Clockwork Master

(Construct can update a hard-drive spell list, similar to a self replicating spell book)

My little Steam Punk

At 3rd level, you gain proficiency with tinkerers' tools, a modified solar charged backpack that charges constructs while you rest, and a semi-sentient construct that accompanies you on your adventures and is programmed to fight alongside you. Choose a Construct that is no larger than Medium and that has a challenge rating of 1/4 or lower. Add your proficiency to the Constructs Armor Class, attack rolls, and damage rolls, as well as to any saving throws and skills it is proficient in as well as (Dexterity)Sleight of hand, if the construct is not already proficient. Its hit point maximum equals the Max hit point number in its stat block or four times your ranger level, whichever is higher. During a rest, the creature will attempt to repair itself if components are in inventory or available nearby - half max hit points on a short rest and full on a long rest. Unlike barding armor for beasts, constructs have a custom chassis.  The armor class of the Chassis can be modified by a player tinkerer with a Tinkerers' tools check DC= the desired armor class, time = 2 hours X desired AC, and 2x the price of comporable base armor from the PHB.  An NPC Tinkerer automatically succeeds at the modification for 1/2 the time and twice the cost.

The Construct obeys your commands at all times unless severely damaged with electrical damage (3/4 of max HP). It takes its turn on your initiative, though it doesn’t take an action unless you command it to. On your turn, you can verbally command the drone where to move (no action required by you). You can use your action to verbally command it to take the Attack, Dash, Disengage, Dodge, or Help action, though Constructs with Passive Perception of 14 or higher, will take reactions on their own whenever possible. Once you have the Extra Attack feature, you can make one weapon attack yourself when you command the Construct to take the Attack action.

If you are incapacitated or absent, the Construct anchors itself to you're gear creating an impenetrable shield, focusing on protecting you and itself.  The shield drains the construct by 1/4 of it's maximum hit points

While traveling the construct can adhere to you armor as an exoskeleton without hindering movement, stealth checks, or perception checks.  The chassis provides no bonus to AC or Saving throws

If the construct's hit points drop to zero, it's restraining bolt will attempt to jump start it rolling constitution modified death saves.  If the construct is stabalized - either with a repair kit (Healing kit for constructs - 5 uses), a spell or potion, a successful (Intelligence) sleight of hand check, or 3 successful death saves - Its hit points equal 1 and it is incapacitated.  Roll a d20.  If the d20 rolls a '1' the drone "goes rogue" and gains back 1/2 its maximum hit points and attacks the party.  Melee attacks against the rogue construct trigger a DEX Save. on a failed save take 1d10-1 lightning damage.  The drone will be fixed and stabilized if it takes any lightning damage

All Clockmaster controlled constructs are resistant to fire, and immune to poison, but vulnerable to electric and frost damage.

Reflexive Programming

Beginning at 7th level, on any of your turns when your robotic companion doesn’t attack, you can use a bonus action to command the machine to take the Dash, Disengage, Dodge, Ready, or Help action on its turn.

Metal Menace

When you command your mechanical companion to take the Attack action, Add 1d10 lightning damage. increase damage to 1d12 at level 13, 2d8 at 17, and 2d10 at level 20. As a reaction, when hit by a melee attack with a creature appendage or metal weapon, electrocute the attacker for lightning damage equal to your ranger level rounded down

When you command your drone to take the [action]Dodge[action] action, add your Intelligence modifier to any saving throw, except for Charisma

Of One Mind and Soul

You've begun pushing the boundaries of what science thought possible.... or ethical
Beginning at 15th level, your machine and you share Intelligence and Wisdom (whoever's were originally highest) ability scores. 

What's more, your machine has learned from watching you and evolved, as have you.  Other players may have trouble (based on your role-playing) understanding who is now in charge - the PC or the construct.  Your construct can now choose 2 PC class levels (1 at ranger level 15, and another at 18), restricted by the multi-class restrictions and with one less spell slot in each spell level per class level

(example:  mechano-giant-crab will probably not have the Charisma to pick up levels of sorcerer. He decides to download the "Berserker Upgrade" (1 level of Barbarian), at player's ranger level 15. It will only benefit from the proficiencies listed in the multi-class section of the Players Handbook.)