Screw Drivers Chains Build Guide

Chains are one of the most powerful new building tools added to Screw Drivers. They let you transmit rotational force between two gears without requiring a solid axle between them, which means you can route power around obstacles, across frames, and between distant components. This guide covers how chains work, when to use them, and how to integrate them into a transmission.

What chains do

A chain wraps around two or more gears and transfers rotation from one to the other through friction. If both gears spin freely and the chain has tension, the leading gear pulls the chain which then pulls the driven gear. The rotation direction reverses on each side of the chain, just like a bicycle chain on the front and rear sprockets.

In Screw Drivers, chains are flexible. They can wrap around gears that are not on the same axis, that face different directions, or that are separated by other vehicle components. This makes them useful for unusual drivetrain layouts where a rigid axle would be impossible.

Where chains shine

Long-distance power transfer is the most obvious use case. Imagine a four-wheel-drive car where the front and rear differentials are far apart. A chain can connect them without adding an axle that would interfere with the chassis. Similarly, engines mounted on top of a vehicle can deliver power to wheel axles mounted low on the chassis using a chain.

Power transfer around obstacles is another use case. A rigid axle going from the engine to a wheel would need to pass through any components in between. A chain can take a curved path around them, freeing you to place structural and mechanical parts without worrying about a straight-line drivetrain.

Custom transmission layouts become much easier with chains. You can place the engine, the transmission, and the wheels wherever you like, then use chains to link them. This is especially useful for engine swaps or repositioning components without rebuilding the entire drivetrain.

Where chains struggle

Slippage is the main downside. A chain transmits power through friction, not through rigid contact. Under heavy load — large engines, steep climbs, sudden acceleration — a chain can slip, causing a momentary loss of power at the wheels. Axles do not have this problem because they are rigidly connected.

Realistic chain behavior means your chain must have the correct tension. Too loose and it slips under load. Too tight and it can damage the gears it wraps around. Experiment with chain length until you find the sweet spot where the chain has just enough tension to drive without slipping.

Engines with extreme torque can break chains. High-power combustion engines, multi-engine configurations, and very heavy vehicles can exceed what a chain can transmit. If you notice your chain skipping or breaking, fall back to a rigid axle for the heavy-duty sections.

Building a chain drivetrain

Step 1: place the gears

Start by placing the gears you want to connect. Make sure each gear is properly attached to its rotating component (axle, wheel, engine output). Chains only transfer rotation between gears, so the gears must be spinning for the chain to do anything.

Step 2: position the chain

Select the chain from your parts inventory and place it between the two gears. The chain will visually wrap around both gears if positioned correctly. If the chain appears straight rather than wrapped, adjust its position so it touches both gears at their teeth.

Step 3: adjust the length

Chains can be extended or shortened to fit the distance between the gears. A too-short chain will not reach. A too-long chain will sag and lose tension. Adjust until the chain has a slight curve between the gears but no visible sag.

Step 4: test

Switch to driving mode and test the chain. The driven gear should spin in sync with the driving gear. If it does not spin, check that the chain is touching both gears and that the gears are properly attached to their mounts.

Common chain patterns

Chain to a distant differential

Place an engine near the center of the vehicle. Run a chain to a gear on a differential mounted far from the engine. This pattern works well for vehicles where the engine cannot be co-located with the driven wheels.

Chain to a suspended axle

Mount an axle with springs or other suspension. Rigidly connecting the engine to a suspended axle is difficult because the axle moves. A chain can accommodate the small movements because the chain is flexible.

Chain between two gears of different sizes

The gear ratio of a chain is determined by the size difference between the two gears. A small gear driving a large gear through a chain gives a reduction ratio (more torque, less speed). A large gear driving a small gear gives overdrive (more speed, less torque). The same rules as direct gear meshing apply.

Chain plus rigid axle hybrid

You can mix chain and rigid axles in the same drivetrain. Use the rigid axle for sections where you need maximum power transfer (engine to gearbox, gearbox to main differential) and the chain for sections where flexibility matters (main differential to a distant secondary differential).

Tuning tips

• Keep chain length as short as practical. Shorter chains are less likely to slip and look cleaner on the vehicle.
• Avoid chains that cross over each other. Crossing chains cause them to lock up.
• Test under load. A chain that works at idle throttle may slip under full throttle. Test your build on a steep hill before declaring it finished.
• Pair chains with small-to-medium loads. Use rigid axles for the heaviest sections of your drivetrain.

Related pages

• Gear Transmissions for transmission design principles
• Gears for the gear catalog
• Transmission Guide for transmission builds
• Beginner Builds for first-vehicle designs