LEGO Conveyex Imperial Transport

Este artigo é a parte 1 de 1 da série  Conveyex

So another never-to-be-completed project.

I like Star Wars but usually don’t care for LEGO Star Wars sets. But when the Conveyex set was released I liked it a lot. Probably because it looked like a monorail train and I was already gathering a few old LEGO monorail pieces. So I ordered one… or so I tought.

When I order from LEGO I take the chance to buy a few MINDSTORMS motors and some Power Function elements like cables or batteries. I had a few items already on my desired list so I didn’t notice exactly how many items I was ordering… and so I received 3 (three!) Conveyex sets.

Oh boy. What I am going to do with all these Conveyex?

Then I realized that the size of the set wagons is simillar to the monorail wagons. After assembling the first set I took off the wheels and with just a few extra bricks I got my first monorail version:

Since I was already trying to use Powered Up as a way to control the monorail motor it seemed natural to extend this first version to a bluetooth controled one:

This way the Conveyex could be controlled not just with the Powered Up train headset but also programmatically. That would allow me to use the Conveyex on a large animated diorama, with MINDSTORMS and other controllable elements:

So this was the beginning. Now I “just” needed to extend the train with a few more wagons. And the rail with a few more tracks. Seemed simple.

But the old LEGO monorail system wasn’t meant for long trains. The system was designed for just 1 engine in the middle and 1 wagon at each side:


The wagons connect to the engine through a custom coupling system. As far as I know, there is no way to connect other LEGO elements to the engine couplings. Extending the length is possible by adding wagons and using some LEGO parts as custom couplers, like in LEGO trains.

Fortunately there is a company named 4DBrix that sell a few custom elements compatible with the monorail system. I ordered them some car extensions that has a “male” tab that connects to the engine and a “female” socket that allow extra wagons to be added. It worked but then the overall weight started to be feel too demanding for the monorail motor. Perhaps a single motor could move a train with 2 or 3 wagons and an engine but I also wanted ramps (of course!) and that seemed too much. So I wondered if it is possible to use more than one monorail motor…

It is:

The monorail track is really just a long gear. So the two motors are directly coupled together and just add their force (oh well… after a while I found out that this is not always true).

But the way that the Powered Up Hub was designed it is not the best for such a setup – the 6x AAA batteries would drain too fast and I would have to remove the Hub to replace them. Once in a while it might be acceptable but certainly not every 30 minutes. The good old Power Functions LiPo battery is much better – it allows in place recharging and it also looks like it can supply a few more milliamps than the PUP Hub (not confirmed).

So I picked my LEGO relay idea and built a Powered Up version:

and then applied it to the Conveyex:

So now the Powered Up Hub batteries are only used to keep the Hub ON and sometimes to change the relay state. Need to measure it but I suspect that it would work a few hours. And no custom cable is used, just 100% LEGO electric parts.

So today the Conveyex is already looking good:

The model uses 2 monorail motors, 4 wagons and an engine car:

From left to right:

  • Powered Up Hub wagon
  • Monorail motor
  • Relay wagon
  • Power Functions LiPo battery wagon
  • still no purpose wagon
  • Monorail wagon
  • Engine car

So the Conveyex is really just 2 monorail trains linked together (in the above drawing, the extra space reflects the custom coupling I had to build, longer than the monorail coupling sustem). The wagons aren’t all of the same size because the wagons length from the LEGO Conveyex are in facto a bit too larger and make the monorail derail at regular curves and ramps – so I built the Relay wagon 4 studs shorter.

The weight is not equally distributed, the front train is lighter than the back train. So sometimes, when the Conveyex is moving on ramps, the two trains move at different speeds – like when the front train already reached the top and the back train is still moving up in the ramp:

On the video above the LiPo was adjusted for 4/7 of output power. The front train gained too much speed and the monorail coupling couldn’t handle and disconnected. Now I’m running the Conveyex with the LiPo at 5/7 of output power and this never happened again but probably will need to add more weight to the “still no purpose wagon”… crazy ideas welcome 🙂

LEGO Powered Up Relay

I needed a way to turn a LEGO motor ON and OFF using a Powered Up hub but keeping power supplies independent. This way I can control a large current demanding motor without draining out the Hub batteries (and also without the need to use a custom cable).

So I used a Power Functions switch as a relay:

LEGO Powered Up relay

Also took the chance to try LDCad on linux. Not so easy to use as LEGO Digital Designer (I am a zero with CAD) but after a while I got a pretty close model. To create a PDF with the instructions I then used LPub3D – I couldn’t install the ‘.deb’ file because of missing dependencies no longer available for my Ubuntu laptop but found out that the ‘.AppImage’ works fine.

