Final Design

The design has now been finalized for the crane, and drawn in CAD. Dimensions were adjusted in response to CAD optimization and stress analysis calculations, as well as real life considerations such as making material dimensions that are easy to source.

It is shown below:

Final Assembly

Lifting Block Carrier

Top Beam

End Upright

Quadpod

Feet

Beam to column joint in detail. (Will be welded to box section upright)

Assembly Pins

Top Beam Pins

Optimizing Crane Dimensions

The crane was initially modelled in Solidworks with estimated dimensions to create the basic design of the crane. Convenient numbers were used to make modelling quicker.
The individual parts were then analysed using SimulationXpress Analysis Wizard in Solidworks, by applying the maximum loads which the individual components will have to withstand, and fixtures where the parts will be joined together. The material which was applied was 7075-T6 aluminium from the pre loaded materials file. The optimize tool was then used by selecting dimensions which may be changed (within reasonable applied limits) and dimensions which must stay the same for functional reasons (eg length of top beam) to reduce the mass of the components. Maximum deflection limits were also inputted in order to ensure that no functionality was lost in the alteration of these dimensions. The wizard then gave optimal suggested dimensions and produced diagrams to show where maximum stress and deflection occurred. It also gave masses for each part.
Manual calculations will now be used in order to do stress analysis of the structure, and check for failure methods which may not have been accounted for in the simulations such as buckling.

The stress diagrams and deflection diagrams are shown below:

Deflection Diagram of Top Beam

Stress Diagram of Top Beam

Displacement diagram of Feet Poles

Stress diagram of Feet Poles

Displacement diagram of End Joint

Stress diagram of End Joint

Aluminium Type Decision

From research into materials, 7075 aluminium has been chosen as the type of aluminium which will be used for the crane. This is due to its high strength and corrosion resistance which means it does not require any form of coating. It is also one of the easiest aluminium alloys to weld, most commonly and effectively welded using resistance welding, which is a very quick form of welding. It has a greater springback capability than most forms of aluminium which is also useful in this application where it may suffer a large amount of abuse in the situations it will be required.

http://www.suppliersonline.com/propertypages/7075.asp

Bearing Decision

 

From the research which has been presented roller bearings have been chosen for use in the crane because of the load that they will experience in this application. This is because they will experience a  high radial load with a negligible thrust load, which is what this type of bearing is designed to cope with. They have also been chosen as they are available as a sealed cartridge unit which requires no maintenance in it's lifecycle. This makes them preferable to plain bearings because although they have a greater resistance to axial load, they require good lubrication to work and maintenance to keep them in working order.