# Belt and Rope Drives Brakes

## Introduction

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**Power**is the rate at which work is done or energy is transferred in relation to time. In calculus terms, power is the derivative of work with respect to time.

An

**engine**or

**motor**is a machine designed to convert energy into useful mechanical motion.

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**Vee**cross section, often used in sets of three - side by side. A modern development seen on some cars, is a flat belt with a series of mini Vee's on the inner surface.

## Flat Pulley Drives

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**Flat**, many pulleys used with flat belts are actually slightly curved so that the diameter at the middle is slightly larger than that at the ends.

### At Low Speed

- The maximum torque that can be transmitted between the belt and the pulley occurs when limiting friction is developed around the arc of contact.
The forces acting on a short length of the belt which subtends an angle of at the centre of the pulley, are shown on the above diagram. This is the maximum possible ratio of tensions between the "tight" and "slack" sides of the belt and consequently for a drive between pulleys of unequal diameter, the smaller angle of lap should be used. It should be noted that in some applications such as Capstans and Windlasses, the rope is passed completely round the pulley, sometimes more than once.
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### Allowance For Centrifugal Force

**Centrifugal force**represents the effects of inertia that arise in connection with rotation and which are experienced as an outward force away from the center of rotation.

**centrifugal force**as if passes round the pulley.

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Hence, The Total Tensions on the two sides are then, where and are the tensions transmitting the power and are calculated from equation (3). Equation (3) can now be written as:

## Grooved Pulley Drives

Although rope can be used for such drives, the vast majority rely on V-belts. In many applications the pulley has more than one groove and there are obviously an appropriate number of belts.##### MISSING IMAGE!

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Where The analysis now becomes similar to a flat pulley where is the equivalent coefficient of friction.

### S.i.units

- Power transmitted in Kilo Watts Combining with equation (4) And using equation (6) For a limiting value of , it can be shown that the above equations for the power transmitted have a maximum value when,

i.e. It is usual to assume that the mean tension is constant at all speeds, and is therefore equal to the initial tension .

If is neglected it then follows from equation (4) that: And hence the power transmitted at a given speed is proportional to the initial tension.

**band brake**is a brake in which the frictional force is applied by increasing the tension in a flexible band to tighten it around the drum.

**Band Brakes**are similar to those of the preceding paragraphs, giving in this case the braking torque which can be applied to a rotating drum.

**Shoe**and

**Drum Brakes**by the automotive industry. The method of tackling problems associated with this type of brake can be seen in Example (15)

##### Example - Example 1

What will be the

**horse power**exerted by the capstan under these conditions when there are turns of rope and it is being wound off at 100 ft/min.?

, and From which: When , Using equation (7) the horse-power of the capstan is given by: To which must be added the power supplied manually which is: So the horse-power taken by the trucks

**horse**

**power**taken by the trucks