gyroscopic stabilization

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Canadian Astronaut
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gyroscopic stabilization

Postby Canadian Astronaut » Thu Sep 25, 2008 3:44 am

Hey everyone. I was thinking after the latest crash of one of my rockets that it would be nice to have some kind of automatic stabilization in my rockets, so I thought about how to have a gyroscopic stabilization. First thing that popped into my mind is a Mercury switch. it's simple you have the Mercury switch shaped like a + sign so when your rocket tips over it will send power signals to small servos that pull a string to change a fin surface against the tipping. Causing the rocket to straighten out and NOT crash into the hard thing we call earth. Anybody think this is feasible and where I could get my hands on a Mercury switch

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Postby Tarpazium » Thu Sep 25, 2008 7:50 am

Canadian Astronaut wrote:it's simple you have the Mercury switch shaped like a + sign so when your rocket tips over it will send power signals to small servos that pull a string to change a fin surface against the tipping. Causing the rocket to straighten out and NOT crash into the hard thing we call earth


I personally think this is a very interesting ideas!

However, we need to a little cautious here, as any form of guidance or stability control, may breach the model rocketry codes under which most civil aviation organizations, allow rockets to be flown in public airspace.

The moment you start to wander down the path of any form of guidance systems, the airframe evolves from a rocket into a missile. Can you imagine a issues that would surround obtaining a waiver if you listed at airframe as:

Type: Experimental Guided Missile -
Launch Site: To be launched 45 minutes from CBD
.

(I can hear the phones in National Security Organizations ringing already!)

The development of such a system, would require extensive testing and therefore numerous flights, each of which, may be in violation of the civil aviation codes. I would however consider, that it may be prudent to continue this discussion in terms of speculating on how, commercial aerospace developers may overcome these problems.

Tarp
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Postby air.command » Thu Sep 25, 2008 9:16 am

Tarp,

Are designs for guidance something that can be discussed on the forum or better be left alone?
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Postby Tarpazium » Thu Sep 25, 2008 11:34 am

The last thing, that I'd want to do is to stifle inquiring minds. We do however need to mindful of how the active promotion of such discussion may be be view by regulators. I personally do not have an issue with this subject matter.

This web site is read by all manner of individuals across a range of backgrounds. My principle concern would be in regard to the potential risk of injury to persons and property that may result due to misconceived or uncontrolled experimentation with control surfaces on very fast moving objects.

One of the big questions in mind is "How would you feel about standing in front of a launching rocket ?

Well that's exactly what may happen, if you have a guidance or stability mechanism failure at launch.

There has been some really excellent work done by armature groups already, especially in the UK in this highly experimental field.

(Most times when we say "Highly Experimental", what we are really saying is the we are making a best guess at the outcome or perhaps even the direction).


(Click on Link below for Gimballed Motor Guidance System from UK)
http://www.ukrocketman.com/rocketry/gimbal.shtml

Image

This is cutting edge stuff and as such is HIGH RISK. Therefore due care should be given to this topic tp prevent this knowledge being abused.


Tarp

P.S.

I wonder if Dr Edward Teller (the Father of the H-Bomb) felt this way.

You can just imagine the phone calls back at the NOTAM office

TARP TO NOTAM OFFICE:

"..... about that experimental guided missile, we spoke about earlier ....
...... did we mention it's carrying a warhead?"



Tarp
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Postby Andrew Burns » Thu Sep 25, 2008 1:12 pm

Tarp, CASA 101 doesn't mention active guidance. I'm not a lawyer by any means but I looked into it a while ago (VERY briefly) and I found no regulations prohibiting active guidance in rockets. If anything it would be the clubs prohibiting such things.

That said forget about mercury switches, not a chance. You'd need at the very least 2 rate gyros integrated over time with some manner of digital filtering and a 3rd reference sensor such as a 3 axis magnetometer or horizon sensors as the rate gyros will drift over time (this is all if you want pitch/yaw control btw).

That gyroc system linked uses a hilariously low tech approach, but it looked like it kinda worked.

Bottom line is there's no real point going for active stabilization (I prefer this to guidance really, implies safety not targeting!) until you get to very large rockets going tens of thousands of feet and near/beyond mach. Anything smaller and you're adding weight and complexity at the detriment of vehicle launch altitude and reliability.

