How does a worm drive work? | statically and dynamically self-locking (self-braking) explained

tec-science
tec-science
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Published 2023-12-07
Worms are a special type of gear in which a tooth wraps around a shaft like the thread of a screw. The gear that meshes with the worm is called a worm gear or worm wheel, and the entire gearbox is called a worm drive.

The number of starts of a worm corresponds to the number of teeth of a conventional gearwheel and thus determines the transmission ratio.

The advantages of worm drives are their high gear ratio, load capacity, low noise, and ability to transmit high power.

The material selection for worms and worm wheels takes into account the lowest possible friction and low-wear sliding of the flanks. Depending on their shape, worms can be divided into cylindrical worms and globoid worms. Globoid worms can transmit higher power, but are more complex and therefore more expensive to manufacture.

Worm drives are often self-locking, which means that torque is only transmitted in one direction. A distinction is made between statically self-locking and dynamic self-locking (self-braking). Self-locking gearboxes are generally less efficient.

In certain situations, when moving large masses, it may be necessary for the worm to overrun a little after the motor is stopped to reduce high loads on the flanks. This can be achieved by using special lubricants or special overrunning devices.

00:00 What is a worm drive?
01:11 How is the transmission ratio determined?
02:21 Advantages of worm drives
03:40 Material selection for worm and worm wheel
04:25 Cylindrical worms (cylindrical worm drive)
04:51 Globoid worms (enveloping worms drives)
05:48 Self-locking
06:46 Statically and dynamically self-locking (self-braking)
07:59 Efficiency vs. self-locking
08:38 Over travel
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