I have had my deadCat quad for a while now… It flies great… Very happy with the apm2.6…save one persistent issue that I cannot seem to eliminate… From a level ground takeoff, 99% of the time it wants to dive nose forward to a varying degree… Sometimes worse than others… I’ve tried all the normal things, have calibrated it several times in different configurations… Recently moved to an external compass (which totally solved my loitering problem.)… Bought a shiny new Taranis radio… replaced a buzzy motor, tried a couple different motor/esc combinations…command line level command, and so on… Most of the time it’s really not terribly bad…I can fly it just fine but have to always keep a little nose up pitch… Recently I’ve started trusting it to fly a little further out…which has highlighted the problem… When I fly the quad out a few hundred feet…I have to reaaaallly pull back on the pitch to get it to stop… and if I try to fly it backwards back to me in a straight line… it fights…alot… it wants to keep going forward…and climb… I always have to reduce throttle, pull back further and further and it’s a struggle… I usually get worried that it’ll lead to loss of control…and actually has once… Loiter works great… the yaw is rock solid… everything is awesome, except this weird issue… Can anyone lend some advice? I’ll be more than happy to provide logs, etc. if that will help… I’m completely at a loss now…
Wiki Table of Contents: Checked… I’ve visited this area so many times I dream about it… It’s one of the highest rated in my chrome browser most visited list… Could not find anything relating to my issue… (maybe I’m too dense?) Firmware Release Notes: Checked… Did this long before recently updating the latest firmware… (Which made no difference with this issue…) Also found nothing relating to my issue… Descriptive Title: Perhaps I’m not creative enough, but that is the best I could think of to describe the issue in so many words… Describe the problem you are having: Tried doing that as well… I start, take off, buzz around… It’s ok… I fly for around 200 feet in a forward direction, stop…then try to return under manual control in the reverse direction without changing heading (i.e. going backwards) and it is a progressively difficult struggle to get it to return as it tries to keep going forward…until I almost run out of stick to get it to return…But upon return, it’s fine and flight is normal… Provide hardware information: As I stated… It is an ardupilot 2.6… APM 2.5/6? Using a Lea 6H GPS… 3DR 915mhz Radio and a FrSky Taranis with an X8R Receiver… External compass with a 6% from compassmot(down from alot more…although it was an internal before and the difference is exactly nothing beyond the loitering issue)… deadCat (hobbyKing) airframe… 20amp esc’s…900kv motors… 3300Mah 3S Lipo Battery… GoPro(NO WIFI)… Firmware: Currently 3.1 as I noted… Although I ran 3.01 prior and it exhibited exactly the same behavior… Log Files: I stated I could provide… and so I shall
The closest thing I was able to find anywhere… was a small note in an old troubleshooting page… ( code.google.com/p/arducopter/wiki/AC2_Tweaks ) Where they make a note “My copter angles back in the opposite direction I’m flying after forward flight: Raise your gain in Stabilize Control P.” This doesn’t really cover my issue as mine is that when I fly out away from me, it’s great… After stopping, hovering and returning to me while facing the same direction, it fights… alot… Not to mention the verbiage in that line is confusing…and almost seems like two sentences…
Please let me know if I missed anything! =D Thanks!!!
Passerby,
The desired pitch and the actual pitch are not tracking well at all which means the copter is not pitching at all like the pilot (or autopilot) are asking it to. As for what’s causing this is could be just a badly balanced copter, i.e. the center of gravity is really far forward, is there a camera stuck out on the front? I suspect that if you pick up the copter at the midpoint between the front and back motors you can easily feel that it’s front-heavy. If somehow the COG can be moved back to be in the middle it will probably fly fine.
Other possible solution is to increase the rate pitch I to maybe 1.5 or 2.0 (default is 1.0) and increase the Rate Pitch IMAX to 10 or 15 (default is 5).
I have played with the CG quite a bit… The gopro is on the front, but the battery is all the way in the back… The CG is exactly center to to middle of the ardupilot itself…which is located just slightly forward of the midpoint between the front and rear motors.
I’m not entirely sure there’s any documentation on the deadCat airframe and where its CG should be… but maybe my assumption is incorrect.? I’ll admit, I’m confused as to how CG works out in a quadcopter with a V frame… For reference, the airframe looks like this (somewhat…) hobbyking.com/hobbyking/stor … Frame.html
Does this explain why it gets progressively difficult to control over distance, or is that probably perception? It just seems like it, and I actually have to reduce throttle to keep it from climbing on return… I’m not good enough with orientation at a distance to fly it back facing me quite yet…
Just for reference… Here are a couple photos of the quad in question…
The balance point (just confirmed it) appears to be at the midpoint… and the apm is dead center of that…
(I’ll also state - I forgot to mention I have a 5.8ghz video transmitter…with a 1200mah 3s battery right next to it… - doesn’t seem to contribute to the problem, and it’s mounted all the way to the rear anyway)…
The white wafers you see at the arm connecting point are spacers I am experimenting with to make the from a little taller inside to accommodate the electronics…Very lightweight.
I wanted to thank everyone for the help… I tried a couple of the suggestions… The center of gravity didn’t seem to be the problem, and I started the PID adjustments but was unable to come to a conclusive answer… Unfortunately, this quadcopter met an untimely end today… I was testing it out and the battery went low when it was a little further out than I could see it’s orientation to a small creek below… It managed a perfect automatic landing right into the water. Nearly everything except the goPro was destroyed by water damage.
