I am nearing completion on the airframe side of a single motor variable pitch quad copter design and I need a little help on the software side to get this going. My intention is to use the variable pitch to control attitude and altitude and then run the motor with a speed control that has governor functionality to maintain a constant speed on all the blades. The project has several purposes. The first is to increase the attitude/altitude response and the overall performance envelope. For example using variable pitch opens the possibility of inverted flight and what heli pilots often refer to as 3D flight. The next goal is to improve the efficiency by gearing down the motor and using larger blades to increase the disc area. At the moment the airframe weighs slightly more than a F450 but has about the same rotor area as the F550. Of course the down side to all of this is the cost and increased mechanical complexity.
Where I need help is on the APM. What I would like to do is run the servos that control the variable pitch to ports 1-4 where the speed controls are normally plugged in on the APM. So the APM controls remain 100% the same, it is just controlling a servo instead of a speed control. However, I plugged a servo into slot 1 and the servo went crazy and just twitched all around. I am pretty sure that even in quad mode the APM is outputting standard PWM so I am not quite sure why the servo was not working. Plugging a speed control in to the same port works as expected. Any ideas why the servo failed to respond normally in this situation and is there anything easy that can be done to correct this? Do you think the APM is outputting PWM changes so fast that the servo can not keep up? Thanks in advance for any suggestions!
Here is a pic of the airframe so far.
Replies
The servo was not working because the PWM output is very fast. 490 Hz is the default. You need to lower it to something like 200 Hz to get your servos working.
This is an arducopter parameter : RC_SPEED
I did some approximative drive system simulation for a variable pitch multicopter setup and i did find that it was not possible to get the same efficiency that we can get with a fixed pitch normal propeller setup. At least using commercially available blades.
You could use asymmetrical blades for more efficiency, but in this case reverse flight will not be possible and those blades are quite hard to find.
Let us know if you can get a better flight time compared to a fixed pitch setup.