Gearbox Ratio Calculator

Use our Speed Calculator to find the overall gearbox ratio needed for 1 to 3 stage reductions.

This is a wide calculator so you will need to use the scroll bar at the bottom of the page.

Gearbox Calculator.xls

  Gearbox Ratio Calculator  
  Available Standard Sizes from the Technobots Range (Teeth)  
  Steel Sprockets   8 9 10 11 12 13 14 15 16 17   19 20   23   25   27   30   33 35   38 40           0
  Steel Gears           12     15 16   18   20 22   24 25 26   28 30 32     36   40   44   50 60 0
  Plastic MOD 0.5       10   12       16                       30             42   48   60 0
  Plastic MOD 1.0       10         15         20                           40           0
  Number of Stages   Start with one stage, then increase the number of stages as required  
  Steel Sprockets   Steel Gears   Plastic MOD 0.5   Plastic MOD 1.0   User Defined  
  Motor Drive              
  Stage 1 Driven              
  Overall Ratio :1 :1 :1 :1 :1   Calculated Ratio  
  How to use the Gearbox Calculator:  
  1. Use our Speed Calculator to find the overall gearbox ratio needed. You will also need access to our gear or sprocket table for bore sizes if using steel gears or sprockets.  
  2. Decide on whether you will be using gears or sprockets and which MOD or pitch respectively (to ensure bore sizes are adequate). The larger the MOD or pitch, as well as being able to handle more torque / power, larger sizes can accommodate larger motor axle sizes for small values of teeth.  
  3. Select the motor drive gear or sprocket first (noting that it must fit on the motor drive shaft) on the relevant column of the gear / sprocket type.  
  4. Select the largest gear / sprocket available for stage 1, if the calculated overall ratio is less than desired, select 2 in the Number of Stages box. If not, select different teeth sizes until the desired ratio is found (or close to it). Stages not selected will be ignored in the overall ratio calculation.  
  5. If 2 or more stages are required, the driven gear of the preceeding stage needs to be fixed on the same shaft as the drive gear of the next stage. This shaft is commonly called a lay shaft and should be supported on its own bearing mounts. When using 2 or more stages, unless you are using a stepped shaft with differing diameters, the driven and drive gears / sprockets need to be carefully selected to ensure they will both fit on the lay shaft.  
  6. The final driven gear is typically fitted to the wheel axle so once again, it should be selected with the axle diameter in mind.  
  7. Selecting suitable sizes of gears / sprockets is very much trial and error and is a balance between ratios and gear / sprocket bore sizes.  
  8. Use the user defined column if you wish to use teeth sizes outside of the stock range from Technobots  
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