House Of Shu
Pillar Jib Crane 2018
Project Information
The pillar jib crane was executed as the main project of the first half of the main education period. The project had a duration of 17 days, between the 15th of January and the 6th of February and was not completed on time. The object requirements set in the project description were:
- Lifting Load: 500kg
- Lifting Height: 2m
- Minimum Swing Angle: 180°
- Swing Radius: 3m
- Articulated Arm
- Bolt-based Floor Attachment
These requirements have been met in time and, in some areas, exceeded. In relation to the first requirement, the project required a stress analysis report, which was set up and the results were added to the report. (Within the report, the crane mass is displayed as 2335,33 kg. This value includes the mass of the concrete socket.)
The documentation requirements set in the project descriptions were:
- Gant Chart
- Log
- Sketches
- Assembly Drawings
- Production Drawings
- Part List
- Price Calculation (10 pcs., including wages)
- Stress Analysis
- Assembly Diagram
- Report
Of the above-mentioned requirements, the only requirement that was not met was the Price Calculation, which could not be completed in the allotted time due to the complex nature of the design.
Function Description
The crane can swing at least 300° and can lift up to 500 kg. Even though the hoist can theoretically lift up to 800 kg, the crane structure was only tested for a load of 500 kg in Autodesk Inventor's Stress Analysis module. The main support structure is composed of a pipe with an external diameter of 323.9 mm and a wall thickness of 7.1 mm. Cylindrical items are better at spreading stresses over their entire surface, while bodies with angled surfaces cannot spread stresses efficiently across edges. The large pipe diameter was chosen to ensure crane stability and stiffness in regard to the forces affecting it. The main pipe is welded on a flanged hexagonal plate secured with bolts to a socket of high strength concrete with a specific gravity higher than 2.6g/cm³. Even though a cylindrical shape is very efficient at stress distribution, a circular shape does not necessarily behave in the same manner. On the contrary, the stresses around an arc will focus on the topmost element, while the stresses around a line will distribute the stress equally amongst the elements. The crane's collar secures the arm to the support structure via brackets. However, since the brakets are not very thick, the force they transfer to the main support pipe might damage it, the collar was equipped with vertically bent plate sections which serve two functions: they provide additional strength to the main pipe in a high-stress area and they also increase the area over which stresses from the arm are transferred and distributed to the pipe. The brackets are horizontally secured by plate rims welded on another vertical structure consisting of two spines made of bent plate. The role of these spines is to equalize push and pull stresses between the top bracket, affected by pull stresses, and the bottom bracket, exposed to push stresses.
The pipe is additionally reinforced by the pillar cap composed of another cylindrical structure that fits on the inside of the pain pipe, thus increasing the pipe thickness in the high-stress areas around both brackets. The main joint, between support structure and main arm, is held in place by a long shaft connecting both brackets and thus contributing to the push and pull stress distribution. The joint is composed of the top and bottom brackets, on the support structure side, and, on the main arm side, it is comprised of two arm brackets, one for the main arm, at the top and one for the support arm, at the bottom. All brackets are assembled with bi-directional ball bearings with an interference fit, so that the shaft remains the only spinning part to ensure the main rotation of the arm around the support structure. The angle between the support arm and the main arm, as well as the main support pipe is 45°. The secondary joint is similarly secured to the support arm and, since the angles are identical, it forms a parallelogram, where the joint shaft represents the height of the figure. The hoist is attached to the crane structure by a thick pin held in place by the engine bracket and the pin's axis is located exactly 3m away from the main pine axis. The GIS hoist was selected due to its compact design, high load lifting capacity and low weight (only 14 kg, including chain)
Version History
Finished Product - Version 4
Version 1 consisted only of a couple of part files and two assemblies. Version 2 was set up to support parametric integration. Since setting up a proper parameter scheme for a project can be quite time intensive, the use of parameters did not appear advisable. Version 3 was built around the wrong type of ball bearing and had to be discontinued even though it was viable. By including a unidirectional ball bearing (with a certain height), the remainder of the project was calculated in relation to that particular height. The project however required a bi-directional ball bearing, which unfortunately had a different height. This change prompted version 4. Version 4 was set up using many part files from version 3, but some new parts were added to adapt the model to another design decision and the main assembly and its sub-assemblies had to be re-built. As the most complete version, it was used to create the required production drawings for production as well as renderings. Version 5 became necessary for the stress analysis. Most sub-assemblies in version 4 were set up as weldments and this caused the analysis to fail repeatedly. Version 5 contains the same part files as version 4 but new sub-assemblies were created.
