Transport Specifics

Exactly how BIG is a Range Rover boot??
Thats the design specification we have to adhere to so I thought i'd explore it. As you can see from the pictures. It's quite alot of space, but not when you think that what we have to build has to be able to lift a tonne, as well as fit in there...

Specific Dimension you ask.. 994 Liters maximum capacity with a full car of people. 2099 with the back seats folded.

That equates to a max length of around 3M with a family of rescuers. Food for thought.

MATERIALS

The materials used to manufacture the crane must be strong and resist at the friction and the pressure due to the load.
We have to look for the density, the tensile strength, the yield strength, and the young's modulus of differente materials to help choose which are suitable.
After research we found that Aluminium and Steel are most common materials that can be used in our purpose because of their advantages.
Aluminium: is the most abundant metal to be found in the nature. It is relatively low weigth. Good resistance to corrosion, Good thermal and electrical conductivity. It can be melted, cast, formaed and machined easely.
Young's modulus, 69 GPa
Yield strength, 55 MPa
Tensile strength, 125 MPa
Density, 2.7 Kg/m^3.
Steel:
Low carbon steel( Mild steel) is the most commonly used, readly welded construction material, and has the following typical mechanical properties:
Density, 7.85 Kg/m^3
Yield strength, 250 MPa
Young's modulus, beteen 190 and 210 GPa
Tensile strength, 280 MPa

Lifting a One Tonne Load

The crane will need to be able to lift a 1000kg load and move it 4m, with no guaranteed source of electricity the only source of power will be manual. For a small group of people, the one tonne load can be easily managed using a pulley system as mentioned under ‘Pulley Design’. Even with a 6 to 1 pulley system a two person team will need to each move the equivalent of 83.3kg by 6m to raise the load just 1m off the ground, that’s almost the same as carrying a person up a single flight of stairs. Using a winch, the turning force generated can be multiplied to reduce the effort a 5th of the original work needed.

The winches available on the market will vary from the design shown so the force that will need to be applied will also vary. The calculations are based in an ideal situation and in reality they will be much greater. Factors such as friction, temperature, humidity, strength of the individuals and the elasticity of the cable will need to be accounted during the second design phase.

Hand Winches

Just a quick look at the types of mechanical winch we will try and incorporate into the crane design.

There are several differing designs for hand winches, but they must all follow this specification:

- normally steel material

- plated with zinc or enamel to prevent corrosion and keep winch smooth

-the gear ration needs to be large enough to enable easy winding of the system and to reduce the amount of turns required to lift an object.

The steel cable graph

Material forces & Implications

Having generated a design for the crane, the issue of material is now at its most relevant as seen above.

I will soon upload the material properties of common materials such as aluminium and steel.

Also the type of rope or line material used is of importance as this ideal needs to be able to withstand over 1000kg whilst in tension. I have done some research on the steel cable design and properties utlising : www.s3i.co.uk.

With varying levels of diameter of cable:

Elastic Stretch = (W x L) / (E x A)

W = Applied Load ( kN )
L = Cable length ( mm )
E = Strand Modulus ( kN/mm2)
A = Area of Cable = (D2 x pi) / 4 (where D= Dia of cable mm)

Typical values for E are:
1x19 = 107.5 kN / mm 2
7x7 = 57.3 kN / mm 2
7x19 = 47.5 kN / mm 2

1x19 Stainless Steel Wire Rope Stronger, with less stretch but also less flexibility than many types of cable. Often used in standing rigging, architectural structural rigging and balustrading. Does not allow for kinks or bends. 7x7 Stainless Steel Wire Rope Less strong but more flexible than 1x19. Used in rigging, balustrade infill and catenary systems. The graph shows typical breaking loads for our hardware compared against conventional 1x19 and Dyform 316 stainless steel cables. It should be noted that stainless steel wire rope and strand will start to distort at around 50% of its breaking load. It is therefore advisable not to load cables to more than 50% of their breaking loads. This is just for steel cables but there are alot more options available for wiring such as aluminium or rope itself eventhough in order to hold the weight, quite a thick rope would have to be used and this may not be suitable for our design as it does need to be able to be transported via range rover! The graph is in the next post.

Pulley Design

Having decided to go with good old man-power for the mechanical design of the crane, the options available to us all involve the use of a pulley design. The aim of the pulley system is to try to reduce the amount of work required to lift a particular load. The aim is to increase the Mechanical Advantage to a point where the load of a tonne that we need to be able to lift, is reduced to a fraction of this so that it can be operated via human power: