Gearboxes: Basic Design Versions

Spur Gearbox

is the most common gearbox type, also in JE.

Advantages

  • simple construction with low costs
  • short gearbox length, also for high ratios
  • Motor shaft is in same direction as gearbox shaft, but usually not coaxial (for comparison see planetary gearbox).

    Direction of rotation is being reversed by every gear stage. That means, a gearbox with an odd number of stages reverses the direction.

    Ratio per gear stage is in range of 3 … 8.

    Higher ratios can be implemented too, but diameter of the secondary gear wheel and thus dimension of the gearbox gets quite large.

    Torque load is lowest at motor pinion and highest at the final wheel. For this reason

    • size of teeth (gear module) is different.
    • material is different
 

Gearboxes


Example: Spur gearbox UGD with Stepper motor

  

Example: Spur gearbox UGF with DC motor

 Gearboxes    Gearboxes 

Worm Gearbox

Motor shaft is perpendicular to gearbox shaft.
The gearmotor has a short length in output shaft direction, which can be advantageous for applications with limited space in axial direction (e.g. window lifters in cars).

Gear ratio can get up to 90.

There is friction between worm and wheel, with effect on

  • wear and lifetime.
  • transmission efficiency

The higher the ratio the lower the efficiency (can be less than 50%).
Efficiency also depends on lubrication and surface finishing.

The worm wheel is made of softer material than the worm.
It consists of bronze or of plastics, whereas worm is made of steel usually.

The worm produces an axial force (thrust), which must be supported by motor bearings.

Worm gear has high backdriving resistance.
High ratio worm gears are static self blocking. However, possibly not against vibrations.

 


      

Planetary Gearboxes

The gearmotor has small diameter, same or similar to the motor diameter.

Length is rather long, particularly for higher total ratio.

The output shaft is concentric to the housing.

No reverse of direction of rotation, output shaft always rotates in same direction as motor shaft.

Planetary wheels (usually 3 or 4) are driven by a sun wheel and rotate inside a hollow wheel, which is part of the housing.

 

 

 

Gearboxes

The planet wheels rotate on shafts that are fixed to a planet carrier. This planet carrier rotates slowly alongside the teeth of the hollow wheel.

Output shaft or a next gear stage is connected to the rotating shafts.

Several stages can be cascaded, multiplying to the total gear ratio.

The motor pinion is the sun wheel of the first gear stage.

Ratio of a gear stage is of 3…6.
It can be calculated by ratio = (dSun + dHollow) / dSun (d = pitch circle diameter)

PG20 with stepper motor, d= 20mm

  

PG40 with DC motor, d=40mm