Last month I got myself one of these head trackers that fit inside your Fatshark Dominator goggles. Trinity Head Tracker Module – FSV2413 to be exact. I bought it used from a fellow hobbyist so I got for good price with all the cables needed to use it with my Futaba radio or ImmersionRC ezUHF external transmitter that I use with my mini talon or whatever that needs to go little further.
The head tracker was rather easy to setup and I got it to work with intended settings easily but then when just testing it on the table I noticed a slight issue. The pan axis drifts a little, and “a little” is pretty understatement even though the amount it drifts is not very uniform. Sometimes it does not drift at all, sometimes it slowly creeps to the other end and sometimes it’s there in a second.
Video demonstrating this below. Look for channels 7 and 8 on my transmitter. Ch 7 is pan which drifts like crazy from time to time. Ch 8 is tilt which works like it is supposed to. I tried to keep this video pretty short, I have tested it also for longer periods of time, but it doesn’t get any better with time. Now I don’t think a problem like this is mechanical since it happens quite randomly and once I tested that even zeroing the gyros while pointing goggles to north seemed to have some effect on the issue.
On the video the problem doesn’t appear all the time but when it does it is bad.
When googling and trying to figure out what was happening and why, I think I might have stumbled upon a solution: I found this archived fpvlab forum post which seems to handle similar problems with head tracker drifting.
Most of the thread is just people guessing why this might happen or does hitting certain buttons or power cycling help anything. Then on the latter part Fatshark gets one drifting unit to work with and they figure out this:
“We finally got someone to return a drifting unit back to a repair center and we’ve found the cause; the slider rods in the LCD module for the adjustable IPD were made from steel rods plated in stainless steel – not full stainless steel. I.e. if handled incorrectly during assembly (dropped, in contact with a magnetized tool, etc) the rods themselves can pick up a slight magnetic polarity. The proximity of the rods to the head tracker caused incorrect readings in the compass sensor causing the drift. Replacing the rods with non-magnetized rods fixed the drifting.”
It is worth noting this conversation in that thread was started in January 2015, the solution was found in April of 2015 and in June 2017 someone said: “It shouldnt. Farshark is aware of the problem and started using new rods.” when another user asked if this problem affects HD3 goggles. We could assume that on all goggles released after April 2015 should have this issue fixed.
The fun part is that my goggles are Dominator V2s which were released in 2014 so this problem is still present and very likely cause of this drifting. If nothing else at least my goggles have had the last five years time to get those rods magnetized.
User Aardwolf posted this DIY solution for this problem:
“Not wanting to wait for a fix, or sending my goggles overseas to a repair center(would be a very lengthy/risky process from where I live), I decided to have a crack at replacing the IPD slider rods myself.
It was quite easy once I got the guts to open up the goggles. The 2.5mm rods just slide out if you pull on them with pliers (and they tested to be very attracted to a magnet!), and I replaced them with two (grade 304 or 316??) austenitic stainless steel rods which I then hot glued to stay in position (cut them from a cooking grid found in my girlfriend’s kitchen :p shhh ), and I tested a spare piece to have no attraction to a magnet.
The drifting seems to have completely disappeared. I’ve flown 5 flights now with no issues (except one time it started drifting away from centre rapidly, but quickly resetting the head tracker fixed that).”
At some point I also tried shielding the module with copper tape. That didn’t help at all.
But that’s what I’m going to do, replace those IPD rods with something not magnetic and trying not to break my goggles in the process. Only thing holding me back from doing this is that as you can see from my previous posts my goggles are quite customized. I have to re do many things if take them apart. And I need them to fly fpv.