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Re: gyroscopic stabilization

Postby spacelaunch » Thu Sep 25, 2008 1:26 pm

Canadian Astronaut wrote:Hey everyone. I was thinking after the latest crash of one of my rockets that it would be nice to have some kind of automatic stabilization in my rockets, so I thought about how to have a gyroscopic stabilization. First thing that popped into my mind is a Mercury switch. it's simple you have the Mercury switch shaped like a + sign so when your rocket tips over it will send power signals to small servos that pull a string to change a fin surface against the tipping. Causing the rocket to straighten out and NOT crash into the hard thing we call earth. Anybody think this is feasible and where I could get my hands on a Mercury switch


Some advice - never use mercury switches in a high G high vibration environment - ie rockets. Extremes of acceleration and deceleration renders them unusable, because the mercury is slammed around inside them. You will need to use a gyro, but these are fairly cheap these days. Perhaps you could mod a system like the ones they use in R/C helicopters?. But you will need some electronics skills to develop what you are looking at.
Space is only 100km straight up, see you there :)

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Postby air.command » Thu Sep 25, 2008 1:32 pm

One of the things we have been looking into is using a single rate gyro like used in some RC helicopters to control two opposing surfaces on either side of the rocket to stop it from spinning in order to get a stable platform for video. We are not concerned if it is pitching over or controlling it's direction, as long as the spin is reduced to near zero.

But making a finless water rocket with vectored thrust through a flexible rubber hose would be interesting. :D
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Postby Tarpazium » Thu Sep 25, 2008 7:21 pm

Hi

While guidance overall is not a problem , metal components are ONLY allowable by CASA in high powered rocketry codes and even then for minimal structural usage in strict accordance with the act. I was recently reminded of this fact by a CASA Flying Operations Inspector.

It is therefore difficult to imagine achieving an effective model rocket guidance solution, given that materials you can use for this system are limited to balsawood, cardboard plastic and the occasional composite material under the model rocketry code.

CASA view HP rocketry a little differently and will allow the use of metals if it can be argued that the guidance system is an integral of airframes structural make-up. As such, I was not suggesting that this was legislatively prohibited, but rather it was impractical to achieve on anything but a controlled range.

However both regulators and your local RSO would need to be convinced that the flight would remain stable and controlled. Also the suitability of your range to conduct such experiments (theres’that EX word again).flights of this nature would also have to be examined.

The mechanics of achieving stable and controlled flight are also a awesome task. I have attached blow and extract for discussion on this topic that that I found on PhysicsForum.

Well, veganode, you're attacking an absolutely formidable problem, one that took decades of work by thousands of people to accomplish.

1) The thrust phase of a model rocket motor is only a couple of seconds long, and you'll only have active control during that time. You could conceivably add some movable control surfaces to the rocket, so you could control it during its descent, but control surfaces small enough to not interfere with the ascent won't really be able to have much effect.

2) The gimbals needed to adjust the thrust angle on a rocket motor are formidable. You will need quite good machining skills to make such devices.

3) You won't need just one gyroscope; you'll need three, one for each axis. You'll also need three linear accelerometers, plus the electronics to decode the sensor values and solve a complex set of differential equations to give you the position of the vehicle. You're looking at microprocessor-level electronics, probably a StrongARM or 286 or better. It took tens of thousands of man-hours of work to make an inertial guidance system that could fit in a cubic foot; you simply will not be able to accomplish it by yourself. Here's a document on the history of inertial guidance systems: http://www.imar-navigation.de/downlo...troduction.pdf

4) You can purchase a variety of off-the-shelf radio control equipment from a hobby shop. You can buy the transmitter and receiver units, plus servos and other equipment.

My honest advice? Scrap the idea of building an inertial guidance system. Scrap the idea of gimballing a rocket motor. Go to a hobby shop, buy a pre-made model airplane body and radio equipment, and start small. Once you're an expert on radio controlled airplanes, then you can start strapping rate gyros and microcontrollers in them to start learning guidance. It's a very, very long road ahead.


While topics such as this would hold great interesting for many of us, I am unsure as to what level these interests could be pursued, give the HIGH Risk and large amount of experimentation involved.

