How does a hand winch work?

A hand winch serves the purpose of moving loads both horizontally and vertically. This is accomplished by connecting the load to the hand winch using either a steel cable or a synthetic rope. The hand winch comprises various components including a crank, transmission, drum, cable, brake, and housing. In this article, we will explore into each of these components in detail.

The Crank:

Hand winches can be operated either manually or with the assistance of mechanisms like electro-hydraulic motors. When using a hand winch, the circular motion of the drum is achieved through the exertion of muscular force on a crank. Unlike electric winches that rely on motor power, manual operation has its limitations due to the finite strength of human muscles. Individuals vary in strength, with an average exertion of around 10 to 15 kg force for a few minutes without experiencing extreme fatigue. Moreover, a person can perform approximately 25 crank revolutions per minute without becoming overly exhausted. This sets the upper limit on the force that can be applied to the winch, leading to a maximum pendulum force of 15 kg in MIT Hoist’s hand winches. The average force exerted is typically around 12 kg at maximum load. With a WW7500 hand winch from MIT Hoist, it becomes possible to lift 7.5 Fiat Pandas using just 15 kg of muscular effort.

Transmission, Speed, and Force:

A disparity exists between the force exerted by a person and the desired lifting or pulling capacity of the hand winch. To bridge this gap, a transmission is introduced between the crank and the drum. While in some cases, a lever effect might suffice, a gear-based transmission becomes necessary in most instances. For instance, MIT Hoist’s gear winch TL150 directly links the crank to the drum without an intervening transmission.

Are the concepts clear thus far?

Now that we understand the moment achievable through muscular force applied to the pendulum, let’s proceed to explore the force exerted by the cable on the drum. In the accompanying diagram, the drum of the hand winch is represented by the blue circle.

Considering around 20 components within the winch, there’s some play that leads to force loss. Consequently, the TL150 can lift 150 kg while accounting for power loss (185 kg — power loss — 150 kg). Hence, a hand winch’s maximum lifting capacity achievable with 10 kg of muscle power and a 325 mm crank length stands at 150 kg. While the crank length could be extended, this trade-off renders the hand winch less practical. As a solution, MIT Hoist incorporates transmissions in hand winches that necessitate higher lifting capacities.

Speed — Without Gearing:

In winches without gearing, the rotation speed maintains a 1-to-1 ratio because the crank is directly linked to the drum, as observed in our gear winch TL150. This signifies that each crank revolution corresponds to one drum revolution. The speed aligns with the drum’s circumference, which measures 12 cm in the case of TL150. With an average pendulum rotation rate of 25 times per minute, the speed approximates 3 m/min.

In hand winches employing transmissions, the speed experiences a considerable reduction. This phenomenon is explained in more detail below.

The Transmission:

Various gear mechanisms can be employed, and MIT Hoist employs gear and worm gear transmissions in hand winches. Further information regarding the distinctions between these mechanisms can be found here.

For the current illustration, we are focusing on a gear transmission. By engaging gears of varying diameters, it becomes possible to achieve higher torque at lower rotation speeds, or vice versa. A smaller gear followed by a larger gear result in greater torque, while the opposite configuration yields higher speed.

Given the limited human force and the mandated maximum force set for hand winches, using a smaller gear to amplify torque while compromising speed is a deliberate choice. The outcome depends on wheel size, tooth count, and the number of gears involved.

The presence of a transmission reduces the winch’s speed, as transformations occur. Suppose a gear ratio of 1-to-10 is applied to the TL150. This implies that 10 crank revolutions are required for 1 drum revolution, resulting in a speed of 0.30 m/min (contrasting with the 3 m/min speed sans gearing). However, this also signifies that the force exerted by a 10 kg pendulum is amplified by a factor of 10. Consequently, an individual could lift a load of 1500 kg under such circumstances (note: this is a theoretical value that disregards friction and resultant force loss).

Consequently, the winch’s speed and the desired lifting capacity maintain an inversely proportional relationship. A hand winch cannot simultaneously achieve both high speed and high lifting capacity. If such a combination is required, an electric winch is the solution. Electric winches permit individuals to pull heavier loads using the same muscular power due to the reduced or absent gravitational force, a concept elaborated upon here.

The Drum:

The drum takes the form of a tubular or shaft-like structure with flanges at either end. The cable is secured to the drum using a clamp. Positioned within the winch’s frame (housing), the drum is connected to the large and small sprockets, which in turn are linked to the crank. By winding or unwinding the cable on the drum through circular motion, the load can be moved vertically or horizontally based on cable direction. Clockwise rotation of the crank results in load elevation, while counter clockwise rotation lowers the load.

Moreover, the drum ensures orderly cable storage. The amount of cable the drum can accommodate hinges on flange height, drum length and diameter, as well as cable diameter. These dimensions are adjustable to facilitate the utilization of the desired cable length.

The Rope:

Hand winches can incorporate either steel cables or synthetic ropes. The cable or rope is indispensable as it serves as the link between the load and the winch. Notably, a disparity exists between cable length and the distance the load must be moved. In the provided diagram, the blue section represents cable length, while the yellow depicts the required load movement. Only the segment necessary for load lifting is wound onto the drum. In extreme cases, this segment could be as short as 1 meter despite a cable length of 100 meters.

However, it’s crucial to note that the winch’s lifting or pulling force diminishes with an increased amount of cable wound onto the drum.

The Brake:

Among the critical components of the hand winch, the brake stands out. Hand winches handle hefty loads, and the brake’s function is to keep the load stationary when the crank is released. Lowering the load entails turning the crank counter clockwise, which involves activating the brake by pushing through it. MIT Hoist’s hand winches are equipped with load pressure brakes. These brakes are triggered by the load, implying that they are effective only when a load is present. Consequently, a minimum load of 20 kg must hang from the winch to ensure the brake’s functionality.

The Housing:

The housing refers to a metal structure enveloping all components. Besides structural integrity, the housing safeguards the components from weather conditions and human interaction. Constructed to endure the forces associated with lifting or pulling, the housing undergoes rigorous testing, including break tests. During these tests, winches are subjected to extreme conditions until failure occurs. The insights gleaned from these tests enable adjustments to the housing’s design. A safety factor of 4 is upheld for hand winches, implying that a hand winch rated for a 500 kg load will only fail under a load of 2000 kg.

Furthermore, various finishes are possible for hand winches, including multiple layers of paint, galvanization, or full stainless-steel construction. Regardless of the chosen finish, protection against elements like saltwater is essential to maintain the winch’s functionality.

Should you require further clarification, do not hesitate to ask.