• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

P and I ?

Bobo

Senior Member
#1
Hi guys,
I am a noobie at RC and I have built my fist SK450 quadcopter. I have tried flying it and I totally failed. It fliped over both the times I got it of the ground. I have never flown anything RC related except for a syma x1. I think I have heard that the P and I settings control the sensitivity of the quad. Could you guys help me find a nice stable setting set for a beginner. Also I am using the KK2 board and the 9XR transmitter.

Thanks.
 

ikem

Senior Member
#3
watching a flite test episode, P is the strength for the corrective action to an angle. I is the stopping speed of that action. (i think thats what it is)
 

cranialrectosis

Faster than a speeding faceplant!
Mentor
#4
If you flipped the copter at launch, check to see that your ESCs are connected to the proper KK2 ports for the motor the ESC is connected to. If that isn't the issue, check to see that your motors are spinning the proper directions and that you don't have any upside down props.
 

Bobo

Senior Member
#5
watching a flite test episode, P is the strength for the corrective action to an angle. I is the stopping speed of that action. (i think thats what it is)
So is the higher P and I setting the more stable. Also could you send me a link to that episode.
 

Bobo

Senior Member
#6
If you flipped the copter at launch, check to see that your ESCs are connected to the proper KK2 ports for the motor the ESC is connected to. If that isn't the issue, check to see that your motors are spinning the proper directions and that you don't have any upside down props.
It didn't flip right at launch. It flip when I tried to move forward.
 

Bobo

Senior Member
#12
Here are my P and I settings without change.
Roll (Aileron) Yaw (rudder)
P Gain : 30 P Gain 50
P limit : 5 P limit 20
I gain : 0 I gain 0
I limit :20 I limit 10
 

cranialrectosis

Faster than a speeding faceplant!
Mentor
#17
I fly a Knuckle H Quad that is 14" across. I am running a 3S battery with 1450kv motors and 8045 props.

That means my copter is little and is prone to be twitchy or squirrelly. It limits how much P and I gain I can use to keep the copter stable and it means a little stick goes a long way in stick scaling.

I am running P gain of 75 with I at P/2 as per the manual. My stick scalings are at 75 for all controls except throttle which is at 90 and I keep it there. I am running expos of 20.

This gives me a quick copter that is manageable, I can trim out to hover without my hands on the sticks and responds well in tight corners. I am working up to stick scalings of 125 - 150 so I can flip with authority and so my copter will corner like it is on rails but I am still learning to fly this copter.

I had the best results using the guide. It is well worth it to tune your KK2 to your copter and how you fly. P and I settings are partly determined by your build. Stick scaling is determined by how you fly. Here is the guide I use.
http://www.hobbyking.com/hobbyking/store/uploads/475200704X68736X56.pdf
 
#18
P&I are terms of an control loop called PI(D) Controller google that.
It is not so hard to understand. In a control loop you have a current state and a state you want the system to be ("set point"). So that difference describes an error. The P term is the proportional response to that error and is basically an multiplicator to the actual error. A high P will produce a strong and fast correction but an overshoot as well. A too low P can lead to slow response or never hitting the actual set point ("undershoot"), that's why the idea of an "I" was born. The I helps the "P" out of its undershooting misery and so indirectly helps the overshooting you would produce by an too high P to actually reach and surpass the setpoint. The I accumulates the error overtime. So in that undershooting situation the P is too low to reach the wanted setpoint because the error is constantly too low BUT with the "I" the constant little error accumulates and "lifts" the result to the setpoint (and generally increases reactiontime). This error collecting "I" therfor also helps when holding an angle in acromode because it increases the reaction(and speed) to small changes from outside (wind) or inside (pilot). (NOTE: That is a rough description of "I" because it can be also negative... but it is easier to understand it in the "positive" way..)
So P & I work hand in hand. Too high values for "I" or "P" will produce overshoot and wobble. When dailing in an "I" value you will normally have to decrease the "P" value.
Play with those values and you will see in flight their meanings.
There must be some guides online concerning the KK boards (I don't have one).
The limits describe the maximal influence of each component on the result (tiltangle).
The "gain" describes the multiplicator of the error ("P") or the accumulated error over time ("I").
You can not fly with a "P" of zero but with an "I" of zero.
Generally you increase the P till a constant oscillation appears, than back off that value a good portion (not more than the half of that oscillationvalue, some theory suggests to take 60% of the oscillating "P" as the baseline "P" for further tuning - but from my experience with other FC that theoretical value is too small.), so you have headroom for your "I". Now dail in the "I". If the copter becomes oscillating again or it feels bad on the sticks, it was too much :) .
Cheers Rob
 
Last edited:

Bobo

Senior Member
#19
So here is my final guess on P and I settings + Stick scaling and expos.
Expos: 100% for all
Stick Scaling: 30 for all but 90 for throttle
P gain: 75
P limit: 100
I gain: 0
I limit: 25
Are these all okay. The last flight I did the AIL and ELE where way to sensitive. Even with the slightest movements the quad would flip and land head first.
 
Last edited: