LEGO Technic basics: pins, axles, beams and gears explained
TUREFF• •0
Technic is the LEGO system for building things that move: steering, suspension, gearboxes and working cranes. It uses a different vocabulary from ordinary bricks, and a few key ideas make the instructions and your own experiments far easier. LEGO is a trademark of the LEGO Group; this guide simply explains how the parts work.
The unit of measure
Technic parts are measured in modules, written as L. A beam with five holes is a 5L beam, and an axle five holes long is a 5L axle. The spacing between holes matches the spacing between studs on ordinary bricks, which is why the two systems can be combined.
Instructions show axles and long pins at actual size in a call-out box, with the length in a circle. Lay the part on the picture to check you have the right one. Telling a 7L axle from an 8L axle by eye is a common source of mistakes.
Beams
Modern Technic is mostly studless: smooth beams with round holes rather than bricks with studs on top.
- Straight beams come in many odd and even lengths.
- Bent and angled beams let you build at angles without any extra connectors.
- Frames give large rectangular sections that stay rigid.
- Technic bricks with studs and holes still exist and are useful for combining with ordinary LEGO.
Round holes accept pins and let axles spin freely. Cross-shaped holes grip an axle so it cannot turn.
Pins
Pins join beams together through their holes.
- Friction pins have small ridges and hold firmly, so the joint resists turning. Use them for structure.
- Frictionless pins are smooth and let parts rotate easily. Use them for anything that needs to move.
- 3L pins join three layers, or let you stack beams.
- Axle pins have a pin on one end and an axle on the other.
Colours are used to tell pin types apart, but the colour scheme has changed over the years, so check the part shown in the instructions rather than relying on memory. A pin removal tool, or simply the end of an axle pushed through from the other side, saves your fingernails.
Axles
Axles have a cross-shaped section. They transmit turning force from one part to another, such as from a motor to a wheel. A gear or wheel with a cross hole locks onto the axle and turns with it. Bushes (small collars) hold axles in place and stop them sliding out, and half bushes do the same in tight spaces.
Gears
Gears are where Technic gets interesting.
- Spur gears are the classic straight-toothed gears. The common sizes have 8, 16, 24 and 40 teeth, all multiples of eight, which keeps the maths simple.
- Double bevel gears, with 12, 20 and 36 teeth, mesh both side by side and at right angles.
- Worm gears look like a screw. A worm driving a 24-tooth gear turns it once for every 24 turns of the worm. A worm can drive a gear but a gear cannot drive the worm back, so it holds loads in place, which is ideal for cranes and lifting arms.
Gear ratios in one paragraph
Divide the teeth on the driven gear by the teeth on the driving gear. An 8-tooth gear driving a 24-tooth gear gives a 3 to 1 reduction: the output turns three times slower, with roughly three times the turning force, before friction. Swap them round and you get speed instead of force. Chain several stages together and multiply the ratios.
Getting gears to mesh properly
Gears must sit at the right distance to mesh. Many common pairs, such as 8 with 24, or 16 with 16, sit neatly a whole number of holes apart on a straight beam. Others need half-module offsets or angled positioning. If a gearbox feels stiff, check for gears pushed too tightly together, axles that are bent, or bushes squeezing parts sideways.
A first experiment
Build a simple frame, put a crank on one axle and a wheel on another, and try different gear pairs between them. Feeling the difference between speed and torque in your fingers teaches more than any table.
What was the first working mechanism you built in Technic? Share your experience or questions in the comments.