Power Transmission Glossary
===========================

.. glossary::
   :sorted:

   Pitch Diameter (PD)
      An imaginary circle around a component used for various calculations. For gears, it is the imaginary circle that mates with any other gear's pitch diameter when the gears are properly spaced. For chain and belt, it is the circle which is traced by the middle of the belt or chain as the pulley or sprocket rotates. For gears, the pitch diameter will be smaller then the :term:`Outside Diameter (OD)`, but with chain and belts, the pitch diameter will be larger. :math:`PD = (tooth * pitch)/\pi`

   Pitch
      Pitch refers to the distance between the center of one tooth of a gear, sprocket, or pulley to another. In chains it refers to the distance from one pin to another, and in belts it refers to the distance betewen one groove to another.

   Outside Diameter (OD)
      The diameter of the imaginary circle traced by the outermost face of the teeth on a gear, sprocket, or pulley. This will be larger then the :term:`Pitch Diameter (PD)` for a gear, but smaller then the :term:`Pitch Diameter (PD)` for a pulley or sprocket.

   Clearance Diameter
      The clearance diameter is the diameter of the imaginary circle that contains the entire pulley, sprocket, or gear. For pulleys and sprockets, this includes the belt or chain on the component. Clearance diameter is used to check for interferences with other mechanisms. It is usually larger then :term:`Pitch Diameter (PD)` and :term:`Outside Diameter (OD)`

   C2C
      Center to center (C2C) refers to the distance between the centers of a pair of :term:`sprockets <Sprocket>`, pulleys or :term:`gears <Gear>`. This will affect :term:`chain <Chain>`/:term:`belt <Timing Belt>` tension and gear meshing, so calculating this correctly is essential.

   Idler
      An idler :term:`gear <Gear>`, :term:`sprocket <Sprocket>`, or pulley is one that is purposely not used for driving anything else on the :term:`shaft <Shaft>`. The purpose of this idler is, in the case of gears, to transfer power to another direction.

      For :term:`chain <Chain>` and :term:`belt <Timing Belt>`, idlers are more common, and are usually adjustable to maintain tension.

   Sprocket
      A sprocket is a mechanical part that transfers power through its cogs, which fit into chain. It is similar to a :term:`gear <Gear>`, except that instead of meshing with another gear, the sprocket meshes with chain. See :term:`Chain`

      .. figure:: images/chain/rev-sprocket-20-tooth.png
         :alt: A REV Robotics Delrin 20 Tooth #25 sprocket
         :width: 200

         Delrin  20 Tooth #25 sprocket

   HTD Belt
      HTD belt is a type of synchronous timing belt commonly used on drivetrains. It is available in different widths to accommodate different sized pulleys. The most common is HTD3 (3mm :term:`Pitch`) and HTD5 (5mm :term:`Pitch`) belts, as these are compatible with goBILDA :term:`COTS` pulleys. See :term:`Timing Belt`

   GT2 Belt
      GT2 belt is a type of synchronous timing belt commonly used on drivetrains and other mechanisms. Its available in different widths and pitches, although the most common is GT2 3mm (3mm :term:`Pitch`), compatible with REV Robotics :term:`COTS` Pulleys. See :term:`Timing Belt`