Winching System Types

Block and tackle pulley system:

A block and tackle is a system of two or more pulleys with a rope or cable threaded between them, usually used to lift or pull heavy loads. The pulleys are assembled together to form blocks so that one is fixed and one moves with the load. The rope is threaded, or reeved, through the pulleys to provide mechanical advantage that amplifies that force applied to the rope.

Western Differential Pulley:

A differential pulley, sometimes called a "chain hoist," or sometimes colloquially called a "chain fall," is used to manually lift very heavy objects like car engines. It is operated by pulling upon the slack section of a continuous chain that wraps around pulleys. The relative sizes of two top pulleys determine the maximum weight that can be lifted by hand.

Electrical Winch:

A winch is a mechanical device that is used to pull in (wind up) or let out (wind out). Winches stand at the heart of machines as diverse as tow trucks, steam shovels and elevators. The winch drums have gear assemblies which are powered by electric drives. Some may include a solenoid brake and/or a mechanical brake or ratchet and pawl device that prevents it from unwinding unless the pawl is retracted.

Electric Chain Hoist:

An electric chain hoist will can lift heavy loads easily and efficiently. Some electric chain hoist models offer hook suspensions, fully enclosed non-ventilated systems that protect the motor from being contaminated by outside environmental elements, quick connect chains to prevent chains from slacking, and push button operation. 

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.

Decision matrix for material

 The Pugh decision matrix shows how the factors considered for material choice were weighted and scored. Aluminium is our chosen material.

Factor	Weighting Factor	Steel	Titanium	Auminum	Composites
Strength / Weight Ratio	3	-1	1	0	2
Youngs Modulus	2	1	2	0	-1
Density	2	-1	2	1	0
Cost	4	3	-2	2	-3
Durability	3	-2	2	1	0
	TOTAL	3	9	13	-8
	Position	3	2	1	4

Material Properties

Material	Yield Strength/	Ultimate Strength/	Density/
2800 Maraging Steel	2617	2693	8000
Steel AISI 4130	951	1110	7850
Aluminium Alloy 2014-T6	414	483	2800
Brass	200	550	5300
Carbon steel 1090	250	841	7580
Copper	70	220	8920
High Density Polyethylene	30	37	950
Steel AISI A11	5171	5205	7450
Stainless Steel AISI 302	520	860	8190
Steel API 5L X65	448	531	7800
Steel ASTM A514	690	760	7800
Steel ASTM A36	250	400	7800
Titanium 11	940	1040	4500
UHMWPE	3447	6894	970

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. 

Current crane products

GANTRY:

This crane works by winching the weight up and sliding it along the top boom. It would be broken down and moved to the problem area and reassembled. Early possible problems I would like to investigate include; when the top boom is over four metres long will it deflect under a weight of 1000kg, are the feet stable enough and would it be better to have more legs on each end.  When at an end, would the supports be strong enough and would it cause the other end to be lifted?

SPIDER:

The spider crane mechanically moves to the required position, it then winches the load up and lifts it, it then carries it to the required area. Initial areas to investigate with this is how much this would cost, this could be a massive weakness with this design. Mechanically my worries include; not being heavy enough on the base causing it to tip over when lifting things with the crane head, would this design be able to get over serious obsticles associated with rubble covered areas.

JIB        

                                                             

The jib crane uses a fixed body, with a swinging arm to move what it has lifted it up. If used in this situation it would have to be carried to the desired point and the body would have to be dug into a solid foundation. Main concerns which I will have to investigate include; the crane being to heavy, not being able to dig the base into the ground because of the rubble and whether or not it would be pulled over when dug into the ground by the 1000kg weight being lifted up.

Calculations required to ensure quality:

Stress:  σ/y= M/I= E/R

Buckling: P_critical = 4π2EI/L^2 

Bending deflection: -EI(d^2 v)/〖dz〗^2 

Shear force: dM/dx

Important to ensure that at every point do the maximum stress equation. This will prove whether or not the material chosen will be successful. It is important to me that these equations are all considered to ensure that the crane will avoid failure.