Armoured Repair Arm

An automated repair arm that keeps your defences standing — no construction bots required.

What it does

The Armoured Repair Arm scans a 7×7-tile area every second and automatically repairs the most damaged structure or vehicle in range using repair packs stored in its built-in inventory. Place it inside or behind your wall line and it gets to work immediately — no logistics network, no roboport, no bots needed. Just make sure the repair packs are constantly refilled, either manually or using an inserter from a belt.

• Prioritises the most heavily damaged target first
• Consumes repair packs directly from its own chest inventory
• Animated two-segment arm physically moves to the repair target
• Plays repair sound effects and animation while working
• Works on structures, walls, turrets, vehicles
• The arm doesn't repair itself, but it is heavily armored. So the arm can survive intense attacks and be repaired by other arms
• If you’re using an inserter to reload, make sure to use a filter to load only repair packs, because the arm only has a standard chest as inventory, which accepts any item

Early & Mid-Game design intent

Construction bots are a mid-to-late-game technology. Before you have roboports and logistics, keeping your perimeter walls and turrets repaired during and after attacks requires either manual effort or dedicated repair structures.

The Armoured Repair Arm fills this gap. It is intentionally unlocked early — after Fast Inserter, Steel Processing and Logistic Science — and uses cheap, readily available repair packs. Once you have a full construction bot network, the arm becomes redundant and can be deconstructed. Until then, it is the difference between a breach and a held line.

Crafting & Technology

Unlocked by the Armoured Repair Arm technology, which requires:
- Automation Science Pack
- Logistic Science Pack

Recipe: 1× Fast Inserter · 3× Iron Plate · 2× Steel Plate · 5× Stone Brick

Recommended mods

If you enjoy this kind of automated repair concept and want a more powerful late-game alternative (or something that works alongside bots), check out:

Repair Turret by Klonan
A classic and well-maintained mod that adds a dedicated turret variant with a wider range and more configuration options.

The Armoured Repair Arm is intentionally lightweight and early-game focused. Repair Turret is the natural upgrade once your factory grows.

UPS Characteristics

Performance was a primary design concern. The arm is built to scale to large perimeters with dozens or hundreds of units deployed simultaneously.

Idle cost is minimal:
- Idle arms only scan every 300 ticks (5 seconds) rather than every tick
- Arms are immediately woken up when a nearby friendly entity takes damage — no need for constant polling
- Sprite positions are only recalculated when the arm actually moves
- power_usage is only written to the entity when the operating mode changes, not every tick
- All arms placed at the same time are stagger-initialised so their scan timers are spread across the interval, avoiding synchronised spikes

Active cost is low:
- While repairing, the arm consumes one find_entities_filtered call per scan (only on mode transitions, not every tick)
- Audio and spark effects are gated behind interval checks

A deployment of 200 arms with ~10% actively repairing at any given time has a negligible UPS footprint.

Compatibility

• Factorio 2.0 and above
• Space Age: optional, auto-detected
• Should be compatible with any mod that does not replace the base repair pack item

Credits

Mod concept & design by Morlot.
Implementation developed with the help of Claude (AI assistant by Anthropic).