From the FG in no-gi it is possible to land an Armbar. Your setup will be a little different without the collar and sleeve but it is still possible.
I use to love Armbars when I trained with the gi at Machado Street Sports Jiu Jitsu. Without the gi it can be a little more difficult to catch an Armbar.
In the video above Barret Yoshida goes over like 3 or 4 no-gi setups for the Armbar. This is all quality stuff.
Barret is one of the pioneers of no-gi grappling in California. He has had tremendous success in grappling tournaments as well as MMA.
I have a couple more Armbar setups that I use from the Guard that I will post to the site soon. Keep an eye on the site so you can check em out !