Stress Analysis of Foot Poles

Stress analysis was carried out for the foot poles, modelling the quadpod centre as a built in joint and the tube as a beam. The load was considered as acting upwards from the floor, as it would in a reaction force. The weight of the part itself was considered negligible.

Deflection was calculated first:

Which comes out at 0.5mm and will not affect the performance of the part.

Then max stress:

Which shows it will not fail.

Stress analysis of Top Beam

The top beam was analysed to find the maximum deflection and maximum stress, as shown below.

I = Second Moment of Area and y = distance between load and COM of beam.

Yield Stress is 503 MPa, so the beam will not permanently deform under load

In this case y represents deflection.

This small amount of deflection will not affect the operation of the crane.

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.

Assembly pins and retaining pins

In order to make the crane practical, it must be able to be constructed and adjusted quickly and easily, without the need for tools. To make this possible, the sections which it breaks into for transport will be assembled using pins which will fit into joints, and be prevented from moving in place by the use of retaining pins or 'R Clips'. The inspiration for this has been taken from the way in which a medium girder bridge (MGB), made by WFEL Ltd and in service with the british army, is assembled and held together. Pictures of these pins will be uploaded when we have obtained them.

The 'R' clips are shown below, and it is anticipated that they will be purchased from an external supplier because they are avaliable mass produced.

The pins which will be used in the crane have been modelled in CAD, and will be made from steel.

15mm diameter general connecting pin

20mm diameter top beam connecting pin (showing R clip hole)

CAD model

The initial cad model has now been made, and will be modified later to change the material thicknesses to the values decided through stress analysis. Simulation will then be used to check our calculations and show where the maximum stresses occur and their values. It will also be used to give us a volume and overall weight for the crane.

Assembled

Top Beam, as split for carrying

Crane end support broken down for carrying

Crane base as broken down for carrying

Lifting block carrier

Crane Feet

Connecting pins

This is the joint piece which will hold the I beam to the box section column. It will be welded to the upright box column, and the I beam will slide into the end of this piece, and be secured by 20mm connecting pins to keep the I beam in place. The stresses will be transferred by the coincident faces of the beam and the joint piece, putting minimal stress on the pins and acting as a 'built in' joint for the purposes of stress analysis.

Minutes of Group Meeting 6/12/11

The group met today to present and discuss the work which we had done over the past week, select a concept and to allocate tasks for the coming week. Attending were:

·         Dave Brown

·         Ross Catchpole

·         Rich Brennan

·         James Golding

·         James Flanagan

 The group agreed on a system by which to score the concepts which were drawn out, considering each category and weighting it as to how important the factor was in our design. Each idea was then given a score between -3 and 3 for each category, and the concept with the highest score will be developed to become our final design. To clarify, portability was defined as how easily the crane could be broken down and moved, and mobility was based on the range of positions the load could be deposited in. It was also agreed that the weak link and carrying handle concepts will be incorporated into the design.

	Weighting (multiplication factor)	Gantry Crane	Tripod with Adjustable Legs	Tripod with Rubble weighted Base	Spider Crane
Portability	4	2	0	-1	1
Mobility	3	0	1	-1	1
Cost	4	2	1	0	-1
Ease of Manufacture	3	2	0	1	-1
Ease of Use	2	1	0	-1	1
Total Score		24	7	-6	2
Position		1	2	4	3

The Gantry Crane concept was the clear winner; however it was felt that it was not perfect and 

improvements could be made. These mostly related to stability and adjustability and were agreed on. They have been incorporated into the design sketch which will also be uploaded to this blog.

James Flanagan presented the research which he had done into materials (which will also be uploaded) and it was decided overall that aluminium was the best choice to make the crane out of due to its corrosion resistance, ease of working and good strength to weight ratio relative to its price. Titanium and composites were both superior in their strength to weight ratio however their price, both as raw materials and the increased cost of manufacture related to working with them, made them a less than ideal choice for the design.

Ross Catchpole is to look into joint designs suitable for the chosen concept this week and discuss them with Dave Brown to draw into the design in time for the group meeting next week, due to the huge number of possibilities available when all concepts were considered in research this week.

Tasks to be done and presented and the next group meeting:

Ross Catchpole – Research harnesses and Load connections suitable for the crane

Dave Brown – Sketch Final Design (with joints in)
                        Start CAD of design

Rich Brennan – Start stress analysis of design and determine required second moment of area.

James Flanagan – Assist with stress analysis and CAD.
Find strength values for different types of aluminium and their limitations.
Research coatings.

James Golding – Research winch and pulley systems suitable for crane. Include electric winches and their power sources.

The next whole group meeting will be on 12/12/11. 

Research - Bearing Types and Applications

Research - Types of Crane

Slide showing different types of existing crane

Maximum Crane Specifications - Size and Weight

Maximum Crane specifications – Size and Weight

The brief we have been given states that the crane must:

·         Be able to be disassembled and carried manually over 100m of rough ground.

·         Be able to be carried by a standard Land Rover size 4x4.

From research, it has been found that the average man can be expected to carry 25kg at knuckle height, meaning that any single piece of the crane should not weigh more than 100kg to allow it to be carried by four men.

From http://www.healthyworkinglives.com/advice/work-equipment/manual-handling.aspx

Research into the capacity of a Landrover Defender 130, as recommended by Landrover for this sort of application, shows that the maximum load capacity is 1243kg, which when accounting for occupants (based on being 4 x 80kg workers) means that the maximum weight for the crane is 923kg.

The overall length of the vehicle is 5130mm which would be the maximum length for any part to be carried on the roof, assuming that the vehicle will be fitted with a full length roof rack. The dimensions of the load space of the vehicle are 1640 x 1060 x 1160mm, so will be the maximum size for any item to be carried in the load bed of the vehicle.

From http://www.carfolio.com/specifications/models/car/?car=27676 and http://www.landrover.com/gb/en/lr/defender/explore/double-cab-high-capacity-pick-up/

Concept Sheets

Minutes of Group Meeting 28/11/11

An initial group meeting was held to issue tasks to all of the group members, discuss some initial concepts and create the blog on which to post our work.

Those attending were:

·         Ross Catchpole

·         Richard Brennan

·         Dave Brown

·         James Golding

·         James Flanagan

It was decided that the following people will carry out the following tasks and present their work/findings to the group on 5/12/11 at the next group meeting, as well as posting it on the group blog.

James Golding - Submit Gant Chart onto Blog
                          Submit Group roles to Gareth
                          Research winch / lifting systems and their pro’s and con’s

James Flanagan – Research into material types. Justify choices of materials for different components of possible concepts.

Richard Brennan - Research current crane systems and consider what calculations will be required with different concepts.

Ross Catchpole - Costs of crane system case studies
                            Consider costs involved with tender
                               Research joint types for possible concepts

Dave Brown -      Sketch Concepts and consider pro’s and con’s of each
                           Research size and weight restrictions on crane

The decision was made during the meeting to move the project forward quickly in order to allow maximum time to analyse the design and solve any problems we are to be faced with.