In this tutorial we will show you how to build and integrate another addon with Leo Rover - Camera Mast.
It is inspired by camera mast built on top of NASA's rover Opportunity and is able to rotate camera through an angle of 360 degrees, more than 270 mm above the top of the Rover!
Motors that are used for this application are Dynamixel AX-12A servo's which provide feedback, are quite easy to control with usage of ArbotiX and are in decent price. If you have an access to a 3D printer, everything you need to build this addon is really easy to get and no special knowledge is needed. We will get through creating G-codes for 3D printer, assembling everything and at the end integrating it with Leo Rover.
3D printed parts
01127 (Main tube)
01129 (Second servo mount)
01130 (Second servo cover)
01125 (Rotation shaft)
01131 (Third servo mount)
01132 (Camera mount)
2x 01133 (Bearing shaft)
01134 (ArbotiX mount)
3x Dynamixel AX-12A - (link)
3x Dynamixel cable (link)
ArbotiX-M Robocontroller (link)
FTDI USB-UART cable or FTDI converter (5V)
miniUSB (male) - USB (female) adapter
2x 6800Z ball bearing (dimensions -> 19x10x5 mm)
52x40x7 mm ball bearing
8x M3 nut
4x M3 square nut
4x 2,2x6,5 screw
8x M3x10 hex bolt with button head (actually any M3x10 will be okay)
8x M3x6 hex bolt with button head (actually any M3x6 will be okay)
4x M3 brass inserts
2x M3x10 hex bolt with head cap (ISO 4762)
26x M2x8 hex bolt with head cap (ISO 4762)
26x M2 nut
You can get all of the needed files here:
As at our company we are using Prusa 3D printers, we will show how to prepare 3D models for printing using their software - PrusaSlicer. This application will provide a special file for the printer (G-code) which tells the machine what are the settings and how it should move to create our model.
First thing we need to do is to import our files to the application. Click on the
Add button (box with a plus sign at the top of the screen) and select the files you want to add.
After uploading the files, it should look like this:
Now we need to spread the models in order to avoid interference. To automatize the process, press the
Arrange button (on the right from bin icon).
The arrangement is still not perfect. Our goal is to minimize the number of walls that are "levitating" in the air to avoid support constructions that needs to be printed. Here are some hints for positioning components:
Minimize support constructions - it brings a lot of advantages:
shorter printing time,
smaller amount of used filament,
better quality of print.
Try to use big flat surfaces as base to increase adhesive area.
If some places in component are critical (ex. bearing housing, round holes) try to put them on the top of the print.
By using the buttons on the left, we can rotate and change position of every component. As you can see, we need 2 pcs of Bearing shaft (01133), so click on this part and press
+ button to add another instance of this model. When you are satisfied with the orientation of the models, press the
Arrange button again for optimal arrangement of components at the 3D printer table.
Now we can move on to the settings. You can go through all the detailed options by clicking on different tabs at the top, but if you don't have much experience in 3D printing, we recommend using system presets.
The presets can be chosen from the panel on the right side and they consist of:
They affect the layer height, printing speed and quality of the printed model. For our need, the fastest option -
0.30mm DRAFT will be enough. If you need a better quality print and you don't care about the printing time, you can choose a more detailed preset.
In our case it is
Prusament PLA and it is also our recommendation for you. For more sturdy models, you can use ABS but it is much harder in printing - it may peel of the table or the layers may not stick together and you will have to start the print from the beginning.
Select the printer you want to use. In our case it is
Original Prusa i3 MK3.
For this option, we suggest
support on build plate only. Printer will handle everything that is inside of the models and we will save some time and material. In case of some problems, you can use
support everywhere option.
Infill As the material we are using is not so strong, we are using 100% infill. In lower infill settings, the 3D printer will do grid structures instead of full infill.
If everything is set, click on
Slice now button.
You can now see exactly how your print will look like. Use your mouse to rotate, move or zoom your preview and the slider on the right side to discover individual layers of the build.
When you'll finish admiring your work, you can click on the
Export G-code button that's located on the bottom right corner. Save the file on SD card of your 3D printer, load SD card into your machine and that's it! You can now start printing.
Now, that you've built the mast, it's time to mount it on the Rover and install all the necessary software.
Camera mast needs 2 things for the operation - a power supply and an additional controller that will communicate with the Rover. The device, that we will use for communication with the servos, is ArbotiX-M Robocontroller, also suggested by Dynamixel manufacturer.
A total of 3 cables need to be connected to the controller - output of the power supply, FTDI USB-UART cable and a Dynamixel servo. To make the mounting easier, we designed a special mount for the Arbotix board that can be attached to the Rover.
When the ArbotiX board is safely mounted, we can start wiring the components. Let's start with the power supply. Dynamixel servos are powered with a 12VDC supply, the same as the Leo Rover, so we can power the board from the main battery by soldering a DC barrel jack cable as a second output of the DC-DC converter like in the picture below:
When it is done just plug in the connector to the ArbotiX board.
Next step is to connect the ArbotiX board to the LeoRover's miniUSB socket (located at the top) using a USB-UART FTDI 5V converter. We have tested 2 variations of the connection: using SparkFun FTDI breakout board and a male to male miniUSB cable or using FTDI cable and a miniUSB to USB adapter.
Last step is to connect the Dynamixel cable to any of the 3 sockets that will fit the connector.
In order to properly communicate with the servos, you need to assign them unique ID's. The most common way of choosing the ID is to set 1 for the base joint and increment it by 1 for each next joint in the chain.
Set the Dynamixel ID's like in the image below:
To learn how to do this, you can follow our guide for the Arbotix controller here:
The leo_mast_bringup package contains a configuration for Arbotix driver as well as a script that provides mast lift and lower operation through ROS services.
You can build it like any other ROS package. Start by creating an empty catkin workspace, if you don't have one yet:
mkdir -p ~/ros_ws/src && cd ~/ros_wscatkin initcatkin config --extend /opt/ros/melodic
Clone the package into the source space:
cd ~/ros_ws/srcgit clone https://github.com/LeoRover/leo_mast_bringup.git
cd ~/ros_wsrosdep updaterosdep install --from-paths src -i
Build the workspace:
Source the result space:
Now you can use roslaunch to run the driver:
roslaunch leo_mast_bringup leo_mast.launch
Apart from the topics and services described in the Arbotix tutorial, you will see two new services:
/mast/lower. The first one will lift the mast to standing position, the second one will lower the mast to the back of the Rover and relax the servo.
You can test these operations with rosservice tool:
rosservice call /mast/liftrosservice call /mast/lower
We have prepared a sample UI for the camera mast. It is just a simple control panel that demonstrates its capabilities. Don't hesitate to develop your own one and present your project to the community.
To install it on your Rover, follow the tutorial below:
Then, type in you web browser the LeoRover's address and choose the port number (for example
10.0.0.1:90). If the UI was loaded correctly, you should see the same interface as below: