Help with setup of a trex 450 clone

Good recommendations. I do have symmetrical airfoils. So I am going to use all your suggests to as a starting point.

Really appreciate the help!


I am able to get everything setup. Thanks for the help!

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Glade to hear you were able to get everything set up. In light of a recent number of in-flight motor shutdowns due to the collective going below H_COL_MID, I would recommend setting the H_COL_MID for -1 deg or even 20 PWM above H_COL_MIN. This offers more protection of the heli catching an updraft and causing the aircraft to think it is landed and going through the automated shutdown. This would only happen in Auto, RTL, Land, or Guided modes. Just wanted to make sure you were aware of this. Changes coming in Copter 4.2 which is planned to be released in April 2022 will change the collective setup and offer more protection.


Hi Bill,

Thanks for the heads up. I will make those changes.

I am currently fighting my ESC. If it doesn’t get a signal shortly after powering on then it will not work. It is old, so I ordered a new one. I went with a single drone ESC w/o BEC that is a BLHeli_S. I am hoping it is plug and play, otherwise I need to learn how to do the passthrough to program it. I am going to try and figure out how to use DShot with it, but will start with PWM.

I did try the H_RCS_MODE=2. Got a good feeling for how it works. I am going to go with H_RCS_MODE=3. The governor in the old ESC doesn’t work very well. The new ESC doesn’t have one. I hope it will work good. :slight_smile:

Thanks for all the help! I am making progress and that is a good thing!


Hi Bill,

I am getting further with the setup. I just got my ESC. It seems as the ESC doesn’t support PWM. It only support DSHOT. How do I change the output of the HeliRSC to use DSHOT?



I found the answer in this thread “Help about using dshot on tail rotor - #6 by rmackay9

I needed to setup my SERVO_BLH_MASK correctly and then the output types I would like.

I am using a matek h743 slim FC. There is a grouping for it, so I had to keep that in mind.
My settings:
SERVO_BLH_MASK = 960 (servo 7, 8,9,10 are grouped and have to run the same protocol)
SERVO_BLH_OTYPE = 7 (I am using a RDQ ESC that uses D1200)

Thanks for the help!

Why dont you use the Group1 ? S1 (channel 1) for your ESC and ignore the S2 (leave it alone) . This way you could use the Group2 (S3,S4,S5) for the swash plate servos and the S6 for the tail servo. This way you would save all other PWMs for any other purpose, remember when you set one channel of a group with Dshot, the others inside that group cannot be use as PMW. Please check the messages ardupilot sends when it starts to verify the status.

That would be a better way to arrange the setup. With the matek h743 slim there are so many outputs that I am not sure what to use the rest of them for!?!?!

I am still trying to figure out how to configure LED. It doesn’t look easy. Looks like there is some scripting to learn.

Here is an update on my progress.

@Pedro_Claro I did the wring as you suggested. Works great! Thanks. Not sure what I will do with the other PWMs at this time. That is probably in the next steps. :wink:

I have the ESC working and everything setup. Ran all the preflight tests and everything looks good. Hooked up the motor and everything is spinning how I think it should. No noticeable vibrations. Am very happy at what I was seeing.

Tried my first flight. It didn’t go as well as I wanted. With the motor spinning it sat on the ground for a little bit. It did not want to hover. No response to lift requests. Then all of the sudden it shot up into the air. I killed the motor and it drifted back down. I was able to catch it and don’t see any damage to the frame. So, that is good.

The cyclic servos didn’t handle the torque and the gears are stripped. They were newer servos. I thought they would handle the torque, but just did not. I am going back to servos that I know will handle the simple flying that I do. I am planning on looking for better servos once I start flying more.

@bnsgeyer I am wondering what the normal operation of take off is for traditional helis. I think it is to turn everything on. Arm the heli. Enable the motor interlock. Motor will start to spin. Then wait until the heli starts to hover. At that time lift controls will be available. Is that correct?

I was in altitude hold mode for my first flight. I am guessing that was part of the problem. Once the heli was ‘ready’ it thought I wanted it to be high in the air because I was trying to get lift before it was ready.

My next steps… Get servos that I know work. then try a flight again, but this time use ‘stabilize’ flight mode until I get a better feel of the operations.

