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Rate Gyros for Automatic Control

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Rate Gyros for Automatic Control

Old 06-04-2005, 06:13 PM
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AirQ
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Default Rate Gyros for Automatic Control

Hello,

Where can I find information about rate gyros? I need to know where to buy them, the specifications, how to go about selecting one, and what is best to use with a microprocessor.

I am involved in a research project in which I will show that an inherently unstable aircraft or rocket may be made to fly and maintain any desired angle of attack through the use of automatic control. The rate gyro is needed in a feedback loop to help accomplish this.

Thank you for any and all pointers on this topic. Please post whatever you know about rate gyros. I am an Aerospace Engineer, so feel free to be as technical as you desire.

Thanks.
Old 06-05-2005, 06:04 AM
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Warbirdz01
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Default RE: Rate Gyros for Automatic Control

AirQ......More than likely........your gonna have to touch base with a company like like Sperry, Allied Signal, or one of the Autopilot manufacturers to find out their sources/venders......I am an Aircraft Mechanic with an airline and I do have an FCC as well ..........we pretty much farmed out all that kind of work several years ago after 9/11 or I would call the shop and find out where they obtain replacement parts......Rate gyros are kind of old technology as most of the high tech A/P systems use feedback from accelerometers generally found in the IRS systems or ADIRUs instead of rate gyros........Bill..........
Old 06-06-2005, 06:18 PM
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Johng
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Default RE: Rate Gyros for Automatic Control

go to towerhobbies.com, horizonhobby.com, servocity.com and hobbypeople.com and do a search on gyro. You will find a wide range of gyros. However, if you want to know specific constants for a gyro that mean something in a dynamic control analysis, you may have to buy one and test it yourself.

There are also some cool autopilot devices available from fmadirect.com that use horizon sensors to right an airplane. That could be used as stabilization as well.
Old 06-06-2005, 07:06 PM
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jfitter
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Default RE: Rate Gyros for Automatic Control

Check out Analog Devices ADXRS300 - this is a MEMS rate gyro with a fully conditioned duty cycle output. Much more robust than peizo gyros, and lots cheaper.
Also check out ADXL202/210 dual axis accelerometers. These have digital outputs and are really low cost.

I am doing someting similar to you. The accelelerometers and gyro are on a small pcb with a micro and a buck/boost smps. The circuit fits inside a servo case and a led pokes out the hole in the top for a status display. An r/c receiver interface and data logging are also built in. The purpose of the circuit is to develop mcad models that make use of angular rate AND linear acceleration inputs for flight stability.

Old 06-06-2005, 09:51 PM
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AirQ
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Default RE: Rate Gyros for Automatic Control

Thanks for the replies.

The ADXRS300 looks promising. Since I am researching at a University I can get Analog Devices parts for free.

http://forms.analog.com/Form_Pages/corporate/parts.asp

This source suggests also using an accelerometer. Is the drift really so bad that you need to use an accelerometer and Kalman filter? I have done some work with accelerometers, and I know drift can cause problems. I have to use a signal analysis package to filter out the low frequency drift. But in this application, it is automatic control within the device, so I cannot store and upload data to a computer.

http://www.dprg.org/projects/2003-01a/

This project will have to be completely self contained in the model. I will need to select a microcontroller. What is a good microprocessor? I need something which can work with the rate-gyro and also have decent speed and ability to program in preferably C.

I was originally looking at R/C model sources for the rate gyros, but it looks like I'll go with this AD gyro or something similar. All the hobby shops I have called have been skeptical about what I want to do, and say that the only application of rate gyros is for helicopters. This source (same as above) says that model gyros are not preferrable.

http://www.dprg.org/projects/2003-01a/

"Although a RC hobby gyroscope is cost effective, it is a bit difficult to interface to a MCU..."


Thanks.
Old 06-06-2005, 10:16 PM
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jfitter
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Default RE: Rate Gyros for Automatic Control

It depends if you want attitude or flight path stabilization. The gyro alone will provide enough information for attitude stab. Consider pitch. An unintended pitch up is sensed by the gyro. Your control system corrects it. The airplane is now on a different flight path. So, pitch is not a 2nd order system, but we already knew that. Acceleration sensors can add the extra info you need. Developing the maths models is the tricky bit!!!

(for the pedants - these comments apply to low cost, low weight, low complexity systems for mini aircraft use - this is not a space shuttle).

Try not to do everything with one micro. I do the sensing and basic processing with a pic. Its fast, cheap, does the duty cycle measurement very easily, and some simple maths and comms. This way the sensor (bit in the servo case) can be made to appear like a sensor on a virtual airplane of predefined dynamic specification. Have one of these for each axis and do the heavy maths somewhere else, using a processor more suited to that task (an arm or similar - plenty of prefab boards to choose from). The big processor deals with the virtual vehicle, so if you change the vehicle dynamics there is no need to change the software here.

C - All my pic code is in C - that way I can figure out what it does!!!

Hobby shops are wrong - I use a gyro on rudder in my jet. There are many apps for gyros other than helis. The model gyros are quite unsuitable for what you want to do. About the only bit you would keep is the sensor!!!

Hope this helps.
Old 06-06-2005, 11:16 PM
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andyg
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Default RE: Rate Gyros for Automatic Control

Finding attitude with rate gyros will be very difficult and complex. I would try one of the horizon sensing systems with thermopiles.
Old 06-07-2005, 12:27 AM
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Default RE: Rate Gyros for Automatic Control

Finding attitude with rate gyros IS difficult and complex but it is the method used by many commercial autopilot and stabilization systems on the market, such as MicroPilot, Piccolo, GNU UAV Project, etc.

