Cross Belt Drive
With cross belt drives angle of wrap is always above 180°.
Because the belt crosses over, there is more wear and tear on the belt.
With cross belt drives pulleys turn in opposite directions.
This is the driving pulley. When you increase the power the belt turns faster, as the pulleys are turning faster.
Notice the belt and driven pulley aren't turning properly.
If the belt is too long, it may slip off, and doesn't transfer power well.
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 Crossed 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
Like an open belt drive, a cross belt drive also transfers power from the driving system to the driven system. But here, the power transmission capacity is higher.
One of the big differences is that the belt goes from the top of one pulley to the bottom of the other, crossing over itself. This means that a longer belt is needed to span the same distance between pulleys, and that pulleys turn in opposite directions to each other.
Because the belt crosses over, there are more angles of contact between the pulleys and the belt, and less chances of slipping. The disadvantage is that the belt wears away sooner than with an open belt drive, as there is more wear and tear.
Practice Questions
Test your new knowledge on cross belt drives by answering these questions.
1. Why do cross belt pulleys turn in opposite directions?
2. The angle of wrap on a cross belt drive is always:
3. Calculate belt length if the driving pulley has a diameter of 100mm, the driven pulley has a diameter of 75mm and the centre distance is 90mm.
Formula:
$L = \frac{\pi}{2}[D + d] + \frac{[D_E + d_E]^{2}}{4 \times C} + 2 \times C$