The instructions on this PDF file also have a list of the parts that I needed to get from LDView (LPub3D generates a nice image with all the parts but without describing those parts). I also couldn’t install the ‘.deb’ version so I used the ‘.exe’ for Windows, it runs fine with Wine.

The model uses a Powered Up / WeDo 2 motor but it can also use a Power Function M motor or a MINDSTORMS medium motor so this relay may use with different technologies (IR, Bluetooth, Wi-Fi, USB) as long as you just need an ON/OFF control of the motor.

Using a Power Functions LiPo battery you can still regulate the output power

A video of the relay working:


And another showing how I use it in my LEGO Imperial Conveyex Transport based on the old LEGO monorail system:

Big thanks to Roland Melkert, Trevor Sandy, Travis Cobbs who designed these great open source tools (and probably many others who contributed).

Making an Android app for LEGO Powered Up – explanation

So how does this “App Inventor”-thing work?

To create an app for Android we just need a browser to access the online app creator tool. We have a Design view where we add our components like buttons and sliders and a Blocks view where we use the method blocks provided  by each component we added to our Design.

We can build our app and download an ‘apk’ file to install on our Android phone or tablet but that’s not practical while we are still testing some ideas and debugging the way our blocks work. So the best way is installing the MIT AI2 Companion App on our Android device so every action we make in the online tool is synchronized to it through USB or wi-fi.

App Inventor 2 provides a Palette with lots of usefull components but to use LEGO Powered Up we need to add an Extension that allows AI2 to talk with Bluetooth Low Energy devices. At the moment BluetoothLE is the only supported extension and I must say they have been doing a great work this last year (they even gave me access to a beta version a few months ago while fixing a bug I was dealing with) including writing a good explanation of all the blocks provided with some examples for Arduino and BBC micro:bit.

After importing the extension  we just drag it to the Viewer to get a ‘BluetoothLE1′ component at the bottom of the Viewer, on the “Non-visible components” area. Doesn’t seem much but if we change to Blocks view and look to this component we’ll see lots of blocks.

So let’s start creating our App!

We will use some BluetoothLE blocks to communicate with our LEGO “HUB NO.4” device. This blocks require a ServiceUUID and a CharUUID that we will store in global variables:

Currently the ServiceUUID and CharUUID are the same as LEGO BOOST hub but please note that there is no guarantee that future firmware releases will keep them allways equal.

We will also create a list of our devices:

Yes, a list of one device is silly but I have more devices like my BOOST Vernie and of course I’m planning to have a few more Powered Up devices in a near future so a list is usefull. You can call whatever you want to your devices but you need the Bluetooth address of it (so “PUP#1” is just an easy to remember tag that I choose for my “90:84:2B:06:AB:5D” hub).

You can get your BT address installing Nordic nRF Connect for Mobile app on your Android device and scanning nearby BLE devices while turning your LEGO hub on. If you changed its name with the LEGO App you will see a BLE device with that name, if not you will see “HUB NO.4” or “Smart Hub”, depending on the firmware version of your hub:

Now we go to Design View and add all components needed:

From the ‘User Interface’ section:

  • two buttons: ‘BtnConnection’ and ‘BtnRst’
  • one ListPicker

From the ‘Drawing and Animation’ section:

  • one Canvas
  • one ImgSprite

And from the ‘Sensors’ section:

  • one Clock

I added a few others that are really not needed, just used them for aligning and cosmetic purposes.  I also renamed the buttons names to better remember their purpose and changed some of their properties.

Now back to our Blocks view, we need to take care of what happens when our App starts:

We start a Bluetooth LE scan to find all BLE devices nearby. This is necessary later on when we want to connect to our LEGO device.

Then we create our list of Hubs (seen above), set the text of the Button used for the BLE connection, draw our Joystick at the center of the canvas and initialize our Clock.

This Clock will be used to keep the BLE connection active after we connect: we need to keep talking with the LEGO hub because after a pre-defined period without communication it will shutdown to prevent battery draining.

For now we just keep the clock disabled and set the period  to match the global variable “TRACKSPERIOD”.

We also define what happens when we click our ListPicker:

(we change the text to the friendly name of the chosen LEGO hub)

Now we define what happens when we click on our connection Button – we want it to connect to the device we chose whenever there is no connection yet and to disconnect when already is:

(we also activate or deactivate our Clock at the sametime)

I will not explain the blocks related to the Joystick – they are used to calculate the duty cycle (speed) of the two motors from the position of the joystick. These values are store in two global variables: ‘SpeedA’ and ‘SpeedB’.

