Nix the Wandering Raider (WIP Champ Concept)

Pre thought: I originally posted this on facebook, though I figured it'd suit better here. This concept is extremely early age, it doesn't even have art yet. Though I do believe it is a solid concept, I'm sure it needs its kinks worked out. I will soon update it with specific numbers ranging from his stats to the abilities. Any help would be greatly appreciated, from a positive opinion stating why they believe something is wrong and should be fixed to anybody that'd be willing to work with me on making concept art.

Champion Concept: (this is a WIP, any honest opinion would help, just no "Too OP, re-do")

Nix - The Wandering Raider

Back Story: Nix was once a general in the Noxian army, fighting along side Darius to fight Demacia, but when he got injured in battle and left for dead he took it as a personal betrayal between him and Darius. Wounded and broken he wandered the lands, first stopping in Piltover where he gained his new weapons; a staff that he uses to fight, a drone that protected him, and armor that would heal minor injuries. Once he left Piltover he decided to travel the Shuriman desert, attacking any person that he saw he could make a profit off of and studying the ancient kingdom of Shurima. While he studied, he also plotted how he would one day get his own revenge.

Abilities:

Passive: Scrap - Nix passively gains scrap from his surroundings, allowing him to upgrade his gadgets. (+1 per minion, +5 per assist, +10 per kill)

Q: Static Sting - Nix stabs his staff into his target with his next basic attack, stunning them for a short time (.5-2 sec) and dealing physical damage. Upgrade: Nix swings his staff instead of stabbing, stunning all enemies in a cone. (Upgrade Cost: 80 scrap)

W: Sentry - Nix sends out his drone to a target location, attacking any enemy champions that come into range and dealing physical damage. Upgrade: Nix's drone will follow him and do increased damage. (Upgrade cost: 95 scrap)

E: Battle Hardened - Nix's armor will heal him for a percent of the damage taken recently (5%-25% of damage received 3-6 seconds prior) and increasing his armor for a short time. (4-7 sec) Upgrade: The armor will heal more, but reduce the armor it gains. (Upgrade Cost: 75 scrap)

R: Overdrive - Nix's armor and staff surge with Shuriman power, causing him to attack faster, move faster, have more damage, and his armor radiates arcane power, doing magical damage to any enemies near him. (5-10 sec) Upgrade: Overdrive lasts longer, but at the end of it Nix loses up to 5% of his health. (Upgrade Cost: 105 scrap)

So as stated above, this is a work in progress. I just came up with this while I was playing a game of Robocraft and thought it was really creative. I'd love some feedback, some insight into things that might make Nix too OP or underpowered or if one of his abilities just doesn't click. Thanks!