if you dont have defend3, the important thing is to block his big attacks. his big attacks are every second hit, so you wont be able to block all of them.
an order that you can use (when no defend3) is:
on odd rounds (start, 3rd, 5th,...)
drone->regroup->regroup->defend->tagteam->trueshot
on even rounds (2nd, 4th, ...)
drone->regroup->regroup->tagteam->trueshot->defend
if you notice that you are out of medkits while combat making more before it will help (everyday there is a chance to find antibiotics next to the elevator, which helps), use valhalla in this fight, and i dont remember if the drone uses ammo.