Mini design challenges

Updated 23rd October 2023 mini challenge alpha mini challenge beta mini challenge gamma

The brief

Challenge alpha

Labs Autumn wk1-2

open and closed chain mechanisms.

There are three parts to this challenge

  1. program an n-link open serial chain in Matlab (later we will see how to program closed chains)
  2. Design, rapid prototype and demonstrate a physical open and closed chain with 3 links.
  3. Document this work for inclusion in your report.

1. program an n-link open serial chain

  1. Write a program in matlab so that by specifying the link lengths of a 3-link robot you can calculate its end position and plot the pose.
  2. Given that the robot has links of length l1 = 50 l2 = 90 and l3 = 40 use a trial and error method show you can position the robot at the following points (0,100), at (-170, 0) and at (156,90) (in each case record the three angles you have found)
  3. Show that you could calculate and draw a serial chain linkage with approx 20 links. (think about ways to automatically generating 20 angles for the input),

Some tips for a 20 link robot

>> len=1+rand(1,20); % twenty links with a length between 1 and 2
>> L=tril(ones(20,1)*len); % create a lower triangular matrix from len
>> theta=randn(20,1); % random angles in radians
>> x=L*[cos(cumsum(theta)) sin(cumsum(theta))]; % note angles are radians here
>> xx=[0 0;x]; % add the origin to the data
>> plot(xx(:,1),xx(:,2));axis('equal');grid on;shg

2. Design and rapid prototype planar linkages out of paper and similar stationary

  1. Recreate the 3-link in part 1 with an open chain linkage made of paper or card and link lengths l1 = 50 mm l2 = 90 mm and l3 = 40 mm and confirm it can reach the points (0,100), (-170,0), (156,90) - dimensions in millimetres.
  2. Check the self movement of the link when the end is pinned at (0,100). Can any of the links go through a complete 360 degrees rotation? Where could you locate the end point so one of the links could rotate through 360 degrees?
  3. Show that a 2-link with a pinned end is a structure. Build a 5-link serial chain then convert it into a structure by joining some joints.
  4. See if you can come up with a planar sliding joint made from paper.

For the report

Notes on the complete report are at the end of this file/page

To make sure you have the material you should save the programs and plots from matlab using the 'publish' command.

>> publish('myscriptfile','pdf')

Also take photographs and videos of your rapid prototype linkage and document your results.

Useful resources for challenge alpha

If you can, please bring the following to the Lab session

We will provide the following to make a rapid prototypes of some interesting linkages and structures.

Challenge beta

Labs Autumn wk3-5

Groups of two or three people.

Compliant mechanism design

The challenge is to build two compliant mechanisms

  1. a simple 4-bar linkage and
  2. a mechanism that is more complex for example has at least two identifiable 4 bar mechanisms.

The mechanism should measure less than 8 cms in any direction (including the diagonal)

You have an option to make one joint a continuous rotating crank (Grashof condition) in which case it will need to use a pin axle. The other joints should be based on blade flexures.

You should agree on the intended design and have dimensioned pencil and paper sketches before you begin using any CAD software.

The recommended CAD software is Fusion360 (Autodesk). It is imperative that you sign up for your account using your university of Reading email so you can use features that are not available in the public license.

Useful resources for challenge beta

Useful things to record for your portfolio