The next important part is sending the calculated values to the motors.

The hexadecimal command used to control a WeDo 2 Motor (we should probably call it a “Powered Up Medium Motor) is:

0800810 p 115100 dt

where:

  • ‘p’ is ‘0’ if we are using ‘Port A’ and ‘1’ if using ‘Port B’
  • dt is the hexadecimal representation of the duty cycle (a percentage value)

The AI2 BuetoothLE extension uses a list of decimal values so

8 0 129 0/1 17 81 0 dt

Lucky for us the extension also accepts signed or unsigned values so we don’t need to take care of the conversion when duty cycle is negative:

so every time the Clock reaches our “TRACKSPERIOD” value it sends the commands for the two motors. Setting a smaller period allows a better control but also increases the activity of the App so for too small periods it might not work properly. And, of course, setting a larger period will increase the latency of our control and might also cause our connection to drop.

Hope this explanation is clear enough for anyone that wants to try their own app. Feel free to make questions on my YouTube channel, I’ll try to answer the best I can.

Making an Android app for LEGO Powered Up

The new LEGO trains are now Powered Up based.

Like WeDo 2 and BOOST, this is a Bluetooth 4 Low Energy (BLE) device that uses the new type of 6-pin plug that LEGO announced a couple of years ago with the WeDo 2. At that time this new design was referenced as Power Functions 2 or PF2 but the final name is now Powered Up.

Unlike BOOST, the new smart hub included with the trains doesn’t include motors. LEGO found a way to arrange 6 AAA batteries inside it in such a compact way that the final size is exactly the same of the Power Functions LiPo or AAA batteries… with all the new electronics included:

Others like Sariel and Hispabrick already reviewed this device so I’ll just show how to to use it.

This new hub announces itself as “HUB NO.4”.  It will probably have a much better name but for now I will call it this way.

A good thing with “HUB NO.4” is that it  provides the same UUID services as BOOST. So most of the examples I wrote for BOOST work with Powered Up with just a few modifications.

For instance, the LEGO WeDo 2 motors can be used the same way as with BOOST:

gatttool -b 90:84:2B:06:AB:5D --char-write-req --handle 0x0e --value 0800810011510060

The handle (“0Eh”) is the same. The payload is also simillar, with the same 3 initial bytes (“080081”, hexadecimal) followed by a fourth byte that selects the output port (“00” = port A, “01” = port B), followed by the same 3 bytes (“115100”) and finally the last byte is the duty cycle (or speed) applied to the motor (“60h” = 100d = 100%).

Since I already had an Android app made with MIT App Inventor 2 for the  Vernie model of the BOOST set I made just a few modifications to make it work with “HUB NO.4”:

  • removed the blocks that controlled the head and cannon trigger
  • removed the blocks that sensed the colors
  • added the BT address of my “HUB NO.4” to the list of devices to pick
  • changed the motor commands used by BOOST (simultaneous control of pair A+B) by the motor commands of two WeDo 2 motors

That’s it!

This the Designer view:

and this is the Blocks view:

If you’re interested, I exported the project as an “.aia” file. It’s not polished (for instance the blocks still make references to Vernie) but you get a good base to start.

In my next article I try to explain how this App was created.

RC servo motors with linux

Este artigo é a parte 1 de 2 da série  LEGO-compatible RC servos

You can use RC servo motors with any Arduino. Even with a Raspberry Pi, no need for special hardware – just connect the signal wire to a free GPIO and send a short every 20 ms or so, where the position of the motor is proportional to the length of the pulse (usually between 0 and 2 ms).

A “normal” computer doesn’t have GPIO pins so some kind of controller is needed. I have a Pololu Mini Maestro that can control several RC servo motors at once through USB or UART – in my case up to 24 motors.

It works great with linux – the Maestro Control Center is a .Net Framework application that runs fine with Mono but after initial setup a simple bash script is enough.

So the fastest (not the best) walk through:

Connect the Maestro with an USB cable and run ‘dmesg’ to see if it was recognized – two virtual serial ports should be created:

[ 1611.444253] usb 1-3: new full-speed USB device number 7 using xhci_hcd
[ 1611.616717] usb 1-3: New USB device found, idVendor=1ffb, idProduct=008c
[ 1611.616724] usb 1-3: New USB device strings: Mfr=1, Product=2, SerialNumber=5
[ 1611.616728] usb 1-3: Product: Pololu Mini Maestro 24-Channel USB Servo Controller
[ 1611.616732] usb 1-3: Manufacturer: Pololu Corporation
[ 1611.616735] usb 1-3: SerialNumber: 00094363
[ 1611.646820] cdc_acm 1-3:1.0: ttyACM0: USB ACM device
[ 1611.649542] cdc_acm 1-3:1.2: ttyACM1: USB ACM device
[ 1611.651109] usbcore: registered new interface driver cdc_acm
[ 1611.651112] cdc_acm: USB Abstract Control Model driver for USB modems and ISDN adapters

The first one (‘/dev/ttyACM0’) is the ‘Command Port’ and the second one (‘/dev/ttyACM’1) is the ‘TTL Serial Port’.

