Setting up Trex 450

Dear 450 flyers,

If your trex 450 is flying well (apm 2.5+) I would kindly request , if you can pls. paste a screen shot of the Tuning values (Extended Tuning ) ?

I am having hard time getting it tuned. When I make it loiter it jumps up and down so violently, its scary.

Pitch max travel setup at -11/+11
Version: v3.1.2

I noticed in stabilize mode and acro mode I see little swash travel(roll/pitch) , especially when I give stick inputs or even when I tilt the heli on bench to see the swash compensation .

I wonder in high winds with my max sticks the heli will barely have any compensation to counter the wind when flying in acro/stabilize modes


Can you please post a screenshot of the Heli Setup page as well? And what are your Pitch and Roll Rate FeedForward terms from the Full Parameters List set at?

Rob thanks for replying. I have been trying for past 3 days to get it tuned correct reading numerous posts . I have attached all my parameters.

The jumping up and down of heli is on altitude hold is gone as I reduced the Throttle hold value to 1.2 from 6. However moving throttle up or down during Alt Hold has barely any affect. ( this makes transition back to stabilize mode dangerous as I need to be careful of not moving throttle stick it too far away from hover postion )

My testing area is small so I couldn’t get a chance to put on loiter or check altitude hold with full throttle up and down. I tried with what my guts permitted so. I will be going to field this week as I test loiter.

here are other parameters you mentioned: ( this forum doesn’t allow to attach .txt or .param )

: However if any one has a Trex 450 flying well and loitering well please can you post all your parameters ?

All parameters for trex 450 are included in the attached .zip file

Ok, I would suggest changing Throttle Rate back to 6 or whatever the default is. You probably shouldn’t have to touch that one at all. The jumping up and down is probably because Throttle Accel P is too high. Try playing with this, bringing it down towards 0.1.

And you definitely need some Pitch and Roll FF term. Try moving these together, start at 0.010, and move them up 0.010 at a time. You might even get up to 0.100. Do this in flight, not just looking at the swash on the bench. As you increase them the heli will become much more responsive. There’s a point where it’ll start behaving badly, then back off.

Thanks Rob for your inputs

Here are some questions:

What does the feed forward variable do ? . I don’t see description of it in the full parameter list .

How do I get my hands on default values for APM traditional helicopter? do they exist ?

(Background: I had different versions and vehicles firmware before on my current apm , I am unsure, if my values are default to begin with. Loading firmware doesn’t seem to affect gain values stored in EEPROM . In addition , the drop down in ‘Full Parameter’ section does not have traditional helicopter parameter to load )

Do you fly in stabilize mode or acro mode for testing, which do you prefer ?

The Heli seems to be able to move up/down on altitude hold mode. ( I set feed forward value for roll / pitch to .02 , haven’t got to test it thoroughly , but seem to be working on the face of it. )

I agree,

A Traditional default configure file is needed. I have tried the beginner, medium and advanced parameter setting with the traditional helicopter, and then ran all of the required calibrations from there. I think all of these are for quads.

Im not having much luck getting my project off of the bench. I am going to load your 450 parameters tonight and run through all of the required calibrations again and see what happens.

I wish you good luck with your tuning. please post all of your learnings.

Be safe,


puneetpx: The feedforward parameters are direct commands from a requested rate to the swash output. It is similar to the P-term, except it is not based on error. This is critical to make a heli fly.

thanks for your replies,

Loiter is having serious Toilet Bowl effect . The helicopter when in loiter will slowly start to swirl and eventually become very bad to the point of uncontrollable and wanting to crash.

I played with “Loter PID” value changed it to .5 , 1 (default) , 1.5 and 2.0 The 2.0 the spiral become much smaller(tighter) but toilet bowl gets more severe ,resulting in helicopter eventually tilting such that aggressive piloting is required to prevent crash.

I also attempted to change Loiter Speed value to 250 instead of 500 , that just made it more passive as it drifted into toiler bowl effect slowly but eventually getting into the same difficult to re-stabilize position.

Assuming this was because of compass I have tried re-calibrating the compass, its of no help.

I couldn’t successfully run "Compassmot " for helicopter , as it wouldn’t allow blades to rotate when throttle is raised ?( saw a code change request from Randy on same )

What loiter tuning parameters are you using ?

What can I do to get rid of this toilet Bowl effect ?

