Project Manager's Weekly (Summary Edition)

The Crane Project from start to finish has been an enjoyable, but somewhat turbulent experience. With the disappearance of a group member to contend with, it made the task that much more difficult. We managed to pull something together in the end - and might I say quite a good 'something'. We decided to delegate the work left by the missing member to evenly spread to workload between us, which paid dividends as it gave each member of the group a better insight into other areas of the project and helped us gain a better understanding of the overall task at hand. In order to analyse the project ive split things into 4 main groups :

1. The Maintainence of the Blog

This was mostly spearheaded by myself with weekly updates ongoing throughout the project. The general upkeed of the blog was well organised and although we did not disclose the goings-on of every meeting, the main objectives of each meeting we're posted onto the blog. Eventhough we do not have as many single post numbers as some other groups, we feel this is exemplary of the saying ' Quality Not Quantity' and that the posts that we have uploaded are very relevant and straight to the point with no need for hundreds of download images from google or waffled copy and pasted information everywhere.

2. The presentation

The group presentation went extremely well and I thought that our group set the bar at a high standard being one of the first groups to present its tender. We answered questions directly and gave good answers to what may have been viewed by onlookers as potential short-comings in the design. In hinsight I would have liked to organise maybe one more practise session of the whole presentation as the interchanges from person to person were not the smoothest, but never-the-less the presentation was a success. I think what helped was the fact that we had a very innovative and original design but it was also solid in its approach and technique, and therefore provided us with a strong base on which to present our case. I feel the price that we came in at was very competitive and the concept was reasonably strong. This means that at a 20% reduction at wholesale value, for 100 units the price was:

(1339.99 *0.8) *100 =

£107,120

This is very affordable to NGO's and is well below some of the other groups where even 10 units would have cost this amount.

3. The Group

The group tended to work well together and had quite regular interaction. We managed to distribute work well with no member feeling overwhelmed with his/her workload and I think everyone understood their position in the group and the project as a whole. From a personal standpoint I tried to give direction when possible but was also like an 'assistant' to everyone, helping out in every area from design to finance and stress analysis. I think the project was a success and I walk away having learned a great deal, and with very few negatives.

4. The Improvements

If I had the chance to do certain things again here is a list of what they would include:
- Improved communication between all members of the group. As often it seemed that other group members were constantly meeting and working on the project and others were not.

- Allow people to choose their own group. I feel in situations like these, allowing students to choose their own group would help them flourish as they would be more comfortable and know the limitations of their group members. Of course you could argue that the whole point of the exercise is to work with people from a range of backgrounds you may not have worked with before, and quite a valid point it is.

- More structure. I feel that sometimes it was unclear as to what exactly needed to be done due to the lack of information given to us throughout the task. I think a few more structured deadlines set by Dr thompson for things such as, finance calculations etc would have probably provided more direction in times of uncertainty, although we did managed to gather ourselves and draw the tender to an efficient close.

Labour Costs (2)

The crane cost was rounded to £1339.99 for sake of ease.

Labour Costs

This is just a review of how i deduced a value of the labour undertaken for this project. I admitt the figures maybe slightly speculative to say the least, but atleast it gives some sort of idea as to the thinking behind the project, and the willingness to explore every last detail of the tender.

Finished Product

An animation of the final product.

Estimated Costs

Predict Advantages.

. It should be cheaper as it will be used by countries people with small budgets after disaster.
. It would be moved easily by just a Land rover in its roof rack.
. We do not need the electrical or hydraulic power to use it as it will be used in a desaster environment.
. It can be manipulate easily by hand by 2 or 4 people.
. It will be used mostly over rough terrain.
. It will be strong as it is manufactured in metal (Carbon steel and Aluminium).
. It will load a minimum of 1000kg for about 4 m of distance.
. It should be easy to maintain or repair.

