Monday, May 9, 2011

Tricopter Success!

I'll re-post my settings- I believe they've changed from the last setting summary I posted. Anyway, I'm very close to having the tricopter ready to fly some arial photography.

It is fairly close to stable flight. It still isn't as steady as I'd like, and I need to put in a lot of "up" elevator trim to keep it from putting the nose down and accelerating away, even with the CG set to the exact midpoint of the three rotors. One puzzeling obervation is that the craft seems exhibit the pitch problem less with the CG "behind" the centerpoint of the three prop booms. I'd expect the opposite to occur.

I've also had to do quite a bit of reading on RCgroups to try and understand the tricopter setup, in particular gyro gain setup. (and don't hesitate to correct me if my observations below are incorrect!)

First of all, there are several gyro adjustments available:

1) gyro max travel (screw adjustment)
2) gyro time delay (screw adjustment)
3) gain control (electronic adjustment through separate rx channel)

You adjust the gain by modifying the output of a channel of your RX. Basically, it uses the same PWM signal as servos and ESCs. If you send the gyro a 0% signal, that's max gain. A 100% signal is minimum gain. However, if you send the gyro a signal of 50% or more, it'll be in heading hold mode rather than rate mode. You want the tail servo on heading hold mode and the other three gyros on rate mode. Heading hold mode will try and move the aircraft back to the origional orientation, and rate will simply react to counteract an input acceleration.

Since the tricopter uses two "blocks" of gyros- one three gyro block for the rotors and one block for the tail, you need two RX outputs to control them. I attached the rotor gyro gains to the standard gain channel on the RX (thereby using the heli gyro menu item), then I used the throttle channel for the tail rotor gyro. All confusing as heck and not at all intuitive.

I'm thinking that the following changes will help with flyability:
  • Changing from a 10x5 prop to a lower pitch- this should give the gyros more control as the ESC's will have a smaller output change in pitch inches per prop revolution per ESC step
  • Adding a rear skid so the tail rotor yaw servo doesn't smack the ground on each hard landing
  • Try moving the battery even farther back
  • I'd also like to add more of a visual reference as to which end of the craft is the "front"

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