Group Presentation:

New Crossbar Design

The new crossbar has a triangular face with a base of 125mm and a height of 90mm

nb. it should be 5mm thick

New Leg Design

During the stress analysis we didn't realise how thin the walls were in the crane legs at just 1mm so a new design was made. The walls are now 10mm thick so during the new stress analysis a larger second moment of area was calculated.

I = 1.0479e-6 m^4
P(critical) = 55,862N
mass = 7.53kg

Crossbar Calculations

The crossbar was designed to be hollow instead of solid so the same equations were used in the stress analysis but a different second moment of area was used.

Crossbar ( initial )

The crossbar which was initially designed was similar to andy's , however, andy's design was picked as we developed it to suite the needs of the rest of the crane. Even so, the stress analysis which was initially done for the crossbar is given below.

Calulations for the crossbars

The original idea which was posted up by romi was constructive , however, a sample of calculations for the crossbar have been given below . It was important to make sure the stresses were correct on the crossbar as it has a lot of loading. Below are a sample of calculations.

Calculations for the sidebars

The sidebars took quite some time to do as they were an important part of the structure , hence everything had to be moulded around the dimensions for the sidebars. Below are examples of the sidebars being calculated with a second image showing a more realistic result when doing

the calculations .

The bar was concluded as being 300 mm in depth and 50 mm wide.

initial calculations for the legs

When working out the level at which the legs will buckle at in accordance with the amount of stress induced, a force of 250 g is applied from top . Basic stress analysis was required for the legs. Eulers equations were used to determine buckling. A sample of calculations can be seen below.

Calulations for End bars

The end bars are the two bars at the back of the crane whilst the side sidebars are the bars running along the side of the beam Calculations needed to be made for the end bars so that they could fit inside the top part of the legs, and appropriate dimensions were calculated obtaining a suitable weight . The end bars were circular rather than rectangular like the rest of the bars. The calculations are shown below.



The calculations were fairly straight forward and simple , however, the only hardship was to get the right dimensions in accordance to the other bars in the crane.

Tender Proposal: Leg & endbar calculations

Leg

• Aluminium
• E = 70 E9 N/m ^2
• Stress = 40,000,000 N/m^2
• Stress (crane ) = P= ((Pie ^2) *E*I) / 4L ^2 = 8659 N ( Max load = 2453N)
• b = 15 mm
• d= 52 mm
• I = 1.4489e-7m^4
• 5 mm thick
• Volume = 9.69 e-4 m ^3 ( minus the cut away = 5.94e-4 m^3)
• Density = 2690 kg / m^3
• Mass = 2.61 kg

Endbar

• Aluminium
• E = 70 e 9 N / m^2
• stress = 40,000,000 N/ m^2
• Stress ( crane) = 6,688,013 N/m^2
• diameter = 50 mm
• I = 2.6704 e-7 m^4
• 10 mm thick
• Density = 2690 kg / m ^ 3
• Mass = 20 .282 kg
• Volume = 7.5398 e-3 m ^3

Tender Proposal - crossbar calculations

Crossbar

• mild steel
• E = 200x10^9 N/m^2
• σ yield = 220 MN/m^2
• σ = 71,038,835 N/m^2
• b = 40 mm
• d = 120 mm
• I = 2.4325x10^-6 m^4
• 5mm thick
• volume = 0.0018750 m^3
• density = 7825 kg/m^3
• mass = 14.672 kg

Sidebar

• aluminium
• E = 70x10^9 N/m^2
• σ yield = 40 MN/m^2
• σ = 10,006,703 N/m^2
• b = 50 mm
• d = 500 mm
• I = 1.2867x10^-4 m^4
• 5 mm thick
• volume 0.0054 m^3
• density = 2690 kg/m^3
• mass = 14.526 kg

Runner for Crossbar

This is a website for the runner that the crossbar will use to move in the horizontal direction.

http://www.hepcomotion.com/en/psd-screw-driven-linear-actuator-pg-14-get-24

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.

Beam Dimensions

This is a website for the standard dimensions of I-beams, rectangular hollow section beams flanges etc.

http://www.roymech.co.uk/Useful_Tables/Sections/steel_section_index.htm#tables

Hand Winches

Gear Ratio

One person can't lift 1000kg using a hand winch without a gear ratio of at least 14:1 so that to the person using the winch it would feel like lifting 71.4kg. This is because the amount that an average man man weighs is 60-70kg and the maximum most people can lift is their own body weight.

Maximum Capacity

The winch needed for this design would have to have a maximum capacity of 1000kg or 2200lbs.

Weight

The winch needs to be a suitable weight so that it can be transported manually from the 4x4 vehicle to the disaster area.

Brakes

As the maximum load to be lifted will be 1000kg the winch needs to have a brake so that the person using the winch has time to rest and when the load is at the required height the winch can be locked.

These are the sites of suitable hand winches:

http://www.winchsystems.co.uk/sf-2200-hand-winch.php
http://www.winchsystems.co.uk/sf-5000-hand-winch.php