Choosing a winch

In order to ensure the correct winch selection and correct method of use, we have to take in account somes criterias:
faillure to select correct winch and incorrect operation can potentially reduce the life cycle of our winch and result in premature faillure.
Winches used under certain conditions i.e. Salvage, recovery and off road applications will require a winch high rated winch than that of less frequently used winch.
selection of winch capacity for loading needs to be careffuly considered. It should be powerful enough to pull our charge overcoming the resistance caused by obstacles such as moving gradients, mud, sand or stone.
When choosing a winch we should know the maximum effort that the winch can exert on a single line on the first layer of the winch drum.As the layers of cable build up on the winch drum, the overall cable speed increases, however the rated line pull decreases at the same rate.
I think by using snatch block to obtain a double line pull we can in effect almost double the pulling capacity of our winch, whilst approximately halving the overall recovery speed.

Final Objectives

The following objectives need to be completed for tender:

Stress analyst - Stress evaluation on final design to be passed to chief designer for modelling.

Chief designer - Cad of final model and individual assemblies to be uploaded and dimensions passed onto Financier for pricing

Financier & Materials Specialist - Finalise cost of specified lengths of material and amounts to be passed worked on in conjuction with Financier. Final pricing and passed on to PM for close of tender and final litigation.

Project Manager - Tie up any loose ends regarding the tender and to assist in all areas. Finalise Tender.

After tender - All group members must be present to construct presentation of the project to be shown on 28/04/2010

NB - Individual mini- reports need to be collated by 7 days time explaining how the tender went from your point of view, likes/dislikes, drawbacks, achievements and could-have-done- betters.

Final Assembly Drawing

With the final CAD design finished I was able to then produce a 3rd Angle Orthographic Assembly drawing showing the dimensions of the crane design. The drawing also includes a bill of materials showing what type of material will be used for each part and also showing the part on the isometric view (top right). This drawing will then enable our finance officer to be able to draw up figures in ragards to the cost of the crane materials.

Final Design Assembly

This is the final design assembly for the crane. The structure is standing on four legs which are flexible and move independantly of each other, offering a stable support especially on uneven terrain. the main boom which will take the load is supported by a cable running from the two supporting Steel I-beams on either side. The eye bolts used with this cable can take maximum 750KG loads each and therfore they are more than suitable for our use. This will help in distributing the load across the 3 beams. the 4 pulley system will be hooked onto the eye bolt which is bolted onto the undersurface of the main boom. The eye bolt can take loads of up to 1.5 tonnes therefore it is more than suited for our 1 tonne max. The pulley system is then connected by means of winch (see previous posts) which has a 10 to 1 ratio.

As these beams will be made from steel, each of the parts on the strucure weighs a comfortable weight for two people to be carrying over short distances. Also this crane will be easy to assembly as it incoperates simple bolts and also benefits from some of the parts coming pre-machined. The legs will be kept secure at the required height by means of pins being threaded through the hole features found on the leg.

Not only do the straight I-beams have support but also the main boom has been modified to include a support system through the square steel tube. With the circular base connected to the underside by means of ball bearing, the structure is able to rotate indipendantly of the underside base.

Leg Design

This is the leg design we will be going with for our crane. In designing, it was important to make sure that we kept in mind the fact that the crane will be used mostly on rough terrain. Therefore the support for the whole crane structure needed to be flexible but still maintain structural strength. The led to the chosen design as shown above.

Each of the legs can be moved independantly from each other and then kept at that position by means of a steel bolt put through the corresponding hole. If position needs to be changed this can be done easyliy by repeating process with corresponding hole position.

Having constracted the supporting legs a way of connecting base to legs had to be designed.

The above illustrations show the fixings that will be used to connect the base to the crane legs. This will be done by a standard bolt bolted through the lower base and the legs at eacg of the four intersections as shown. The Upper base will not have any direct connections with the legs as this will allow for the rotation of the plate through the ball bearings between the Upper and Lower bases.

