Helicopter Project

[MDelgado1989]

Hey guys, being as I am new to this site, just want to quickly introduce myself. Names Miguel, reside in Miami, FL, 17 Years old, and I love electronics.

So I am going to be doing a project for school which is going to consist of programming a microcontroller to a RC Helicopter. What I would like to achieve is placing two Altimeters on the helicopter and program the Microcontroller to react to the elevations to keep the Copter balanced out in the air. If anyone can help me out in this and point me in the right direction as to which type of altimeters to use, I would GREATLY appreciate it. Thank you for your time

Take care
- Miguel

[DonRotolo]

Altimeters are not what you want to use - these are generally based on air pressure, or for very expensive versions on RADAR, but are not nearly sensitive enough to stabilize a helicopter.

Instead, consider using an accelerometer and a rate gyroscope. If I were going after this kind of project, I would probably want three axis versions of each.

The basic idea is to tell the controller what the readings on these sensors 'should' be, and then program it to control the helicopter such that the readings on the sensors 'are' where they need to be. The accelerometer is used for detecting large changes, and the rate gyro is used to detect small changes.

This is known as a closed-loop feedback system. There is a LOT of literature out there on this.

You have chosen an extraordinarily difficult project. A human with experience can have difficulty controlling a helicopter in hover; an autonomous system for the same might be considerably more complex than you think.

Not to discourage you - go for it! - but just have a realistic expectation that it's not easy.

Good luck,
Don

[John Gutmann]

I am pretty sure he won't be using the altimeter to stabalize it. he would be using it to beable to tell what elevation he is at. once he is at tat elevation he would use the already preinstalled gyro on the rc heli to stabalize it. Probally from there he will write a PID loop to keep it at exactly the elevation he wants it to be at.

[MDelgado1989]

Thank you both for your repsonces, I greatly appreciate it. Sparks, that is exactly what I intended to do, have the altimeters read the elevation on both sides of the Copter and then have the pre-installed gyro react accordingly.

Don, I appreciate your comment very much, you explained it rather well. I have considered the difficulty of this project over and over but I have been flying planes for sometimes and although I have never really gotten into Copters, I have always wanted to and I figured what better way then to have some fun with this and learn a few things from it as well.

In conclusion, between both your comments, I believe the way I originally planned on doing it, which was the same way Sparks explained, having the altimeters read out the Altitude and having the Pre-installed gyro react accordinly, would be easier then the way you explained it Don. However, I would like both of your opinions on which way you guys recommend I go on this. Again, thank you for your time and responces, GREATLY APPRECIATED

Take care
- Miguel

[John Gutmann]

I think and easy thing to do would be buy a crappy transmitter for the heli, then gut it out. What you can do is hook that up to your micro controller and get some Digital->Analog converters and hook them up to all the pots. this way you can have you micro controller control it while you still have it hooked up to your computer and you can play with the values.

Second thing is make sure you have a transmitter handy while you are doing this and have the same crystal in it. This way if things get out of control you can turn off the one for you micro controller and take over manual control.

Third, get a trainer for the heli, this will allow you to still fly but not more then like 5-10 feet if that. Now if you crash it won't be as bad or as expensive.

Now depending on how much money you wanna spend you can put the transmitter with the micro controller on board the heli this way you will always have communication, but you can still get interference. they other way would to be to totally hack the whole system. write code for the gyro and motor controller and servos yourself, then have a radio modem so you can talk to your computer on the ground.

[MDelgado1989]

Thanks for the respond Sparks.

I have not bought the Heli yet, but I was thinking on getting an electric begginer ($100-130) which already comes with everything and is capable of taking off with some extra load on it just incase so weight does not become an issue, and I have extra transmitters lying around from my planes with extra crystals I can use.

Also, I have been researching on the net for altimeters and am indecisive on which ones to use. I am looking for a rather small one which would fit well on the computer, mounting is not an issue as I could easily find a way to mount it, but I am also looking for one which I can get to transmit back to the microcontroller so it can in return have it register out with the other Altimeter on the other side of the Copter and compare the two out to make sure that they are at even altitudes. This is not going to be a big scale project so they can be low level altimeters.

I was also considering using the Mini Copter (fits into palm) but was concerned due to its size that I might not be able to properly install any additional hardware on it and/or with a little extra weight, it might not be able to take off.

Thank you for your time and all your responces, you have been of great help to me man

Take care
- Miguel

[MDelgado1989]

Sorry for posting this now but I just realized since altitude is measured by air pressure and I don't plan on hitting anything over 20, mainly at 5-10, seems as though I am going to have to find a different route for this as I doubt it would pick up any difference in air pressure between 5 - 20 feet. Any ideas anyone? Thanks in advance

Take care
- Miguel

[Qbranch]

A word of warning: gyros have a tendency to spit out bad data occasionally, so i suggest having redundant sensors so you can tell if one is lying to you.


-Q

[John Gutmann]

Originally Posted by Qbranch

A word of warning: gyros have a tendency to spit out bad data occasionally, so i suggest having redundant sensors so you can tell if one is lying to you.


-Q

The normal gyros in helis don't have a problem. as long as you read them at a fast enough rate some bad data shouldn't be a problem.

[Chris Fultz]

A few things to consider / be careful for -

Remote controlled helicopters are very challenging to operate. You should plan for lots of practice and lots of spare parts. Maybe look for a local RC club and see if someone there is flying helicopters and can give yousome pointers.

Many sensors do not have tight tolerances on their accuracy. Be sure to check the device specifications and be sure you will be able to develop the logic you are planning. The more sensitive and accurate the device, the more if costs. The smaller the range you want to measure the more accurate the device can be.

From the standards books, the ambient pressure at Sea Level is 14.696 psia.
At 10 feet, it is 14.6907, a difference of 0.036% or 0.0053 psi. To measure this requires extremely sensitive instruments. You will want to set up your program to look for a change in pressure from the starting point to help offset the accuracy of the device.

As a reference, a standard pressure transducer for a 'real' helicopter often carries an accuracy requirement of +/- 1% and might cost $1000. 1% accuracy means if the real pressure is 100 psia, the indicator might output anywhere from 99 - 101 psia and still be within it's accuracy capability.


Good Luck, sounds like a fun project.

[jakep]

You might want to check out http://autopilot.sf.net

Apparently, a project like this is quite a bit more complicated than you may expect. The people on that site spent quite a while getting to a hovering point. Software wise, they used an insane multiple input Kalman filter. They may have some good code examples to use though. (I adapted their Kalman filter for a simple 2 input gyro+DAA setup for use with the 2004 FIRST RC this summer)