Belts

Question 1

How do Belts transmit power?

Answer 1

By relying on friction to transfer power from the source pulley to the output pulley.

Question 2

What are the advantages of belt drives?

Answer 2

Able to transmit power over large distances
Provide high angular velocities
Inexpensive
Quiet

Question 3

What are the disadvantages of belt drives?

Answer 3

Susceptible to slip
Limited tension and so limited power transmission
Back tension increases bearing loads.

Question 4

What are the advantages of a flat belt?

Answer 4

Simple construction
Low cost
High flexibility
High tolerance to overload
Good resistance in an abrasive environment

Question 5

What are the disadvantages of flat belts?

Answer 5

Noisy
Sliding is possible
Low efficiency at low speeds
Tensioning is required

Question 6

What is a V belt?

Answer 6

It has a wedge that will wedge into the pulley and create a higher normal and frictional forces. The v will run along the length of the belt, can have notches that run across the belt.

Question 7

What are the advantages and disadvantages of V belts?

Answer 7

They have high torque transmitting capabilities.

But they have low flexibility

Question 8

What is a synchronous belt?

Answer 8

Also known as a timing belt, this has zero slip which ensures that it maintains perfect timing. It has teeth that go into grooves onto the pulleys that maintain this timing. Having this teeth makes it noisy though.

Question 9

What does the style of belt for an application depend on?

Answer 9

The overall speed ratio
Belt speed
Distance between pulleys
Requirement for constant speed ratios

Question 10

Is the velocity of the belt at each pulley the same?

Answer 10

Yes because the belt wont stretch or shorten.

V1 = V2

Question 11

What are the equations for the speed ratio of the belt?

Answer 11

Assuming that there is 0 slip:

W1 / W2 = D2 / D1

Question 12

What are the torque ratios

Answer 12

T1 / T2 = D1 / D2

Question 13

What tensions do we apply to the belt?

Answer 13

Both sides have different tension, we will have one tight side and one slack side. Generally have the tight side on the top. So the torque on a single gear can be found as: T1 = (P1-P2) x D1/2.

Question 14

What are the power equations for Belt drives?

Answer 14

The Power at each pulley must be equal:
Power1 = Power2
T1 x W1 = T2 x W2

Question 15

When we construct a belt, what do we look for?

Answer 15

Maximise the tensile strength
Maximise the friction coefficient
Minimise belt wear

Question 16

Why do we need to include a belt tensioner system?

Answer 16

Because over time, the belt will stretch due to being under constant tension.