Trex 700/800 parameters for pixhawk

Hey everyone, Im just wondering if anyone will be willing to share there parameters using pixhawk and arducopter 3.4.6 for a trex 700/800. The helicopter is stock standard with DFC, Castle ice2 hv120 esc and Align 3gx FBL. I have heard mixed opinions with running pixhawk along with a FBL controller. I was in the process of setting up pixhawk in an old esky belt cp 450 sized heli but had a prop strike and parts are no longer available in New Zealand, so going to go straight to the trex 800, if anyone has any parameters that I can use that are close and I can fine tune from there just to get me started in the right direction. Eventually I will be using the helicopter for precision agriculture and thermal imaging of power lines. I would possibly go to a petrol/gas setup for this to type of stuff for flight duration and ease of just pouring in more gas while out on the field. Later I will be looking at a decent size heli that is capable of spraying. If anyone has any relevant links/information that would be great, I know there are options already available out there, but way out of my price range and I quite like all the features of the pixhawk and arducopter. Cheers

All I have for that size is piston helicopters, which is not even close to the same. Frankly, Mathew, I think it would be best to tune yours from scratch. Using somebody else’s params for a heli might crash it because no two of them are the same. And it depends on how fast you’re running the head, what the disc loading is, what your mechanical setup is for rates, and how fast the servos are.

There’s one param, ACCEL_Z_P that you’ll find set to 0.5 for multi’s by default. That one is a “gotcha”, especially with a big heli with a lot of power that can climb and descend at 20 feet/second, and it is not well-documented for Trad Heli to adjust that. But I recommend setting that to 0.3 for your size heli to prevent a surprise the first time you try an altitude controlled flight mode.

The rest of it I would recommend just going thru the tuning procedure, and watch Rob’s video on head setup. Make sure to make all adjustments only in the Full Parameter List and don’t use any of the extended tuning screens or anything, in any of the ground station software applications, that is designed for multi’s. And if you have problems, post and ask.

For tuning the rate controller, different than what the wiki explains, I had good results setting the rate PID’s for pitch and roll to zero, set the rate VFF for pitch and roll to .15 or whatever looks like normal swash response to your stick inputs, and tune rate VFF for pitch and roll to get the desired vs actual rates to match. Then tune the rate PID’s. I like this method MUCH better than the way the wiki describes because you always have control of the helicopter during tuning, which is really important the bigger they are.

If you desire to use a downstream FBL unit, then all the rate tuning will be done in the FBL unit, the rate PID’s will be left at zero, you will tune the rate VFF the same way (turn it up until desired vs actual match), and you will set H_FLYBAR_MODE = 1. Pixhawk does not need a downstream FBL unit, but it does provide redundancy and give you straight-thru rate control of the helicopter in Acro flight mode in the event the EKF2 has a problem. Whether or not you use a downstream FBL unit is totally up to you. It will work either way.

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I will second Chris’s suggestion of tuning on your own. Use a training gear it helps a lot. I have a 800 size Flybarred heli but it has 4 servos and I am running a modified version of 3.4.6. I am still tuning it but it is flying decent. If you are interested I can provide it to you. I also have a 600 size Trex on which I am running Arducopter 3.3.3. If you want I can provide that parameter as well. I was using a cheap servo on 600, recently I updated to a better faster servo and I was able to tune my heli for higher P values.

HI Matthew
If you have a lot of time read this blog: This should be interesting
Over 850 replies a lot in it for a beginner to setup a Pixhawk in a TREX 700-800.
I agree with Chris Olson 100%.
I do have a TR 700E - 3 Rotor blade head with a Pixhawk, direct drive vp tail.

Oh how true that statement is! Having been in those shoes before, wishing it would be as easy as copy and pasting some parameters, i feel ya.
That being said, i further agree wirh Chris’s sentiment on tuning. Its no where near as bad as I initially thought it would be. Looking back I took some pretty big precautions on my initial tuning flights, even going so far as to weight it down with a 2x6 and some cement blocks, now I feel like I kinda over did it as tuning isnt that bad and as long as you follow tbe instructions and are ready to set it down quick if it starts to ossicilate youll be im there.
I am using a big Trex myself, but its mechanics are quite different than the DFC so any numbers I have would likely result in a mess… As stated by others, tuning it for your heli specifically is certainly the best idea. Assign a parameter to ch6 via a rotary knob if you have one and start low and bring up the parameters one by one, if you follow the procedures people have laid out, its not that hard to get a decent flying heli out of it.

I always prefer doing that with a newly built heli. It gives you a way to test it at full power and collective pitch, and see if you have something screwed up that could cause it to flip on takeoff, with the safety of the big weight holding it down so you don’t wreck a set of blades (or more) if something goes awry or is wrong with your setup.

I’ve read about at least a couple heli’s here on the forum that could’ve been saved on that first runup if it would’ve been done in a tiedown - both of them had servos accidentally misconfigured.

Thanks for all the great feed back everyone, I went out and bought a second hand trex 450 to play around with before breaking the 800, I know it is a bit on the small side but have seen people get good results. It actually came with an align aps autopilot but it is very limited.

Why can you not tune in extended parameters? I have noticed it makes the changes directly to the full parameter list? So basically just check and check everything is setup correctly. Are there any other parameters that should be changed for a helicopter that could cause trouble?

Because it does a bunch of a “hand holding” for multi’s, the parameters for helicopters it considers “out of range” and it will make settings by itself to parameters that will turn your helicopter into a smoking crater. Don’t use it. Use only the Full Parameter List to make settings for a heli. APM Planner2 and Tower don’t do it, but Mission Planner even attempts to tell you your settings are out of range in the Full Parameter List. So I don’t use Mission Planner either.