I have looked around the forums and have seen several discussions about variable pitch. Most revolve around construction and configuration.
What I want to know, is does it make the quad fly any better?
If I go the route of variable pitch, I will use tail booms and tail rotors from a T-rex 450 going to a single main gear in the center and one or two drive motors. Obviously, this set up would cost more that a conventional quad with four prop/motor/speed control arms.
Anyone flown both types (fixed and variable)? What did you think?
22,000 members and no one has done this? Share! pretty please!
Still looking for comments from anyone who has flown both types of quad.
We too looked into doing this. There was a company I saw was starting to make one doing it as you mention, which is the easiest starting point (Design wise). I think what pushes most into doing it the traditional way is because of less parts count, less tweeking etc doing it direct drive. If it were gas ran I would believe that having a steady RPM like that of using a governor would be a huge bennie as you could set pitch curves to match max economy/power etc. unlike the insane rpm needed to fly using direct drive. I am no PHD on this and many here are.
Thanks for your input Dave. I have flown R/C helis for years and I remember the days before collective pitch. Today you can only find fixed pitch on very small 'cheap' copters that are not taken seriously. I have done a "rough" cost comparison:
Traditional parts: $120
I think it would help make it much more complicated...
...and increase the frequency response of your thrust vectoring controller
Adding variable pitch means you have twice as many actuators now - one speed controller and one pitch controller for each motor/propellor. You can begin to see why most like the simplicity of a fixed pitch quad instead...
That is exactly why we quit working on our idea like that. In the field you want the lowest parts count you can possibly have. And if you can repair it w/o tools thats a big plus as well!
Andrew, there will be on one speed control set to constant RPM to drive one motor then four servos to control each boom pitch. So control wise I will have one extra channel for throttle. The pitch controls will use the same channels that would normally control the ESC of each motor.
I can deal with the cost and complexity.....the real question, does it fly better?
yaw is a function of drag. so reducing pitch will have the same effect as slowing the motor.
Yaw control comes from the actual accelerating of the motors and props in addition to the torque reaction from the prop drag.
You can easily feel this in a quad held in your hand when you deflect the rudder stick - the initial yaw moment you feel is quite high, then it backs off as the motors reach their newly assigned speeds.
This means the yaw response is non-linear, making the life of the yaw PID controller harder. Constant RPM should make the yaw response more linear.
It actually surprised me how responsive quads are to fly - I expected cyclic response like the collective response of the little indoor fixed pitch helis, but my 600 mm quad is about the same as a Shuttle (remember those) with heavy paddles.
The yaw response is pathetic compared to what you get with a proper tail rotor, however.
Thanks for you input Phil!