Final Conclusions:

Following discussion and observation of the other presentations, the following points were brought forth for future consideration when conducting a similar project.

- Much of the research, analysis and development of our design provided a sound basis for our tender proposal.
- However, following our presentation of the proposal it was evident that certain elements had not been fully developed.

• Our costings did not take labour, production and profit margins into account, and as a  result were incomplete leading to a misleading quote for the price of our crane.
•  In retrospect the crane, although fulfilling the brief, could have been more ingenious in solution, unfortunatly the analysis of some of the more complex designs initially left us confused, and contained many mistakes, so the simplest option was seen as the most logical choice as it could be pursued to its full potential. 

-  On a positive note, the group did work well together, the group members worked to their strengths with romi and andy focussing on the basic design and stress analysis elements of the process, allowing the other group members to complete separate tasks such as further research to assist the analyses and solve problems encountered as we went along.
- The schedule was kept on top of with regular meetings, and individual taskings, ensuring that the project at no point fell behind its originally planned timescale.

A. Compton.
J. Collins.

Group Presentation:

CAD

Close up of the end of the crane, showing detail of position of pins, beam end caps and telescopic legs.



Crane with legs collapsed



Crane with legs extended



Short video showing an animation of the components of the crane being exploded.

Types of Bearing

When considering bearings, the main factor to consider is the type of load required for the bearing to withstand, the two main types are radial and thrust.


For use in the turning mechanism of the crane, a large thrust load and very small radial load will be applied to the bearing.

Plain Bearing


This is the most simple type of bearing, which simply consists of two surfaces that move past each other with no other mechanism. Often one or both of the surfaces is coated in a non-stick layer as well as being lubricated to further reduce the friction. This type of bearing has a very high load carrying capacity but also creates a lot of friction. They have a fairly high radial and relatively low thrust capacity.


Ball Bearing


Ball bearings have both a high radial and thrust capacity, and are found in a large range of applications where the load is small. Any load applied is focused onto a very small area, which makes it run smoothly and quietly, however this creates high internal pressures which may deform the balls should the bearing be overloaded.


Roller Bearing


Roller bearings are similar to ball bearings in the way they are made, having the key difference that they contain cylindrical rollers instead of balls. The rollers distribute the internal forces over a larger area, which reduces the internal pressure, making the components less likely to deform and vastly increasing the radial load capacity. Although the radial load performance is increased, this type of bearing has a very low thrust load capacity comparatively.


Magnetic Bearing


Magnetic bearings are ideal for high speed applications as they support the load using magnetic levitation which has zero friction and requires no maintenance. These bearings require a constant power supply as well as a sensor circuit to keep the inner and outer rings at a constant distance. This means that often a set of backup bearings is required in the event that a power loss to the device occurs. They have a relatively low radial load and extremely low thrust load capacity, and are most suited to continuous low load applications such as power generation or machine tooling.


Ball/Roller Thrust Bearing


This type of bearing is similar to ball and roller bearings in the way which they work, however the layout of the components allows a far greater thrust load capacity. This type of bearing is well suited to high thrust load applications, where radial load requirements are low. Rollers have the benefit of increased total load capacity, while ball bearings are smoother and run a lot more quietly as a result of decreased friction.

Original Design (from meeting 18/03/10)

Initial Design


After discussing each of our initial designs as a group, we came to the conclusion that the best type of crane to meet the specification would be a luffing crane with a counterbalance. A basic schematic of the layout was drawn in order to give a sense of the proportions and scale of the design.

With a 2.6 metre boom at 40 degrees to the horizontal, the total reach of the crane would be 2 metres about the centre of its rotational axis. This allows for an object to be lifted and moved a total of 4 metres from its initial point of pick up. Using a large base, and keeping the main body of the crane fairly low to the ground will lower its centre of gravity and increase stability.


Developed Initial Design #1


The initial design was then developed to include a cable spanning from the counterbalance to the tip of the boom, as well as a support up from the main body. The rotational axis of the crane was moved back slightly on the base to increase stability, thus reducing the required weight of the counterbalance.

It was also decided that a the crane could be rotated via a handle situated on the counterbalance, and also that a hand powered crank would be situated here to operate the winch.

21/03 - Design 3

Design 3 ( The British Bulldog )



This design is a mixture of design 1 and 2 . It is interesting as it is something totally different to what is out in the market. It consists of a boom with supersonic legs and has the load sliding down the boom . The reason why we called it the british bulldog is because the front 2 legs are higher than the back two and the overall design looks like the shape of a dog. This also has marketability.

Advantages

As the struts or legs give more balance to the boom there may not be such a need for a counterweight.

The crane has a sliding system which is quite simple as there is no need for bearings.

The legs can be adjusted causing the boom to change in angle which can reach loads which are higher up with greater ease .

It can be de-constructed within seconds. The legs can be detached and the boom can retract into 2 causing very little space to be used up within the 4 x 4 rover .

bending moment and stress calculations would not be too complex .

Disadvantages

As the load is sliding down the boom, it may hit the ground before the intended point. It is important that the load is kept close to the crane or enough clearence is givin at the bottom.

There is no rotation which can lead to a bit of restriction.

21/03 - Design 2

Design 2





This design has a different approach all together to design 1 and some may consider it to be more 'simple' . It consists of 4 main legs which will be adjustable with 2 rollers on the upper struts which will roll backwards and forwards in the x direction. There will be 2 winches, one to move the rollers in the x direction and one to move the pulley ( load ) in the y -direction. Andy is working on a sliding system for this design.

Advantages

The bending moments and stress analysis is simple to work out.

The legs are adjustable allowing them to reach places which are not each to get to .

There are no bearings involved which means there is less chance of failure within the crane .

No counterweights are needed for steadyness as the crane will be steady.

Disadvantages

Motion is limited. The load can only be transorted in a linear direction rather than at an angle as there are not bearings for rotation.

The cable can get caught with the winch.

As some legs would be shorter than others in certain situations, there can be a danger of tipping or the load sliding down at a faster speed.

21/03 - Design 1 (simplified from original)

Design 1

This is a simplified version of the original design. The design consists of a hand winch placed above the trunk and has a counterweight to allow steadyness within the crane.

The advantages and disadvantages of this design are stated below.

Advantages

Bearings will allow the crane to rotate , therefore there is greater accessibility for different angles.

The base is steady with four adjustable ( anglular adjustment ) legs.

The base does not take up much space and can access areas which are difficult.

Disadvantages

The bending moments and stress analysis will more complex .

The crane would suffer from the possibility of tipping over.

Bearings make the system more complex.

Types of Cranes Research

The different types of cranes available was researched to give a broad idea of the different designs currently in use.