@dpcsar I’m sorry that your first flight did not go as well as you had hoped. We recommend conducting first flights in Stabilize mode only. It provides the good stabilization and the most pilot control (meaning the pilot controls all axes). In Althold the autopilot controls the vertical axis and the collective stick controls vertical speed. I suggest you stick with stabilize modes in future flights until you get confidence in the aircraft and your setup.

So the aircraft will NEVER lift off unless it is given the command in some way. In stabilize, it requires you to control the collective to lift off. In modes where the autopilot controls the vertical axis, it requires the rotor to be at operational speed dictated by the H_RSC_RUNUP_TIME and the pilot to raise the collective stick above the midpoint. In auto modes, it depends whether you arm in auto or are in another mode with the rotor spinning that determines the what tells the aircraft to begin the mission (takeoff).

You have the sequence correct but after enabling motor interlock, wait until the rotor reaches the operational speed. Then you would use the collective in stabilize mode to lift off.

If you have a log, please post it so I can have a look.

2022-02-13 12-32-13.bin (853.7 KB)

@bnsgeyer Here is the log. Thanks for looking.

By what you wrote and what I saw… I did not wait the ramp up time. It was set to 10 seconds. I think at that time I had it at full lift. :confused: :cry:

Since this is an electronic heli, I am going decrease the ramp time to 2 seconds.

New servos and stabilize mode are next things I am going to try. :wink:

You can put the H_RSC_RAMP_TIME to 1 second as long as the ESC has a governor that is handling the spool up. That is just how fast the signal is ramped into the ESC. If your ESC doesn’t have a governor then I would not recommend that short of a time. Be sure the H_RSC_RUNUP_TIME is set for the time it takes your heli to spool up. For most heli’s that is more like 10 seconds. DO NOT shorten this for expediency, it will only cause your heli to try to take off in modes that use althold in the vertical axis before the rotor is at a flying rotor speed.

Interesting. I thought that electric helis spun up a lot faster that 10 seconds.

I am not using an ESC governor. 10 seconds seems like a long time for an electric heli. I will leave it at 10 and after everything is looking good I can play with moving it to a quicker time.

I don’t think I want to spin up my 600 faster than 10 seconds. Never owned a 450 so I don’t know what a typical spin up time is. I saw that you have your H_RSC_RAMP_TIME at 1 second. So it means that it is ramping the ESC from 0 to the throttle curve in 1 second. I would suggest you increase that at least to 5 seconds.

How did you decide on your throttle curve values?

Also I noticed that your collective was at the midpoint during your spool up. You will need to pull the collective stick to the bottom stop during spool up in stabilize mode and slowly increase it to the midpoint for takeoff. Otherwise if you leave it at midpoint then it will takeoff during the spool up as your collective blade pitch would be whatever corresponds to the stick midpoint.

I will change the spin up time. I think I was dealing with an old ESC that was having issues and that is why I did it.

I think I got the throttle curve off of one of the videos that was linked in the documentation. What do you suggest?

I will take into advisement and keep the collective low as I am spinning up. I have started my quad copters with the viatical axis in the middle. I though it would be the same way, or not affect it very much. I have the quad arming with a switch also.

Thanks for the help! And please keep the questions and suggestions coming. Super helpful!!! :smiley:


I reset the parameters to the defaults. H_RSC_RAMP_TIME default is 1. That is were I got the parameter. :roll_eyes: I am going to set it to 5 (half of default H_RSC_RAMPUP_TIME)

The default throttle cure is 25, 32, 38, 50, 100. What should it be?

Thx for the help!

I don’t know. You have to determine that through flight test. It depends on your collective set up, the weight of your heli and rotor speed you want to maintain.

@bnsgeyer okay. Some thing to play with. :wink: :slight_smile:

I was checking your log and how do you know the rpms of your rotor?
I could not find any rpm sensor, you will need that! You have a dshot ESC capable, does it send back the eRPMs? If not I recommend you to get or build one, ex: here with 3144 hall sensor.
From the described issue you had above maybe you configured wrong the dshot ESC and it just fire when you pull the throttle up. I recommend you swapping one of the wires of your engine, to revert the engine rotation so you can verify/pratice at home to simulate the arming, motor interlock and even thortling up. Reversing the motor wont make the rotor spining, but watch out the first time, ensure is really rotating opposite way.

Also you have this parameter set SERVO_DSHOT_ESC=1, if not wrong this makes all output with dshot. Maybe you dont want that, try disabling this to 0.