Chief Engineer

you knowledge of mechanisms  and master craftsmanship earned you the title of Chief Engineer. you can do a many number of things that would be difficult for a normal person

Walking Workbench

By 3rd level, your tinkering and experimentation has allowed you to create a custom weapon of your own design. The weapon is comprised of a core weapon form that dictates what modifier is used along with what weapon properties it has. Later on the weapon form also determines what modifications you can put on it. The weapon forms and the innate damage, weight, and properties that come with them are as follows.

As you level up you may add modifications to your weapons; you can select one weapon form, minor mod, and one major at level 3, another minor mod at 5 as well as at 9 and one final major mod at 15. If a modification has a prerequisite, you must meet that prerequisite in order to benefit from the modification. You may reconfigure it during a long rest.

Saving Throws. Some of these upgrades require your targets to make a saving throw to resist the effect. The saving throw DC is calculated as follows:

Weapon Modification save DC = 8 + your proficiency bonus + your Intelligence modifier.

weapon forms

Choose the form for your unique weapon.

Ranged, Heavy

You craft a heavy two-handed ranged weapon of your design. It has the Ammunition, Heavy, (Ranged 120/480), and Two-Handed weapon properties.

The weapon deals 1d10+DEX modifier damage on a hit.

The damage increases to 2d10+DEX at level 9.

Ranged, One-Handed

You craft a small one handed ranged weapon of your design. It has the Ammunition, (Range 30/120), and Light properties.

The weapon deals 1d6+DEX modifier damage on a hit.

The damage increases to 2d6+DEX at level 9.

Ranged, Two-Handed

You craft a two-handed ranged weapon of your design. It has the Ammunition, (Ranged 60/240, and Two-Handed weapon properties.

The weapon deals 1d8+DEX modifier damage on a hit.

The damage increases to 2d8+DEX at level 9.

minor modificaton

Choose your minor modifications.

Aim-Assist

You alter your weapon to have a form of magical aim assist. You may use your intelligence modifier instead of your dexterity or strength modifier for this weapon.

When you select this modification please hide weapon attacks not applicable to your current configuration.

Arm Guard

The weapon is altered in a way that allows the weapon to protect your hand and arm more while wielding it; your AC increases by 1.

Lightweight Materials

The weight of the weapon is cut in half using lightweight materials. If it has the heavy property it is lost. If it doesn't have the heavy property and lacks the light property it gains the light property. 

Variable Attack

The weapon is altered in way that allows it to have multiple damage types; when making an attack you may choose to make it slashing, piercing, or bludgeoning damage. Additionally the weapon deals +1 bonus to damage rolls made with it. (Must be added to rolls manually.)

Major Modificatons

Choose your major modifications.

Arcane Guidance

As a bonus action, you can overcharge your weapon with arcane energy that tries to guide your attacks. For the next minute, or until you roll a 19-20, you may crit on a 19 or 20. You can charge your weapon this way a number of times equal to your intelligence modifier (minimum of once), and regain all uses after a long rest.

Ethereal Shot

As a bonus action, you can overcharge your weapon with ethereal arcane energy. Until the start of your next turn, whenever you make an attack you can choose for the shot to be a 5ft wide 30ft long line originating from the first object or creature you hit. The shot passes harmlessly through objects, ignoring cover. Each creature in the line must make a Dexterity saving throw, taking the damage of the attack on a failure or half as much on a success. You can charge your weapon this way a number of times equal to your intelligence modifier (minimum of once), and regain all uses after a long rest.

Exploding Impact

As a bonus action, you can overcharge your weapon with arcane energy. Until the start of your next turn, whenever you make an attack you can choose to make the attack a 15ft cone originating from yourself instead. Each creature must make a Dexterity saving throw, taking the damage of the attack on a failure or half as much on a success. You can charge your weapon this way a number of times equal to your intelligence modifier (minimum of once), and regain all uses after a long rest.

Extra Attack

Beginning at 5th level, you can attack twice, instead of once, whenever you take the Attack action on your turn.

The number of attacks increases to three when you reach 9th level in this class and to four when you reach 15th level in this class.

heavygun expert

you are an expert with heavy artileray

Mechanic

you can fix, make and reverse engineer anything in half the time it would normaly take

Extra Attack

Beginning at 9th level, you can attack three times, instead of twice, whenever you take the Attack action on your turn.

The number of attacks increases to four when you reach 15th level in this class.

Arcane Enhancement

At 15th Level you manage to enhance every attack you make with your custom weapon. It's damage die doubles unless otherwise specified.

Extra Attack

At 15th level, you can attack four times, instead of three, whenever you take the Attack action on your turn.

Action Surge

Starting at 10th level, you can push yourself beyond your normal limits for a moment. On your turn, you can take one additional action.

Once you use this feature, you must finish a short or long rest before you can use it again. Starting at 17th level, you can use it twice before a rest, but only once on the same turn.