A right-angle gearbox is applied to drive a rotary motion at right angles, but which right-angle gearbox is the best for a specific application? What are the individual characteristics and what are the pitfalls? What is the efficiency of right-angle gears, and which is best suited in servo technology?
The reasons to use a right-angle gear unit are:
- Space saving: as a motor with gearbox combination becomes too long for the space available.
- If you want a gearbox with hollow shaft, to feed a shaft or cables through.
- In the event of shaft mounted gearbox there are other benefits.
Here is a brief summary of the different types of existing right-angle gears, with their specific characteristics:
Bevel Gears
These bevel gears are used to transmit rotational motion at right angles, whereby the two axes of the gears intersect. This type of gear is therefore often built symmetrically. The movement consists of rolling without sliding of two bevels, hence the name. Gears with spur or spiral teeth are used.
Hypoid Gears
Hypoid gears are special bevel gears wherein the axes of the gears are offset. This allows a larger spiral angle on the pinion which means the pinion can be larger and transmit higher torques and give higher gear ratio options. They are used, for example, in cars and fork-lift trucks to achieve the rotation of the drive shaft on the rear axle and thus to drive the wheels. With this principle, the toothing is always spiral (helical).
Worm and Worm Wheel Gears
A worm and worm wheel are considered as gears. If the “worm” (a spiral gear) is driven, the worm wheel will rotate slowly (for example, one tooth per revolution of the worm), but with a high torque.
Worm boxes can give a much larger ratio reduction with high torque increase. With normal worm gears the higher ratios give the inability to back drive the gearbox giving a self-locking property. The traditional worm gearbox is very inefficient though and requires higher power to overcome the friction within the gear movement. Common applications for worm boxes are conveyors & escalators where high ratios and high friction is not a concern or in elevation a benefit as the drive will self-lock and restrict the load driving the gear backwards.
In addition to these more ‘standard’ right-angle transmissions there are countless more “exotic” right-angle gears which we will not attempt to describe in this summary.
Efficiencies and Precision can vary between manufacturers, but typical characteristics are below.
Technical Characteristics and Differences By Type:
Of course, manufacturers of servo gearboxes do not have the “antique” cage gear in their programmes now. The worm gear has the advantage that it can easily be made low backlash at a high ratio and is inexpensive, however, the disadvantage is the poor efficiency: approximately 70%.
Because of this poor efficiency the servomotor has to be heavier to compensate for this loss. Also the servo amplifier or frequency converter often has to be forced cooled. Eventually, the drive combination can be much more expensive. And in S5 operation, the wear of the teeth is often large.
The intended benefit of self-locking ability is void in the eyes of CE: Since a gear unit must not be seen as self-locking in the event this could cause personal injury or other danger.
Apex Dynamics is a major supplier of servo gearboxes, and we have in our product range for right-angle variations the choice of bevel gearboxes and hypoid gearboxes, whether or not fitted with a front or end planetary stage. As with our other servo gearboxes they have low backlash and low inertia for dynamic applications.
