Joining Methods

There are a number of different joining methods which could be used in our design. This is a very important issue as the joints within a structure holding heavy weights will be put under great pressure. we must make sure that the method chosen is the most suiable.

Nuts and bolts

this is an acceptable form of connecting 2 or more parts together. they are very adaptable and can be purchased from a number of different distributors at a very cost effective price. each joint will be put under different amount of pressure. this means that the nuts and bolts used at each joint will vary when determining the properties. such as the type of metal used, the thickness/diameter and even the length. another factor to consider is weathering. as the crane is designed to be used outdoors, it will be exposed to the elements. this means that there is a posibilty that the nuts and bolt could corrode. This is why the material selection is very important.

Transportation Limitations

As th design brief states that the crane must be able to be disassembled and put either into the back of a land rover sized 4x4 or on top of the vehicle, this means we only have a limited amount of space available.



The maximum space available is:
Width - 1146mm
depth - 1950mm
height - 1027mm

This means that all of the components must be within these limits once bundled together

Materials Research 2

MATERIALS

Our crane must be strong and durable. In order for us to succeed in choosing the best material, we have to look into many different properties of different materials.

We have chosen to decide out of steel and aluminium for the material of our crane. Below you can see some advantages of each material

Aluminium:

Aluminium has the following properties:

Density, 2.7 Kg/m^3.
Yield strength, 55 MPa
Tensile strength, 125 MPa
Young's modulus, 69 GPa

This would be an ideal material to use for the crane. It is low in weight, does not corrode easily and can be melted easily

Steel:

Steel has the following properties:

Yield strength, 250 MPa
Density, 7.85 Kg/m^3
Young's modulus, beteen 190 and 210 GPa
Tensile strength, 280 MPa

Steel would also be an ideal property, however it is very costly compared to aluminium.

Chosen Lifting Mechanism

After considering all the different type of lifting mechansims which would be suitable, we have decided to go with a puller/winch as shown below.

Clarke CHP1250 Heavy Duty Power Puller

we have chosen this product for a number of reasons. it is readily available from a number of different distributors, so replacing the product in the event of a failure will not be too much hassle. This product contains a limited number of components which means there is less to go wrong. It only costs £21.14 inc. VAT. Also It can cope with weights up to 1250kg, which is more than enough.

this product can be found at http://www.machinemart.co.uk/shop/product/details/chp1250-heavy-duty-power-puller

Dimentions for cross section

From previous calculations, i worked out that the available cross sectional area to ensure that each 3m section of the beam only weighed 30kg was 1282.05mm2.

With this in hand, the dimentions for the cross section can be found.Where a is the outer square side length, b is the inner square side length and c is the wall thickness.

Now, i would think that a 80mm - 120mm size for a would be substantial enough to take a load of 1000kg therefore using a as 120mm,

a2 - b2 = 1282.05mm2
(120^2) - b2 = 1282.05
b2 = 13117.95mm2
b = 114.534mm

therefore the wall thickness c would equal (120 - 114.534)/2 = 2.733mm

I do not think that this wall thickness would be large enough so take a as 80mm

a2 - b2 = 1282.05mm2
(80^2) - b2 = 1282.05mm2
b2 = 5117.95mm2
b = 71.54mm

therefore the wall thickness c would equal (80 - 71.54)/2 = 4.23mm

this wall thickness is more substantial and might give us a strong structure for our purpose.

How Does a Winch Work?

The mechanics of a winch

Winches are normally found on the front bumper of off road vehicles. They are also found on trailers that are used to help load boats. It is a motor-driven unit that contains a spool of wire or rope. Some electrical winches use a 12-volt motor to power them, while others use hydraulic fluid from the power steering unit. The latter is mostly found on military applications. Depending on the direction chosen, when the winch is turning, it rotates the spool, which either sends the winch cable in or out.

Recovery

The primary reason to have a winch on a vehicle is to aid in recovering it should it become stuck such as in mud or sand. The winch line is spooled out of the winch, and connected to another vehicle or something solid via a large clevis hook on the end of the cable. The winch is then put into gear using a switch on the body; once power is applied, the cable is brought back toward the vehicle and spooled onto the winch, effectively getting the vehicle unstuck.

Safety

When purchasing a winch, you should first know the weight of the appliance or structure that the winch will go on. This is because different winches are rated for specific weight limits. For example, putting a winch that has a maximum pull rating of 2 tonnes on a vehicle that weighs 2 tonnes wouldn’t be a good idea. If the vehicle gets stranded then the winch would not be able to help it get out. In the case of a vehicle that weighs 2 tonnes, a winch with a maximum pulling rating of 3 tonnes would be adequate.

When using the winch, it is important to always wear gloves. Grabbing the steel winch cable can fray and cut the hand. It is a good idea to place a heavy jacket or other soft weight in the middle of the winch line when pulling, because if the cable snaps, it can release a lot of energy at once and snap violently. A weight will transfer that energy to the ground and make it safer for everyone around it.

If using an electric winch, it is probably a good idea to pull for only 30 seconds at a time, so the motor does not get hot and burn up. A hydraulic winch will not experience this and have a 100 percent pull cycle. With an electric model, pull for 30 seconds and wait for a minute, then repeat until the vehicle is free.

http://www.abtechsafety.com/UCLWIN%20Lightweight%20Man%20Riding%20Winch.html

http://www.westernsafety.com/dbi-uclsafety/dbi-uclpg3.html

http://www.stu-offroad.com/recovery/winchline/winchline-2.jpg

Pros and Cons of manual & electric winches

The pros and cons are the following:

Advantages for manual winches:
The pros for using these hand winches is that they are strong, well built, and versatile. There is no installation required and almost nothing can go wrong throughout its lifetime. Also it has little and in some cases no maintenance required. Another advantage of a manual winch is that it is much cheaper than an electric winch

Disadvantages for manual winches:
From research the only cons that I can find these hand pulling winches is that they are heavy and that manual labour is required in order for the load to be lifted.

Advantages of electrical powered winches:
An electric winch is permanently mounted and ready to go all the time.An electric winch requires a lot less effort to use and is a lot quicker too. Having an electrical winch is probably best for this projects situation. Manual labour would take a lot longer to lift up 1 tonne at a time.

Disadvantages of electrical powered winches:
The disadvantage of having an electrical winch is that it can get very expensive. First of all buying one that suits your needs. The heavier the load, the more expensive the winch would get. And maintaining the winch can be costly too. Unlike a manual winch, parts for an electrical winch are expensive.