Booster Separation Control

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ebruce1361

ebruce1361

The man with the plan. And some duct tape.
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I've done detachable external boosters before, but those were detached via ejection charge of the booster motors. Now I want to try something a bit different: I want to have boosters detach a couple seconds before their ejection charges fire for a nice, clean separation where the boosters will coast in the same direction as the core rocket while decelerating. This will be for a BT80 scratch-built Delta IV Heavy flying on a 29mm F10 for the core and the boosters will ideally be on E15s and will have their own parachutes.The method I want to go with for separation is to use two pairs of rail buttons on the core that slide into notches on the boosters and two 5vdc solenoids with their pins keeping the boosters from sliding back/down. The solenoids will be triggered to retract a few seconds after launch, and the boosters will slide back on the buttons until the notches widen (think of a sliding chain door lock but with the notch in more of a V shape) and the boosters fall off.

What I need help with is the control electronics. I was thinking of the SparkFun Wake On Shake accelerometer starting a timer relay, but I wonder if an electronic staging altimeter would be better. What say ye?
 
I'm not sure any altimeter I can think of will drive solenoids directly. Could you use servos?

I've done something similar but with a small BP charge for separation, and that could be easier. Be warned that you may well have a hard time getting all of the motors lit at the same time. Use igniter leads as long as possible.
 
I had thought about servos, but those would inherently be larger and require a basic speed controller. I plan on having the altimeter or accelerometer+timer trigger a relay that would in turn supply power to the solenoids rather than have the solenoids rely on output from the accelerometer/altimeter.

As for the clustering issue, I do have an igniter whip setup with 30 in. leads, and I have been successful in clustering up to five BP motors with it. Still, I may also put together an additional circuit that would either detect the vibrations/acceleration of the core motor to trigger the side boosters as if they were airstarts but started immediately, or maybe even have some kind of switch triggered by the core exhaust. (My first thought is a fusable link with a thin piece of solder wire over the nozzle that would immediately melt and open a circuit.)
 
You can drive small solenoids directly with an Eggtimer Classic, Quantum, or Proton, just be sure to include the usual flyback diode in the circuit across the coil (in REVERSE with the "normal" polarity). You may want to go to a 3S battery instead of a 2S, and/or a separate battery for the solenoid and the Eggtimer.
 
Depending on the electronics setup, I have a couple of ideas in mind. For sure, I want to use a pack of four AA batteries to power the solenoids directly through a relay because they can double as weight in the nose. (this thing is going to be heavy in weird places due to the solenoids and wiring as it is, so I'll need good ballast up front plus lexan fins) As for the control electronics, I have a bunch of 3.6v 2S lipo batteries that should do just fine if they are only powering the electronics and the relay coil. After going over it in my head for a day, I think I might cheat a bit and not use an altimeter or accelerometer at all, but rather a simple timer triggered by a 12v pulse. The igniter leads would feed the actual motor igniters, but also connect in parallel to an additional relay coil. When the 12 volts are sent at ignition, it will also close the second relay which will start a timer set for around three seconds which will then power the solenoid relay, pull the solenoids in and release the boosters. Of course, this additional connection would need to be one that can detach from the rocket easily as it lifts off the pad, so I'm thinking a pair of header pins on wires clipped to the igniter leads that plug into a socket near the tail of the core booster.

In addition, I think I may also use a similar setup for the side booster igniters where the actual power from the launch controller only serves to close a switch so an internal power supply can feed the igniters. That way, the side boosters are able to start even if the rocket has begun to lift off the pad a bit and maxed out the igniter lead length. Also, the core F10 motor is designed for a long burn with low thrust, so by itself it won't be able to lift the whole model very well. This control arrangement could have the effect of the core motor starting and burning for a half second or so before the side boosters start; thus making for a more dramatic liftoff.
 
ebruce1361 said:
Depending on the electronics setup, I have a couple of ideas in mind. For sure, I want to use a pack of four AA batteries to power the solenoids directly through a relay because they can double as weight in the nose. (this thing is going to be heavy in weird places due to the solenoids and wiring as it is, so I'll need good ballast up front plus lexan fins) As for the control electronics, I have a bunch of 3.6v 2S lipo batteries that should do just fine if they are only powering the electronics and the relay coil. After going over it in my head for a day, I think I might cheat a bit and not use an altimeter or accelerometer at all, but rather a simple timer triggered by a 12v pulse. The igniter leads would feed the actual motor igniters, but also connect in parallel to an additional relay coil. When the 12 volts are sent at ignition, it will also close the second relay which will start a timer set for around three seconds which will then power the solenoid relay, pull the solenoids in and release the boosters. Of course, this additional connection would need to be one that can detach from the rocket easily as it lifts off the pad, so I'm thinking a pair of header pins on wires clipped to the igniter leads that plug into a socket near the tail of the core booster.

In addition, I think I may also use a similar setup for the side booster igniters where the actual power from the launch controller only serves to close a switch so an internal power supply can feed the igniters. That way, the side boosters are able to start even if the rocket has begun to lift off the pad a bit and maxed out the igniter lead length. Also, the core F10 motor is designed for a long burn with low thrust, so by itself it won't be able to lift the whole model very well. This control arrangement could have the effect of the core motor starting and burning for a half second or so before the side boosters start; thus making for a more dramatic liftoff.
Click to expand...

How will you inhibit unsafe staging? It does sound dramatic.
 
With the Eggtimer hardware, I think you’ll find the Proton does better/lower launch detection than the Quantum. The accelerometer does a nice job.
 
Steve Shannon said:
How will you inhibit unsafe staging? It does sound dramatic.
Click to expand...

