Helicopter Project
 

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

Re: Helicopter Project
 

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

Re: Helicopter Project
 

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.

Re: Helicopter Project
 

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

Re: Helicopter Project
 

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.

Re: Helicopter Project
 

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

Re: Helicopter Project
 

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

Re: Helicopter Project
 

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

Re: Helicopter Project
 

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.

Re: Helicopter Project
 

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.

Re: Helicopter Project
 

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)

Re: Helicopter Project
 

Hey guys, how you doing?

First off just want to thank all of you for all of your inputs and advices, I greatly appreciate it and it has helped me better understand what I am getting myself into and what I would need to do in order to have this project come out right.
Despite all the posts on the level of difficulty on this project, I have decided to still go on with it and try to expirement a little and just have some fun with it.

I have also decided to go with either the ADXL213 - ±1.2g Dual Axis Accelerometer with Duty Cycle Modulated Outputs or the Memsic 2125 Dual-axis Accelerometer. I did some research on it and seems as though these would be a good choice for me to use. Although I have decided to go with one of these accelerometers, I am still looking at which Microcontroller would be best for this. Please keep in mind I have little knowledge on programming but I have a neck for computer programs and I pick up VERY fast on these kind of things.

Again, thank you all very much for your inputs/opinions/comments. I greatly appreciate all the help and support

Take care
- Miguel

Re: Helicopter Project
 

Try using a ultrasonic range sensor pointed downward to get an accurate height. Though a microcontroller on the heli will be required.
http://www.sparkfun.com/commerce/pro...roducts_id=639

I don't know about amtel but I have been pretty successful with picMicrochips(go with 18 series so you can program smilar to the RC)
Can anyone explain to me the difference?

Re: Helicopter Project
 

If you're planning on keeping the helicopter inside, a novel way to track your position would be with the CMU cam pointed at a colored target. Indoors, under controlled conditions, you could also use one of the Sharp IR proximity sensors to measure your altitude.

Here are some comments based on personal experience. Your ideal platform would be a large fixed-pitch helicopter like the Lite Machines Corona. There are only four channels to control and it can carry some weight if you upgrade to a brushless motor. A small fixed pitch helicopter, like the Honey Bee or Dragonfly, doesn't have enough lift to carry the extra gear required. You will have to upgrade to brushless motors and lithium polymer batteries, which turns your $100.00 toy into a $350.00 money pit. I don't know how it would work in reality, but in theory you could use a futaba heading-hold gyro on each axis to keep the helicopter stable in roll, pitch, and yaw. It won't keep the helicopter in place, but it should keep it stable on each axis. Those are about $100.00 each, so you're up to about $650.00. Your primary control inputs would be the throttle, which controls altitude, the ailerons, which controls side/side, and the pitch, which controls forwards/backwards.

Here is another way to approach it. Get a coaxial helicoper like the ESky Co-Co Lama or Blade CX. Put a brightly colored target on the nose that that you can track with the CMU cam. Build a robot that can manipulate the heli transimitter and build a robot that "flys" the helicopter. Based on the camera feedback you'd be able to determine its altitude and orientation. If the target is square then the height would correlate to the range and the width would correlate to its orientation. You control loop would need to try and keep the nose pointed at the camera at all times, then apply throttle/aileron/pitch to keep it in one place. Those helis are very stable and almost fly themselves.

Re: Helicopter Project
 

Atmel AVRs are relative newcomers to the field. While they don't have the same grip on the market as PICs they are fairly popular. They're much easier to get in to for hobbyists as their open architecture allowed the development of cheap programming hardware, as well as free C compilers based on the GNU GCC toolchain. They have decent capabilities and are quite capable chips.

They always have a strong support following at: http://www.avrfreaks.net/

If you'd like to know more, drop me a PM

Re: Helicopter Project
 

I agree with the AVR option. I've started using them for the same reason(s). Free C compiler, lots of application notes, software examples (assembly and C) and development hardware is cheep!

You may want to look into the mega AVRs since they have hardware multipliers which may be handy for processing multiple PID loops quickly (not necessary, but nice).

Re: Helicopter Project
 

Hey guys, once again, thank you for all your comments.

Before I get into target operation and manuevering (sp), I would first like to get the Copter to atleast hover on its own under the programmed codes.

Running it through my head, I figure what I would need for this, simply to get the Copter hovering on its own, would be the Copter, ADXL213 Dual-axis Accelerometer or Memsic 2125 Dual-axis Accelerometer, whichever I decide to use to balance the Copter out, and the Microcontroller along with all the programming sofrware. If there is anything I am missing, please let me know. Again, thank you all

Take care
- Miguel

Re: Helicopter Project
 

hovering is actually the most challenging aspect of this auto pilot project.

When the HC starts to hover the downdraft of the blades will push the air straight down. After a few seconds the air will start to swirl in a donut pattern, the air that was being pushed down goes outward, then back up, and is then sucked through the blades again.

the result is, the air at the center of the HC developes a downward velocity. In order for the HC to maintain its height you must apply more and more pitch/power.

So you are going to need a way to measure altitude in order to hold a fixed altitude while hovering.

Re: Helicopter Project
 

[quote=
So you are going to need a way to measure altitude in order to hold a fixed altitude while hovering.[/QUOTE]

IR or Ultrasonic range sensors...

Thats the problem I had with 16 series pics when I started working with pics: no free C compilers. So I started using 18F series pics and used the RC code as a guide to make mine work. After a while I finally got a 18f458 to run a servo!

Re: Helicopter Project
 

At minimum you will need three gyros and three accellerometers. It took me about 3 hours of flying time to hover a battery pack without crashing. That's flying time, not counting time spent waiting for spare parts. Micro helis are so cheap becase they make money on the spare parts. As Ken was saying, any change in roll or pitch requires an increase in throttle. The best analogy I've seen is balancing a marble on a piece of glass. I'm not going to say it can't be done, but it will be very difficult. As I said in a previous post, it's not just controlling the heli, its being able to carry your sensor and processor payload too. A micro heli can only handle a couple of extra onces of weight.

Go to http://rcgroups.com and visit the micro heli forum. There is a sticky with a PDF called the "Electric Helicopter Beginner's Guide". Essential reading.

Re: Helicopter Project
 

Actually there are two phases of hover - HIGE and HOGE
Hover IN Ground Effect and Hover OUT of Ground Effect.

What Ken describes is IN ground effect - the ground is causing the air to recirculate and can cause turbulence, but it can also require less power to hover in this condition.

Hover OUT of ground effect means the helicopter is high enough that the air dissipates and the ground has no effect on the rotor system.

Re: Helicopter Project
 

I dont think it is limited to the ground effect altitude.

I found this on a website - it appears to be a run-away sort of thing, once it starts to happen you cannot lift out of it, unless you move forward out of the ring of airflow:

Re: Helicopter Project
 

I haven't seen it with the model helis, but with a fixed-pitch model you have little or no control when dropping altitude because the blades aren't spinning fast enough to maintain cyclic authority. If you hover at about 20' then try to land the tail will drop and the cyclic turns to mush. You'd have to be pretty good to drop straight down.