The crank arm is the component of the bicycle that connects the pedal to the    drive sprocket. On one side of the bicycle the crank arm is normally integrated  into a component called the spider which connects directly to the sprocket, on  the other side of the bicycle the crank arm is a separate component - this is the part that you are required to redesign. You can find a good summary of these   components on the Wikipedia page for Crankset https://en.wikipedia.org/wiki/Crankset.

Your company is aiming for an initial production run of 50,000 units and the      manufacturing budget that is available would give you access to most forms of  casting, forging or subtractive machining operations with a wide range of          aluminium alloys and steel alloys. 3D printing would be impractical at this scale of production and your Chief Technical Officer has ruled out composite materials as your manufacturing team has not prior experience working with them.          Titanium alloys could be possible, but you would need to make a strong case to justify the increased cost in materials and manufacturing.

An initial design has been created from a basic model which is highly sub-          optimal. It is currently made in the aluminium alloy Al6061 in the -T6 heat         treatment condition. Many of the dimensions of the part can be altered as part of your redesign but some must remain the same. Those critical dimensions are      shown in figure 1 below. This basic crank model is available as a Solidworks part file from the MMME3074 Moodle page.

Your chief engineer has determined that the maximum load applied at the position of the pedal would be 800 Newtons. This force can only be achieved   when the sprocket end of the crank is fixed, representing equilibrium between   the forces acting on the pedal and the reaction forces from accelerating the bicycle. You may however wish to consider the crank arm at various points of its rotation around the sprocket, as the crank arm may be weaker when loaded in  some orientations. Also note that when the load is applied to the pedal it does   not act on the same plane as the crank arm. The centre of the pedal is offset by half the width of the foot, typically 75mm from the outer face of the pedal end of the crank. This will introduce a torsional component to the load which you should consider in your calculations and simulation.

Outer face

Figure 1 – Dimensions of the crank arm which are to remain fixed.

(All dimensions in mm)

You should develop and present an optimised design. This will require you to balance the requirements for reduced mass, high strength and high stiffness as well as materials and manufacturing limitations.

You will need to identify what goals and constraints you will be using in your design process. There is no specific weight value that you must achieve, instead your design optimisation will be judged on how well you have managed to balance these requirements.

Your work will be assessed based on two components. 1) A Solidworks part file of your optimised design and 2) a report on your optimisation process.

1) The Solidworks Part file

You should submit a single Solidworks Part file showing your chosen optimised design. This should include the definition of the design studies that you have  used but it should not include the results files. All Solidworks files will be evaluated to check authorship.

2) The Report

The report should comprise

•   A title page which should include your ‘name’, ‘studentID’ and ‘username’ .

•   A summary section (maximum 300 words) briefly describing the task, your methodology, major findings and conclusions.

•   A discussion section (maximum 1400 words and any reasonable number of figures for describing your design approach). The discussion section should contain these three sub-sections.

A. Verification In this section you should demonstrate that you have

made reasonable choices for the loads, fixtures and other conditions of your FEA simulation. It should include a set of analytical calculations representing your crank as a simple beam and               evaluating its behaviour. Alongside these you should provide a         description of an FEA simulation with identical loading conditions and geometry, and present the results for comparison to the calculations. Provide a discussion of how this verification demonstrates or fails to  demonstrate a reliable FEA simulation result. Your confidence in the  FEA result should inform your later design decisions.

B. Investigation/optimisation In this section you should describe the   approach that you used to develop your optimised design. It should show the major design decisions that you made during your           optimisation and when showing how your design has developed you should provide evidence from the results of your FEA analysis to     support the design decisions that you have made. You should         describe the design tools, briefly discuss their operation and how    they allowed you to make your design decisions. This is expected to be the longest of the three sub-sections.

C. Practicality/Manufacturability The final section of the report should    reflect on the design that you have presented, and it should evaluate how practical it would be to manufacture this product commercially. You will need to demonstrate how the features of your design make  it suitable for batch or mass production.

•    Conclusion (maximum 300 words, no figures) in which you should identify   the most significant findings of your work. This may include reflection on the challenges that you had to overcome or how you would approach this task   differently if you were asked to complete it again.

This report should not be a description of how to operate Solidworks, i.e. where to click or the order of operations, it should be focussed on the challenging design tasks and how you overcame those challenges. This is a formal report for your employer and as such it should be written following the guidelines already  laid out in your course for formal reports.

Marking Scheme (see detailed scheme on Moodle)

This project is worth 40% of the MMME3074 module and will be marked out of 100 :

•     Design and FEA of the crank (60) marks will be awarded for:

o Effective use of design studies to optimise crank geometry (20).

o Rigorous modelling techniques that are robust enough for optimisation

(10) marks. Note that this assessment will consider modelling, unlike CW2 which did not. Here we only interested in how you have made your modelling robust enough to be

altered and developed during optimisation.

o FEA analysis with appropriate settings for fixtures, mesh, solver and evidence of convergence (10) marks.

o Rigorous verification of the FEA analysis by analytical calculation (10) marks.