We download and extract the Maestro Servo Controller Linux Software from Pololu site. To run it we need Mono and libusb, the (excellent!) User Guide gives this command:

sudo apt-get install libusb-1.0-0-dev mono-runtime libmono-winforms2.0-cil

I already had libusb and with current Ubuntu (17.04) the Mono packages are different:

Package libmono-winforms2.0-cil is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
However the following packages replace it:
 mono-reference-assemblies-2.0 mono-devel

so I ran instead

sudo apt install mono-devel

It will work but it will give an access error to the device. We can follow the manual and create an udev rule or just use sudo:

sudo mono MaestroControlCenter

We will probably find our Maestro ruuning in default serial mode, i.e. ‘UART, fixed baud rate: 9600’ but we change that to ‘USB Dual Port’ so we can control our servos directly from the shell without the Maestro Control Center:But now that we are here let’s also see Status:

We can control our servos from here if we want.

Now back to the command line – in ‘USB Dual Port Mode’ we can control our servos sending commands to the Command Port (i.e. ‘/dev/ttyACM0’). There are several protocols available, let’s just see the Compact Protocol:

echo -n -e "\x84\x00\x70\x2E" > /dev/ttyACM0

Four bytes are used:

  • the first byte is always “84h” and it means we are using the “set target” command
  • the second byte is the channel number so my Maestro can accept a number between 0 and 23
  • the third and fourth bytes is the length of the pulse but in a special format:

The value is in quarters of microseconds. So for a 1.5 ms (1500 µs) we will use 6000. Usually this is the middle (center) position of the servo.

Also «the lower 7 bits of the third data byte represent bits 0–6 of the target (the lower 7 bits), while the lower 7 bits of the fourth data byte represent bits 7–13 of the target». So

So 6000d = 1770h

The third byte is calculated with a bitwise AND:

1770h & 7Fh = 70h

And the fourth byte is calcultated with a shift and an AND:

1770h >> 7 = 2Eh

2Eh & 7Fh = 2Eh

So 1500 µs is represented as 70h 2Eh

Pololu makes life easier with a bash script, ‘maestro-set-target.sh’:

#!/bin/bash
# Sends a Set Target command to a Pololu Maestro servo controller
# via its virtual serial port.
# Usage: maestro-set-target.sh DEVICE CHANNEL TARGET
# Linux example: bash maestro-set-target.sh /dev/ttyACM0 0 6000
# Mac OS X example: bash maestro-set-target.sh /dev/cu.usbmodem00234567 0 6000
# Windows example: bash maestro-set-target.sh '\\.\USBSER000' 0 6000
# Windows example: bash maestro-set-target.sh '\\.\COM6' 0 6000
# CHANNEL is the channel number
# TARGET is the target in units of quarter microseconds.
# The Maestro must be configured to be in USB Dual Port mode.
DEVICE=$1
CHANNEL=$2
TARGET=$3

byte() {
 printf "\\x$(printf "%x" $1)"
}

stty raw -F $DEVICE

{
 byte 0x84
 byte $CHANNEL
 byte $((TARGET & 0x7F))
 byte $((TARGET >> 7 & 0x7F))
} > $DEVICE

So instead of echo’ing “\x84\x00\x70\x2E”  to the Command Port we can also use

./maestro-set-target.sh /dev/ttyACM0 0 6000

So now we can control a servo with common bash commands. For example this script makes the servo rotate from left to right then back in 20 increments then repeats it 4 times:

#!/bin/bash

sleep 5
for j in `seq 1 5`;
do
  for i in `seq 4000 200 8000`;
  do
    ./maestro-set-target.sh /dev/ttyACM0 0 $i
    sleep 0.1
  done
  for i in `seq 8000 -200 4000`;
  do
    ./maestro-set-target.sh /dev/ttyACM0 0 $i
    sleep 0.1 
  done
done

So we can now control up to 24 servo motors.

