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Old Jun 13, 2012, 12:32 AM
Atomic Playboy
United States, MN, Inver Grove Heights
Joined Jun 2012
218 Posts
Discussion
Interesting idea for setting gains/PIDs

I was doing this with my KK board tricopter tonight, but had to stop because my servo went bad. Until the servo failed, it really seemed like a good way to adjust the gains... if not a little dangerous.

The KK board is running 1.6 acro. So as I understand:
Yaw pot = P and I for yaw
Roll pot = P for roll and pitch
Pitch pot = I for roll and pitch

So my plan is/was to hold it level over my head at half throttle. Then:
- Adjust trims so it doesn't feel like it's tilting in any direction
- Adjust yaw pot, twist it quickly and see if it oscillates side to side. If not, increase gain. If so, decrease.
- Adjust roll pot. Roll or pitch it by hand or with stick, feel for oscillation. Increase gain if none, decrease if some.
- Lightly move tricopter laterally in any direction and feel it try to move back to the original position. Adjust Pitch pot (I).

I am assuming I'm testing each one of these correctly. Remember the 1.6 firmware doesn't do what the pots say. They are P, I, and P+I for yaw. If anyone has a better way to test, I'm all ears. I keep crashing when I fly it, and I cannot keep it hovering long enough to figure out where the pots need to be. I'm just trying to at least get it as good as possible before I take it up again.

Thoughts? Suggestions on better ways to twist/turn/tilt it for testing each pot?
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Old Jun 13, 2012, 02:42 PM
KK Tri Flyer
mattcro's Avatar
United Kingdom, Scotland, Glasgow
Joined Feb 2012
346 Posts
If the trims and/or gains are way off then that's not a bad way to test... just be careful of those props!!

Set up a throttle curve (or endpoint) that prevents you applying full throttle, so that you can't accidentally knock the stick and rip it out of your hand.

Hold it out sideways and out to the side instead of over your head, so it can't fall on you if you lose your grip. It does not have to be held horizontal if your board is an ordinary KK and does not have accelerometers.

Once you've got it roughly set up and trimmed, do some test flights to fine tune the gyros and trim. Holding it in your hand will affect the gyro operation because you'll probably dampen the movements a bit.
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Old Jun 13, 2012, 03:04 PM
Expat
Japan
Joined Apr 2010
3,089 Posts
Ya, matts on it. Was going to mention you'll notice some difference in actual flight and wind as well. I also found thermal drift is huge on mine. If its sunny out, after 1 minute flight itll vear off sharply. Disconecting lipo and waiting a couple minutes solves it.
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Old Jun 13, 2012, 05:29 PM
Quad Whisperer
Joined Jul 2008
943 Posts
You only need to lower the throttle to zero for a few seconds to get rid of thermal drifting.
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Old Jun 13, 2012, 06:38 PM
Atomic Playboy
United States, MN, Inver Grove Heights
Joined Jun 2012
218 Posts
I grabbed a new servo that truly has all metal gears in it (Spektrum A4020). Tonight I was able to hold the thing above my head and start doing some adjustments. It's WAY better than it was when I started. It really wanted to drift all over the place and oscillate before.

I've got Yaw at about 10%, Roll at 5%, and Pitch at 25%. Reducing the roll pot really reduced the drift, and reducing the roll pot significantly reduced pitch and roll oscillations.

One thing I noticed though, when I put the rudder stick to the right, the rear motor doesn't tilt at all, but works fine in the other direction. I thought it might be the servo, but I put the servo directly into the transmitter, and it's got full travel in both directions. I haven't flown it outside yet, waiting for my battery to charge. Maybe it's a non-issue, but it sure seems like something is up.
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