Design Challenge 1: Mechanisms.

(https://www.personal.reading.ac.uk/~shshawin/teaching/naturalrobotics/designchallenge1.html)

There are three stages

• 1a. Demonstrate a n-link serial chain in paper and in software (wk1-2)
• 1b. Show a paper/cardboard version of any two interesting four-bar linkages.
• 2a. Rapid prototype a compliant 4-bar linkage (wk2-3)
• 2b. Demonstrate a plain and a ball bearing joint (wk4-5)
• 3a. Simulate and animate a 4 bar linkage based on wk1 in software (wk5-7)

Work will be in groups of 2 (or 3 by arrangement)

All elements including photographs of the working prototype should be part of your engineering design portfolio.

Stage 1 Rapid prototype of two types of 4 bar linkage

Four bar linkages a common in mechanism for design. Some examples are given below.

Challenge is design and prototype two types four bar linkages. The prototypes can be made of anything and should demonstrate the principles of the mechanism.

These two mechanisms should be different, e.g. the a leg of the strandbeast, the mechanism of an umbrella, the expanding ball (breathing ball or Hoberman sphere), a single degree of freedom finger or knee mechanism etc.

Materials you might need

• D = Desirable, you should try to get hold of these
• P = Possibly might be helpful to have
• M = Must be there

If you can get 'blank pin tie tacks' or 'butterfly clutch' (often sold with a flat headed drawing pin) these may make your prototype joints more robust. However they not necessary for the first challenge and you can also be creative about alternative ways of prototyping joints.

Stage 2a

• Produce a remote centred joint based on the double four-bar linkages.
• Ideally this would be a single print using compiant (folded blade) joints but can be done with pin joints.
• If possible include a stress analysis of the component using the Fusion360 stress analysis tool.

Stage 2b Demonstrate a plain and a ball bearing

• You should receive an 8 mm bearing kit
• bearing kit (flanged ball bearings)

You can request as many additional 8mm dia x 12 mm shoulder bolts (M6) for the plain bearings You will need to design the bearing and calculate the appropriate dimensions. You could, if you like, pair up with another group at the end and demonstrate a 4-bar linkage

Stage 3

Using the mathematics of planar serial chain linkages, along with a minimization method such as Nelder-Mead (e.g. fminsearch in Matlab), write a program to animate any 4 bar linkage based on the link lengths and the desired angles of one of the joints. The portfolio should show the linkage in a set of typical configureations as well as the locus of a point on an extension of the floater mechanism. If possible produce a single pdf document using the matlab publish command (publish('yourfile','pdf'))

Portfolio Elements

This is challenge 1 (so should be a directory in your portfolio) It will need an entry in your Commentary file as well as each individual file appearing in the index document.

Portfolio results could be

• Hand drawn sketches of what you are trying to achieve
• Videos of working prototypes
• Photographs of assemblies
• Engineering drawings (e.g. produced as pdfs from Fusion 360)
• A small number STL files or animations produced by Fusion 360
• notebook or 'publish' files from matlab, showing the program and mathos
• pdf of stress analysis of a component in the 4-bar linkage
• videos of the prototypes or the 3D printed joints
• video of the 4-bar animation.