So let’s control a special servo motor, more related to my hobby:

That’s a 4DBrix Standard Servo Motor, a motor that 4DBrix sells for controlling LEGO train or monorail models. They also sell their own USB controller but since it is in fact a pretty common RC micro servo inside a 3D printed LEGO-compatible ABS housing we can also use the Maestro:

The same script:

These motors work fine with 4DBrix LEGO-compatible monorail parts:

But better yet… the Maestro also works fine with ev3dev:

I now realize it wasn’t very clever to show motors rotating slowly when the monorail switches only have two functional states so this new video looks a little better, with the three 4DBrix servo motors and the LEGO EV3 medium motor changing the state of the monorail switches every second:

So I can now control 24 RC Servo motors with my MINDSTORMS EV3.

Even better: we can add several Maestros through an USB hub… so why just 24 motors? With 126 Mini Maestros 24ch and an USB hub we could use 3024 motors 🙂

Codatex RFID Sensor

Some time ago, when I started to use RFID tags with an automated LEGO train, I found out that there was a RFID sensor available for the MINDSTORMS NXT, the Codatex RFID Sensor for NXT:

Codatex doesn’t make them aymore so I ordered one from BrickLink but never got it working with ev3dev. I put it on the shelf hoping that after a while, with ev3dev constant evolution, things would get better.

Last month Michael Brandl told me that the Codatex sensors were in fact LEGO sensors and he asked if it was possible to use with EV3.

Well, it is possible, just not with original LEGO firmware. At least LeJOS and RobotC have support for the Codatex RFID Sensor. But not ev3dev 🙁

So this holidays I put the Codatex sensor on my case, decided to give it another try.

I read the documentation from Codatex and the source code from LeJOS and RobotC and after a while I was reading the sensor properties directly from shell.

After connecting the sensor to Input Port 1 I need to set the port mode to “other-i2C”:

echo other-i2c > /sys/class/lego-port/port0/mode

Currently there are two I2C modes in ev3dev: “nxt-i2c” for known NXT devices and “other-i2c” for other I2C devices, preventing the system to poll the I2C bus.

To read all the Codatex registers this line is enough:

/usr/sbin/i2cset -y 3 0x02 0x00 ; /usr/sbin/i2cset -y 3 0x02 0x41 0x83; sleep 0.1; /usr/sbin/i2cdump -y 3 0x02

(first wake up the sensor with a dummy write, then initialize the firmware, wait a bit and read everything)

Error: Write failed
No size specified (using byte-data access)
 0 1 2 3 4 5 6 7 8 9 a b c d e f 0123456789abcdef
00: 56 31 2e 30 00 00 00 00 43 4f 44 41 54 45 58 00 V1.0....CODATEX.
10: 52 46 49 44 00 00 00 00 00 00 00 00 00 00 00 00 RFID............
20: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
30: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
40: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
50: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................

The “Error: Write failed” is expected because the dummy write that wakes the Codatex sensor fails.

I got excited, it seemed easy.

So to read just once (singleshot mode) this should work:

/usr/sbin/i2cset -y 3 0x02 0x00 ; /usr/sbin/i2cset -y 3 0x02 0x41 0x01; sleep 0.25; /usr/sbin/i2cdump -r 0x42-0x46 -y 3 0x0

(wake up, send a singleshot read command, wait for aquiring, read the 5 Tag ID registers)

But it didn’t work:

Error: Write failed
No size specified (using byte-data access)
 0 1 2 3 4 5 6 7 8 9 a b c d e f 0123456789abcdef
40: 00 00 00 00 00 .....

The next days I read lots of code from the web, even from Daniele Benedettelli old NXC library. It seemed that my timings were wrong but I could not understand why.

After asking for help at ev3dev I found the reason: the Codatex sensor needs power at pin 1 for the RFID part. So the I2C works but without 9V at pin 1 all readings will fail.

LeJOS and RobotC activate power on pin1 but the two ev3dev I2C modes don’t do that. ITo be sure I tried LeJOS and finally I could read my tags:

package PackageCodatex;

import lejos.hardware.Brick;
import lejos.hardware.port.SensorPort;
import lejos.hardware.sensor.RFIDSensor;

public class Codatex
{
    public static void main(String[] args)
    {
    	RFIDSensor rfid = new RFIDSensor(SensorPort.S1);
		System.out.println(rfid.getProductID());
		System.out.println(rfid.getVendorID());
		System.out.println(rfid.getVersion());
		try {Thread.sleep(2000);}
		catch (InterruptedException e) {}
		long transID = rfid.readTransponderAsLong(true);    
		System.out.println(transID);
		try {Thread.sleep(5000);}
		catch (InterruptedException e) {}
	}
}

David Lechner gave some hint on how to write a driver but honestly I don’t understand at least half of it. So I made a ghetto adapter with a MINDSTORMS EV3 cable and a 9V PP3 battery and it finally works – I can read the Codatex 4102 tags as well as my other 4001 tags:

I created a GitHub repository with the scrips to initialize the port and to use singleshot reads. Soon I will add a script for countinuous reads.

