FCGear CycloidGear

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Revision as of 21:10, 27 December 2021 by Jonasb (talk | contribs) (Add some special cases)

FCGear CycloideGear

Menu location
FCGear → Create a Cycloide gear
Workbenches
FCGear
Default shortcut
None
Introduced in version
v0.16
See also
FCGear InvoluteGear

Description

Cycloidal gears are very sensitive to an inaccurate adjustment of the centre distance, which then leads to a change in the transmission ratio. For these reasons, cycloidal gears are hardly found in mechanical engineering but are only used in special cases such as in the watch industry, for roots type blowers or for the drive of gear racks.

From left to right: Spur gearing, helical gearing, double helical gearing

Usage

  1. Switch to the FCGear Workbench.
  2. Invoke the command several way:
  3. Change the gear parameter to the required conditions (see Properties → Data below).

Properties

Data

Base

  • DataPlacement: Placement is the location and orientation of an object in space.
  • DataLabel: User name of the object in the Tree view.

cycloid_parameter

  • Datainner_diameter: Default is 5,00. Diameter of the rolling circle of hypocycloid, normalized by the Datamodule (see also the information in Notes).
  • Dataouter_diameter: Default is 5,00. Diameter of the rolling circle of epicycloid, normalized by the Datamodule (see also the information in Notes).

gear_parameter

  • Databackslash: Default is 0,00. Backlash, also called lash or play, is the distance between the teeths at a gear pair.
  • Databeta: With the helix angle β a helical gear is created (positive value → rotation direction right, negative value → rotation direction left).
  • Dataclearance: Default is 0,25 (see also the information in Notes).
  • Datadouble_helix: True creates a double helix gear (see also the information in Notes)
  • Dataheight: Value of the gear width.
  • Datamodule: Module is the ratio of the reference diameter of the gear divided by the number of teeth (see also the information in Notes).
  • Datanumpoints: Default is 15, change of the involute profile. Changing the value can lead to unexpected results.
  • Datateeth: Number of teeth.

View

The parameter descriptions of the View tab will be found in Property editor, further below at Example of the properties of a PartDesign object.

Notes

  • Cycloidal gears must always be specially matched to each other and can generally not be exchanged at will: In a gear pair, the value of inner_diameter on one gear must equal the outer_diameter on the other, and vice versa. See also the information in Properties cycloid parameter view below.
  • clearance: At a gear pair, clearance is the distance between the tooth tip of the first gear and the tooth root of the second gear.
  • double_helix: To use the double helical gearing the helix angle β (beta) for the helical gearing must first be entered.
  • module: Using ISO (International Organization for Standardization) guidelines, Module size is designated as the unit representing gear tooth-sizes. Module (m): m = 1 (p = 3.1416), m = 2 (p = 6.2832), m = 4 (p = 12.566). If you multiply Module by Pi, you can obtain Pitch (p). Pitch is the distance between corresponding points on adjacent teeth.

Special Cases

Straight Line as Hypocycloid

To obtain a straight line, directly towards the center, as hypocycloid, use the following expression for the Datainner_diameter: teeth / 2.

Such a tooth form is often found in historical clockworks and thus called "clock toothing". A larger Dataclearance makes the effect even more visible.

Full Hypocycloid/Epicycloid as Tooth

To obtain a gear made of complete hypocycloid and epicycloid curves use the following expression for

  • Datainner_diameter: 0.5 + 1e-6
  • Dataouter_diameter: inner_diameter
  • Dataclearance: -1 + 1e-6
  • Datahead: -1 + 1e-6

Note: At the time of writing, the development version of the FCGear Workbench is required, as the current stable version does not offer Datahead! The additional explicit tolerance value (1e-6 above) is required to overcome coincidence issues.

Such "gears" allow the the number of teeth to be as low as two and are used as rotary vanes in pumps or compressors (cf. Roots-type Supercharger).

Infinite large Epicycloid

If the radius of the epicycloid's rolling circle becomes infinite large, it becomes a rolling straight line. Such a degenerated epicycloid is called involute. Gears with such a tooth form are handled by the involute gear command. It is by far the most common tooth form Today.

Limitations

Limitations are not known yet.

Useful formulas

For more information see Involute gear.

Properties cycloid parameter view