As the original thread on this topic got locked, here is a new thread with some additional information and attempted fixes.
To recap:
One of the connectors of the uBlox GPS module touches or rather presses against the I2C connector cable on top of the Pixhawk, also causing the Pixhawk not to be isolated from the frame anymore.
The result is that this connector squeezes the cables and damages them over time due to the vibration of the frame transmitted over the hull to the uBlox.
Have a look at this report which included this picture:
[attachment=4]pixhawki2cconn.jpg[/attachment]
You can clearly see the damaged I2C connector cable.
After a closer inspection I found out the following:
- The Pixhawk on the consumer version is position further to the front than on the developer version, thus moving it underneath the uBlox module. Have a look at this picture from the Developer Edition to compare.
So I started with a few ideas and tests to see how to fix this:
- First I placed a small piece of rubber between the front of the Pixhawk (on top of the cables) and the GPS module. This is not ideal as there are still two problems with it:
- The cables are still being crushed, just by rubber this time and not by metal or sturdy plastic.
- As someone in the other thread pointed out: “Connecting " PIXHAWK with the UBLOX (even by foam), will affect vibration damping.” So this indeed doesn’t help with vibrations.
This is how vibrations looked like. Note: There is no difference in vibrations with the foam in between and without. That’s why I didn’t attach a picture without the foam.
[attachment=2]VibrationBefore.png[/attachment]
The amplitude of the vibrations along all three axis looks pretty good. But there are two problems: z-axis vibrations have a lot of sudden spikes (which are supposedly a cause for barometer failures). And the x-axis vibrations seem to have a superimposed pattern, so it’s not really the white noise that it should be.
That leads to the assumption that the Pixhawk isn’t really freely dampened with this setup, but still connected to the frame.
After removing the rubber again, you could clearly see marks in the soft rubber of where the uBlox pressed into. Not very reassuring.
-
Next I investigated moving the Pixhawk to the back (just like in the Developer version). The problem here is that the Telemetry module is also mounted differently in the Consumer version than in the Developer version. It is therefore in the way of the Pixhawk and would need to be moved as well.
That was a little bit to much of a hassle. So I had to find something else. -
Next I figured to raise the hull by a few millimeter in order to remove the connection between Pixhawk and GPS module.
In order to do this, I replaced the three screws holding the top hull with longer ones (M3x12mm) and placed rubber grommets on top of the screws between the hull and the top plate.
The result looks like this:
[attachment=3]IRIS_Raised_Top_Hull.jpg[/attachment]
You can clearly see the gap between the hull and the top plate. I placed electrical tape over this gap (not shown here) in order to prevent wind entering the hull. Also now the hull is only resting on three places, making it a bit wiggly. So you have to be a bit careful when carrying IRIS.
Also flying IRIS like this will give it a different sound. So don’t be scared.
The good news: Looking through this gap into the hull you can see that the GPS is not touching the Pixhawk anymore:
[attachment=1]IRIS_Raised_Top_Hull_2.jpg[/attachment]
Thus the Pixhawk should not be directly connected to the frame anymore. As a result, this is how the vibrations look like:
[attachment=0]VibrationAfter.png[/attachment]
The spikes on the z-axis vibrations are gone and also the x-axis vibrations don’t seem to be following a pattern anymore. Now the vibrations are really white noise, as they should be.
The drawback: The amplitude of the vibrations have increased.
This lets me believe that the vibration mount between Pixhawk and IRIS frame is to soft. I will therefore try to replace this foam with a gel mat (amazon.com/gp/product/B002U2GS2K/).
The other benefit of this gel mat is that it is thinner than the stock foam on the IRIS. With this I might be able to lower the top hull again.
@3DR: It would be great if you could chime in here and give some guidance on this topic. Am I moving down the right path with these workarounds?
Note: For everyone who isn’t comfortable taking his new RFT model apart in an extended arts and craft session, I recommend to wait until 3DR comes up with a recommended/permanent fix.