I personally think that you'd break more airframes than you'd save. I would however like to encourage any and all opinion or speculation on the inherent risks as well as the advantages of the various technologies involved.

Tarp
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Postby Canadian Astronaut » Fri Sep 26, 2008 4:03 am

i think that having a rocket that could control itself on the way down would be great! :D i would love not having to run about 2 miles to get my rocket back. but i think the gyros on the rocket would be to heavy and not do to much, why i put this subject up was beacuse of one of my rockets that in midflight did a 180 that i later found out that was because of the wind. and keep in mind i was still under power when it did the 180. i was thinking that a gyro system would help keep the rocket from doing that. :lol: oh well. how about we try and build a system that keeps the rocket from drifting to far. (or i'm going to have to get a better bike)

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Postby The Wombat » Fri Sep 26, 2008 7:47 am

In reading the above, three questions come to mind that could define the boundries of what is practial:

Would a feedback-control system be classified as 'active guidance' i it could be demonstrated that its mode of operation can only provide flight stabilization and not 'targeting'?

Would 'active guidance' made a rocket a missile if the guidance is only provided after ejection, when the rocket is no longer a 'ballistic vehicle' - specificly, the guidance system was in the recovery system?

If the ban on rockets having any sort of 'active guidance' is absolute, how does one explain the commercial availability of rocket-launched RC gliders?

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Postby air.command » Fri Sep 26, 2008 7:59 am

Hi CA,

Gyroscopes do not need to be heavy at all. The ones used in model aircraft only weigh a few grams. If you were thinking of using a gyroscope as a heavy flywheel with the axis fixed to the rocket to stop it pitching over, then that would not work. This is because the gyro's input axis is perpendicular to the output axis. This means that as the rocket exerts a torque on the gyro as it is pitching over the gyro applies a reactive torque at 90 degrees to that, meaning that the gyro will not try to straighten the rocket but pitch it in a direction 90 degree from what you want.

For this reason you would need a gimballed gyro feeding either a mechanical system that provides the 90 degree cross linkage to control surfaces, or electronic system that drives the servos providing that 90 degree cross linkage.

If the rocket turned over 180 degrees mid-flight it sounds more like a stability issue. If it was still under power in the water phase, then the Cg must have been quite a ways back. One of the problems with water rockets is all that heavy water near the tail of the rocket. This has a tendency to make the rocket unstable during launch. Although briefly the CP can be ahead of the Cg. You need to make sure that your fins are quite a ways back, or have a heavier nose to ensure proper stability during the boost phase.
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Postby whipfest » Fri Sep 26, 2008 10:06 am

air.command wrote:If the rocket turned over 180 degrees mid-flight it sounds more like a stability issue. If it was still under power in the water phase, then the Cg must have been quite a ways back. One of the problems with water rockets is all that heavy water near the tail of the rocket. This has a tendency to make the rocket unstable during launch. Although briefly the CP can be ahead of the Cg. You need to make sure that your fins are quite a ways back, or have a heavier nose to ensure proper stability during the boost phase.


Active stabilisation (thank you Andrew !) is a fascinating field, but I think Air.Command may have hit the nail on the head with your issue 8)

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Postby water rocketry man » Fri Sep 26, 2008 2:37 pm

time for mythbusters :)

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Postby PK » Fri Sep 26, 2008 6:09 pm

air.command wrote:One of the things we have been looking into is using a single rate gyro like used in some RC helicopters to control two opposing surfaces on either side of the rocket to stop it from spinning in order to get a stable platform for video. We are not concerned if it is pitching over or controlling it's direction, as long as the spin is reduced to near zero.

But making a finless water rocket with vectored thrust through a flexible rubber hose would be interesting. :D

Done it :-) will post some video when I get home.
A better approach is I use an electronic compass sensor.
You get a digital heading out of it and then you only need to worry about little things like control gain varying with speed.
PK

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Postby Canadian Astronaut » Sat Sep 27, 2008 2:01 am

my rocket that did the 180 was very stable on the ground and in the air. i tested this meny times before i put it in the air. and when in the air it would fly very nicely. the thing that made this flight different was the fact that right when i pulled on the string and big gust of wind can into the pic. i was thinking that a gyroscopic stabilization system would help the rocket fly strighter or would help it not do the missle thing and fly level with the ground


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