This workshop is designed to work with the
LEGO Mindstorms EV3 kit
and a standard
box of lego bricks.
This is an updated version of the workshop originally developed by the National Alliance for Medical Imaging Computing which used the previous generation LEGO Mindstorms.
The phantom hasn't changed from the previous workshop, so you can use the same inststructions to construct it. Note that the newer box of lego bricks does not have the same bricks as the old one, so substitutions have to be made, and since the automatic registration has not yet been implemented, the towers are optional.
Construct the robot according to the instructions in this repo at Instructions/RobotAssemblyInstructions.pdf. Additionaly connect the robot to the phantom, and wire the motors according the instructions at Instructions/MiscAssemblyInstructions.pdf. Attach a touch sensor and an infrared sensor to any ports.
We are using the 3rd party ev3dev operating system to program the EV3 brick. If you are using a kit that has already been used for this workshop it most likely already has that OS installed. However, if not follow the instructions here.
The brick must be connected to the internet somehow, both to download the script and to communicate with the PC. Since we don't need mobility, there is no reason to set up a wireless connection, and the USB connection should be fine.
To get the script on the EV3 brick you can either clone this repository, or just
copy and paste the contents of the lego-workshop.py file into a new file on
the EV3. If you do, make sure to mark the new file as executable.
For the PC, download Slicer. This workshop has been tested with version 4.8.1 but it should work with similar versions.
Open the Application Settings by clicking Edit->Application Settings:
Go to the Modules tab:
Add a path under Additional Module Paths which points to the folder named
LegoWorkshop in this repository:
Now that directory will be in the list:
This will require a reboot of the program to take effect:
To use the module, load it from the Modules menu:
Make sure that under LegoWorkshop - Configuration
the server address matches the address of your brick, (probably ev3dev.local).
If ev3dev.local doesn't work, get the IP of the EV3 from the menu
WirelessAndNetowrks->AllNetowrkConnections->[Wired or other]->IPv4.
If the module loaded correctly it should look something like the following:
Download the
CT volume of the LEGO phantom
and extract it somewhere. Now open that data with File->Add Data and point to
the first file in the series:
Show additional options:
Uncheck the Single File box:
Click OK. Now you should see the CT scan of a LEGO phantom:
Then add a Fiducial to the point you want to target by clicking on the icon with the red dot and blue arrow:
Then click somewhere you want the robot to probe, and then choose the feducial
namespace (F) and that position will displayed on the list:
Then choose which point(s) you want the robot to 'probe' by ticking the box next
to them. When you are ready (and assuming you are running lego-workshop.py),
press the Go button:
This should make the robot move!
A calibration of the robot to the phantom was already programmed into the Slicer
module, but if you want to move the robot to somewhere else around the phantom,
while still having it within range of the injector, you can perform a manual
registration. This is done by selecting at least 3 feducials and getting
measurements of how those relate to the robot in the real world. Once you have
your points ticked, press the Replace Calibration Points button:
This will bring the points up to the table, but you will notice that the joint
values are empty. To fill those we will use another python script that outputs
the joint values without running the motors. It is called lego-debug.py and
should be run through ssh so that you can see the output. Move the robot to
point towards the calibration points you chose (keeping in mind that they need
to correspond 1:1), and fill in the values.
Note that the inject motor's encoder is spotty, and sometimes doesn't work so
it is currently not implemented (lego-debug.py will either show 0 or a huge number)
so you have to measure the distance from the orange circle of the upright large motor
to your calibration point in millimeters, and that value will be Dst.
robot@ev3dev:~/lego-igt-workshop$ Python/lego-debug.py
Press the touch sensor to read the motor positions
WARNING! The inject motor does not seem to work, you will have to measure that manually
Dst Azm Elv
-1467 38 44
-1467 38 44
Enter those numbers into the table:
The press the Rerun Calibration button to get a new calibration:
Now you can test out your new calibration!
Note that if you think something is wrong you can set Check_Calibration=True in
LegoWorkshop.py and if you run Slicer from a terminal you can get the details of
the linear algebra, including the RMSE which (if you used more than 3 points) lets
you know how well the calibration points agree on a registration.
The robot can be equiped with either an ultrasonic or infrared range sensor, which can be used to sense the phantom and perform a fully automated registration (similar to how registration is done in the OR). However, this has not been implemented in the code, so it is up to you to take on this challenge. Good luck!