Robotics in Medicine: The Design challenges

The design challenges 2025

There are three design challenges that will run until the end of enhancement/reading week.

1. Rapid prototype of open and closed chain linkages (13/2/2025 -> report deadline))
2. Demonstrate one open and one closed chain linkage with compliant joints (optionally include a simple bearing) (20/2/2025 -> report deadline)
3. Use a Dynamixel to throw a pingpong ball at a target (27/2/2025 -> report deadline)

Teams

• First challenge: teams of between 2 and 3 people.
• Second and third challenges: teams of 4-5 people, at least one member of the team must be from year 2.

• Teams will be announced, or shold be declared, on the first day of the challenge.

Design challenge 1: Rapid prototyping linkages

open and closed chain mechanisms.

There are three parts to this challenge

 1.1 program an n-link open serial chain in Matlab 
 1.2. Design, rapid prototype and demonstrate a physical open and closed chain with 3 links.
   -  Use the open chain to compute the forward kinematics
   -  Use the closed chain to demonstrate grashoff and nongrashff conditions
 1.3. For extra mark, adapt your matlab code in 1 to simulate a closed chain 4-bar linkage
 1.4. Document this work for inclusion in your report.

1.1 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 8-12 links. (think about ways to automatically generating 20 angles for the input),

Some tips for a multi link robot

>> len=1+rand(1,8); % $n$ links with a length between 1 and 2
>> L=tril(ones(8,1)*len); % create a lower triangular matrix from len
>> theta=randn(8,1); % 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


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

1. Use the templates in paper_robot_grid.svg and paper_robot.svg to make a 3 link openchain robot.
2. Check the self movement of the link when the end is pinned any of the points A, B or C. 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. Compute (from your model) the joint angles needed to reach points A, B and C with the third link oriented along the pink lines. Is there only a single solution at each point?
4. Show that a 2-link with a pinned end is a structure.
5. See if you can come up with a planar sliding joint made from paper.
6. See if you can make that into a 4-bar linkage by pinning the end of your third link to a point on the y-axis. The '4th' bar of the linkage is the base coordinates. Can any of the links do a full 360 degree rotation? Experiment by changing one joint from a revolute to prismatic (sliding)

Questions

• What conditions make the moveable robot into a structure?
• What would you need to do to change a 5 link serial robot into a structure?

1.3 lazy way to calculate inverse kinematics

• This is covered in - Four bar linkage maths and uses a similar principle to the lazy inverse outlined

in [[https://www.personal.reading.ac.uk/~shshawin/teaching/mrp/nlinkplanar_slide.html][nlinkplanar]] "Calculating the inverse kinematics the lazy"

1.4 For the report

• To make sure you have collected all the material you need for your report.
• Save the programs and plots from matlab using the 'publish' command.

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


• You can also save figures in vector formats (.svg .eps .pdf) using the 'File' / 'save as' menu

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

See Tech briefs on ReportWriting.html and details in report2025.html

Design challenge 2: Building a linkage with compliant joints

Using Fusion360 design two linkages with compliant joints (blade flexures)

• One linkage should be an open chain
• One linkage should be a closed chain (i.e. at least a 4-bar linkage)

Details to follow

Design challenge 3: Throwing a pingpong ball

Design and print a light weight arm to attach to a dynamixel servo to throw a pingpong ball at a target.

Details to follow

Useful resources for challenges

• Four bar planar linkages
• n-link planar mechanisms
• n-link serial chain in paper

• Guidance for the 2025 report

Lab sessions for the design challenge

	Date	time	Activity
Thur	13 Feb	10 to 13	RP 4 bar
Thur	20 Feb	10 to 13	Compliant 4 bar
Thur	27 Feb	10 to 13	Compliant 4 bar/Dynamixel intro
Thur	13 Mar	10 to 13	Dynamixel 1
Mon	17 Mar	15 to 18	Dynamixel 2
Thur	27 Mar	10 to 13	Dynamixel toss