Tag: ev3

I’ve been pondering the use of Lego EV3 robots on the OU TXR120 residential school again, and after a couple of chats with OU colleagues Jane Bromley (who just won a sci-fi film pitch competition run by New Scientist) and Jon Rosewell (who leads on our level 1 robotics offerings), here’s where I’m at on “visioning” it…?!;-)

The setting for the residential school is 8 groups of 3 students per group working with their own Lego EV3 robot to complete a set of challenges. Although we were hoping to have laptops from which the robots could be programmed wirelessly, it seems as if we might end up with wifi-less desktop machines (which will require tethering the robots to the desktop machine to programme them) with big screens, though I could be wrong.. and we may be able to work around that anyway (a quick trip to Maplin to buy some wifi dongles, for example, or some cables we can plug into a wifi routing switch, for example…) Having laptops would have been a boon for making the room a bit more flexible to work with (but many students have their own laptops…;-) and having a big screen that laptops could be mirror displayed against would possibly improve student experience.

The Lego bricks come with their own firmware, but as described in Pondering New Ways of Programming Lego EV3 Mindstorms Bricks we can also put Linux on them, and make use of a python wrapper library to actually programme the bricks using Python.

In what follows, I’ll refer to the EV3 brick as the client and a laptop or desktop computer that connects to it as the host.

One of the easiest ways to access the Python on the brick is to connect the brick to the network and then ssh in to it – for example (use the correct IP address for the brick):

ssh root@192.168.1.106

Each time you ssh in, you have to provide a password (r00tme is the default on my brick), but passwordless ssh can be set up which makes things quicker (you don’t have to enter the password).

To set up passwordless ssh onto the brick, you need to check that an .ssh folder is available in the home directory (~) on the brick for the ssh key. To do this, ssh in to EV3, cd ~ to ensure you’re at home you home, then ls -a to list the directory contents. If there is no .ssh directory, create one (this post suggests install -d -m 700 ~/.ssh).

If you don’t have an ssh key set up on the host machine you want to get passwordless ssh access from to the brick, follow the above link to find out how to create one. Once you do have ssh keys set up on host, run something along the lines of the following, using the IP address of your connected EV3, to copy the key across to the EV3:

cat ~/.ssh/id_rsa.pub | ssh root@192.168.1.106 'cat > .ssh/authorized_keys'

You will need to provide the password to execute this command (r00tme for the version of Ev3dev I’m running).

You should now be able to ssh in without a password: ssh root@192.168.1.106

Rather than prompting for the password, ssh will use the key provided to log you in.

In my previous post, I described how it was possible to run an old IPython notebook server on the brick that can expose notebooks over the network, although it was a little slow. It’s also possible to ssh in to the brick and run an IPython terminal on the brick:

ssh root@192.168.1.106
ipython

A third way I’d have expected to work is to access a remote IPython kernel on the brick from an IPython console on my laptop: ssh into the EV3 brick, launch an IPython kernel, and pick up the location of the connection file. For example, if the command:

ssh root@192.168.1.106
ipython kernel

to run an IPython kernel on the EV3 responds with something like:

To connect another client to this kernel, use:
    --existing kernel-1129.json

Back on the laptop I’d expect to be able to run:
scp root@192.168.1.106:/root/.ipython/profile_default/security/kernel-1129.json ./
to grab a local copy of the connection file from the brick and copy it over to my host machine (which works) and then use it as an existing connection for a Jupyter console on the laptop host:
jupyter console --existing ./kernel-1129.json --ssh server

But that doesn’t work for some reason? CRITICAL | Could not find existing kernel connection file ./kernel-1129.json

Whatever…

So far, so much noise – the important thing to take away from the above is to get the passwordless ssh set up, because it makes the following possible…

Recall the basic scenario – we want to run code on the brick from a computer. The bricks will run an IPython notebook, but it’s slow. Or we can ssh in to the brick, start an IPython process up, and run things from an IPython command line on the brick.

But what if we could run a Jupyter server on host, making notebooks available via a browser, but use a remote kernel running on the brick?

The remote-ikernel package makes setting up remote kernels that can be accessed from the Jupyter server relatively straightforward to do – install the package on your host machine (eg my laptop) and then run the remote-ikernel command with the settings required:

pip3 install remote_ikernel
remote_ikernel manage --add --kernel_cmd="ipython kernel -f {connection_file}" --name="Ev3dev" --interface=ssh --host=root@192.168.1.106

This creates a kernel.json file and places it in the correct location. (On my Mac this was in the directory /Users/MYUSER/Library/Jupyter/kernels/. )

The kernel.json file created for me (/Users/ajh59/Library/Jupyter/kernels/rik_ssh_root_192_168_1_106_ev3dev/kernel.json) was as follows:

{
  "argv": [
    "/usr/local/opt/python3/bin/python3.5",
    "-m",
    "remote_ikernel",
    "--interface",
    "ssh",
    "--host",
    "root@192.168.1.106",
    "--kernel_cmd",
    "ipython kernel -f {host_connection_file}",
    "{connection_file}"
  ],
  "display_name": "SSH root@192.168.1.106 Ev3dev",
  "remote_ikernel_argv": [
    "/usr/local/bin/remote_ikernel",
    "manage",
    "--add",
    "--kernel_cmd=ipython kernel -f {connection_file}",
    "--name=Ev3dev",
    "--interface=ssh",
    "--host=root@192.168.1.106"
  ]
}

Launching the notebook server using jupyter notebook in the normal way should result in the server picking up the remote kernel from the new kernel file.

To list the kernels available, I launched a Jupyter notebook with the normal (local) Python kernel and ran:

from jupyter_client.kernelspec import KernelSpecManager
list(KernelSpecManager().find_kernel_specs().keys())

My newly created on was there, albeit horribly named (the name was also the directory name the kernel.json file was created in): rik_ssh_root_192_168_1_106_ev3dev.

So here’s where we’re at now:

• a single desktop or laptop computer with passwordless ssh access to a Lego EV3;
• the desktop or laptop computer runs a Jupyter server;
• Jupyter notebooks are available that will start up and run code on a remote IPython kernel on the brick.

Where do we need to be? The most immediate need is to have something that works for residential school. This means we need 8 desktop computers and 8 EV3s.

One thing we’d need to do is find a way of marrying computers and EV3s. Specifically, we need to have known IP addresses associated with specific bricks (can we assign a known IP based on MAC address of the wifi dongle attached to the bricks?) and we need to make sure that passwordless ssh works between the computers and the EV3s. The easiest way of doing the latter would be to use the same ssh keypair in every machine, but this would mean student group A might be able to mistakenly connect to the Student Group B’s machine.

One way round it might be to set up a Jupyterhub server that is responsible for managing connections. The Jupyterhub server is a multiuser hub that will set up a Jupyter server for each logged in user. If we set up the Jupyterhub attached the same wifi network as the EV3 bricks, with 8 users, one per student group, each user/student group could then presumably be assigned to one of the bricks. Students would login to the Jupyterhub, and their Jupyter server would be associated with the remote_ikernel kernel.json file for one of the bricks. Anyone who can connect to the local wifi network can then login to the Jupyterhub as one of the group users, launch a notebook, and run code on one of the bricks. This means that students could write notebooks from their own laptops, connected to the network. Wifi-less desktop machines provided for the residential school could presumably be added into the network via a local ethernet cable?

So we’d have something like this:

Does that make sense?