Version 4
This is version 4 of the project. Before this assembly was completed, three additional versions were set up and it was followed by a version 5 that was set up after the completion of the version 4 model.
Version 1
This version only contains the support assembly. Upon completing this assembly other ideas were considered as it did not seem likely for this support to work efficiently. The materials used in the rendering were only applied as a means of highlighting material differences.
Version 2
This version was discontinued because the central support pipe could not be replaced with one of a larger diameter without altering the dimensions of the other elements to impractical sizes. Additionally, it did not appear likely that the designed system of transferring stresses would prove efficient.
Version 3
"Knapp vorbei ist auch daneben." (A near miss is as good as a mile). Besides the ball bearing issue, upon closer study other minor flaws were detected. They could have been solved but the shrinking time-constraints made this option impractical.
Version 5
This is the last version of the crane and was only used for the stress analysis. The assembly and its sub-assemblies do not contain any type of fasteners because they would only take up space without contributing to the analysis.
Technical Drawings and Overview
Part List and Drawing Overview
Overall, the crane is composed of 45 unique part files, organized in 15 sub-assemblies and 1 main assembly as well as a number of parts that have been used from Inventor’s Content Center and would, in a real-time scenario, have to be purchased separately or be checked out of a company’s inventory.
Pillar Collar Sub-Assembly
Three sub-assemblies, four manufactured parts and five bought parts. While this structure seems slightly overkill, it has been designed to distribute stresses transferred from the swinging, jointed arm to the support pillar over a larger area, thus making it less likely for the pillar to suffer damage. The two inner vertical supports spread the stress from the two brackets over a larger area. The two outer vertical supports at the back are designed to hold the four brackets in place.
Even though the requested material calculation, the central pillar is by far the most expensive part in the crane, most likely since it is made of P23TR1 steel. The pipe (outer Ø 323,9 mm, thickness 7,1 mm) was not selected because it must transfer and contain pressurized content, it was solely selected due to diameter. Due to pricing, it was important to ensure that the central pillar does not suffer stress damage if it can be avoided.
Main Pipe Bracket
This bracket holds the long pin in place and is assembled with bi-directional ball bearings (interference fit). Because all other parts this bracket is assembled with are cylindrical, the part was also given a certain degree of cylindricity. Section A was created to allow the display of Detail B, focusing around the slot for the ball bearing, adjusted to both the ball bearing’s outer diameter as well as to the shaft’s diameter.
Detail C was needed to display the angular distance between the holes that hold up the back of the bracket against the spine assembly. Linear distances could have been measured and displayed but the hole pattern is wound around circular geometry and the measurements would not have been relevant. Detail D displays the linear distances and positioning of the 4-hole pattern securing the spacer sub-assembly between two mirror-positioned bracket subassemblies (mirrored: ball bearings facing inwards). Additionally, it displays the positioning and angular distances for the curved slot that fits the vertical collar supports. GPS tolerances were only used in regard to cylindricity, as most parts the bracket is assembled with are also cylindrical. Cast was not relevant due to plate thickness and the only important tolerances were those required to create the interference fit between bracket and ball bearing.
Project Documentation
Gant Chart
The time estimates, in light green, are evenly distributed amongst all categories, with substantial amounts of time reserved for CAD parts, assemblies and production drawings as well as for the report.
However, the manner in which the time was actually spent, displayed in dark green, paints a different picture. Far more time than previously estimated was required to produce a final assembly that could be used for both setting up the technical drawings and for running, and passing, the stress analysis test. Subsequently, the time allotted to other sections, such as for example Project and Material Description, was cut short without diminishing the projects overall quality. Even though there was no requirement for the crane to pass the stress analysis test it was deemed important and thusly substantial time and effort was invested into designing a structure that could pass. As the log data automatically and dynamically alters the Gant chart, there is no difference between the two separate files and therefore, as shown in the chart, the actual time spent working on the project, at school or otherwise, does not exceed the allotted project time but does not add administrative interruptions.
