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M4 Wobble That Forces Flight to End
https://www.spirit-system.com/phpBB3/viewtopic.php?f=21&t=6108		 Page 1 of 1
Author:  sankaperera [ Wed 29. May 2024 12:59:45 ]
Post subject:  M4 Wobble That Forces Flight to End
Hi,

I thought I would post this here just in case as well. I have a new to me M4 that I've put together and installed a spirit GT on. It develops what can be described as a flight ending wobble randomly. I have attached a video: https://youtube.com/shorts/P59WYXQuYOI?feature=share

Originally, I assumed it was mechanical and ended up replacing the blades, the damper, the main shaft, the 3M Vibration resistant tape. I also played with the tightness of the blades. None of this resulted in fixing the wobble, and there was no consistency to when it would occur. Sometimes I get a few minutes of flying, sometimes it happened immediately. Sometimes it would start and solve itself as I tried to land.

Now I've moved onto the Spirit GT and thinking maybe its a cyclic feedback loop. I have my tail gyro at 1.10X and this looks more like a wobble then tail wag. I had my cyclic at 65%, and lowered it to 60%. I have adjusted my headspeed from 2200 RPM (in the video) down to 1800 RPM.

My next move was to try and reduce the cyclic down further to 50%. I am still unsure if this is resonance or a mechanical issue.

I should also note that I was told that based on my video I am running nearly 4000RPM. I do feel like its too fast but when I plug the spirit in and remove the blades and run my IU1 @ 70%, Spirit says I am at 1800RPM. So maybe there is something else afoot as well.
Author:  Mattes61 [ Wed 29. May 2024 15:43:36 ]
Post subject:  Re: M4 Wobble That Forces Flight to End
Hello,
have you reduced your tailgain ? For me it sounds to much tail gain - In the video I can't see if its too much tail gain or too high Cyclic gain - can you make an video where more can be seen because its too small to see it clearly -

Regards
Author:  rburrow87 [ Thu 30. May 2024 16:36:58 ]
Post subject:  Re: M4 Wobble That Forces Flight to End
sankaperera wrote:
Hi,

I thought I would post this here just in case as well. I have a new to me M4 that I've put together and installed a spirit GT on. It develops what can be described as a flight ending wobble randomly. I have attached a video: https://youtube.com/shorts/P59WYXQuYOI?feature=share

Originally, I assumed it was mechanical and ended up replacing the blades, the damper, the main shaft, the 3M Vibration resistant tape. I also played with the tightness of the blades. None of this resulted in fixing the wobble, and there was no consistency to when it would occur. Sometimes I get a few minutes of flying, sometimes it happened immediately. Sometimes it would start and solve itself as I tried to land.

Now I've moved onto the Spirit GT and thinking maybe its a cyclic feedback loop. I have my tail gyro at 1.10X and this looks more like a wobble then tail wag. I had my cyclic at 65%, and lowered it to 60%. I have adjusted my headspeed from 2200 RPM (in the video) down to 1800 RPM.

My next move was to try and reduce the cyclic down further to 50%. I am still unsure if this is resonance or a mechanical issue.

I should also note that I was told that based on my video I am running nearly 4000RPM. I do feel like its too fast but when I plug the spirit in and remove the blades and run my IU1 @ 70%, Spirit says I am at 1800RPM. So maybe there is something else afoot as well.


Which governor are you using, ESC or Spirit? I have more than one of these helicopters and that is definitely closer to 4000 RPM than 2000 RPM!

For the RPM to read correctly, Spirit needs to know the gear ratio and the sensing divider (motor poles). The ratio is of course 1.0 since this is direct drive, and the motor pole count is 42. Spirit requires you to enter the motor poles / 2, so enter 21 in Sensing Divider. Then you will see the actual headspeed.
Author:  sankaperera [ Mon 03. Jun 2024 2:59:39 ]
Post subject:  Re: M4 Wobble That Forces Flight to End
It seems that this is due to high headspeed. I reduced my IU1 to 30% which is obviously not accurate but it reduced the motor speed enough to have 2 uneventful flights!

I am using the spirit governer (yellow signal wire plugged into fbl, governer checked). However, upon checking the settings they were quite strange, sensing divider=5 gear ratio=10. Maybe I didn't reset the fbl?

I adjusted the settings to what you suggested (picture attached). Do those settings actually effect the throttle or just the sensor itself?


This is only my 3rd heli build so would appreciate any insight: Is this an ESC issue or a fbl setting? issue? E.g. a 30% throttle curve is odd.

Attachments:
20240602_192106.jpg
20240602_192106.jpg [ 9.83 MiB | Viewed 416 times ]
Author:  rburrow87 [ Mon 03. Jun 2024 3:52:51 ]
Post subject:  Re: M4 Wobble That Forces Flight to End
Yes that will have a huge impact on your throttle curve. It uses the gear ratio and motor poles to calculate how many pulses from the ESC is 1 revolution of the main rotor so that it can govern the headspeed. It needs the correct information to work right.

The way you have it now in the screenshot, a 100% throttle curve will (correctly :)) result in 2400 RPM headspeed.
Author:  sankaperera [ Tue 04. Jun 2024 18:43:00 ]
Post subject:  Re: M4 Wobble That Forces Flight to End
That didn't seem to solve the issue. I flew it starting out with a 50% throttle curve and could tell it was still too high. Unfortunately, as I was trying to come down the tail blade control arm popped off and I had to come down in a spin.

I'll get it on the bench and see what the rpm tester says.
Author:  rburrow87 [ Tue 04. Jun 2024 18:47:39 ]
Post subject:  Re: M4 Wobble That Forces Flight to End
To confirm, do you have the yellow RPM wire from the ESC connected? And if you do, where is it connected?
Author:  sankaperera [ Mon 19. Aug 2024 15:26:30 ]
Post subject:  Re: M4 Wobble That Forces Flight to End
thanks Rburrow. You got it. I wasn't plugging the yellow wire in the middle. Part of my confusion was that the HW ESC comes with a standard JST and not a single pin, so I had to cut the connector to plug it in the middle versus yellow right. But it worked well after that.
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