How to Calculate Gearbox Losses

Written by andrea helaine
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How to Calculate Gearbox Losses
Each type of cog has its own efficiency ratio. (cog image by Andrzej Solnica from

A gearbox uses cogs to reduce or increase the speed of a motor. Depending on the cogs used, the gearbox will lose some energy in the process. Most gearbox manufacturers give the efficiency ratio of the box, but it is also possible to calculate the losses if you do not have access to the gearbox's specifications.

Skill level:

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Things you need

  • Tools necessary to open the gearbox

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  1. 1

    Open the gearbox, or open the plans of the internals if you have them.

  2. 2

    Determine and write down the type of cogs used in the gear box and their efficiency in percentage.

  3. 3

    Write down the gear type and number of contact points. For example, number two gears have one contact, while number four gears have three contact points.

  4. 4

    Multiply the efficiency by itself for each contact. For example, four-spur gears have three contact points and have an efficiency of 90 per cent, so .90 * .90 * .90 = .73, or 73 per cent. The gearbox has an efficiency of 73 per cent, or an energy loss of 27 per cent.

Tips and warnings

  • The percentages used here are ideal percentages that can be decreased by worn out gears, poor construction or poor lubrication.
  • If you need to open the gearbox, make sure to document the disassembly to be able to put it back together correctly.

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