Engineering Drawings

These are the engineering drawings of all the different parts of the crane. Dimensions are included.

Nuts and Bolts Material

The nuts, blots, pins and fixings used in this crane would not be made of aluminium as this would cause many problems. Aluminium is too expensive to make small components out of, which means that if any were lost or misplaced (which would be very likely in the chaotic environment of a disaster zone) it would be very expensive to replace them. Also there will be more shear stresses and torsion stresses on these fixings so it is better to air on the side of caution and make them of a stronger metal. Finally the weight of the fixings wouldn't matter as they are only small components, so heavier metals such as steel can be considered.

The majority of readily avalible fixings are made of stainless steel. If the crane was a permanent structure it would be important to state that stainless steel will corrode faster than aluminium alloy and will therefore need replacing frequently. However as the crane is to be put up then taken down for a job at a time, a quick inspection of the fixings before they are used to check for corrosion and spares to replace fixings that are is all that is needed.

Crane Design

A near complete CAD model of the Crane design. It is an extension of the CAD model already seen. New Features consist of.

• Flexible A frame design, allowing for extra strength but can also fold.
• A hinged beam , allows for easy construction. Although it may weaken the design however Hinged beams have been used on commercial Gantry cranes that can lift up to two tonnes , so it will be strong enough.
• A stablising leg , this indirect leg will only come into play if the crane is at the point of toppling, say if the crane had been put in a precarious position and the main beam was not straight where it may fall over, As an extra safety.

Chosen Material

The chosen material for the crane is Aluminium alloy 7075. It is commonly used in bikes and aerospace as a light metal with high strength and moderate toughness.

It is also important to note: The yield stress has been used to compare the calculated values not the ultimate tensile stress as by the time the stresses had built up so much to reach the ultimate tensile stress the material will have completely plasticly deformed and the crane would be unusable. The yield stress is the point at which the material begins to plasticly and permanently deform which is very undesirable.

For untreated 7075 aluminium:

Specific Density: 2810 Kg/cb.m
Youngs Modulus: 72 Gpa
Yield Stress: 145 x10^6 pa
USD/LB: 0.97

Compared to steel:

Specific Density: 7850 Kg/cb.m
Youngs Modulus: 210Gpa
Yield Stress: 300x10^6 pa
USD/LB: 0.55

It isn't as strong with a Youngs modulus of 75Gpa whereas steel has 200Gpa. However it is much lighter with a specific gravity of 2810 compared with 7850. Its yield strength is 145 x10^6 pa which is below steel but should be more than enough for our crane.

Specific Density: 2640 Kg/cb.m
Youngs Modulus: 68 Gpa
Yield Stress: 60 x10^6 pa
USD/LB: 1.04

Compared with pure aluminium:
It is stronger than pure aluminium, as aluminium's value is 68Gpa but it is the yield stress that is greatly different as pure aluminium is only 60 x10^6 pa. It is slightly heavier by around 200kg/cu.m but this shouldn't make that much difference for the small amounts we'll be using.


To conclude Aluminium alloy 7075 is well suited for our crane as it is light (lighter than steel), it is strong so it should easily be able to withstand the loads and it is reasonably priced. As with all metals prices do fluctuate with the market but at current values it is 0.97 USD/LB.

Crane Design

A final design iteration was drawn up on Solidowrks to give some idea how the final product might look.
Below are two images of the final design:

Once this was complete there was a team meeting. From that meeting it was decided that a 3rd stabilising leg needs to be added. The reason for this was that it’s being used on unlevel ground. The final design does have completely adjustable legs so that the I beam can remain horizontal. However, it was thought that a 3rd leg would be for the just in case situation.

The Final CAD is now being updated to include the 3rd leg.

Gantry crane Design

As the Gantry crane had been adopted here were some ideas before building a Gantry on CAD

. We looked through and decided an A frame would be suitable. This would stop the crane from buckling as well as provide extra support to the joins, relieving them of some of there bending moment. We also adopted a compact approach. The legs could be taken off , the A frame would be collapsible, the whole thing would be adjustable , and a split I beam allowing for easy storage and transportation. A stabilisation leg could be added , in a just in case

scenario if it was to topple at its end , E.G. if the crane was set up so the beam was not straight, it would act like a safety feature. Many of the features seen on this gantry crane are very common with industrial gantry cranes, although un-innovative it does however mean they are effective.

Hinge Design

To make the horizontal beam easier to set up and easier to transport it has been decided to integrate a hinge into the design. The hinge will be located on the underside of the beam and act as a connecting plate as well as a hinge. The hinge will be permanently connected to the beams and only on the top of the I-beam will a connecting plate be used.

Below are preliminary drawings as to how it will work and utilised into the final design. A good material choice for the hinge will be steel as it will be underneath the beam and hence have the load exerted directly on it. Steel is a cheap and convenient way of creating this part to the assembly as it will carry the loads exerted on it with ease as well as being easy to manufacture on a large scale.