I plan on making it heavy enough that the complete rocket can't leave the rail with only the center motor lit so the side boosters HAVE to start to actually fly the rocket. Of course, there's no way to absolutely guarantee simultaneous ignition, but I can limit the variables as much as I can by using igniters with nearly identical resistance, lead length, secure connections, as well as motors from the same batch/date code. I've never had a problem with good cluster ignition, but I know it's potential problem that others have encountered. Worst case scenario, the center and one booster starts, it will be incredibly unstable and will almost certainly crash before the timer triggers booster separation. I don't think there's a way I could save that, so my only real plan is to set it up on one of the pads further back to keep it away from the crowd and make sure the LCO calls a "heads-up" before the countdown.


Charles_McG said:
With the Eggtimer hardware, I think you’ll find the Proton does better/lower launch detection than the Quantum. The accelerometer does a nice job.
Click to expand...

I don't have much experience with Eggtimers as yet. I do have a Quark that I have been playing with, but that's only good for dual deployment and won't do anything in regards to launch detection besides sensing the air pressure change to give me an altitude. I will look into the Proton and see if that can help with this project.
 
ebruce1361 said:
I plan on making it heavy enough that the complete rocket can't leave the rail with only the center motor lit so the side boosters HAVE to start to actually fly the rocket. Of course, there's no way to absolutely guarantee simultaneous ignition, but I can limit the variables as much as I can by using igniters with nearly identical resistance, lead length, secure connections, as well as motors from the same batch/date code. I've never had a problem with good cluster ignition, but I know it's potential problem that others have encountered. Worst case scenario, the center and one booster starts, it will be incredibly unstable and will almost certainly crash before the timer triggers booster separation. I don't think there's a way I could save that, so my only real plan is to set it up on one of the pads further back to keep it away from the crowd and make sure the LCO calls a "heads-up" before the countdown.




I don't have much experience with Eggtimers as yet. I do have a Quark that I have been playing with, but that's only good for dual deployment and won't do anything in regards to launch detection besides sensing the air pressure change to give me an altitude. I will look into the Proton and see if that can help with this project.
Click to expand...

Protons have 6 outputs, so there's plenty of options for running servos or lighting boosters. If the boosters are all lit at the pad, then I don't see much issue with using a timer for booster separation. If they are lit in flight, I would definitely want to have ignition inhibited by speed/altitude/time limits.
 
I think using weight to keep it on the pad is going to limit your thrust:weight options. A lot - though I haven’t trialed any motors to verify.

Have you considered burn strings or other hold-down options? Take a look at some of the BPS.Space videos. Joe has built a hold-down system for his falcon heavy model.
 
@boatgeek, the boosters are all supposed to be lit on the pad, so I am also leaning towards a simple timer started by ignition that counts down only to separation.


Charles_McG said:
I think using weight to keep it on the pad is going to limit your thrust:weight options. A lot - though I haven’t trialed any motors to verify.

Have you considered burn strings or other hold-down options? Take a look at some of the BPS.Space videos. Joe has built a hold-down system for his falcon heavy model.
Click to expand...

I still have yet to begin weight calculations, but with the solenoids, batteries, nose ballast to accommodate the motors, miscellaneous wiring and electronics and the tubes I plan to use (heavier than regular BT80 tubes; these are re-purposed candy packaging that doubles as a coin bank), I'm anticipating a slow liftoff that should offer plenty of time for the side boosters to start. While that does limit the thrust to weight ratio, I don't necessarily want this rocket to go incredibly high or fast. If the boosters light as intended, they will add plenty of thrust to lift the model a few hundred feet so the separation is nice and visible from the ground, and from there the F10 will still have plenty of time to get the central core to a nice altitude (those motors have an eight-second burn time).

As for different hold-down methods, I'll take a look at those videos! To be honest, the solenoid release is my first-version idea, so that might change. I'm not sure how to set up a burn string that won't release right at ignition. Unless... perhaps using an electronic cable-cutter that will snap the strings holding the boosters on only after the timer's delay. I have a home-brew chute release in the works that uses an electronic cigarette lighter to burn an elastic cord to let the parachute loose. Maybe I can use a similar setup that is activated by a timer in place of the dual-deploy altimeter I have for the chute release.
 
I was actually thinking of a burnstring arrangement for holding the rocket to the pad if all three motors didn’t light. I think the BPS example might have used a combination of mechanical and electrical to do the same.

But thinking about booster release after burnout, I -have- done a hot wire cutter powered by an Eggtimer Quantum
 
I'm building a custom Falcon Heavy at the moment (and have been for the last two years...), and I'm taking the approach of letting the boosters drag separate once they burn out. There's nothing that holds the side boosters onto the center other than their thrust; I can share a pic of the hooks used to do that if you care. Seems like the lightest, simplest, most foolproof method to me.

This does require some kind of detection for all three motors lighting at launch, and a hold-down that prevents liftoff in an unsafe condition. I haven't got there, yet.
 
How about having the motors cut through nylon fishing line when they light? All three would have to light for it to leave the pad, assuming that you sized the fishing line correctly.
 
@KilroySmith I'd love to see your setup! Have you flown that kind of booster arrangement before successfully?


@cerving That's not a bad idea. It's plenty simple, and would definitely prevent the rocket from going up with only two motors; which would be the worst-case scenario. Additionally, I could incorporate the hold-down lines into the booster release mechanism (if I decide to go with that in lieu of the Falcon 9 Heavy setup described above.)
 
@wrad Awesome! That's pretty much what I'm wanting to do, but on a bigger scale and more elegant. This definitely gives me some ideas for improving my setup. Thanks!
 

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