Open Belt Drive
This is the driven pulley. It receives power from the driven pulley.
Friction is important for transmission of power, and preventing slippage.
The belt is made of a flexible material.
Both pulleys turn in the same direction.
Angle of contact between the belt and pulleys should be taken into consideration when designing an open belt drive.
This is the driving pulley. The motor or power source makes it turn.
Notice the driven pulley and belt aren't turning properly.
When working with open belt drives, you need to make sure you calculate the belt length accurately in order to have good tension and friction.
If the belt is too long, it may slip off, and doesn't transfer power well.
If the pulleys were moved closer together, you would have the same problem.
Test it out
Tap the diagram for more information and click on the buttons to change a component and see what happens!
 Increase Power Make Belt Longer Change Direction
Example calculations
In order to work with Open Belt Drives, mechanical engineers need to understand and work with a variety of calculations. Here are just a few:
Power Transmission (P):
$P = Te \times V$
Belt Velocity (V):
$V = \frac{\pi \times D_E \times N}{60}$
Belt Length (L):
$L = \frac{\pi}{2}[D + d] + \frac{[D_E - d_E]^{2}}{4 \times C} + 2 \times C$
 Diameter of the Driving Pulley D Effective Diameter of the Driving Pulley De Diameter of the Driven Pulley d Effective Diameter of the Driven Pulley de Centre distance C Revolutions per minute N
An open belt drive is one of the easiest and cheapest ways to transfer power within mechanical objects, tools and appliances.
This type of belt drive has two rotating pulleys connected to each other by a belt, all turning in the same direction. The driving pulley is connected to the power source, or motor, and transfers power to the driven pulley through the rotation of the belt.
Because of the friction between the belt and pulleys, a pulling action is created between the two pulleys. If there is more friction, there is better power transmission and less slippage. Other factors responsible for power transmission include velocity of belt, belt tension and the angle of contact between the pulleys.
Practice Questions
Test your new knowledge on open belt drives by answering these questions.
1. What happens if the belt is too long?
2. Which of the following statements is FALSE?
3. Calculate belt length if the driving pulley has a diameter of 300mm, the driven pulley has a diameter of 200mm and the centre distance is 500mm.
Formula:
$L = \frac{\pi}{2}[D + d] + \frac{[D_E - d_E]^{2}}{4 \times C} + 2 \times C$