Feric Jagger
Posts: 37
Joined: 8/10/2007
From: Brisbane, AUSTRALIA
Status: offline
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quote:
ORIGINAL: Popriv
Thanks for the info...
What would you suggest for a coaxle starter?
I've flown RC Gliders and I'm still trying to grasp the controls of rc helis.
It looks like the coaxles dont have a tail rotor? how do you control the flight?
TIA
Pops
In my humble view you have two choice: cheap and less cheap.
The cheap solution is the Walkera 5#4. The less cheap solution is the Blade CX2. I have purchased (and wrecked) two of the Walkeras and they work well enough. The advantage of the Blade is better quality and a 2.4 GHz transmitter. If I were to buy another coax I think I would go for the Blade.
The tiny option is, of course the Walkera 5G6 2.4GHz. I have owned a couple of these as well. They are probably OK for beginners but due to the poor quality materials and small size they are almost impossible to repair.
Coaxial copters are quite interesting. But lets talk about normal copters first. Due to Newton's third law of motion, the rotation of the main rotor in a single rotor copter results in a tendency for the rest of the copter to rotate (or yaw) in the opposition direction. The speed of the counter rotation is proportional to the speed of rotation of the main rotor (and of course the ratio between the mass of the rotor and drive train and the mass of the rest of the copter). This tendency to rotate is countered by the tail rotor. So in your average fixed pitch copter the blades rotate clockwise, the body tends to rotate counter clockwise, and the tail rotor applies a clockwise force on the back of the copter which stabilizes the tail. To turn the nose of the copter left you slow down the tail rotor and to turn right you speed it up. This is complicated a little because fixed pitch copters increase vertical lift by speeding up the main rotor which increases the counter clockwise yaw on the body of the copter. I think the gyro is supposed to compensate but with a cheap copter like the 4-1 and the 4#3 the gyro isn't very clever. The tail rotor also pushes the entire copter left which is countered by tilting the swashplate (and main rotor) to the right with a bit or right hand push on the cyclic control. You can try to counter this left hand push by trimming the swashplate to tilt to the right but the left hand push varies with the thrust of the tail rotor which varies with the head speed of the main rotor so there is not much point.
So, take off with a single rotor fix pitch copter involves advancing the throttle control to the take off position which leads to yaw which has to be countered via the rudder control which leads to lateral thrust which has to be countered via the cyclic (roll) control. Every time the throttle control is adjusted the yaw and roll controls also have to be adjusted. So flying a single rotor copter involves continual juggling of three different controls. I think that is one reason why single rotor copters are hard to fly.
Coaxial copters are relatively simple. A coaxial copter has two rotors (driven by two motors) rotating in opposite directions. The torque created by these counter rotating rotors cancels out. The cyclic control still control pitch and roll (to move the copter forwards, back and laterally left and right), but yaw is controlled by one of the rotors speeding up or slowing down. With the coaxial copter the throttle control doesn't affect yaw and the absence of a tail rotor means there is no lateral thrust to counter. That is, the throttle in a coaxial copter is not associated with the yaw and roll controls. If the copter is properly set up you can take off and land without touching any control except the throttle and you can fly it around a room by steering it like a model car. Very easy to fly.
One point to note. My understanding is that most plank fliers fly mode one whereas most copter flies fly mode two. In my opinion the mode two controls (with the cyclic controls on the right stick) is more intuitive and probably easier to learn on. I would advise choosing mode two over mode one for helicopters.
Also, if you don't have one already, get a flight simulator. FMS and Heli-X are for free but ClearView is very good and only $40. HeliSimRC is also for free but is not as pretty as ClearView or Heli-X.
If you are going the cheap flight simulator route I would recommend buying one of these cheap USB controllers. It is basically an eight axis no button USB joystick, and it comes with FMS on a disk. You could use a 360 controller (which I did for a while) but it kind of turns the flight simulator into a game. If you want to go the expensive route I won't make any suggestions for fear of being flamed out of existence. You can check out various flight sims via this chart and make up your own mind. I ended up with RealFlight G4 (which came with a very nice USB controller) and consider it AU$300 well spent.
Stephen
< Message edited by Feric Jagger -- 5/5/2008 10:52:28 AM >
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RE: Walkera #4 Fixed Pi... - 
