If anyone is still playing the Iokath storyline, I figured out how to defeat the sentinels. This is for the Showdown on Iokath - the part where you are fighting three champion Iokath sentinel droids after Empress Asina uses the superweapon.
Be sure to have your BEST companion up before you enter the room. If you die, restart at area and bring out your companion, then head to the location where the map tells you to enter and redo the instance. I was on my Shadow, so I stealthed to the location.
Once inside, experiment with the best damage, but the stomp is NOT the best way to kill them. Use all your abilities, but you will probably only get one sentinel down. When you die, revive INSIDE THE ROOM and - when invisible after reviving - put your walker as far from the two remaining sentinels as possible. Hopefully, you will not aggro them and you can use your healing ability to get your health to full. AND your companion should be in the room with you. At least mine was. The heals from her weren't great, but they were better than nothing. She was in there to fight with me against the last two sentinels.
If you die again, revive in the room and repeat until the last one is down.
This was the only way I was able to defeat the Sentinels and get past this part of the quest. That's my experience, FWIW.
May the Force be with you,
Arial