Transforming rotation into translation and reverse – Glossary

  1. Definition of a motion transformer
  2. Motion transformer types
  3. Focus: Rack & Pinion
  4. Focus: Crank & Rod system
  5. Quiz
  6. Glossary


Crankshaft – is a mechanical part able to perform a conversion between reciprocating motion and rotational motion. In a reciprocating engine, it translates reciprocating motion of the piston into rotational motion, whereas in a reciprocating compressor, it converts the rotational motion into reciprocating motion. To do the conversion between two motions, the crankshaft has “crank throws” or “crankpins”, additional bearing surfaces whose axis is offset from that of the crank, to which the “big ends” of the connecting rods from each cylinder attach.

Electric motor – is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor’s magnetic field and electric current in a wire winding to generate force in the form of rotation of a shaft. Electric motors can be powered by direct current (DC) sources, such as from batteries, motor vehicles or rectifiers, or by alternating current (AC) sources, such as a power grid, inverters or electrical generators. An electric generator is mechanically identical to an electric motor, but operates in the reverse direction, converting mechanical energy into electrical energy.

A gear – is a rotating circular machine part having cut teeth or, in the case of a cogwheel or gearwheel, inserted teeth (called cogs), which mesh with another (compatible) toothed part to transmit (convert) torque and speed. The basic principle behind the operation of gears is analogous to the basic principle of levers. A gear may also be known informally as a cog. Geared devices can change the speed, torque, and direction of a power source. Gears of different sizes produce a change in torque, creating a mechanical advantage, through their gear ratio, and thus may be considered a simple machine. The rotational speeds, and the torques, of two meshing gears differ in proportion to their diameters. The teeth on the two meshing gears all have the same shape.

Mechanics (from Ancient Greek: μηχανική, mēkhanikḗ, lit. “of machines”) is the area of mathematics and physics concerned with the relationships between force, matter, and motion among physical objects.[3] Forces applied to objects result in displacements, or changes of an object’s position relative to its environment.

Pinion – is a round gear—usually the smaller of two meshed gears—used in several applications, including drivetrain and rack and pinion systems.

Rack and pinion – is a type of linear actuator that comprises a circular gear (the pinion) engaging a linear gear (the rack), which operate to translate rotational motion into linear motion. Driving the pinion into rotation causes the rack to be driven linearly. Driving the rack linearly will cause the pinion to be driven into a rotation. A rack and pinion drive can use both straight and helical gears. Though some suggest Helical gears are noted for “quieter” operation, there is no science to support this theory. Helical racks while being more affordable, have proven to increase side torque on the datums, increasing operating temperature leading to premature wear. Straight racks require a lower driving force and offer increased torque and speed per percentage of gear ratio which allows lower operating temperature and lessens viscal friction and energy use. The maximum force that can be transmitted in a rack and pinion mechanism is determined by the tooth pitch and the size of the pinion as well as the gear ratio.

Reversible – Whose effect and cause can be reversed. Most electrical machines are reversible, i.e., instead of supplying electricity through a mechanical motor, they can vice versa transform electrical energy into mechanical work.

Rotation – is the circular movement of an object around an axis of rotation. A three-dimensional object may have an infinite number of rotation axes.

Translation – is a geometric transformation that moves every point of a figure, shape or space by the same distance in a given direction. A translation can also be interpreted as the addition of a constant vector to every point, or as shifting the origin of the coordinate system. In a Euclidean space, any translation is an isometry.

Wheel – In its primitive form, a wheel is a circular block of a hard and durable material at whose centre has been bored a hole through which is placed an axle bearing about which the wheel rotates when torque is applied to the wheel about its axis. The wheel and axle assembly can be considered one of the six simple machines.

Wheel and axle – is a machine consisting of a wheel attached to a smaller axle so that these two parts rotate together in which a force is transferred from one to the other. The wheel and axle can be viewed as a version of the lever, with a drive force applied tangentially to the perimeter of the wheel and a load force applied to the axle, respectively, that are balanced around the hinge which is the fulcrum.