Recent KK2.1.5 nightmare


Senior Member
I built a 400mm knuckle quad using the KK2.1.5 FC. It flew well from the beginning. I always felt in control, never quite got it totally smooth at hover but I always had control, it always did what I told it to do.

Until one evening. When I popped it up for hover it just felt weird. It was trying to go away from me so I trimmed it out, seemed like it took alot of trim, but it did stop moving forward, so I went off for a nice, peaceful, evening flight with LED lights on.

It got out about 80 yards, i turned it towards me and told it to come back, it did not. It went backwards and to the left. I have very bright green LED's on the front, it was facing me for sure. After several minutes of many maneuvers to try and get it to come home to no avail I had to do a hard landing, as it was now 400 yards away and approaching pavement. The only damage I had to the quad was broken landing gear, which is made from plastic coat hangers so no big deal.

The real damage was the broken confidence I had in the quad. I needed to find out why my previously controllable quad went beserks. I had made a change prior to that flight. I had used the foam box the KK came in for mounting, I removed it for aesthetic reasons. In it place I used 2 layers of self sticky tape and velcro, both on the quad and kk board. I felt like this would give me a soft enough pallet to eliminate vibrations as much as possible for the KK. I have seen many videos where people use less cushion than that for their FC board.

I was pretty sure my KK was toast, why else would it act like this ? I put my quad back together, came up with even more cushy pallet for the kk to rest on as well, thinking that was the problem. Took it out for test, at first it hovered well.
Then I spun it 180 degrees to face me and it immediately took off rather rapidly backwards and left. I spun it back around and it was fine. I did testing in front, rear, left, right positions and it would only behave when when facing forward.
Then I noticed I was at full stick forward to keep it from backing up into me. The longer it ran, the more it was trying to go away. Like the error was getting bigger over time. I left the field feeling lost and unsettled. Still not understanding why my tame quad had become a belligerent monster.

My usual flight routine was to install the battery, getting the quad carefully balanced, then calibrate the ACC on level ground. Then go in and do the receiver test to get the inputs to zero. I noticed that each time I did this I would have to make slight adjustments. I was using CPPM, KK2.1.5, Orangerx 6 channel receiver and radio. It did not seem right that I would have to adjust the sub trim each time, being new to quads I wasnt sure.

After all of this I did more research on the KK board and issues people had with it. I looked into Lemon receivers and ordered some of those. I had recently received my dongle ( for updating the KK board, but had not done so because I figured there was no need to fix what wasnt broke. Also I watched the hobbyking video series on configuring the KK board. I have watched many videos on this and never really quite understood how to finely tune it, but it was fairly stable and totally controllable until that one evening.

After 3 or 4 days of research and pondering over the whole catastrophe I decided on a plan of action based on new learning's. This is what i want to share, I know there are alot of KK boards out there and there is alot of scattered info on PI settings etc... so maybe this info will help someone.

1) be sure and have your KK board mounted in a way that motor vibrations will not affect the gyros and servos on the board. I used several layers of double sticky tape and loose fitting velcro. I still want to develop a better way for this, using the foam balls I see online, but are always out of stock.

2) I went ahead and updated the KK board to stevis 1.18 version. I recommend doing this. You should be able to use your previous PI settings, that didnt seem to change, but the new version does give you more options to use that are very helpful. The ones I liked the most are the gyro and servo bubble.

After finally obtaining a successful flash update the first thing I looked at was the bubbles. What I found was the servo bubble was atleast 1/4" off in one direction. I attribute this to the run away issue I was having. I dont know how I got such a bad ACC calibration, but I realize now that I probably should not re-calibrate each time I go to the field. Calibrate it at home in a perfectly level environment, then leave it alone !

You can use the bubble level to visually check your calibration before flying. And after calibration as well.

3) After watching the KK videos I finaly understood how to calibrate. The P gain settings I did understand, it was the I gain settings that I did not understand. All other videos said to look for "slow" oscillations on I gain. But he called it "searching" and gave an example on his small quad. The light came on !

Also in the KK instructions, kk recommended that the limit settings not go over 20. In the hobbyking video he was using 100 for the limit and his quad was perfectly stable.

P gain-- look for the fast oscillation, this indicates P gain is too high. It is OK to use 90 or 100 in the limit of P gain, nothing bad will happen.

