Gyro stabilization =advanced=

[denverdoc]

Can anyone help me understand the stabilizing influence a rapidly spinning mechanical device not intended to detect vertical, but just spin as a top does, might have?
John S

 

[brianc]

https://en.wikipedia.org/wiki/Gyroscope

HTH!

 

[rstaff3]

Google 'rolleron'

 

[denverdoc]

Brian.
Thanks, very helpful and I think I have a handle on doing a "shadow sim" in Rocksim by adding weights to simulate the Gyro effects. If I understand, what we have done is increase the longitudinal moment of inertia substantially. Therefore perturbations are much less likely to deflect the rocket from its flight path, but once deflected, its a new flight path, and so a double edged swor--although perhaps less susceptible to a gravity turn,
John

 

[denverdoc]

Not to dbl post, but short of a truly active stabilization system, I'm thinking an adaptive approach might be an interesting way to improve performance. One of our challenges obviously is we get stuck with a mandate right out of the box to provide enuf restoring force at very low velocities to get our rocket on the beam, and then suffer drag consequences from there on out by having more fin than we need. Obviously a hybrid can drive the geometry backwards, but usually the cp/cg relationship and the normal restoring forces all improve big time as we get moving.

So as long as we are carrying batteries and often in need of ballast, why not make the dumb ballast smart? Even getting it spinning at high RPM from external sources in advance of liftoff might enable us to reduce drag substantially.
JS

 

[powderburner]

That is a clever idea, to try using battery ballast in the form of a gyroscope.
A few considerations: I think you are going to have to get that weight spinning at a fairly high rate to generate any corrective forces gyroscopically, and I am not sure at all that you batteries would hold together (or even balance) at any sort of useful spin rates. Not to mention making an electrical connection through the framework of the gyro (to extract your electrical power)
If you run some numbers I suspect you will find that the added weight of the gyro system will hurt your performance more than the drag of the fins. And many of us can do a LOT to reduce fin drag with the use of proper fin airfoiling and streamlining (a much cheaper and simpler approach).
One last thought: if you do somehow manage to get your gyro spinning at 10,000 or 20,000 rpm (or more?), I suggest you find a solid bunker to stay behind in case that gyro comes apart.

 

[rstaff3]

A motor from a dead DVD drive might spin purty good.

 

[jwagner61]

Denverdoc: If I understand, what we have done is increase the longitudinal moment of inertia substantially.

It might be useful to consider the effects of a gyroscope as mimicking the effect of an increase in mass, but the dynamics are quite completely different. For example, if a torque is present about a horizontal axis making the gyroscope rotate from vertical, this will induce a rotation about a third axis - also horizontal but perpendicular to the first. This is called precession and will make the rocket execute a gyroscopic wiggle about the vertical axis. The greater the force, the faster the precession with only a small increase in amplitude.

I'm new to a lot of this rocket stuff, but this is something I understand.

Others can correct me, but I think the early rockets like the gemini (https://grin.hq.nasa.gov/IMAGES/SMALL/GPN-2000-000612.jpg) that lacked prominent fins must of had some form of gyroscopic stabilization. This combined with the cg located so far forward resulted in stable flight.

It would be interesting to take a motor from a 30000 rpm hard drive and spin it up with a rotor in a rocket. Without trying any calculations, this seem as if launch stands and fins would be unnecessary....

John

 

[rstaff3]

Sounds like a fun experiment. Would a pair work better?

 

[powderburner]

Ohh, you're making me remember my college engineering mechanics classes, and my head is starting to hurt already.

Gyros were (and are) used on many missiles for guidance and control, but they don't work by brute force. The gyroscopic forces generated by these things are electronically sensed and fed into a flight control computer. Those black boxes remember which way is up and compare to whichever way it is pointed at the moment, and send correction/steering commands to actuators on the nozzle gimbals.

A bit more than I want to mess with for low-power modrocs.....

 

[rstaff3]

Gyros are certainly common on satellites, and are used in conjunction with other attitude sensors. The only descritpion I've seen that uses the gyro directly is in rollerons. IIRC these were free spinning wheels, turned my airflow and are bounted in free-moving tabs at the end of the fins. Earlier I had wondered about mounting three motors in the fins to see what they'd do. No motors and too litle ambition stalled my ideas.

 

[rstaff3]

...of course a momentum wheel also works by gryo action, so I guess I lied in my earlier post.

