Transforming rotation into translation and reverse – Overview

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

Overview of motion transformer types

The following section introduces some examples of mechanical transformers and highlight their advantages and disadvantages.

Screw & Nut

The screw and nut system allow to transform a rotational movement into a translational movement by combining the movements of a screw and a nut.

Screw and Nut


Advantages: This mechanism allows to exert important forces and pressures. It also allows for fine adjustments.

Disadvantages: This mechanism generates a lot of friction.
Its fragility can lead to guiding problems.
The system is slow unless it has a large screw pitch. Example: Jack, vice-grip…

Rack & Pinion

The rack and pinion system transforms the rotational movement of the pinion into a translational movement of the rack or vice versa.

Rack and Pinion


Advantages: There is no slippage during the transformation of this movement. The strength of this system is relatively high.

Disadvantages: The gears that are used may require extensive lubrication as there is a lot of wear.
This mechanism requires precise adjustment because of the teeth between the wheel and the rack.
It is not a cyclic movement; it is a finite movement (you must stop when you reach the end of the rack). 

Use cases: Car steering, net tensioners (badminton net for example), adjustment mechanisms of some microscopes, camera tripods, etc.

Crank & Rod system

The crank and connecting rod system transforms rotary motion into reciprocating motion (straight back and forth) and vice versa.

Crank and Rod system


Advantages: This mechanism can operate at high speed.

Disadvantages: There is a lot of friction due to the many joints in this system. This requires a lot of lubrication.

Use cases: Petrol engines, diesel engines, pumps, medical respirators, steam locomotives, old sewing machines, spinning wheels, grinding wheels, etc.

Cam & Roller System

The cam and roller system (also known as the cam and push rod system or guided rod) transforms the rotational movement of the cam into a reciprocating movement of the push rod.

Diagram Cam and Roller System


Advantages: The cam can be configured to vary the movement of the rod from one translational motion to another.
There is no slippage, the speed ratio is constant.
This system allows a considerable reduction in speed.

Disadvantages: The rod must be guided in translation.
A return spring is usually required to allow the rod to rest continuously on the cam.
There is a risk of severe vibration if the cam rotates at high speed.

Use cases: Mechanical toys, mechanisms for controlling the opening and closing of valves in a car engine (camshafts and valves), sewing machines, etc.

Comparison of motion transformer types

Screw & Nut -Allows  important forces and pressures 
-Used for fine adjustments 
-Generate friction 
-Can lead to guiding problems 
Efficiency: ++ 
Speed: ++ 
Stability: +++ 
Rack & Pinion -No slippage  
-High strength 
-Required fine adjustment 
-Finite movement 
Speed: ++ 
Stability: ++ 
Crank & Rod system -Operation well on high speed -Poor efficiency (due to friction) Efficiency: + 
Speed: +++ 
Stability: +++ 
Cam and Roller System -Constant speed ratio 
-Can lower the system’s speed 
-Rod has to be guided 
-Risk of vibration at high speed 
Speed: +  
Stability: + 
Table of advantages and disadvantages of the different systems