Materials Update

Due to the disapperance of The Materials specialist he has been vacated from the group and the materials work is spread between the rest of us.

Project Manager's Weekly- Finish

Edition 4-

The finish of the fastenings and crane does matter also. I have researched on paint and galvanised finishes to even normal factory standard finish. From a strength and preload standpoint the ideal steel fastener would have a plain black finish. This finish would be unacceptable as it corrodes easily. The common solution is to apply a zinc or cadmium plating to prevent corrosion, and apply a conversion coating such as chromate to keep the finish looking nice. The fastener is usually polished and chrome plated.

Plating causes problems with high-alloy steels due to something called hydrogen embrittlement, if appropriate measures are not taken after plating to "bake out" the hydrogen. This is especially true of chrome plating which tends to lock in the hydrogen. Plating does not adversely effect the mild steel used for fasteners.

For an emergency crane this would be especially important as it will be used in many weather conditions where corrosive forces are bound to take effect. The torque-tension relationship is greatly affected by plating due to its effect on the friction coefficient. Cadmium plating reduces the friction by 25% and zinc plating increases the friction up to 40%. This requires a corresponding 25% reduction or 40% increase in required torque for the same tension. The fasteners used for the crane should therefore have this finish applied so that friction is reduced and to ensure the longevity of the parts.

As for the actual crane body, the type of finish would be less of a worry. The main base of the design would need to be plated with the same finish as the fastenings so that the level of frictions and longevity would be of equal terms. Places like the base of the legs, and mechanical winch needs to be especially looked at, as the winch would need a lubricant of some sort to ensure it maintained operation after several times use. Something along the lines of WD40 would be a good idea although with the right surface finish expressed above this would seldom be needed.

Because the emergency crane would be used in areas where there are higher disaster rates and specifically third-world countries where the climate tends to be extreme. The type of finish describe above offers protection in temperatures you are likely to find in these places.

I Beam Support

Having chosen the ideal type and dimensions of I-beam I then went on to design the beam support which would be bolted on to the base so as to stop buckling when the beam was loaded. For this support, another industry standard was used, this time in the form of a SQ steel tube with dimensions 2x2x0.25. This is easily machined and would then be machine-cut at 45 degrees from each sized so as to fit perfectly onto the base and the standing I beam. The support itself only weighted a very small 3.592 KG and therefore is more would be very ideal if the structure passes the stress anaylsis.

Having done this it was now possible to carry out a stress analysis test on SolidWorks so as test if our chosen beam and support could take the max load that it will be subjected to.

Having carried out the test with the I beam in both set-ups as shown above, it was eveident that the beam was more structurally sound if the load was applied across the flange. The beam was under a lot more stress with a load applied along its width and therefore the flange was the best solution. When both the load and support where applied from the flange the stress anaylsis showed that the structure was not under any major stress. as shown I modelled the structure as fixtured on two surfaces (bottom of beam and support) which is where the structure would be bolted to the base. A load of 5070N (10140N halved between two beams) was applied at a point where the cable would pass through and the result shown was the van Mises stresses remaing in a comfortable zone.

The above screenashot is one showing the displacement that this load would have on the said beam. This was also a good results as the beam only showed displacement of maximum 9 tenths of a millimetre. As shown in read this displacement would occur at the point where the load was applied. This anaylsis showed that we could carry on with the beam size and support because they we able to take the load well.

Graph of materials

Material Choices

We chose to use the Aluminium Alloy 7075-O because with zinc as the primary alloying element, It is strong, with strength comparable to many steels. It has good fatigue strength also. Its relatively high cost is why most of the design is not made of this material.

Many groups looked at using 7075 but we chose 7075-O in particular because it is un-heat treated has maximum tensile strength of no more than 276 MPa, and maximum yield strength of 145 MPa. This is more than enough for our crane. The material has elongation of 10% and therefore stretches before ultimate failure.