 

[denverdoc]

Agreed, the intention is not to sense deflection and send corrective forces thru vanes, a gimbaled motor, moving control surfaces, or anything like that--more like a dumb gyro. We spin our rockets deliberately all the time to average out normal deflections, can the same thing be done internally and how does one go about converting the rotational inertia into a corrective force--in other words how would one compute the angular velocity needed and mass. It may not be 30000rpm as suggested, but hell if I know! Just a wild and crazy idea is all that probably has zero merit, but would like to understand the physics a whole bunch better.
John S

 

[rstaff3]

https://naca.larc.nasa.gov/reports/1955/naca-rm-l55c22/

Don't know how much this will help, but you can take a gander. bobkrech will eventually see this and will have good input.

 

[Micromeister]

One of our club youth members had a similar thought about helping stablize a model with small fins. His model was a cluster powered Aries-1. His model was a BT-80 size model powered by 4 D12's. To help stablize the model Andrew build an internal Gyro using a 4 AAA batteries battery pack, 6v - 10,000 rpm about 2" dia. electric motor and somekind of flywheel he balanced himself, it was about 3" in dia. and at least 1/2" thick, I think it was aluminum but it was painted. Can't tell you what it came from but it had some weight. The motor mounted in a replacement shoulder of a PNC-80K nosecone with plywood bracking and a couple strips of aluminum across the bottom into the motors threaded mounting holes at the base. Andrew Attached the BT-80 coupling shoulder to the PNC with i'm guessing the size 4 - 4/40 machine screws into hex nuts imbedded in fibreglass reinforced epoxy inside the shoulder coupling ring. I believe the weight of the unit may have done more to add stability to the model then the gyro effect but it did seem to work.
I witnessed 4 seperate flights of this "test" model on the same day. First two flights were launching the model with only 1 and then 2 motors positioned on one side of the motor mount only. The model still flew very well and optically straight, though not very high. The 3 and 4 D12's flights were more impressive in altitude both of which were very nice flights.

Spinning the gyro unit up outside the model, mounted in a 2' piece of pipe, it was very difficult to move the gyro from its spin axis. Was it enough to keep the model stable on its own without fins? I doubt it, but it may have helped correct the offset thrust of motors on one side of the cluster and help those small fins?
I was pretty impressed with the engineering this 13 year old showed with this model Incidentally these test fligths were done in isolation, with only 4 people on the field and two remote recovery kids

 

[denverdoc]

John

Sounds like a young man to keep an eye on. Obviously the icing on this cake would have been to launch with the gyro un-spun using the same motor imbalance just to make sure it was not an artefact of nose weight. If it had then flown much more crooked, I think that would constitute proof of concept,

Your mention of the effort to rotate the pipe, reminded me of this odd golf conditioning device i had for a while. One would start the gyro with a pull string and then by good timing and flipping it back and forth by rotating the wrist (pronation/suppination) the gyro would accelerate to a high spitched scream and after a very few minutes of such, the increasing effort requires to flip it would leave to unbelievable fatigue--device was the size and weigh near that of a baseball and w/o spin took as much effort to rotate.
John

 

Originally posted by jwagner61
Others can correct me, but I think the early rockets like the gemini (https://grin.hq.nasa.gov/IMAGES/SMALL/GPN-2000-000612.jpg) that lacked prominent fins must of had some form of gyroscopic stabilization. This combined with the cg located so far forward resulted in stable flight.

John

As has been pointed out, the "gyro stabilization" in finless rockets is a closed-loop feedback system wherein the gyros sense displacement and command corrective actions.

In the case of finless liquid-fueled rockets, the engines are mounted on a "gimbal" (spherical bearing point) and hydraulically actuated about the bearing per the flight control or guidance system commands.

OTOH the V-2, a liquid-fueled rocket with fixed fins, thrust vectoring vanes were placed in the engine exhaust and the gyros controlled the vane angle and thus effected vehicle control.

