T-Rex 600E with APM2 - Test Flight

As requested, here is a clip of one of my test flights with the APM2 on my 600. This may be the most boring video ever, but in this case, boring is exciting! The APM2 works amazingly well mounted on Align gel, where a tail gyro normally sits. Stabilization is very good using  these parameters, though I need to lower the yaw values since there's still just a bit of tail wagging.

I've had this bird for a couple years, so unfortunately I think there is a bit of play in the linkages, and a couple of the servos have sticky spots. This causes small variations in the rotor disc (leading to slight wandering) which the APM is not responsible for.

The previous stabilization system I had was a Robbe HeliCommand. Absolute rubbish. That caused more grief and wasted time than I can imagine. Although, I was terrified of tuning it and knew very little about the effects of vibrations, so maybe it was good and I didn't know it!

Either way, APM2 + TRex is awesome so far.

Cheers

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Comment by John Arne Birkeland on June 5, 2012 at 1:59am

Nice work. 600's are scary compared to a quad but much better performers when everything is tuned.

Have you considered using a flybar-less head? Much simpler linkage and less slop. HobbyKing has some cheap conversion kits.

Comment by Eric Tweet on June 5, 2012 at 4:11am

Yeah, I'm pretty excited how well it runs with APM on it.

I actually have one of the HobbyKing 600 FBL head kits. I have just started playing with the heli again, and I already have the quad and HK EPP FPV plane to keep me busy so I haven't gotten around to installing the head. Trying to do 3 things at once keeps me pretty busy, but I'm itching to try it without a flybar. 

Comment by Anish on June 5, 2012 at 4:25am
@eric that is cool, btw when someone publishes PID's for a 500 size clone of trex (razor) I might give that a go :) or for a blade 450 :)
Comment by Eric Tweet on June 5, 2012 at 4:31am

Thanks. If I'm not mistaken, the default heli parameters are for a 450. There certainly aren't a whole lot of 600's around with APM's on them, but I had this one for heavy camera lifting, so it was a perfect goal for me to install the APM. Tuning for this from the defaults was not nearly as bad/tricky as I expected, so I would think something closer to what it was intended for (450-500) would be even more ideal. Either way, I hope you get to give it a shot sometime.

Comment by Rob_Lefebvre on June 5, 2012 at 4:39am

Eric, good job.

I've been flying the APM on my 600 for a few months now.  You should try dropping your Stab_I_pitch and roll numbers to 0.  I found that after doing an auto-leveling routine inflight, that the heli was able to hover hands off, and really only got moved around by the wind.  Good work getting this far though.

So far I prefer the flybar on my HK600GT compared to the Flybarless HK450GT.  It's far, far more stable.

Watching your video, I was going to ask if you lived in far northern Canada.  But I see it's actually Nome.  Interesting that it looks so similar.

Comment by Eric Tweet on June 5, 2012 at 4:54am

Thanks, Robert. I'll give that a try. What effect will that have when I use batteries of a different weight (i.e. switching from a 5800mAh to a 4500, or even to a 8000)? I imagine I would have to go through the auto-trim process again, or will that be accounted for even without the Stab_I terms? I just recall that the Stab_I is used to compensate for CG irregularities for quads.

The extra stability with the flybar is one of the main reasons I've kept it on during these first flights. The last thing I need is for too many things to change at once. I'm an amateur at piloting, but professional at crashing ;)

Comment by Şuayb TOZMAZ on June 5, 2012 at 5:42am

I'm watching this closely. I'm thinking to install APM2 on Trex700 when its all stable for air video platform.

Comment by Rob_Lefebvre on June 5, 2012 at 6:09am

Eric, I think the I-term is much less important for helis than quads, but you would always want to balance your heli properly.  If it was way off balance, then you will have a problem of course.  In my experience, the effect on a heli if the balance/leveling is not right manifests itself mainly in a tendency to drift in a given directly, but not much more than that.  At least, I haven't had the CG so bad to see anything worse than that.  

The biggest problem I'm having right now is vibrations causing "leans".  On my 450 last night, I believe I was suffering from a main bearing that had previously been damaged, going out and causing more and more vibration over the course of 3 flights.  On the 3rd flight, it just go so bad that it led to another crash.  

It seems to me that the 450 is having much more problems with vibration than the 600 did, though the 450 mounting was not good and I've yanked it and will try something else.

Comment by Rob_Lefebvre on June 5, 2012 at 6:16am

I believe the issue with the I-term is that it basically integrates the vibrational error, and thus can lead to a "random walk".  You can try with it on, but I found that after doing a leveling, and with I=0, the heli hovered hand's off, only moved by the wind.  Very very stable.

Comment by Rob_Lefebvre on June 5, 2012 at 8:02am

Just had a beautiful test flight with the rebuilt 600.  Awesome!  I actually turned the compass off and... man...  SO much better.  The compass is the source of many of my problems.

And blind taste test, I accidentally left Stab I pitch and roll at 0.025, and I thought "gee, something isn't right..." I saw what happened, and set it to 0, bingo.

I got some video, but it's not great as I was fiddling with the yaw tuning.  So it isn't the most stable. Then when I got it, my camera died. :(  I'm maybe going to upload what I got anyway, just to show.

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