An important note for those who might try the ghetto cable: despite many pictures on the web saying that pin 2 is Ground, IT IS NOT. Use pin 1 for power and pin 3 for Ground. And preferably cut the power wire so that if you make some mistake your EV3 pin1 is safe.

Now I really do need to learn how to write a driver instead of hacking cables. Ouch!

Update: Since yesterday (25-July-2017) the ghetto cable is no longer needed. David Lechner added the pin1 activation feature to the “other-i2c” mode so since kernel 4.4.78-21-ev3dev-ev3 a standard cable is enough.

Thank you David!

Using Grove devices to the EV3

After David Lechner announced ev3dev support for it I’ve been planning to offer myself a couple of BrickPi 3 from Dexter Industries (just one is not enough since the BrickPi 3 suports daisy chaining).

While I wait for european distributors to sell it (and my budget to stabilize) and since I’m also playing with magnets, I ordered a mindsensors.com Grove adapter so I can start testing Grove devices with my Ev3. Also got two Grove devices from Seeed Studio at my local robotics store, will start with the easiest one: Grove – Electromagnet.

ev3dev doesn’t have a Grove driver yet but since the adapter is an I2C device it recognizes it and configures it as an I2C host:

[  563.590748] lego-port port0: Added new device 'in1:nxt-i2c-host'
[  563.795525] i2c-legoev3 i2c-legoev3.3: registered on input port 1

Addressing the Grove adpter is easy, just need to follow the ev3dev documentation (Appendix C : I2C devices):

robot@ev3dev:~$ ls /dev/i2c-in*
/dev/i2c-in1

robot@ev3dev:~$ udevadm info -q path -n /dev/i2c-in1        
/devices/platform/legoev3-ports/lego-port/port0/i2c-legoev3.3/i2c-3/i2c-dev/i2c-3

So the Grove adapter is at I2C bus #3. According to mindsensors.com User Guide, it’s address is 0x42. That’t the unshifted address but fot i2c-tools we need to use the shifted address (0x21 – at the end of the ev3dev Appendix C doc there is a table with both addresses).

robot@ev3dev:~$ sudo i2cdump 3 0x21

     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f    0123456789abcdef
00: 56 31 2e 30 32 00 00 00 6d 6e 64 73 6e 73 72 73    V1.02...mndsnsrs
10: 47 61 64 70 74 6f 72 00 00 00 00 00 00 00 00 00    Gadptor.........
20: 4a 61 6e 20 30 34 20 32 30 31 35 00 31 32 46 31    Jan 04 2015.12F1
30: 38 34 30 00 00 00 00 00 00 00 00 00 00 00 00 00    840.............
40: 00 97 03 32 00 00 00 00 00 00 00 00 00 00 00 00    .??2............
50: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................

Acording to the User Guide, this is the expected content of the first 24 registers:

0x00-0x07: Software version – Vx.nn
0x08-0x0f: Vendor Id – mndsnsrs
0x10-0x17: Device ID – Gadptor

So I have a v1.02 Grove adapter.

To use the Grove – Electromagnet I just need to send a “T” (0x54) to the Command Register (0x41) to set the Grove Adapter into “Transmit” mode and next set the Operation Mode, which can be “Digital_0” (sending 0x02 to the Operation Mode register at 0x42) or “Digital_1” (sending 0x03 to the Operation Mode register).

So to turn the electromagnet ON:

sudo i2cset -y 3 0x21 0x41 0x54
sudo i2cset -y 3 0x21 0x42 0x03

And to turn it OFF:

sudo i2cset -y 3 0x21 0x41 0x54
sudo i2cset -y 3 0x21 0x42 0x02

Just a warning: with an operating current of 400 mA when ON the electromagnet gets hot very quickly – not enough to hurt but don’t forget to switch it OFF after use to prevent draing the EV3 batteries.

The same method (“T” + “Digital_0” / “Digital_1”) can be used with several other Grove devices, like the Grove – Water Atomization:

(a great way to add fog effects to our creations – just be careful with short circuits; if you add some kind of parfum you can also have scent effects)

Final note: you can use the mindsensors.com Grove Adapter with native EV3 firmware (just import the available EV3-G block) but if you are using ev3dev like me be sure to use a recent kernel (as of today, “4.4.61-20-ev3dev-ev3”) because older versions had a bug that caused some communication problems with I2C devices (the Grove Adapter is an I2C device).

