right, got a bit of a complex scenario here:
"A spell cast on a non-living, non-magic target is not resisted, as
the object has no life force and thus no connection to mana with
which to oppose the casting of the spell (note that only Physical spells
will affect non-living objects; mana spells have no effect). Highly processed
and artificial items are more difficult to affect than natural, organic
objects. Spells cast on non-living objects require a Success Test
with a threshold based on the type of object affected (see the Object
Resistance Table). Note that objects targeted by Combat spells get to
resist the damage as they would any ranged attack; use their Armor
rating x 2 (or just Armor against spells with elemental effects) to resist
the damage (Barriers, p. 166)."
i read it as you'd either need to get 6 successes on your test to affect a drone with a spell (seeing the object resistance chart) or that because you're casting a combat spell, we just treat it as an "object" (because it is not alive) and just use armour x2 to resist the physical damage.
the latter makes the most sense to me, so that's what i'll run.
EDIT
Direct Combat spells cast against nonliving objects are treated
as Success Tests; the caster must achieve enough hits to beat the item’s
Object Resistance (p. 183). Net hits increase damage as normal (the
object does not get a resistance test).
Object resistance for a drone is 6:
{Highly Processed Objects
(Computers, Complex Toxic Wastes, Drones, Vehicles)
6+} pg 183 SR4a