Various folks in the IRIS forums at DIYDronres, Ardupilot, and the IRIS Facebook group have complained about poor GPS performance on their IRIS. Others (including myself) weren’t quite sure if there was something wrong with their GPS module, but weren’t quite stunned with the performance either. So I decide to shield my GPS module with a piece of copper shield and find out what difference it makes.
Required materials and tools
The following materials are required.
- WD Copper Shielding Foil 8″ X 12″
- A piece of paper
- Scotch tape
The following tools are required:
- Pair of scissors
Follow these steps to assemble your copper shield for IRIS:
- Out of the WD Copper Shielding Foil cut a square of the size 8 cm x 8 cm / 3 in. x 3 in. Do not remove the paper from the tape side.
- Cut a piece of paper of the exact same size as the WD Copper Shielding Foil.
- Place the piece of paper on the shiny side of the WD Copper Shielding Foil.
- Use scotch tape around the edges of the piece of paper and the WD Copper Shielding Foil to tape the two together.
You should receive a “sandwich” of paper – copper – paper with scotch tape all around the edges.
- Open the top hull of your IRIS.
- Place your copper foil “sandwich” over the GPS module. Affix it to the hull with scotch tape (See Figure 1).
- Make sure that the antennas from the FrSky R/C transmitter are not underneath the copper shield.
If necessary move them to the side of the copper shield.
Note: The FrSky R/C can cause interference with the GPS module. Thus part of this fix includes ensuring that the antennas of the R/C module are away from the GPS receiver.
Now the big question: Does it make a difference? To answer this question I performed two test flights: One with the copper shield in place and right afterwards another one with the copper shield removed. Here are the results:
- Flight 1: Copper Shield in place
After the warm start of the GPS, the horizontal dilution of precision (HDOP) goes down to ~1.3 and the number of visible satellites is around 13-14.
- Flight 2: Copper Shield Removed
Here the HDOP varies between 1.4 and 2.4. The number of satellites available is around 10-11.
Looking at the Satellite Prediction website for the date and location when the tests were performed, we can see that the number of available satellites is between 12 and 14 at 16:50 – 17:20 GMT.
After looking at these results, I did put the copper shield back in. The difference in HDOP and number of visible satellites might be small, but it did make a difference for me. And the cost and effort for this fix was minimal.
Since applying the fix I have not have had any satellite coverage issues (e.g. in Loiter mode) and time to first acquisition is very fast.