Winch Crab

To calculate the efficiency of Winch Crab

i. Single Purchase Winch Crab

ii. Double Purchase Winch Crab

SINGLE PURCHASE CRAB WINCH

Introduction:

In a single purchase crab winch, a rope is fixed to the drum and is wound a few turns round it. The free end of the rope carries the load W. A large toothed wheel known as spur wheel is rigidly mounted on the load drum. Another small toothed wheel, called pinion, is geared with the spur wheel.

Formula Used:

Let, Tl = Number of teeth on the pinion

T2 = Number of teeth on the spur wheel

L = Length of the handle

d = Diameter of the drum

Consider one revolution of the handle. Then, distance moved by the effort = 2πL

Number of revolutions made by the pinion = 1 and number of revolutions made by the spur wheel = T1 / T2

Distance moved by the load = πd / (T1 / T2)

V.R = (Distance moved by P) / (Distance moved by W)

= 2πL / πd / (T1 / T2)

= (2L /d) / (T2 / T1)

M.A = W / P

η = M.A / V.R

Procedure:

1. Firstly stabilize the single purchase crab machine and wrap the cord around the load drum and the effort wheel.
2. Put some weight on the load drum. And add the some effort to the effort wheel via hanger.
3. Hit the machine with some material, thus you will see some kind of movement in the load drum as well as in effort wheel.
4. Write down the reading in the observation table
5. After this apply the above procedure, four to five times with gradually increasing the Load as well as Effort to the load drum and effort pulley respectively.
6. Write down the all reading in the given observation table.
7. Measure the radius of the load drum and the radius of the effort wheel.
8. Calculate the MA, VR and η of machine.

Observation table:

S.No.	Load (W) in gram.	Effort (P) in gram.

Precautions:

1. Lubricate the screw before starting the experiment.
2. Trapping should be done after adding the weight in the effort hanger.
3. Overlapping of string should not be there.

Source of error:

1. Frictions in the pulley.
2. Effort being pulled suddenly.

Result: The efficiency of the single purchase winch crab is………………………..

DOUBLE PURCHASE CRAB WINCH

Introduction:

In a double purchase crab winch the velocity ratio is obtained in two stages. In this lifting machine there are two spur wheels of teeth T2and T4 and two pinions of teeth Tl and T3.

The arrangement of spur wheels and pinions is such that the pinion with teeth T1gears with the spur wheel of teeth T2.

Similarly, the pinion with teeth T3 gears with spur wheel of teeth T4. The effort is applied at the handle.

Formula Used

Consider one revolution of the handle.

Then, distance moved by the effort = 2πL

No. of revolutions made by the pinion 1 = T1

No. of revolutions made by the spur wheel 2 = T2

No. of revolutions made by the spur wheel 3 = T1 / T2

No. of revolutions made by the spur wheel 4 = (T1 / T2).(T3 / T4)

Distance moved by the load = πd.(T1 / T2).(T3 / T4)

V.R = (Distance moved by the effort) / (Distance moved by the load)

= 2πL / [πd.(T1 / T2).(T3 / T4)]

= (2L / d).(T1 / T2).(T3 / T4)

M.A = W / P

η = M.A / V.R

Procedure:

1. Firstly stabilize the double purchase crab machine and wrap the cord around the load drum and the effort wheel.
2. Put some weight on the load drum. And add the some effort to the effort wheel via hanger.
3. Hit the machine with some material, thus you will see some kind of movement in the load drum as well as in effort wheel.
4. Write down the reading in the observation table
5. After this apply the above procedure, four to five times with gradually increasing the Load as well as Effort to the load drum and effort pulley respectively.
6. Write down the all reading in the given observation table.
7. Measure the radius of the load drum and the radius of the effort wheel.
8. Calculate the MA, VR and η of machine.

Observation table:

S.No.	Load (W) in gram.	Effort (P) in gram.

Precautions:

1. Lubricate the screw before starting the experiment.
2. Trapping should be done after adding the weight in the effort hanger.
3. Overlapping of string should not be there.

Source of error:

1. Frictions in the pulley.
2. Effort being pulled suddenly.

Result: The efficiency of the double purchase winch crab is………………………..