Triplex – an holonomic robot

Este artigo é a parte 1 de 3 da série  Triplex

A few months ago, trying to find an use for a new LEGO brick found in NEXO Knights sets, I made my first omni wheel. It worked but it was to fragile to be used in a robot so I decided to copy one of Isogawa’s omni wheels and keep working on an holonomic robot with 3 wheels.

Why 3 wheels?

At first I only had NEXO parts to build 3 wheels but I enjoyed the experience – my first RC experiments seemed like lobsters. Controlling the motion is not easy but I found a very good post from Miguel from The Technic Gear  so it was easy to derive my own equations. But Power Functions motors don’t allow precise control of speed so I could not make the robot move in some directions. I needed regulated motors like those used with MINDSTORMS EV3.

So after assembling three Isogawa’s omniwheels and making a frame that assured the wheel doesn’t separate from the motor it was just a matter of making a triangled frame to join all 3 motors and sustain the EV3:

First tests with regulated motor control seem promising: Triplex is fast enough and doesn’t fall apart.  It drifts a bit so I’ll probably use a gyro sensor or a compass to correct it.

In this demo video I show Triplex being wireless controlled from my laptop keyboard through an SSH session. It just walks “forward” or “backward” (only two motors are used, running at the same speed in opposite directions) or rotates “left” or “right” (all motors are used, running at the same speed and the same direction).

For the code used in this demo I copied a block of code from Nigel Ward’s EV3 Python site that solved a problem I’ve been having for a long time: how do I use Python to read the keyboard without waiting for ENTER and without installing pygame or other complex/heavy library?

#!/usr/bin/env python3

# shameless based on
# https://sites.google.com/site/ev3python/learn_ev3_python/keyboard-control
#

import termios, tty, sys
from ev3dev.ev3 import *

TIME_ON = 250

motor_A = MediumMotor('outA')
motor_B = MediumMotor('outB')
motor_C = MediumMotor('outC')

#==============================================

def getch():
    fd = sys.stdin.fileno()
    old_settings = termios.tcgetattr(fd)
    tty.setcbreak(fd)
    ch = sys.stdin.read(1)
    termios.tcsetattr(fd, termios.TCSADRAIN, old_settings)
    
    return ch

#==============================================

def forward():
    motor_A.run_timed(speed_sp=-1200, time_sp=TIME_ON)
    motor_C.run_timed(speed_sp=1200, time_sp=TIME_ON)

#==============================================

def backward():
    motor_A.run_timed(speed_sp=1200, time_sp=TIME_ON)
    motor_C.run_timed(speed_sp=-1200, time_sp=TIME_ON)

#==============================================

def turn_left():
    motor_A.run_timed(speed_sp=1200, time_sp=TIME_ON)
    motor_B.run_timed(speed_sp=1200, time_sp=TIME_ON)
    motor_C.run_timed(speed_sp=1200, time_sp=TIME_ON)

#==============================================

def turn_right():
    motor_A.run_timed(speed_sp=-1200, time_sp=TIME_ON)
    motor_B.run_timed(speed_sp=-1200, time_sp=TIME_ON)
    motor_C.run_timed(speed_sp=-1200, time_sp=TIME_ON)

#==============================================

print("Running")
while True:
   k = getch()
   print(k)
   if k == 'a':
      forward()
   if k == 'z':
      backward()
   if k == 'o':
      turn_left()
   if k == 'p':
      turn_right()
   if k == ' ':
      stop()
   if k == 'q':
      exit()

Thanks for sharing Nigel!

Now let’s learn a bit of math with Python.

For those who might interest, I also have some photos with the evolution of the project.

 

Running LEGO LDD on linux

I’m finally going to try the EV3DPrinter.

3D pen

Now that my 3D pen arrived from China I downloaded Marc-André Bazergui LDD file to understand how to assemble it and then it striked me… dang, need Windows to run LDD!

I still have the Windows VM I used to update the firmware of my EV3 but I don’t want to use it (yes, I’m stubborn) so I decided to try wine. I once had LDD working with wine but never really used it and now that I got a new laptop I didn’t even bothered to install wine again.

So after a few tweaks I got LDD running – it seems that running 32-bit MS Windows programs on wine on a 64-bit linux breaks some things but essentially one just needs to add some 32-bit gstreamer plugins to make LDD work fine.

To show the full process I created a 64-bit virtual machine (1 CPU, 4 GB RAM, 32 GB thin provisioned disk), installed Ubuntu 16.10 (64-bit) on it (default installation, just enabled the download of updates while installing and the installation of 3rd party software).