I gain -- when I gain is too high the quad will "search" or "roam" around as if to be seeking its rightful place, so tune it back down to where the "searching" stops. A good point of reference for I limit is half of the P limit.

After watching these videos I tuned the KK board by removing all I input and starting with the P gain. I had done this before, but never quite understood what I was looking for in the I gain, until now. End result is I now have a well tuned KK board.
When I click the switch to go from auto level to acro mode, my quad does not flinch. Before it would quickly begin dancing around and would take much nerve racking thumbing to keep my quad from crashing. Now it behaves as it should.

Which led to me a better understanding of what KK auto level actually is.

Non auto level KK : when giving a stick input, example: forward, the quad will lean forward and move in that direction. Center the stick, quad holds the same leaning angle and continues moving forward until you give it a different input.

KK auto level : when giving a stick input, example: forward, the quad will lean forward and move forward. Release the stick and the quad will return to the level position. It does continue forward due to momentum.

I know this is a simple concept and probably everyone knows it, but these definitions clarify to me what auto level truly is. It is NOT a magic setting that makes the quad sit perfectly still and not move until you tell it to. It simply returns the quad to a level position, which is THE position that was set by you when doing the ACC calibration.

4) CPPM: When reading the RC groups forum on the Lemon receiver, one of the big wigs in that company responds to customer input there. I saw where when asked about CPPM, he stated the CPPM is not fast enough for multi rotor use, therefore they did not put that capability in their 6 channel receiver.\
This was the first time I had ever heard of such an issue and it made me think that this could possibly be one of the reasons my quad had went beserks too.

I calibrated the PI settings as described above using CPPM, then I took out CPPM in the KK board and installed 5 servo wires, one for each channel, to see for myself if there was any difference.

The first thing I noticed was I was now able to use my subtrim and obtain a ZERO input status to the receiver. When using CPPM I could only get +1 or -1 at best. Then I popped the quad up for hover and began doing slow movements and I can say for sure that the quad is slightly more stable and responsive using the standard receiver configuration of one wire for each channel instead of CPPM with 1 wire for all signals.

The nightmare is now over. My quad is now dialed in better than ever. I am very happy now to know the KK isnt toast as well as having a much better understanding of my creation.

A quick summation of my experience to have a good experience with a KK2.1.5 board.

1) Install the board in a creative way that will have padding under the board to eliminate as much vibration from the motors as possible.

2) Update the board to stevies 1.18 use the bubbles to aid in confirming you have a great ACC calibration

watch these videos to learn about KK settings. Particularly video number 3.

4) Be very precise when doing the ACC calibration ! Once accomplished, keep it. Avoid calibrating in the field unless you can do it with precision. Use the bubbles to verify you have a great calibration before flying.

5) Use standard configuration of 1 servo wire for each receiver channel instead of CPPM on a multirotor.

6) When adjusting your PI gains, use the system in the videos and dont allow other peoples settings to influence your settings. Every quad is unique, every pilot is unique, so the PI numbers that you end up with are THE numbers that work for you !
If your quad is behaving proper and it "feels" smooth and under control to you, then you have it right. There are no magical settings to make it perfect or better.

You find your settings with auto level off, once happy with them then you calibrate your auto level settings, which are not so hard once you have the other settings right.

You know you have good settings when you pop your quad up off the ground and it moves straight up vertical in the air and just sits there happily. This will give you confidence in your quad and your ability to control it.

Flip the switch from auto level on to auto level OFF and your quad should not flinch or move, it should remain as it was, happy and content. Unless there is wind, which ofcourse will move your quad around.

I am not an experienced pilot or RC guy, I only started into this hobby in December 2014. these are just my experiences that I share in hopes that it may help someone else out. Which is one of the things I enjoy with this hobby and this flitetest sight, people are so helpful and willing to share their knowledge and experience. Which greatly helps and inspires a noob like me.

It looks like its going to be a beautiful, warm calm day out, so Im charging batteries and preparing for a day of flying my quads and hoepfully getting better at flying the FT flyer that I built.

take care, HarleyRev.


Senior Member
Sounds like your quad wasn't eating a balanced diet appropriate to it's physiology. Or, that might have been a bad receiver too.