The FreeTrack site describes what third party items can be used and I'm pretty sure that I have seen TIR clips used as well as how to use reflective strips, etc. Best to have a browse on their website.
Quite a few seem to have a reflector set up working well.

The TrackClip Pro uses active LEDs.

I agree with SEE, on the Freetrack site you'll find everything you need... I didn't used IR leds but just white leds on a cap, with a cable to plug in to the USB. The first time i downloaded freetrack i was frustrating how difficult was to configure... but now i can't fly without it... it's just so natural to look around without press some hat switch on the joystick. I still use the 2 DOF and not the 6 DOF cause i haven't modded my IL2, but i'm fine with it right now. Another thing you'll find difficult will be the camera setup, after that you'll only have so much fun with it and will enjoy every flight.

Alberto

Freetrack needs an active LED source pointing at the camera, while TrackIR works both ways. You can have active LEDs that the TrackIR camera tracks (just like Freetrack), or you can have reflectors that bounce back IR rays that the camera emmits towards you.

In the TrackIR software, there is a choice as to what kind of "target" to use. If you choose to use reflectors, there are 4 LEDs facing you on the TrackIR camera that light up, the radiation from which is bounced back by the reflectors. If you choose the trackclip pro, the 4 camera LEDs turn off and the active LEDs are 3, mounted on the clip that attaches to your headphones.

I prefer using Trackclip Pro, because it's easier and more comfortable to wear a thin set of headphones to attach it to, than wearing a cap with reflectors. In that sense, if resolution is comparable, i guess Freetrack is just as good a choice (ie, you don't lose much by lacking the option of having active LEDs mounted on the camera itself). My only gripe with Trackclip Pro is that it's too flimsy. Mine broke a mere 2-3 months after i bought my set and i have it fastened with duct tape ever since :grin:

I think a reasonably cheap and easy way to go would be to combine both. You could use a Freetrack modified camera as the tracker and buy a Trackclip pro to use as the emmiter.

What's stopping freetrack from using reflectors?

probably because you need to have a light pointing to your face? :grin:

You can't see IR :)

It doesn't matter whether you can see IR or not. What matters is that reflectors need something to reflect. ;)

The trackIR camera has a built in emitter, so it's both an emitter and a receiver. Freetrack cameras however mostly function as receivers only, because they lack built-in LEDs.
MSPaint to the rescue: :grin:

http://img705.imageshack.us/img705/9895/trackir.png

Yes I'm aware of how it works - but what's stopping you from buying some IR LED's (the same as I use on my headset), positioning them near your camera and pointing at you, and using the same sort of reflective material as TIR does to reflect the light back to the camera?

Most freetrack users make their own system anyway, so is there anything that I'm missing that's stopping them from doing it this way? It's easier to do with regard to avoiding extra wires running to your head.

Yup, if you position LEDs near the camera i think there's nothing stopping you from using reflectors.