• Large transmission ratio (single - stage i = 5~100, or even higher)
• Stable transmission with low noise
• Self - locking property (the worm can be self - locking under certain conditions to prevent the worm wheel from being driven in reverse)
• Low efficiency (usually 30%~90%, depending on lubrication and helix angle)

The Working Principle of Worm Gears

2.1 Basic Transmission Principle

2.2 Transmission Characteristics

• Motion relationship: The ratio of the rotational speed of the worm (n₁) to the rotational speed of the worm wheel (n₂) is the transmission ratio: i = n₁/n₂ = z₂/z₁, where z₁ is the number of worm heads (usually 1~4) and z₂ is the number of worm wheel teeth. For a single - head worm (z₁ = 1), the transmission ratio is the largest, but the efficiency is low; for a multi - head worm (z₁ = 2~4), the efficiency can be improved, but the reduction ratio is reduced.
• Direction of rotation of the worm:
  • Right - handed worm: Use the right - hand rule. Hold the worm with the right hand, and point the four fingers in the direction of the worm's rotation. Then the thumb points to the linear velocity direction of the worm wheel at the meshing point.
  • Left - handed worm: Use the left - hand rule. Hold the worm with the left hand, and point the four fingers in the direction of the worm's rotation. Then the thumb points to the linear velocity direction of the worm wheel at the meshing point.
• Self - locking property: When the helix angle (γ) of the worm is smaller than the equivalent friction angle (φ), the transmission has self - locking property, that is, the worm wheel cannot drive the worm in reverse. The self - locking property is often used in lifting mechanisms, lifting platforms and other occasions that need to prevent reverse rotation.
• Efficiency: The efficiency of worm gear transmission is low, mainly due to sliding friction loss: η = tan(γ + ϕ) / tanγ, where γ is the lead angle of the worm and φ is the friction angle.

The Design of Worm Gears

3.1 Main Parameters

• Module (m): A series of standardized modules (such as 1, 1.25, 1.5, 2, 2.5, 3...).
• Number of worm heads (z₁): Single - head worm (z₁ = 1) is used for large reduction ratio, and multi - head worm (z₁ = 2~4) is used for high - efficiency transmission.
• Number of worm wheel teeth (z₂): Usually z₂ = 30~80. Too few teeth are easy to cause undercutting, and too many teeth will lead to too large volume.
• Center distance (a): It affects the transmission size. The calculation formula is: a = m (z₂ + q)/2, where q is the worm diameter coefficient (q = d₁/m).
• Helix angle (γ): It affects the transmission efficiency, generally γ = 3°~25°.