I have been experimenting with Marcelo Garcia's situp escape. Here is a video
https://www.youtube.com/watch?v=V7vmzcc3ldA
Marcelo posts on the opponent's nearside shoulder and bicep to keep some distance, then he sits up by posting his farside arm behind him and stiff arm the opponent with near side arm, usually by gripping the opponent's collar or shoulder.
I am not quite getting the timing right, and kept getting my nearside arm armbarred. I suspect I am taking too much time getting up. Any advices are appreciated.
Are you sure it's not where he's posting more on the tricep? I've been working that a lot and the three options off that...basic guard recovery, pseudo fireman's carry sweep if he comes N/S, if he grabs my legs with his back facing me I glue my chest to his back keeping my legs spread and backroll to top position.
all 3 of those options work great. First step is to keep his chest pointed away from you.
Meatgrinder
the one where MG posts on tripcep is a different escape. In that one, he brings the opponent nearside arm over his head, and he then pushes on the tricep and lead to the three options you mentioned. As seen in the video below.
https://www.youtube.com/watch?v=bDVO9kXu5Lc
Marcelo's side control escapes are my go to escapes.
One thing I've noticed that made a difference for me and may help you as well.
1. You have to start early. Don't let them establish good control
2. Post all the way up on the far hand. I was stopping on my elbow and not having any success. It's not easy to get all the way to your hand but that's what makes the move work and should prevent your near side arm from getting armbarred because of the angle your at. 
This escape is solid it just takes a lot of work. With the arm you're framing with, if you straighten it to stiff arm you can get arm locked, instead keep your elbow bent with your forearm against his chest and your elbow pointing down.
Meatgrinder -Any videos of the pseudo firemans carry u mentioned
Are you sure it's not where he's posting more on the tricep? I've been working that a lot and the three options off that...basic guard recovery, pseudo fireman's carry sweep if he comes N/S, if he grabs my legs with his back facing me I glue my chest to his back keeping my legs spread and backroll to top position.
all 3 of those options work great. First step is to keep his chest pointed away from you.
Paging Jeff Rockwell...mr Rockwell...
murryhill - Elbow push to fireman carry
https://www.youtube.com/watch?v=7t3dG_8-j54
MG just stands into the fireman's so easy...I've found that your don't even need to do that. It's can be really difficult to sit up enough and have enough posture to go into the fireman's esp if he gets there quick. I just try to get my head to his hip like that then I turtle and barrel roll sweep him.
There's an additional move in this sequence where instead of doing the last move tha the shows, you keep your legs the way they are and backwards shoulder roll ending in top position. Watch the vid where Eddie Bravo visits MG's academy and they record a long roll. Looks like it's difficult to pull off, but it's really not. Just make sure you keep your chest glued to his back.
This entire sequence is awesome.
http://youtu.be/4WNlRtbx7zA
Here's Jeff Rockwell showing some of this escape system, which includes the hip roll escape Meatgrinder mentioned.
I would recommend subscribing to www.MGinAction.com and watching all the vidoes by MG. He has a ton of video and several discussions on the position. But in the meantime, check out this series of videos:
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Good advice so far. Hard to say without seeing live, but to the OP, if you are getting arm locked while sitting up, your problem is most likely an issue of where you are pushing with your framing hand, not getting up high enough on your posting hand, or timing. Or all three. :)
Tboney8669 -Meatgrinder -Any videos of the pseudo firemans carry u mentioned
Are you sure it's not where he's posting more on the tricep? I've been working that a lot and the three options off that...basic guard recovery, pseudo fireman's carry sweep if he comes N/S, if he grabs my legs with his back facing me I glue my chest to his back keeping my legs spread and backroll to top position.
all 3 of those options work great. First step is to keep his chest pointed away from you.
Not yet Tboney... Primarily keep your head outside his hip and load him over your shouler and barrel roll. If he's perpendicular to you, it will be difficult. If he's too close to N/S he won't roll over you.
The details of the grip on his arm during the roll are important. You need to make sure that you're not clamping down on his arm in a way that gives him anaconda/darce/arm-in-guillotines.
As far as pushing with you're framing arm at the beginning... I like to push below their tricep (also a little on the inside b/c you can flare their elbow out too). You have the most leverage to rotate his shoulders away from you. A lot of people frame up near the arm pit. I might start there if just to start making space while I'm on my back, but I work towards their elbow as I post on my own elbow (trying to work to my hand). If you stay at the armpit, you don't get their shoulders to rotate as well towards your legs. Their chest is still facing towards your chest, so that clamp on your arm and arm bar you.
Do people find this type of escape effective on opponents who are larger/heavier then them? I can't get it to work on bigger guys, or people with a good base from side control, I can't shift them.
James
murryhill - I have been experimenting with Marcelo Garcia's situp escape. Here is a video
https://www.youtube.com/watch?v=V7vmzcc3ldA
Marcelo posts on the opponent's nearside shoulder and bicep to keep some distance, then he sits up by posting his farside arm behind him and stiff arm the opponent with near side arm, usually by gripping the opponent's collar or shoulder.
I am not quite getting the timing right, and kept getting my nearside arm armbarred. I suspect I am taking too much time getting up. Any advices are appreciated.
You're leaving your arm hanging out too long, not being explosive enough with the movement and not posting your farside arm quick enough.
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Sir Taps - Do people find this type of escape effective on opponents who are larger/heavier then them? I can't get it to work on bigger guys, or people with a good base from side control, I can't shift them.
James
You can't let anyone settle into the side control position for this to effectively work. You have to hit it before they start to settle their base. When you watch MG do it, he rarely lets anyone settle and get comfortable, he usually hits it in the transition.
See this video for examples: https://www.facebook.com/video.php?v=386493384862605&set=vb.384517195060224&type=2&theater
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i was having a similar set of problems with this escape, but a teammate (brown belt, i'm a blue) pointed out to me that your head needs to be above their hips as you're pushing.
Thanks Joe, I had a feeling it was my lousy timing more than anything else! Do you find that you have a higher success rate if the opp is closer to your hips then up by your head when starting the escape?
James
murryhill - Meatgrinder
the one where MG posts on tripcep is a different escape. In that one, he brings the opponent nearside arm over his head, and he then pushes on the tricep and lead to the three options you mentioned. As seen in the video below.
https://www.youtube.com/watch?v=bDVO9kXu5Lc
ah... yeah.. Sorry guys. I didn't actually look at OP's clip right away. That's just the one what I think of (and gave it for a name "Marcelo's sit up escape sequence") when his back is towards you (his crossface arm is across your body) and you push on his tricep.