Log
The log displays the daily distribution of time spent working on the project. In total, the log contains nine pages but only the first page is being displayed, as an example.
The log file data automatically updates the gant chart and displays irregularities originating in the way time was used within the project. In theory, the project had a duration of 17 days (119 hours, assuming that each work day equals 7 hours of work on the project). Practically however, some of the school time was spent in class, discussing topics like bolts, weldments, materials and so on. As such, additional time was spent at home, working in the daily 7 hours without exceeding the total amount of 119 hours (17 days) spent on the entire project. Even though this peculiar time distribution was not required for the current project, the effort was deemed necessary to produce the best possible results in the allotted time, theoretical or otherwise.
Assembly Diagram
While the diagram is neither a process chart nor an assembly instruction, it displays a mixture of the two and thus provides valuable insight into the construction itself, as well as into how the separate parts are assembled into sub-assemblies and then into the main assembly. In the image below, the part labels display the part (or sub-assembly) name, the drawing number, so that they can be easily located both in the drawing overview as well as in the physical annex that contains the production drawings and is appended to the report, and the number of parts needed.
Unlike the process chart, this diagram does not take manufacturing processes and durations into account. Such information is valuable, especially correlated with a price calculation, but time constraints made it impossible to do all the needed calculations, given the volume of parts the crane requires for assembly.
Conclusion
Even though the project had a completion percentage lower than 100% at the end of the allotted time, the project was successful in other ways:
- Experience: The amount of work done in Inventor and the speed at which it was completed has significantly impacted the working knowledge of the program. Additionally, by comparison with earlier projects, the time estimation and the spent time were more in tune with each other, despite the variations displayed in the gant chart. The consideration that the product development phase is the most time intensive part of any project was confirmed. While drawing in Inventor does take a certain amount of time, most drawing time was spent on envisioning the whole product and defining the role the current part had to fill. Even though at a first glance such a definition does not appear to pose much of a challenge, every part of the whole interacts with all other parts and influences them in function, form, design and so on.
- Knowledge Working on this project required a deeper understanding of materials as well as fastening methods. Unfortunately, there was too little time to allow delving deeper into these areas. Had there been more time for the project, gathering more knowledge in these areas might have resulted in a better prototype and a shorter design stage. However, this type of knowledge can sometimes be accumulated only in time.
- Time Management Even though balance is generally considered a valuable asset for most endeavours, sometimes it must be sacrificed in favour of focus. In a production environment, this statement can be deemed as inaccurate but, in an educational environment, it holds true. Education requires focus and understanding as well as experimentation and, sometimes, failure. While it would have been entirely possible to simplify the design and give no thought to the stress analysis test and thusly present a complete project, doing so would have failed to teach some very valuable technical lessons.
Overall, the design was influenced by two major factors: modularity and stress distribution. Modularity was chosen as a guiding principle because it allows the use of replaceable parts, thus giving a potential customer the possibility to simply exchange damaged parts rather than be forced to commit to the substantial financial effort of acquiring a completely new crane. The selection of this principle was also partly influenced by the hefty price tag attached to the main support pipe. Stress distribution was chosen as a natural principle due to the requirement of performing a stress analysis on the model. This has had significant impact on the design process because a lot of weldments were used instead of bolt fasteners, which might have weakened the crane’s structural integrity. As a consequence, the design is likely to be expensive and impractical, despite of the effort invested into its creation. The purpose of any endeavour, human or not, is to generate value. Endeavours that fail to generate said value, are nothing beyond a waste of time, effort and resources. However, the success or failure of an endeavour is not defined by the value it has produced, but by the manner in which the value is defined. Additionally, value itself can be either internal, as defined, consciously or otherwise, by the individual, or it can be external, defined by other persons. While a balance between the internal and external definitions of value is a desirable goal, when set conditions preclude this balance, the internal value, while theoretically of lesser importance, is the actual motivating factor that counts.
"It is not winning or losing, but how one plays the game"
Carolyn Clowes - "The Pandora Principle"