As I’m using VirtualBox I also installed the VirtualBox Guest Addictions, enabled bi-directional clipboard to allow copy&past of commands between the VM and my desktop and enabled a shared folder to exchange files (just the LDD 4.3.10 setup file and the EV3DPrinter .lxf file).

Then a full last update:

sudo apt update
sudo apt upgrade
sudo apt dist-upgrade

followed by a reboot and a safety snapshot (“trust no one”).

So this is the full process:

sudo dpkg --add-architecture i386 
sudo add-apt-repository ppa:wine/wine-builds
sudo apt-get update
sudo apt-get install --install-recommends winehq-devel

at this moment, I have wine 2.4 installed:

wine --version
wine-2.4

I could install LDD right now but it will not work because at first run it tries to play some music and or video and it fails. The trick is to install some plugins for gstreamer:

sudo apt install gstreamer1.0-plugins-good:i386 gstreamer1.0-fluendo-mp3:i386

So we install LDD by just double-clicking it. As it is the first time wine runs, it first asks to install two dependencies: mono and gecko (that assures some .Net Framework and Internet Explorer compatibility).

LDD setup asks for a language (“English”) then asks us to accept the License Agreement and suggests creating two shortcuts (“Desktop” and “Quick lauch”).

Then it asks to install Adobe Flash Player and to choose a destination folder (default is fine).

When completed, we may check the option to “Run LEGO Digital Designer” but it will not work, it just shows a black window that we need to force close.

But if we launch LDD again, it works now.

Just a last issue: when opening the EV3DPrinter .lxf file we get a request for a FLEXnet license file, it is located at the installation folder:

~/.wine32/drive_c/Program Files/LEGO Company/LEGO Digital Designer/RL278-1000.lic

Everything seems to work, even creating a Building Guide and the HTML Building Instructions.

I recorded everything in this video:

It’s a long (21 min) non edited video so you may want to skip most of it (the download and installation of wine components, the install of LDD and the creation of the Building Guide).

And by the way, this is nothing really new – Marc pointed me this video with LDD running on Ubuntu 7.10 (2007!)

Virtual Mindstorms – using LEGO EV3 software on Linux

Yesterday Marc-André Bazergui incentivized me to make a video showing how to use LEGO MINDSTORMS EV3 Software inside a virtual machine. It is a shame that a product running Linux inside can only be used on PC or Mac – and that’s one of the reasons I started using ev3dev as I only have linux systems (laptops, Raspberry Pi’s, old DIY desktops without a Windows license…).

I got my first EV3 exactly 3 years ago as a birthday gift from my wife. I don’t remember if I ever installed the Windows software on a VM before – I did installed one or twice in Ubuntu with Wine (not sure why) and I did installed a Microsoft Robotics Developer Studio in a VMware Workstation virtual machine and do remember having connected it to the the EV3 thorough a bluetooth USB dongle (most modern hypervisors have this nice feature to allow a local device on the host to be passed-through into the guest).

I no longer have VMware Workstation but I have used Innotek VirtualBox in the past and knew that Oracle somehow managed to keep it alive after buying it (Oracle has the morbid habit of poisoning every good thing it owns – Java, Solaris, OpenOffice, MySQL…).

So I installed Oracle VM VirtualBox 5.1.4 (there is even a x64 .deb package for Ubuntu 16.04 “Xenial”) and after that the VirtualBox 5.1.4 Oracle VM VirtualBox Extension Pack.

It was quite easy and also very fast. After that I got a licensed version of Microsoft Windows 8 Professional (x64 also) – this is my work laptop so people immediatlely started making fun of me – hey, he is installing Windows on his laptop, finally!

The rest of the process was also quite easy after all – like I thought, it is possible to use a Bluetooth USB dongle and also just the direct USB cable connection:

  • create a Virtual Machine
  • make sure “Enable USB Controller” is checked and USB 2.0 (EHCI) Controller is selected – it might also work with USB 3.0
  • add an USB Device Filter for each USB device you want to passthrough into the VM (the EV3 itself and/or the Bluetooth dongle)
  • install Windows
  • present VirtualBox Guest Additions CD Image and install
  • define a Shared Folder so you can pass drivers and binaries into the VM
  • if the Bluetooth dongle is not automatic configured, install the proper drivers
  • pair the EV3 (or plug the USB cable)
  • install LEGO Mindstorms EV3 software and run it

I made a video showing every step (just skipped the LEGO Software as it’s pretty straightfoward):

Just one note: although USB cable connection seems to work fine, i tried to upgrade my EV3 firmware several times with no success – every single time it hangs at 0%. Perhaps it behaves better with another Windows version… who knows?

Edit: Laurens Valk and David Lechner know. So I made a second post showing how to upgrade the firmware.