20 Mechanical Principles Machine

This Lego machine demonstrates 20 different mechanical principles. You may call it a do-nothing machine or useless machine, as all it does is rotate those beautiful mechanical principles. At the end of the chain there is a slowly turning minifig statue.

Download building instructions PDF:

Download parts list:
BrickLink wanted list XML file
CSV file

Download 3D model:
BrickLink Studio 2.0 file


Buy a full kit (with original Lego parts and printed instructions):

The four mechanisms in the back side are just for display: they move but don’t affect other mechanisms. Putting them into a chain reaction proved too difficult and error-prone.

List of 20 mechanical principles

1. Schmidt coupling transmits rotary motion between two radially displaced shafts. Used for example in printing industries to accommodate rollers whose distance change often.

2. Constant-velocity joint (CV joint) transmits rotary motion through variable angles while keeping constant speed. Used in cars between wheels and the drive shaft.

3. Universal joint transmits rotary motion through variable angles. Similar to CV joint, but this mechanism doesn’t keep constant speed. The problem is partially overcome by connecting two U-joints 90 degrees out of phase, also known as a Double Cardan shaft. Universal joints are used in the long driveshafts of trucks.

4. Bevel gears transmit rotary motion at right angles. Used in car differentials.

5. Slider-crank linkage converts rotary motion to linear motion, or vise versa. Used in automobile petrol engines between piston and the crankshaft.

6. Sun and planet gear converts rotary motion to linear motion, or vise versa. Similar to crank, but requires two revolutions from the driver gear to complete one full beam stroke. Was used in steam engines in the Industrial Revolution because the crank was patented.

7. Scotch Yoke converts rotary motion to linear motion, or vise versa. Used in valve actuators that require a lot of torque.

8. Chebyshev Lambda Linkage converts rotational motion to approximate straight-line motion. Used in walking robots.

9. Chain drive transmits mechanical power from one place to another. Used in bicycle between pedals and the drive wheel.

10. Belt drive transmits mechanical power from one place to another using flexible material. Used in automotive engines to transmit power to alternator, water pump, and other parts.

11. Constant-mesh gearbox is a type of manual transmission where a gear stick is used to select gears. A dog clutch slides on the main shaft and meshes with desired gears. Used in modern cars.

12. Oscillating direction changer is a device that periodically changes the direction of rotation of the output shaft. Usage not known.

13. Torque limiter is a device that protects equipment from mechanical overload. The Lego part (60c01) uses an oval shaped center that slides against bending metal plates. Torque limiters are used for example in fishing reels.

14. Winch is a mechanical device to pull in or let out rope. Used in sailboats.

15. Rack and pinion converts rotary motion to linear motion, or vise versa. It consists of one circular gear (pinion) and one linear gear (gear rack). Used in automobiles between the steering wheel and front wheels.

16. Offset gear is a spur gear where the shaft is mounted offset from the center of the gear. In this Lego example the offset gear is used to intermittently rotate the other gear. Usage not known.

17. Uni-directional drive is a gearbox that converts bidirectional rotary motion to unidirectional rotary motion. Used in ocean wave generators.

18. Camshaft converts rotational motion to reciprocating motion. The shaft contains one or more pointed cams. Used in piston engines to operate valves.

19. Intermittent mechanism is a device which regularly advances an object and then holds it in place. Note that this simple Lego device doesn’t hold the object in place. By combining it with a worm gear it fulfills that behavior. Used in movie cameras and projectors to move the film.

20. Worm gear is a gear in the form of a screw. When combined with a spur gear, it produces high gear reduction. Only worm gear can be the driver gear. Used in musical instruments for tuning the strings.


The machine consists of 520 Lego parts and one non-Lego item (a string for the winch). For the string I used 100% cotton, fairly thick one. Link to the string.

The dimensions (WxDxH) for the machine are 31x12x17 cm (12.2×4.7×6.6 inches). Weight (with batteries) is 500 grams (17.6 ounces).

The first version of the machine was presented in a YouTube video. Many people in the comment section asked, where can you buy this, so therefore I improved the machine for reliability, created the instructions, and put it up for sale on buildamoc.com.

List of improvements done to the build since the video:
-changed expensive Rechargeable Battery Box (8878) to cheaper AAA Battery Box (88000)
-changed Power Functions XL motor (8882) to M motor (8883)
-added a 5:1 gearing to the motor to reduce speed
-changed CV joint connectors (part id 44) to universal joints to make it more robust
-increased sun and planet gear shaft length by one stud to prevent jamming
-many other small changes to improve reliability and to make it easier to build
-note: no changes to the 20 principles involved

If you’re thinking about building it, you can:
-reduce noise by powering it with Rechargeable Battery Box (8878) that is set to minimum speed
-reduce gearbox snapping sounds by 1) tuning the length of the red crank on the gearbox changeover catch and 2) using a weaker rubber band for pulling the gear rack. For a quick solution, just remove the 8-tooth gear that connects the torque limiter.
-add furniture pads to the bottom to prevent scratches to the table
-connect gears and bushes loosely on axles to ensure smooth operation

About reliability. The machine should run at least 30 minutes without a hiccup. But if you run it long enough, it will jam eventually. The gearbox changeover catch plate may disconnect, the belt drive may start to slip, the uni-directional drive may jam, and some of the gears may slide out of their axles. A lot of the problems are caused by the winch and rubber band introducing tension to all parts earlier in the chain. To quickly increase reliability, remove the 8-tooth gear that connects the torque limiter.

How much does it cost if you buy the parts yourself? At the time of writing this (Nov 2022), using 6 months avg price on http://www.bricklink.com, the total cost is 160 EUR. If you buy only used parts, the total cost drops to 100 EUR. If you leave out the motor and battery box, the price drops to 60 EUR. The machine contains a Power Functions motor and battery box, for which you may find cheaper alternatives. The postage cost may be high, as none of the sellers on bricklink.com have all required 144 lots available, so you will need to use at least 2 different sellers. Alternatively, you can buy the machine in a single packet from buildamoc.com for 199 EUR. Declaration of bias: I receive 10% commission from every sale.


Photograph on white table, front side.
Photograph on brown table, front side.
Photograph on brown table, back side.
The minifig statue rotates once in 18 minutes.
3D model, front side.
3D model, back side.
Moving parts highlighted, front side.
Moving parts highlighted, back side.
Orthographic front side.
Orthographic back side.
Orthographic left and right side.
Orthographic top side.
Orthographic bottom side.
Snippet from instructions.
Snippet from instructions.
Download full instructions here.


Rotate animation gif.
Build animation gif.

Any questions? Feedback? Feel free to comment below.

2 thoughts on “20 Mechanical Principles Machine

  1. D Phillips


    I have a requirement for number 12 (oscillating direction changer). I don’t suppose you would be able to advise me where I could source the parts just for this? I’ll need to add a motor. It’s for spinning a basket in a cleaning solution (an idea for a DIY watch parts cleaning machine).



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