Lifting Equipment

To carry the load a hoist must be connected to the beam. A manually controlled hoist is the best idea as this will allow the load to be lifted without the use of electric motors. By using a mechanical winch this excludes the chance of electrical failure and hence the lifting apparatus will not work. Before the hoist can be connected a trolley should be attached to the I-Beam.

Trolley:

The trolley selected should be easy to connect and disconnect from the I-beam as this will decrease the time take to set up the lifting apparatus and also be safer for a single person to connect. With the ability to connect and disconnect at any point the trolley can then freely roll to each end.



The selected trolley has a universal connection underneath allowing any hoist to be connected. The Hoist has a lifting capacity of 1Tonne and a flange width from 65mm to 145mm. This is good for the specified design as the bottom width of the I-beam is 105mm and it is within the briefs lifting requirements. The model number is the HMT10 and the method of connection is shown in the engineering drawing below.



As you can see the trolley is solely connected to the lower section of the I-beam and once the load is lifted it is manually pushed from one end of the gantry to the other.
The cost of this trolley is £60

Hoist:

The method of lifting the load will be done by a ratchet lever hoist. The reason for this method of lifting apparatus is its lifting capabilities and its reliability. The chain lever hoist can be operated by one hand and once lifted it will hold at its location. Rope must be securely fastened around the load and then connected to the hook.



The height of lift from this hoist is 1.5m and its lifting capacity is 1000kg. The hoist itself is constructed from aluminium and only weighs 6.6kg which is within the area of portability.

The device is fully enclosed which promotes safety. The tensile lifting action is countered by an automatically acting load pressure brake. This is the mechanical device which prevents the load from falling once lifted off the ground.
The hooks which are connected to the trolley and load are forged steel which has the highest strength of any method of steel manufacture. This is because these points will be under extreme stresses and forging allows the stresses to be exerted linearly across its internal structure.

The name of the hoist is the Yale ALUMINIUM rachet lever hoist. The model which has a 1000kg lifting capability is priced at £215

Shear Force & Bending Moment Diagrams

Depending on the location of the winch loads and stresses will vary. I have illustrated the shear force and bending moments on the beam.

The beam length will have to extend past the 4 metre distance required to move the load and so 4.2 metres has been selected.

The problem which may arise during practical use of the gantry is at the midpoint. A 4metre beam will not be able to be transported manually and therefore a break will be present in the finished crane. At this point the loads will be exerted on the method of joining and could create loads unsustainable by the joining method.

The weight of the beam has been selected from existing beams. The beams researched are used in portable gantry cranes and are light weight with the sole purpose of manual assembly.

With constant movement of loads across the vertical beam fatigue could be an issue. Fatigue will be cause by continually changing loads on the crane.

It can be seen from the Diagrams shown that higher shear forces and bending moments will be present towards the location of the load. If this continually changes the beam could fail under fatigue stress and so the lifetime of the crane will be dependant on the ability to withstand this factor.

Gantry Crane- Team Meeting

It has been decided that the most practical design would be a gantry crane. This has alleviated the problems of legs, centre of mass problems and counterweights and as such can be made relatively lightly, however the focus for the group is to look at a collapsible main beam which is to be of 4m in length. Different ways of joining the beam and on starting the CAD design.

My design for the collapsible beam is a simple one but it is one that allows for the pulley system of the crane to still movefreely along the beam (on the inside).These can even be made lightweight through use of aluminium and can be stored easier in the back of pick ups.

My proposal for a Gantry crane (pictured left) it has the collapsible beam so it can be taken apart and split into 2x2m sections, an I beam as this gives the best performance for picking up a load directly beneath it. It has fully adjustable legs which can be used on uneven ground, The A shape can be made collapsible also to aid in transportation. Important to note the top of the A shape has a metal plates which strengthen the join at these points. It will also incorporate a manual hoist which will slide along the interior of the I beam. The height of the crane vertically will be no more than 2 m , this allows for long beams to be brought out and moved over small amounts of rubble efficiently. The structure to be able to save weight , will be of high strength aluminium which may be more expensive but its advantages in terms of weight and transportation by hand far outweigh the higher cost. There may be a problem due to the I beam that the crane may have a tendency to tip over sideways , however having enough angle on the legs should remedy this.

Second Moment of area

I did some calculations to work out which shape of beam would be most useful for the gantry design. I looked at three main shapes: circular tubing, square tubing and I beams. I used the same rough dimensions for each shape.

The results were:

Circular tubing with diameter 300mm and thickness 20mm

10.83x10^6 mm^4

This value would be the same for all directions

Square tubing with diameter 300mm and thickness 20mm

24.56x10^6 mm^4

The square tubing is double times stronger than the circular tubing, however this is only at right angles to the faces.

I beam with 300mm height, 20mm thickness and 260mm high post with 30mm thickness.

201x10^6 mm^4

This is 8 times the strength of the square tubing but this is only in the vertical direction.