Thread: Quadrocopter project

if you were sitting in the quadhellicopter for example engine one would be on the left side. engine two would be infront. engine three would be on your right side. engine four would be in back. engine one rotates clockwise while engine three rotates counterclockwise. if you increase the rpms in engine one you get more torque therefore you get yaw. if you increase the rpms in engine one you get more thrust therefore you get more lift therefore you get roll. by increasing the rpms in engine one you get both torque and thrust therefore you get both yaw and roll. independent control may mean you get only one axis but i do not see it happening here meow as explained above. if engine three decreases in rpms the offset only becomes more sensitive and happens faster.

Nope. INDEPENDENT control means you can change any one without affecting others.

get it flying yet ?

for example engine one would be on the left side. engine two would be infront. engine three would be on your right side. engine four would be in back. engine one rotates clockwise while engine three rotates counterclockwise

No, see the diagram for rotation direction.
Quadrotor - Wikipedia, the free encyclopedia

If you increase front engine and decrease back engine by the same amount, you get pitch and nothing else.

If you increase left engine and decrease right engine by the same amount, you get roll and nothing else.

If you increase both front and back and decrease left and right all by the same amount, you get yaw and nothing else.

If you increase all engine by the same amount you get lift and nothing else.

took a closer look at the engines configuration on wiki page. so it is like kirkoff where everything has to equal 0. that is what was missing one increases in rpm while other decreases by the exact same amount with that config.

you need alt so you do not hit ceilings or go real high and run out of battery and come crashing down. bar would work. so you also know where gnd is. set 0 before lift off. landing pads needed ?

there is one other thing that you may want to consider adding to your quadhelicopter robot. that is a dmu <distance measuring unit>. why ? if you set the alt to 0 and it take off one foot up then goes over a cliff you alt will read 1 while there may be hundreds of feet below or no close ground below or near. totally optional. most mobile robots have some type of switch sensor at the bottom so they do not go over stairs. like a cut off switch so when it hits or releases it flips the switch depending on how it is set up. for something flying a dmu would be better. there are several types. ultrasonic is the most common. meow. used mostly for landing.

there is one other thing that you may want to consider adding to your quadhelicopter robot. that is a dmu <distance measuring unit>. why ? if you set the alt to 0 and it take off one foot up then goes over a cliff you alt will read 1 while there may be hundreds of feet below or no close ground below or near. totally optional. most mobile robots have some type of switch sensor at the bottom so they do not go over stairs. like a cut off switch so when it hits or releases it flips the switch depending on how it is set up. for something flying a dmu would be better. there are several types. ultrasonic is the most common. meow. used mostly for landing.

Yeap, thought about it. There are pros and cons between infrared and ultrasonic, but I'm pretty sure either will work. I'm not planning to do automatic landing at this stage, though, so that can wait.

Thanks for pointing out the Gumstix modules, cyberfish. I'm enthralled by the Overo Fire and I'm particularly interested in the package including the Chestnut 43. It looks like you could almost build your own touch screen mobile phone with that kit, except of course it doesn't include a GSM radio.

I'm an ARM junkie, and I'm excited there are things like this out there.

That would be really cool.

GSM modules are available, too (SparkFun Electronics - Cellular) if you don't mind some soldering. But I don't think any of the ones available to hobbyists support 3G, yet. You'll probably also need to write a driver for it, though I think some GSM chips/modules have very simple interface that just takes simple messages (the module does a lot of things for you).

Theoretically, with magnetometer (which gives you yaw), and accelerometers (which give you roll and pitch), you can determine your orientation.

The problem is, and it's specific to choppers, there is a lot of vibration, and that introduces a lot of noise in accelerometers.

That's why we integrate (mathematically) gyroscopes to get accurate orientation, and accelerometers to correct the drift (inherent in integrations) over time.

I've been watching this for a while now.

I have to say, I'm so very jealous. ;_;

Soma

Ah, by orientation I mean yaw, pitch, and roll. I need all 3 axises of rotation because the computer needs to stablize the chopper. Pitch and roll are actually more important than yaw for me.

For yaw I am using GPS, but many people use magnetometer.

For pitch and roll, accelerometer with low pass filter may have too high latency. For stable flight, the computer needs accurate orientation (in 3D) data about 10 times a second.

Gyroscopes give very good short term accuracy.

Accelerometers can measure both dynamic acceleration and static acceleration (due to gravity). That's a very common approach.

I am using a 6 DOF IMU.
SparkFun Electronics - ArduIMU+ V2 (Flat)

Gyroscopes don't just give short-term accurate results. You are right, there's error inherent because the only way the gyroscope could perfectly keep its orientation is if it had infinite angular momentum (accuracy is proportional to power consumption). But, the error can be taken into account, and will be described in the data sheets.

Hmm. Gyroscopes output a voltage proportional to angular velocity (how fast it's spinning). They are available with different resolutions. If we integrate that, we have orientation (pitch and roll).

The error comes from integration. Since we don't have infinite sampling rate, the integration will drift over time. That's why we use accelerometers to correct it. In theory, they produce redundant data. In reality, one is good for short term accuracy, and one for long term accuracy. We combine the 2 inputs with something like a Kalman filter.

The control loop will most likely run at 10Hz, and I'm pretty sure it's not possible to design a filter (digital or electrical) that will get rid of the noise, and still have good enough response time. On the other hand, gyroscopes have almost no short term noise, as they are not affected by vibration. So no filtering is needed on the gyroscopes. They may include one to filter out things higher than the Nyquist frequency, but the bandwidth of that would be much higher. According to the datasheet of the one I'm using, it's 140Hz.

My brushless motor controllers can change speed every 20ms (50Hz), but going that high would be overkill.

I AM talking about using accelerometers for orientation. But we have different definition of orientation (I think). By orientation I mean 3D orientation (pitch, roll, yaw), and I'm guessing you mean 1D orientation (yaw).

I've bought most of the parts. Keeping a detailed log on my site, too.
http://cyberfish.wecheer.com/quadrocopter

I'm done the mechanical design. Working on the circuitry now.

The upper and lower propeller design is good for stability, but EXTREMELY power inefficient (due to one propeller blowing into another), and will run your battery dry very quickly.