It is quite surprising just how well low cost rate gyros will perform if you throw enough computing grunt at them. Piccolo I think is using fibre optic gyros, which are somewhat better than piezo and mems gyros but bigger and more expensive.

Check out [link=http://autopilot.sourceforge.net/]GNU UAV AutoPilot Project[/link] if you want to get "up to speed" on this technology.

Cheers,
JohnF
Old 06-07-2005, 02:54 PM
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AirQ
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Default RE: Rate Gyros for Automatic Control

Thanks again for the help. Looks like this is more of an electronics discussion rather than unstable aerodynamics discussion. I might start a separate thread on microprocessors.

But at least one more question, please.

How are the AD gyros for drift? A couple balancing robot pages say that both a gyro and an accelerometer are needed along with a Kalman filter to obtain accurate orientation data. I am willing to learn how to program and implement a Kalman filter, but I have never used one before. The datasheet for the ADXRS300 indicates low drift, so I thought this would not be a problem.

Thanks for any advice on a gyro/accelerometer combo or on the Kalman filter.

Old 06-07-2005, 05:58 PM
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Default RE: Rate Gyros for Automatic Control

Sorry - can't help. The answer to your question is one which I am investigating myself using the "brute force" method - make the thing and go fly.

For sure, I have been a bit more rigorous than that, and the manufacturer's data seems ok for my application if I do enough number crunching - BUT - manufacturer's data as we all know is little short of outright advertising, so the "suck it and see" method represents a valid engineering approach.

cheers,
JohnF
Old 06-08-2005, 05:50 PM
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Default RE: Rate Gyros for Automatic Control

Some good sensors are the the NEC/tokin CG-16D which are fairly old now but still a good rate sensor suited for this type of operation, you could use three of these for angular rate sensing of roll, pitch and yaw. Also if you require to measure linear rates, such as vertical acceleration some good sensors are by by Analogue Devices model number ADXL202E. these are dual axis.
you may want to ampilfy and filter the outputs
Old 06-10-2005, 12:44 AM
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Default RE: Rate Gyros for Automatic Control

Try the Murata gyros that are used in the SF autopilot project. They are pretty good, but you'll need an accelerometer to remove the bias and drift of the gyro (kalman filters etc.). The autopilot project is pretty much dead, but the software in there does work to some extent and at least one person got it sucessfully to hover a helicopter between predetermined spots. The source code is self-explanatory and should save you tons of time.

P.
Old 06-10-2005, 02:51 PM
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AirQ
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Default RE: Rate Gyros for Automatic Control

Thanks for the replies.

I am going to order a couple rate gyros and accelerometers, check them out for drift, and see what I can come up with.

Every reference I find on this subject notes that Gyros drift (and accelerometers too). Even robotics books mention this (Embedded Robotics, Braunl). It looks like the solution is always a gyro/accelerometer combo with a Kalman filter.

So certainly there has to exist a ready made device that has all this capability built in? If not, is there no market? Or should I make some money by perfecting this design and selling it.

I have seen "inclinometers," but I do not know anything about the drift for these devices. I do not know how they work, but have not pursued them very much because I have a source that says the response time for these devices is too slow for aerodynamic automatic control. It said to use rate gyros instead, as these have a fast enough response time.
Old 06-10-2005, 05:52 PM
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Default RE: Rate Gyros for Automatic Control

Do not try any airplane attitude control using gravity as a reference (inclinometers etc.), because it will not work. Attitude control requires either inertial references (gyros) or reference to objects fixed in the earth's frame of reference (horizon, ground, etc.).

The inertial references (gyros) either recreate a fixed reference relative to the earth (attitude gyros - artificial horizons), or they provide information about motion relative to the earth (rate gyros).

If you put an inclinometer in an airplane, such as a glass of water, and you do a balanced turn, the water level would not change at all and so would convey no information relating to the attitude or motion of the airplane.

The human balance organs are inclinometers with angular acceleration sensing (note: NOT angular rate sensing). This is why humans cannot fly in cloud without reference to instruments. If you try you die, EVERY time!!!
Old 06-11-2005, 02:31 PM
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Default RE: Rate Gyros for Automatic Control

Can I use any of the information presented here to develop a bank limiter control?

If so, what would I use?

I'd like to have the ability to limit the bank angle of my 13' U-2 turbine model to say, 30^.

All comments welcome.

Thanks,
Jack
Old 06-12-2005, 05:36 AM
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Warbirdz01
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Default RE: Rate Gyros for Automatic Control

AirQ.....I 'm not sure where Honeywell gets their accelerometers(probably manufacture their own)....but they are so accurate that if you try to Align IRU with wrong latitude , the accelerometers can measure the rotation of the earth and the IRU will not align and show a fault until correct Latitude is keyed in.......most of internal components of IRU or ADIRU and proprietary.....due to their commonality with military configurations............but I am interested on how you resolve this issues........keep us posted..........while were on this sort of topic.....have any of you gentlemen tried any of the newer telemetry systems?.............I would like to try it on my Hangar 9 Cessna 182 and eventually move it to my Multi-engine warbirds...........airspeed/altitude/engine RPM would be what I'm most interested in.............Bill

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