 

[Micromeister]

Originally posted by denverdoc
John

Sounds like a young man to keep an eye on. Obviously the icing on this cake would have been to launch with the gyro un-spun using the same motor imbalance just to make sure it was not an artefact of nose weight. If it had then flown much more crooked, I think that would constitute proof of concept,

Your mention of the effort to rotate the pipe, reminded me of this odd golf conditioning device i had for a while. One would start the gyro with a pull string and then by good timing and flipping it back and forth by rotating the wrist (pronation/suppination) the gyro would accelerate to a high spitched scream and after a very few minutes of such, the increasing effort requires to flip it would leave to unbelievable fatigue--device was the size and weigh near that of a baseball and w/o spin took as much effort to rotate.
John

Alas Andrew has Grown and Gone.. I understand he is now a boat mechanic, over on the eastern shore of Maryland, Not even flying rockets anymore
Wish I could say we did fly that model with a static payload but, we simply ran out of time and motors I truly can't say if he ever even finished the model. Maybe one of the other Hamsters here might remember if Andrew Miller ever entered an Aries-1 in one of the regionals or a Naram? The model may be sitting in his fathers basement to this day.

 

[JPC]

This page has some interesting videos to watch in regards to mechanical gyroscopes, the science may not be up to date since it is from 1974 but it covers gyroscopic precesssion and other topics.

https://www.gyroscopes.org/1974lecture.asp

The rest of the page is interesting also and there is a 'math' section with a big calculculator as well.

 

[utahrc]

So as long as we are carrying batteries and often in need of ballast, why not make the dumb ballast smart? Even getting it spinning at high RPM from external sources in advance of liftoff might enable us to reduce drag substantially.

I saw this done last year, I believe at Plaster Blaster. The rocket was finless and was launched from a tube. The gyro was spun up from an external power source just prior to launch.

 

[utahrc]

Another idea that might work is spring-loaded fins that fold back, presenting a lower drag profile as the rocket increases in speed.

 

[denverdoc]

Please tell more, how'd it fly? Was is so heavy it staggered to a few hundred meters or did she rip?

J

 

[denverdoc]

We are thinking somewhat parallel, l have often wondered about retractable fins. But where do you put them? Obviosly in a non-min diameter rocket you have some room, but otherwise?
I've considered telescoping fins that would tuck in span wise, etc. Then I got really out there thinking the thickness of such a retractable fin was a deal buster, so why not just blow off the span extenders
More elegant soluions exist I'm sure. Best ideas I have had yet IMO is to cant the fins to induce a high roll rate early on then pull em parallel, or blow off spinnerons. Or of course figure out a way to use the Eiffel tower as launch guide.

 

[utahrc]

How about fins that are curved to conform to the diameter of the rocket? They're static state is to be fully deployed but they could be designed such that aerodynamic forces would cause them to collapse around the body as speed increased.

 

[utahrc]

I'm afraid I don't remember much about the flight. I do recall that it was a stable flight, but beyond that I don't know.

 

[denverdoc]

Originally posted by utahrc
How about fins that are curved to conform to the diameter of the rocket? They're static state is to be fully deployed but they could be designed such that aerodynamic forces would cause them to collapse around the body as speed increased. [/
QUOTE]
I.m intrigued but lost, can you ecxplain more graphicaly?
J

 

[utahrc]

Imagine fins that have been cut from a piece of body tubing the same diameter as the rocket. Hinge them where they attach to the rocket so they can fold flat against it and use a spring mechanism to keep them deployed at low speed. A small tab or a little creative shaping of the fin could make it fold in against the body at high speed. Additional gains could probably be realized by cutting recesses into the body for them to fold into.

 

[denverdoc]

Originally posted by utahrc
Imagine fins that have been cut from a piece of body tubing the same diameter as the rocket. Hinge them where they attach to the rocket so they can fold flat against it and use a spring mechanism to keep them deployed at low speed. A small tab or a little creative shaping of the fin could make it fold in against the body at high speed. Additional gains could probably be realized by cutting recesses into the body for them to fold into.

I get it now, more like sails than fins which have a collapsing strut. Cool. Sort of a ring fin with variable diameter. Concept seems great, engineering -wise, perhaps tricky plus.
J

 

[powderburner]

(Yes, I'm a big Forrest Gump fan.)
It really is hard to beat a good design for fixed-geometry fins. Make them a good size and shape, use a good airfoil shape, and put a smooth finish on them and they will give you a lot of stability for very little weight, drag, and cost.
Unless you are just wanting to test some other approaches, it is pretty hard to beat plain old fins.

 

[denverdoc]

Powdeburner,

I hear you, as good fins are what 10 to 30 percent of the entire Cd. Always curious about other approaches, however, esp with these progressive or neutral burns most of the big motors give. Otherwise, always been partial to tiny fins on longer rockets with enough initial punch to get things moving in a hurry.....
John S