( attached pic for reference , compass/gps is placed where traditionally gyro is mounted, apm is on vibration isolators )

Hi puneetpx,

I also try to find correct setting for my HK450 trad. heli. But I dont have much experience about rate_yaw and other stuff params to prevent tilting. I broke down tail blade so far for 4 days. Moreover Many times I luckily saved the heli from a big crash. After it tilts hardly, APM disarms and tries to arm itself. In that time interval blades turn as it commanded lastly.

So Do you know which parameter exactly prevent those tilts(back-forth, right-left etc.) At least to hang hover mode to ensure me settingp up pitch_roll_rate in flight by knob switch.

I will put my param and my helis tilting videos tomorrow.

Best regards.

You might want to run compassMOT or consider moving it back to the middle of the tail. Take your blades off and you should be able to free spin the helicopter for running compassMOT (it’s a CLI command)


Having the compass that close to a swash servo is probably not going to work for you. I tried mounting a APM 2.5 with a built in mag in that same area. As soon as I put power to the servo’s the compass became erratic. Just my opinion.
David R. Boulanger

Thanks David ,
I am going to try your suggesting next and move it out using another external mount away from electronics to see if it works.
This mounting was not very acceptable however due to short cables I went ahead with it. Will try to rearrange and see how far away I can get from electronics and ferrous materials.

dear netflow
I saw code change request to Make CompassMOT work from developer Randy. I am not sure if it has been implemented for traditional heli ( )
Where you able to run CompassMOT for Traditional helicopter successfully and spin up blades, if yes is your throttle cabling different ? ( from … ctions.jpg )

Dear Em_Tech,
You can attempt using the servo trims under ‘heli setup’ to in order get helicopter stable( it will drift however ) and then work further on setting other gains. Lift gently and see how it is and repeat till it stops tilting.

 I would kindly request you to start a new thread so you can resolve your issue in depth and here it will get confused with existing thread.

Your toilet-bowl problems are almost certainly due to magnetometer problems, and not Loiter PIDs. The default PIDs should not give you TBE. I quite often just leave them at defaults.

I have run my magnetometer successfully in that location, but you have to be very careful about having any steel nearby. The worst culprit would be the screws actually holding the anti-rotation bracket, one them is almost directly under the magnetometer chip. I actually purchased some stainless-steel M2.5 screws for just this reason. I use them on all the locations in that area.

But even after going to all that trouble, the setup is still not ideal. In the end it’s just easier to mount the magnetometer directly to the tail.

Daer all
I have 2 Questions (TREX 450 FBL)

-Which mode / Prog should I use in my Futaba t7c transmitter

  • Could somone send me his PARAM file ( as a referenc)

Thanx a Lot

Greetings MABA

I did the remounting of GPS away on tail boom, few weeks ago however to no avail.

The Toilet bowl effect is very severe in Loiter mode. Once toilet bowl effect starts , it becomes very difficult to control the helicopter even after moving back to Stabilize mode. I just saved a crash. Testing is becoming difficult.

Video 1 :
Video 2 :

New GPS mounting picture is attached, its mounted using all plastic and wire ties no ferrous materials even remotely close by other than the tail servo rod which runs below / across the tail boom .

Do you think vibration has anything to do with it ? I do see vibration reaching the autopilot through the vibration isolators )
What do you guess is the reason for toilet bowl ?

Puneet, toilet bowling is almost always caused by magnetometer problems. Thing is, I’m not sure that what you’re seeing is toilet bowling. It’s almost impossible to say what’s going on without logs. It could be vibration for sure. But it could also be that your Rate tuning gains are just not working at all. And/or, mechanical setup is so bad that the Loiter is struggling.

Rob ,thanks ,

I have attached the Log files , please have a look.

On looking at the graphs I do see Loiter and Stabilize modes overlapping is that normal ?

Puneet, you have extremely extreme levels of vibration. That is definitely why Loiter is not working. I’m surprised it even flies in Stabilize. You must have something really bent, like the main shaft. Or the vibration damping is not working at all. You should not fly like this until you get it sorted out.

You’re showing vibration of more than 10 m/s/s, and it should be less than 2 for Loiter to work properly.

Yes, it’s normal for the mode flags to overlap. It’s just an appearance thing. The mode begins when the flag starts (the left edge signals the change). The flag length is at least long enough to be able to fit the mode name into it.

Rob, Thanks for the suggestions,

a) Apart from vibration did you find any other issue in the log file as you as suggested earlier ( for example some of the rate controllers not working or similar ) ?

I will get to reducing the vibration levels ( increasing isolation and verifying parts ) and report my findings here.