We decided to go with a mild carbon steel for pretty much the rest of the design but quite a lightweight carbon steel because of its cost benefits and strength. We did undergo stress analysis using aluminium but it was consistently failing and so we decided to go with the stronger, cheaper alternative. The graph above illustrates how much stronger steel is than other materials we considered.

Type Of Beams To be Used

Having established that we will use S type steel I beams for our two support beams and the the main boom, I was able to look up on the international I-beam standards so as to select one with the paremeters that we needed. As this is a mobile crane weight of individual beams/components is very important as we want to maintain weights that two people can comfortably carry to and fro the site. Considering the dimensions for our crane base the s5x10 beam standard was the ideal choice and coming in at a mere 13KG per metre, it is quite light. if this passes the stress analysis of being able to take load of upwards 500KG then we will go aheard with this choice. I was able to create this beam to exact industry standards thanks to the 'structural steel' tool on Solidworks and from here an accurate stress anaylsis can be carried out.

I beam examples

A few examples of the boom type beams I was referring to.

The Big BOOM

The boom design is critical to the success of the crane and so I have evaluated the cost and materials available to us for this part of the crane.

Wooden- This type of beam is structurally strong in tension and compression but does have weaknesses when it comes to shear forces. Generally it would not be sufficient as the wood would have to be made of probably oak and be very heavy to cope with the lifting of a tonne of material.

The cheapest price I was able to find was £30 per cubic foot less of VAT which means it would be very cheap but because of transport issues and also deterioratory issues it wouldn't be first option. I decided to go for manufacturer prices because trying to evaluate an estimate from raw wood market prices is frivolous.

Metallic - This is more of a realistic option as there are a wide range of materials available which are more expensive than wood but provide the strength requirements that wood, would not (excuse the pun). Generally a low carbon steel would be most ideal but the lower the carbon content the higher the prices generally goes because of the extraction process involved from the kind folks over at the blast furnace. I wasn't able to find exact prices on a fairly low carbon steel of our sort of sizing range but generally speaking (having to refer to market prices) it would be around £40-£60 per cubic foot minus of finishing previously mentioned in the post 'Finishing'. This would tend to add £8-£10 per. The extra price of this material and finish would pay countless dividends in extenuating the life of the crane itself.

For the less important parts of the crane, costs of the boom can be offset to these areas and materials costing less can be employed here. As long as strategic strength is not lost where it is needed, of course. Also, wood would have to be a custom made beam and the metallic beam could be of a standard size already mass produced driving down cost further.

Toppling

The main problem with a hoist crane is the need for large counter weights. There will be an allocated zone for the counter weight that can be picked up from the disaster area. A counter weight is only needed when lifting over 650kg (711kg actual); in a case where over 1000kg (up to 1200kg) is lifted a counter weight of 600kg is needed. Iron counter weights will be supplied but debris can be used. The table below shows the counter weight required when lifting larger masses:

Project Manager's Weekly - Fastenings

Edition 3-

Metal fasteners are normally of two kinds. Those producing a permanent bond and those requiring either a releasable or a sliding bond. Because of the nature of the emergency crane the permanent bond type is obviously not what we are looking for. Screws, nuts and bolts, rivets, retaining rings and clamps are examples from what might be suitable. Non-permanent fasteners include quick-release couplers and clamps intended for removal at a specified time and pins, which allow relative movement of fastened parts.

Metal fasteners must be strong to bear significant loads. In many cases they can be manufactured by powder metallurgical or casting techniques. Iron is a constituent of many types of metal fasteners, although titanium increasingly is coming into use in applications where strength must be balanced against light weight. Steel is probably the best material for the pins for its balance of weight and strength and its relatively low cost for amount of material. After research I have found that probably the most cost effective and safe way of fastening is using the Clevis pin type fastening. This does not require the use of hex nuts and does not run the risk of losing 'grip' or thread like a screw or bolt may. I also researched U bolts and hex bolts.

