Laser battling robots, takes The Cultivatormobile with a laser and light sensor so you can play laser tag with your Nerves robots. Two were given as prizes at ElixirConfEU 2017.
Hopefully you've got your robot home, intact and without any wires coming loose. In order to control the device, though, you'll need to get it onto your won WiFi network. This will involve building this repository.
- Follow the Nerves installation instructions for your platform.
cd apps/fwcp config/secret.exs.example config/secret.exs- If you are on OS X, you will need to have Docker installed.
- Edit
secret.exs, adding your WiFi SSID export MIX_ENV=prodexport MIX_TARGET=rip0mix deps.getmix firmware- You'll need to put the micro-sd card into an SD card writer on your computer. (Sorry for not supplying one).
mix firmware.burn. In my experience this can sometimes require taking the card out and resinserting if you get the error** (Mix) Could not auto detect your SD card- ???
- Profit
You can then reinsert the SD card and power up. The PI zero should connect to your WiFi and be listenign on port 80. If you have nmap installed on your computer, a quick way to scan your local network for listeners on port 80 is given below.
Let's assume your local subnet is 192.168.22.x
nmap -p 80 192.168.22.2-254 | grep -B 4 open
Connect a micro-usb data cable from your computer to the USB port (not the power port) on the Pi Zero.
ls /dev/tty.usbmodem*
Pick the tty with the smallest number, eg /dev/tty/usbmodem1
screen /dev/tty.usbmodem1
Then you'll be connected to the iEX session that the PI boots into.
This is an Elixir Umbrella application, that can be run in dev and test on a non-linux environment, specifically OS X. From root, or a specific app, you can run mix test or iex -S mix.
Applications are:
Here the Nerves magic takes place. It is from here that the release is built; it also contains some networking related utilities that will only need to run on the target machine. As is now Nerves standard practice, this application will only start if the application is built with the MIX_TARGET environment variable set to a value other than empty or host.
In addition to being the place from which firmware is created, this application is responsible for connecting to the WiFi network, and setting the system clock via ntp; for the latter see ntp.ex.
WiFi should be configured in apps/fw/config/secret.exs. This file is excluded from source contol, as WiFi connection credentials should be secret.
See above for how to build the firmware, and burn to the sd card.
Contains test-friendly replacements for hardare facing modules, that tend not to compile on OS X. Only build in dev and test
Runs the simple web interface for controlling the robot. When built for prod then it binds port 80; in dev port 4000. The interface is vanilla Plug over cowboy.
Controls the stepper motors, through the named GenServer Locomotion.Locomotion.
Simple interface for broadcasting and subscribing to application events, via Events, such as detecting a laser hit.
Fires the laser in half-second bursts.
Listens to the Arduino (Uno clone) unit, that sends the reading from the photo-sensitive resistor over the serial interface. If a laser hit is detected (by the reading being over 300) then a hit event is broadcast via events. (The laser and locomotion contols then become disabled.)
The Arduino code is in laser_read.ino.
Contains utilities for disabling controls when the bot is hit, and flashing GPIO pins if (for instance) you want to attach a LED to a pin.
Our general philosophy is that code should be unit-testable, especially when there's a certain amount of logic involved. Consequently mix test will work from the root of the umbrella, even if you're developing in OS X. iex -S mix will too. We achieve this by, Isolating network related processes in the fw application, and selectively only including certain hardware dependencies in when MIX_ENV is prod.
The Firmware is built from fw, and as is now standard Nerves practice, the application is only started when MIX_TARGET is not "host" (meaning the development machine); there is no attempt to do things like start WiFi or set the system time with ntp.
Dependencies like Elixir ALE will not compile on OS X so are only included when compiling for prod. Replacement modules are supplied in the app dummy_nerves. eg, from deps in laser/mix.exs:
{:elixir_ale, "~> 0.6.2", only: :prod},
{:dummy_nerves, in_umbrella: true, only: [:dev, :test]},
Parts listed are from UK suppliers, but you should be able to find something similar wherever you are. Joel Byler put together an Amazon whishlist for the relatated Cultivatormobile project: https://www.amazon.com/registry/wishlist/1RB8HLPX63U1Q/ref=cm_sw_r_tw_ws_x_N6P4xb8ZN9RGN .
