tenths of a second more to light... if they're not lit by that time, they probably wouldn't have lit anyway.

 

[dhbarr]

I've seen quite a few where the excess length of connector is suspended a ways, such that the wire goes down and hooks under the motor before coming back up through the throat. In this arrangement the outboard igniters have a bit of extra dwell time.

 

[Steve Shannon]

I've seen quite a few where the excess length of connector is suspended a ways, such that the wire goes down and hooks under the motor before coming back up through the throat. In this arrangement the outboard igniters have a bit of extra dwell time.

I have a picture somewhere of the Deuces Wild rocket lifting one of my pad boxes off the ground when a motor failed to light.

Another approach would be to clamp the rocket to the launch pad until all the motors light. It would be hard on the launch pad but prevent Wild flights.

Still, I agree with Jim that ways already exist to augment igniters and usually ensure rapid ignition of all the motors.


Steve Shannon

 

[DavidMcCann]

Only D12's, but an example of a cluster gone wrong-

I think the best way to do it is to have a central motor capable of lifting the whole shot, and using a timer set to zero to light all the outboards. Not really a new idea, just one most people are too lazy to do.


I've found AT blues the best to cluster. CTI seem to ignite well, but I don't have personal experience. I'd avoid AT greens.

 

[Handeman]

I agree with David. The best way to cluster is to ground ignite a central motor that is strong enough to provide a safe and stable flight. Let the on board G-switch detect the successful launch and fire the cluster motors. If one of the cluster doesn't fire at that point the rocket should have enough speed to remain stable and obtain a safe flight. It might angle off if one or more of the cluster motors doesn't light, but the strong central motor should still give it a successful although less then optimal flight.

Of course this is all predicated on the deployment being electronically controlled and successful. Relying on a motor eject from a motor that might not light is not a good plan. Failed altimeters are another issue.

 

[MikeyDSlagle]

But not all rockets have a central motor. The LOC Vipers and Mother Lode are the ones that spring to mind. So you have to light them all on the ground or quickly after. I have zero experience with clusters just pointing out that the best way isn't always the best way, or even possible.

 

[DavidMcCann]

But not all rockets have a central motor. The LOC Vipers and Mother Lode are the ones that spring to mind. So you have to light them all on the ground or quickly after. I have zero experience with clusters just pointing out that the best way isn't always the best way, or even possible.

One may argue these are poorly designed clusters. They can work, but don't allow for the best approach.

I'll just leave this here-

[youtube]csjyBYriWwg[/youtube]

 

[AdAstraPerAspera]

Even if you are flying a cluster with no central motor, make sure any one motor that you are trying to light on the pad can safely lift the rocket in a stable (if arcing slightly) flight. The problem with clusters is that people fly them in a rocket so heavy that they need all to light for a safe flight.

 

[Sooner Boomer]

Another approach would be to clamp the rocket to the launch pad until all the motors light. It would be hard on the launch pad but prevent Wild flights. Steve Shannon

I don't see how you can do this. Some motors have burn times of less than one second. For example, the I-800 has a burn time of aprox. 1/2 second (at 200 lbs thrust!).

 

[dhbarr]

I've seen Models w/ burnstring holddowns.

 

[AdAstraPerAspera]

This was done by one of the hybrid manufacturers to ensure the rocket didn't leave the pad before the motor was up to pressure. I believe they used zip ties.

 

[Steve Shannon]

I don't see how you can do this. Some motors have burn times of less than one second. For example, the I-800 has a burn time of aprox. 1/2 second (at 200 lbs thrust!).

Yes, and the H999 only burns for a third of a second. Because it might be difficult to guarantee that motors will ignite in that short of time, Warp 9 and Vmax motors would probably be a bad choice for clustering.


Steve Shannon

 

[prfesser]

I've only clustered once, but my understanding is that the effect of duds can be minimized by construction such that the long axis of each MMT passes through (or near) the rocket's CG. Not a complete fix, just minimizes the off-center thrust.

Best,
Terry

 

[burkefj]

Yup, I was just going to suggest that as well...

I've only clustered once, but my understanding is that the effect of duds can be minimized by construction such that the long axis of each MMT passes through (or near) the rocket's CG. Not a complete fix, just minimizes the off-center thrust.

Best,
Terry

 

[Andrew_ASC]

Could one simply run dual igniters in parallel into each motor to minimize failure to ignite? Or could that cause a CATO? Just a noob here.

[video=youtube;J-15ZUpcUSU]https://www.youtube.com/watch?v=J-15ZUpcUSU[/video]

This was that one video that scared a team of university students away from trying a free hybrid research motor with clustered solid outriggers...