Help please: Optoma hd 33 and 3d corp glasses

Hello,
I'm new to 3d and just got the Optoma HD33 projector. It did not come with any glasses, but did come with an RF emitter.

I'm not a big 3d fan, but thought it would be fun, so I got some cheap ir 3d glasses off amazon (http://www.amazon.com/DLP-LINK-3D-Projectors-Samsung%C2%AE-Mitsubishi%C2%AE/dp/B004G2VJM6) with the understanding they would work.

They do work, sort of, for about 5 seconds. I have two pair, and both behave the same, which is:

I charged the glasses overnight.
I turn on the comcast 3d channel
I turn the projector into 3d mode so the images overlap
I turn off all the lights in the room
I stand about 10 feet from the screen dead center
I turn the glasses on and...

in about 5 seconds, the shutters seem to kick in... but then they turn back off again. Occasionally, I can get them to kick back in, but normally it requires turning the glasses off and on again.

I'm not sure how this works - does the projector send the signal via IR? Does it sync from screen flicker? Are the glasses crap (they are well reviewed on amazon, despite being cheap)? Do they need an IR emitter?

I'd prefer not to pay the 180 for two pairs of rf glasses and I was under the impression that the IR ones should work with this projector.

Any thoughts would be very much appreciated!

Thanks!

It's on SBS - is there a different setting to use IR instead if RF?

Haha - yup, that was it. It has two 3d modes, dlp link and vesa 3d. Had no idea.

Thanks!!