Clevis pin - A clevis pin is also used in the design of different moving vehicles, including cars and trucks. Since the pins provide a means of creating a secure connection between components while still allowing for a small range of movement, they are much less likely to be affected by any types of vibrations from the engine or while on the road. This is especially useful for the crane as no doubt there is bound to be movement of the crane required and small vibrations or shudders should not mean that the fastenings used should fail. Absorption of lateral stress can be achieved using the pin, which in turn can help minimize the potential for wear and tear on the components connected with the use of the device.

Greater design flexibility, and compared to bolted joints and riveted joints, there is less need for machined holes, and additional machined components. and compared to bolted joints and riveted joints, there is less need for machined holes, and additional machined components.

There are fewer stress concentrations associated with these joints and thus increases fatigue resistance for more durable products versus other mechanical fasteners.

Wheel vs Plugs update

We actually decided to go with plugged legs just for costing issues and ease of design and stability factors.

Pin 3

Pin 2

Picture 2

Pin Cad

Stepped into my CAD shoes for the day, and drew up a few designs of the type of pin that will go into the leg to hold them. My cad is not the best and leaves a lot left to imagine.. Its made from carbon steel for strength because the weight of this bin doesn't matter on the grand scale.

Enjoy.

Analysing Stress on Main Beam

For the team to decide on a material we need to know which criteria need to be met. The design involves a large beam that will take the majority of the load and will be supported by cables and smaller beams. In some cases the calculations can be made and a suitable material can be found, or the type of beam can be used with a single material chosen first. As the material specialist has not been available to aid this decision the team have worked together and decided on plain carbon steel for the build. Plain carbon steel is a very versatile and cost effective material. We can reduce the size of the beams without compromising strength and hence reduce weight.

To carry out the initial stress analysis I have used SolidWorks, however, the loads have been exaggerated to account for material defects, modelling errors and over working. The results show that the main beam will take the load with a stress of 220.59GPa where the yield stress of steel is about 280GPa. The final design will have support beams and cables so the maximum experienced stress will be noticeably smaller.

Final testing will be carried out by Onwell, the design engineer.

After testing various beam types and size from the SolidWorks ‘Toolbox’, this beam (dimensions below, found on http://www.franklinsteelplc.co.uk/steel/unibeam.htm) is the best suited for the task.

Wheels examples

A few examples:

Wheels VS Plugs

After pondering over this for some time, I've decided to blog the discussion currently taking place within me. Should the crane have wheels or should it just have legs that literally plug themselves into the ground? Both situations have their pros and cons:

Wheels - I was thinking of something along the lines of trolley wheels, specifically designed to go over the bumpiest of 'city pavement' terrain. Made of cheap to buy rubber and very accessible. The obvious problem is their stability. Because the wheels actually roll and rotate 360 degrees it is virtually impossible for them to stay still. The only way this would be possible is with a brake type system employed on some shopping trolleys to stop them from being taken out of the centre. Where the force of a human foot would press the brake down and stop the wheel from turning. And lift the brake back off again when the material wanted to be moved. The thing is, shopping carts aren't made to carry upto a tonne in weight so they would have to be slightly modified, utilising stronger material and the joining of the leg base to the wheel would have to be immensly strong.

Plugged legs- This is the more straight forward option as the legs of the crane simply sit on the floor and plug slightly into the ground if possible or just sit on concrete. This removes the cost of attaching wheels but obviously limits manoeuvrability. Also the stability of the crane may be affecfted in certain situations. For example if the legs were not able to plug into the ground and there was a strong cross wind, because the crane would have no real leverage into the surface.. once holding a tonne of mass into a blowing crosswind could make the crane a real hazard.

After noting down both options I feel as if the wheels are a worthwhile investment. Because of the added ease of movement and stability once a brake is applied, It effectively kills two birds with one tonne of stone