| Part | Available from |
|---|---|
| Pi Zero W | PI Hut: https://thepihut.com/products/raspberry-pi-zero-w?variant=30332705425, or Pimoroni: https://shop.pimoroni.com/products/raspberry-pi-zero-w. Note that stocks are limited to one per customer. |
| 40-pin 2x20 male headers for the Gpio | eg https://shop.pimoroni.com/products/male-40-pin-2x20-hat-header or the solderless https://shop.pimoroni.com/products/gpio-hammer-header (not tried) |
| Female / Female jumper cables | At least 15, eg from https://www.amazon.co.uk/gp/product/B00OL6JZ3C/ |
| 5v power bank (portable phone charger) | Something like https://www.amazon.co.uk/gp/product/B00VJS9R4C. They should come with a USB to micro USB cable to connect to the PI |
| Micro SD card, at least 4GB | Bigger is ok. eg https://www.amazon.co.uk/Kingston-8GB-Micro-SD-HC/dp/B001CQT0X4/ |
| 2 x 28Byj stepper motors with ULN2003 controllers | eg 5 pieces from here https://www.amazon.co.uk/gp/product/B00SSQAITQ |
| Battery for stepper motors | For the giveaway we a used battery holder for 4 AA batteries, https://www.amazon.co.uk/gp/product/B00XHQ18DW. You need to provide between 5v and 12v to the steppers |
| Wheels | 4tronix, a UK company, sell wheels that fit the stepper motors http://4tronix.co.uk/store/index.php?rt=product/product&keyword=wheels&category_id=0&product_id=176. Alternatively here's some 3D printing files that I have found http://www.thingiverse.com/thing:862438 |
| Lasers | eg https://www.amazon.co.uk/gp/product/B00JWJ1Y8W/, soldered to female jumper cables |
| Light sensors | These were self assembled using Photoresistors, 100 ohm, resistors, bits of Veroboard cut with a Stanely knife. |
| Shrimp Arduino | These kits are available from Shrimping It. You will probably want the Shrimp parts, the stripboard kit, and the USB UART module |
| Something to attach various parts to the LEGO |
Note that the current reason for using the Arduino units was to read the analogue values from the photoresistor. A simpler alternative, that we did not follow because of delivery times, might be connecing a MCP 3008 chip over SPI.
The chassis was assembled from LEGO, for simplicity and lack of access to a 3d printer. Here are the list of bricks:
| Brick | Brick Design ID | quantity |
|---|---|---|
| BRICK 1X2X5 | 2454 | 2 |
| SLIDE SHOE ROUND 2X2 | 2654 | 1 |
| BRICK 2X4 | 3001 | 8 |
| BRICK 2X2 | 3003 | 1 |
| BRICK 1X8 | 3008 | 2 |
| BRICK 1X6 | 3009 | 5 |
| BRICK 1X4 | 3010 | 2 |
| PLATE 2X4 | 3020 | 1 |
| PLATE 6X16 | 3027 | 1 |
| PLATE 6X10 | 3033 | 1 |
| PLATE 4X8 | 3035 | 1 |
| PLATE 1X6 | 3666 | 1 |
| PLATE 2X6 | 3795 | 2 |
| FLAT TILE 1X6 | 6636 | 2 |
| FLAT TILE 2X4 | 87079 | 1 |
| Bearing element 2x2 | 10313 | 1 |
| Rim | 4624 | 1 |
Specific bricks can be bought from LEGO's online shop.
PI Zeros come without a means of securely attaching wires to the GPIO which is used to control the motors. If you use a PI Zero, then you'll want to solder on some GPIO headers. Here is one video on how to do it: https://www.youtube.com/watch?v=MSGIrtGMYRM . Alternatively, sSolderless headers are now available from Pimoroni, though we have not tried these.
You will probably also need to solder is the connection from the batteries to the power input of the ULN2003 stepper motor controller. We suggest connecting each the positive and ground to two female-ended jumper cables. See the illustration of the battery case in the parts illustration of the original cultivatormobile.
The lasers came with wires which we needed to be soldered to female jumper cables to connect to the GPIO. If you use the same lasers We would recommend soldering to the wires rather than directly to the laser; we found that heating the ground connector on the laser too much caused the laser to fail.
todo
- Connect each of the stepper motors to the ULN2003 controllers; the connection is obvious and will only be connectable in one direction. Depending on your chassis, you may want to cable tie the motors back to back.
- Connect the ULN2003 controllers to the raspberry PI. Refer to a pin map such as this from Element 14; the SD card on the PI zero is at the top of the map. The actual pin mapping is changeable in the configuration, but the default configured mapping is
- GPIO 6 to IN1 on the left ULN2003 controller
- GPIO 13 to IN2 on the left ULN2003 controller
- GPIO 19 to IN3 on the left ULN2003 controller
- GPIO 26 to IN4 on the left ULN2003 controller
- GPIO 12 to IN1 on the right ULN2003 controller
- GPIO 16 to IN2 on the right ULN2003 controller
- GPIO 20 to IN3 on the right ULN2003 controller
- GPIO 21 to IN4 on the right ULN2003 controller
- Connect the positive (marked '+') pins on both ULN2003 controller to the positive terminal of the battery case.
- Connect the negative (marked '-') pins on both ULN2003 controller to the negative terminal of the battery case.
Note that some motors appear to be wired in reverse; if you find one (or two) going the opposite way to expected then simply reverse the wiring to the controller.
todo
Follow instructions on the Shrimp site. There is also a writeup here.
Upload the Arduino code to the board via the USB UART control. You will need to install the USB driver modules
Connect the +5v and the ground to the same outputs on the Shrimp, and the sensor to analogue pin 3 - that is the third down from the right. See this diagram.
- Suggestions for improvements (eg control steppers via Arduino)
- Suggestions for enhancement (eg more sensors. Simulate a recharge period for laser)