The drones are basically biters with the skin of a engineer. So they only have one attack option. In the current version they attack with 5 points of physical damage from a range of 0.5.
Klonan has fixed the damage the drones can do within his mod so he can do calculations based on that number for how long it would take to mine a resource in his control.lua code when creating proxy target for the drones to attack on the resource patch.
I could change the range of the attack, but then it would look very odd when the drones are able to mining from a distance.