Do I have a problem with the altitude sensor in my geolink?

[Helipilot]

I am very new to Spirit FBL units and I am just starting to become familiar with how they work.

So far I have my TREX 500L Dominator flying very nicely using my Spirit GT FBL.

I also have a Geolink, and this afternoon I decided to start trying out some of the GPS Features.

Before flying with the Geolink enabled I calibrated it at the field.

I started off by enabling Position Hold in conjunction with Coaxial stabi mode.

I was extremely impressed with how well it held position, the helicopter was nicely locked in and could hover by itself completely hands off.

The next thing I tried was to enable Position Hold and Altitude hold. I lifted the model up to around 5m and switched to Bank1 to enable Coaxial stabi, position hold and altitude hold. The model increased in height by about 1m it then immediately fell by around 2m, it then continued to bounce up and down between 4m and 6m from the ground. I switched back to Bank 0 and landed the model safely.

I came back home and looked at my flight logs and was surprised to see that my altitude values looked totally erratic. My log was sampled at 10Hz, you can clearly see that logging did occur 10 times per second but the altitude data looks wrong to me. Throughout the entire flight log the altitude was increasing and decreasing. I have zoomed in to a portion of the graph to show what is happening.

Looking at my logs it looks to me like the altitude sensor data is not reliable.

Do I have a problem with my Geolink unit or have I made an error configuring something?

Is it possible that the pressure sensor in the Spirit GT is "fighting" against the height sensor in the Geolink?

Please find attached my Bank files and an image showing the altitude log.

Any advice would be aprreciated

thanks

Alan

[Habásek]

Please update on version 3.3.2r2

[Helipilot]

Habásek, thanks for your reply,


I am already using Spirit Heli 3.3.2-r2 [12.8.2021] firmware.


Alan

[Helipilot]

I was back at the field today and had another go at getting altitude hold to work along with position hold.

I tried the following :-

Reducing vertical gain in the geolink menu. ( I am now running around 60%)

This reduced the speed of the oscilation and made it oscilate slower but it did not resolve the issue. The model continued to climb and drop. Over a peiod of time the helicopter got gradually lower and if I had not taken over the controls it would have flown into the ground.

Smoothing out the pitch curve in the radio

This made very little difference.

Reducing the head speed of the helicopter.

This had a similar effect to reducing the vertical gain, making the helicopter oscilate slower but did not cure the problem.

I then tried a second Spirit GT and Geolink fitted to an older Trex 500. The older helicopter is a lot less agressive than the 500L Dominator, but once again it displayed the exact same behaviour when I tried Stabi Coaxial with position hold and altitude hold from geolink. Both models are using Spirit Heli 3.3.2-r2 [12.8.2021] firmware and geolink 1.2.1

Any ideas?
The fact that both models with different Spirit GT/Geolinks are exhibiting the same behaviour would suggest to me that something is not quite right, possibly my configuration?

Has anyone else managed to get the combination of Spirit GT/Geolink, Coaxial stabi, position hold and altitude hold to work together?

I was hoping that "Coaxial stabi, position hold and altitude hold" combination would allow the helicopter to fly in a similar manner to a dji camera drone. Am I being a bit optomistic?

thanks for any help

Alan

[ZeXx86]

Hello,

If GeoLink is used then sensor from Spirit GT is used.
If your model will change collective pitch it will change pressure near the GeoLink and cause change in altitude.

The problem is likely not wrong sensor. But in the most cases it is due to collective pitch center.

Please try to enable Subtrim (tuning) in the Servos tab.
Then verify if swashplate is levelled and there is 0° between main blades.

[Helipilot]

The problem is likely not wrong sensor. But in the most cases it is due to collective pitch center.

The 500L Dominator was at zero pitch centre.

The old 500 was out by a couple of degrees. I set it to zero degrees and modified the max and minimum points on the radio pitch curve. This appears to have cured the problem on the old 500.

Thanks for your support.

The biggest difference between the two models is the head speed.
The Dominator has always run what I consider to be a very high head speed (around 3000 rpm with throttle at 55%) could this be what is causing the problem, or is there something else I could change in the Spirit GT configurtion?

[ZeXx86]

Regarding mechanical head setup, I recommend to follow these instructions::
http://manual.spirit-system.com/index.p ... tive_Pitch

Making equal pitch with pitch curve is not ideal solution unfortunately, but if it was helpful it is good. The results might be even better if you will follow guide also for other flight parameters.

3000 RPM for this helicopter is quite high. The RPM should not be reason, but you can try to lower it to compare behavior.

In next updates we will focus on steering so that flying in the Coaxial mode will be very easy and precise as with drone.

[Helipilot]

I have changed the receiver in my 500L dominator to a Futaba Sbus unit. This allows me to continue using bank switching to put the model in geolink position hold and then use a 3 position switch to bring in altitude hold.

Yesterday I flew the model with this new configuration in very calm weather. I put the model into bank 1 which activated position hold and the model behaved as expected.

I then tried the switch in the position where I have altitude hold with pitch control. The model climbed gently as the switch was engaged there were no height oscilations and I was able to adjust height using pitch stick. After about 10 to 15 seconds the pitch control was no longer available and the model started slowly sinking towards the ground. I disengaged altitude hold and recovered the model to a safe height.

I then tried the switch in the position where I had altitude hold but the Spirit controls height. The model started slowly sinking towards the ground. The model held position fine but it was unable to hover so I disengaged altitude hold and recovered the model to a safe height.

I tested this on the bench and found that once again I only have pitch control for 10 to 20 seconds.

Is it normal for pitch control to only work for 10 to 20 seconds?