Tricopter flips on arm – please help!

[rc468]

Hello, I am a new user here. I’ve built several quadcopters and have some experience with problem solving. But this is my first tricopter and it behaves completely wrong.

I use Quanum Trifecta frame, Omnibus F4 Pro V3 with INAV 1.9 firmware, TTSRC ESC 20A, Tarot 2208 2100KV motors, 3S 3300 battery.

The problem is: when I arm the tricopter with props on, it instantly engages max thrust and violently flips to the right. Without props it just arms and motors are spinning smoothly.

FC and ESCs and motors have previously flown on a quadcopter so they are ok.

The scheme for tricopter is as shown in Inav configurator: motor 1 is tail, motor 2 is right, motor 3 is left. However, all motors in the scheme are shown as CCW, but I used CW for left motor.

I triple checked motors order, motors directions and propeller orientations.
Tail works as expected: when I push the yaw stick to the right, it tilts left, and vice versa.

I also have the Omnibus FC installed upside down but I made all needed corrections in the configurator. Rotating the copter in all directions corresponds to the 3D model movement in configurator.

I also set the PIDs to the smaller values so the copter won’t do any strong movements, but that did not help much.

I have no GPS and camera/VTX installed, the configuration is minimal and I enabled only one ANGLE flight mode which is activated on arm.

To me it seems that motor order is still incorrect. Can it be an error in the tricopter scheme drawing in the INAV configurator?

Should I try the Triflight firmware? But I don’t think the problem is in the firmware. Even if INAV is worse, I expected it should at least arm without flip.

[Kevin_Erik]

Triflight uses the following Motor orientation, not sure about iNav but chances are that they’re the same:

Anything other than this and your going to have serious issues with stability.

Other things to check:
-If not using DShot, Calibrate your ESC’s
-Test the motors to ensure that your they’re not swapped some how. (Motor #1 isn’t Motor 3 ect)
-Flight Controllers Orientation is correct.
-Problems due to motor mixing
-Failing ESC

Edit: Can you post a few pics of your configuration screen showing the motors spin direction, the motor resource assignments and a few physical pictures of the copters wiring to-from the motors and ESC’s.

[rc468]

Hi, thank you for your reply. Indeed, you listed all possible causes, but I did the same and everything is checked.

By the behavior, it is a clear sign of swapped motors. The problem is, they are attached correctly as I have checked them one by one.

I’m going to just swap them and see what happens. Will show some images after I get home.

[rc468]

So I swapped the motors in all combinations, but in all cases copter flipped. I returned all to proper order and lowered PIDs almost to zero, and also set idle RPM to a lower value.

After that copter stopped flipping on arm. But when I tried to increase the thrust, it started tilting to the right and also spinning around yaw axis.

After some PID setting iterations I managed to get the copter in the air just above the floor and basically it flies but I have to roll left to keep it from drifting to the right. The yaw spinning seems to have stopped.

So the problem was in too aggressive PIDs I guess. I used preset something like “330 sized tricopter” and then I additionally halved the PIDs but that didn’t help, so now they are completely different from the preset.

While on the floor and armed, I noticed that when I push roll stick to the right, copter tilts to the right, as expected. But when I roll to the left, it tries to tilt to the left but without enough thrust it cannot do it. ESCs were calibrated just before. So it looks like left motor is somehow stronger than right motor. I’ll do the RPM test next.

[Kevin_Erik]

The Spin you saw when throttling up was the copters inability to right it’s orientation or correct for the motors torque while the PID’s were zero’d. Try physically swapping the suspect motor and its corresponding ESC to the other side of the copter and see if the problem follows. That will allow you to narrow it down if it is indeed a motor or ESC is the issue. Personally, I suspect NOT as you’d notice problems even with the PID zero’d.

Question: Are all of your ESC’s using the same firmware and settings? Any disparity can drastically alter the copters stability as this isnt what the FC would be expecting.

Also the following:

-Default your PID’s and filters.
-Use a lower value battery for testing if one is available. (will keep shit from blowing up in your face)
-Check your resource settings vs what you know your documentation to be. While it’s rare it’s possible that your FC maybe dead / dying if your know for a fact that everything is setup correctly.
-If possible, Flash Betaflight and see if the problem persists. This will help you figure out if the problem is hardware or firmware based.

Question: Are you familiar with the Half-Split Method of troubleshooting?

In a nutshell, you test the middle of a problem thereby isolating one side or the other. This allows you to reduce a problem by 50% for each iteration of a test depending on the discovery(s) made.

Per the internet: http://troubleshoot.hnd-computing.info/?page_id=44

[rc468]

Thanks for the advices. At this point I think the remaining problem is with motors. I checked their idle and max rpm and left motor has 16560 rpm idle and 27051 rpm full, whereas right motor has 9818 rpm idle and 16342 rpm full, that’s a big difference. I’ll be checking them on a standalone rig with stabilized power source tomorrow, it is late night now.

P.S. Something is strange with these Tarot 2208 motors. I have recently bought a new set, looks the same but it is 1500kv, and they also have different actual kv. One pair is about 1600kv, ok, it is close to 1500, but the other pair measures up to 2600 kv. Now I have found that motors from the old 2100kv set are also different. Weird.

[Kevin_Erik]

Have you checked the esc firmware to ensure they’re all the same?

[rc468]

I didn’t since I have no tools for that, I can say for sure that all escs are the same model and were bought as one set. Anyway I’ll check all motors with one esc, so whatever firmware is there, the difference between motors will be noticeable.

[Kevin_Erik]

The software for the ESC’s is ussually free… I know BLHeli32 is.

[rc468]

> The software for the ESC’s is ussually free… I know BLHeli32 is.

Software – yes, but I heard I’ll also need some USB adapter which I don’t have.

[Kevin_Erik]

Not really… most FC’s allow you to do what’s called a serial-pass-thru.

If your current FC does not, then it’s worth moving the ESC’s to another FC that does, flashing them and then wiring them back. This is a poor man alternative to using adaptors.

[rc468]

Thanks, I’ll try it later

[rc468]

I replaced the motors with the 100% tested ones and now it flies much better than before. Manual control is harder compared to quadcopter but I think it is normal for a tricopter? I did not fine-tune PIDs yet.

[rc468]

Flew a maiden today. It flies great, exceeded all my expectations. But I have two problems while ascending or descending. After the speedy ascent, it destabilizes for a moment (something like roll + yaw jerk) and then returns to stable position. During the speedy descent, it yaws around. Everything else is fine. I guess I need a closer look to the PIDs.

Here’s a video I shot with my phone in my left hand while trying to control the copter with my right hand

[Kevin_Erik]

What is that hanging from your copter ?

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