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A Beginners Guide to Gearbox Design. You can find the computed Gear Ratios here: Gearbox Ratios

Notation Conventions:

  • A shaft location will be denoted by its row and column, for example 8C is the top row, third from left
  • When discussing gear ratios a “/” denotes one gear that meshes with and turns another. For example 5/3
  • When discussing gear ratios a “*” denotes two gears that share a single shaft. For example 3*5
  • An example would be 5/3*6/5/3. This means a 5 tooth gear turning a 3 tooth gear. On the same shaft as that 3 tooth on a different layer is a 6 tooth gear, which turns a 5 tooth gear, which then turns a 3 tooth gear

The Rules and Concepts

  • Every gearbox must start at “1A” (the lower left hand corner as you face the gearbox)
  • Every gearbox must have at least one, but no more than three outputs in the top row (Row 8)
  • You may use up to, and no more than, thirty (30) gears in your gearbox
  • You may use up to, and no more than, fifteen (15) shafts in your gearbox. A shaft is a row and column intersection that has one or more gears (e.g. B2)
  • There are three layers in a gearbox. Gears can only mesh when they are on the same layer. The input and output layers don’t matter.
  • There are eight rows numbered 1 to 8
  • There are eight columns numbered A to H
  • Gears come in 1,3,4,5,6, and 7 tooth.
    • 1 tooth is a “Spacer”, and costs no materials. However, it does count for your gear total
    • 3 and 4 are considered “Small Gears”, and will cost 2 debens of metal to cast.
    • 5 and 6 are considered “Medium Gears”, and will cost 15 debens of metal.
    • 7 is considered a “Large Gear”, and will cost 100 debens of metal
File:GearSize.png
All the Gears by Size
  • The sum of adjacent gears in the horizontal or vertical axis must be 6. Therefore only 3/3 is valid when moving one space in either the horizontal or vertical axis
  • The sum of adjacent gears in the diagonal axis must be 8. So 4 and 4, 5 and 3, and 7 and 1 are valid configurations.
  • The sum of the gears in the horizontal or vertical axis that are separated by one space (so not adjacent) must be 11. Therefore valid configurations are 6 and 5, 7 and 4
  • The sum of the gears in a “Knight’s move”, which is to say two space away and one off the axis, must be 12. Therefore 6 and 6 or 7 and 5 are valid pairs.
  • Whenever a gear turns another gear, it is a ratio based on the fraction created from the number of teeth.
    • If a larger fear turns a smaller gear, the output value increases. For example, if a 5 tooth turns a 3 tooth, the output will be increased by 67% because five thirds (5/3) is equal to 1.67.
    • If a smaller gear turns a large gear, the output value decreases. For example, if a 3 tooth turns a 5 tooth, then the output will be 60% of the input because three fifths (3/5) is equal to 0.6.

Tricks and Tips

  • If you have a multiple output gearbox, see if one or more the ranges overlap. For example, if the requirement is A90-A120 C95-C125 G80-G110, a single ratio of 100 will satisfy all three requirements. This will greatly simply your design process
  • If you have a multiple output gearbox, and not all of the ranges overlap, or none of them do, look for ratio chains that use the same sets of gears. For example, you have a gearbox that is A150-A180 and F310-F340. Clearly, neither of those ranges overlap. But if we lookup at the ratios in those ranges we see that 167 uses a 5/3 gear set and 333 uses a 5/3*6/5/3 gear set. Therefore, we can use a 5/3 set for both ratios, thus saving us gears and shafts.
  • Since the gears are simple math, you can increase ratios and then decrease them. To give an example, say we had the reserve of the above gearbox requirements, A310-A340 and F150-F180. You could use the chain of 5/3*6/5/3 to get to A333, and then from the last 3 tooth gear put a set of 3/5/6, giving a total of 5/3*6/5/3/5/6. This actually a horrible example, and is used only to illustrate the point.
  • Try to avoid using 7 tooth gears. Not only are they much more expensive than other types, they are harder to work around. If you must use one, try to put it on either layer 2 or 3 where it is more likely to be out of the way.