When thinking about the design of a outdoor field research robot we have to think about the requirements it has to fulfil. First it has to drive around autonomously, ideally also through rough terrain. Secondly it should house all the parts required for the sensor to work, including the microscope, bubbling mechanics and syringe pumps. In order to do this it has to be in the rough size range of 30x40cm. Ideally we need a multi layer structure in order to be able to fit everything in a confined space. Additionally to the minimum requirements, there are a few extras like building a modular platform such that future research projects can make use of it. With these guidelines in mind we evaluated different concepts. Using a RC Car as a base and building on top of that or using an electrical rectangular box and adding wheels to it were both options we thought of but quickly discarded. While these approaches seem easier to implement they are not suitable for our task due to their fixed rigid structure which makes it hard to add additional components. There are however professional solutions available for tasks very similar to ours. One example is HUSKY. It is a unmanned ground vehicle designed to carry research sensors and to drive around in the field. Unfortunately such a robot costs around 20‘000 EUR which makes it way too expensive for our project. Thus we decided to develop and build the whole robot from head to toe with flexibility and affordability in mind.
To design the 3d objects we used Autocad, for which a free student version is available. By modeling the whole robot with all its parts we had a very good idea whether everything fits together and how it would look like before actually printing the parts. When the design was verified, we export the files for the 3d printer (.stl file) and the laser cutter (pdf file). We had the opportunity to use a 3D printer and a laser cutter from our department at ETH. We used the 3D printing material ABS, which is impact resistant, dimensionally stable and can handle high temperatures very well. This makes it a good choice for our mechanical parts. The general design of our robot is based on using screws and nuts to hold the parts together. By using mainly standard m3 or m6 screws the robot can be fully disassembled into its single components. This also makes it easy to replace and redesign individual parts. Thanks to the precision of the 3D printer and laser cutter, it was easy to design the parts such that they fit neatly into each other.
|External Dimensions||450x380x400 mm|
|Operating System||Linux/ ROS|
Main Plate The robot has one main base plate (blue), where the four electric motors with the respective wheels are fixed. We leave a cut out for the battery in the middle and designed respective holes to mount the majority of our electrical components.
Support Connection As we only use 5mm plexiglass for our plates and have a very wide wheel base we need to support the robot. This is why along the front and back axle we 3d printed two long supporting parts (red) in order to increase the rigidity of the robot. Additionally the front one houses the two motor drivers.
Lower Plate The support connection not only increases the stability of the robot but also connects the main plate with the lower one (blue). On this plate we mounted the battery (red) allowing us to get a very low center of mass. As the microscope (green) is very tall, we mounted it on the back of the lower plate decreasing our total height.
Wheels With a corner bracket we mounted the four motors and wheels (blue), driving the robot around. The fixed wheels enable AROMA to turn around its own axis. We chose a long wheel base to reduce the friction significantly when turning.
The top Plate The top plates’ (light blue) main purpose is to hold the three syringe pumps (dark blue). Additionally we fit the motor drivers on there too, which are necessary to drive each syringe properly.
AROMA obviously comes with electronics too. A small motorcycle battery provides sufficient power. We added a On/Off Switch and a fuse to protect the components against potential high currents. With the help of a converter we not only get the direct 12V from the battery but also 5V, used by the stepper motors and the Raspberry Pi, the brain of the robot. The Raspberry Pi is essentially a small computer, where we installed Linux and ROS - a software framework for robotics. Learn more about software . A big advantage of having the raspberry pi are the Genral Purpose Input/Output (GPIO) pins. With these we are able to interface with all the external devices like motors and sensors directly. They can be configured as an input or an output providing 0 or 3.3V. Together with our motor drivers we can use this binary signal to steer the robot around and coordinate the syringe pumps and lights.
The Cost / Result
As mentioned above, there are similar systems existing on the market offering a mobile robotic platform. The big difference here are two main factors. One is flexibility: while some systems may be more durable they are not as customizable as our system. We provide the CAD files to download and build our system, such that future teams are free to build their own version of AROMA, either as we did or customized with additional or alternative parts for different applications.
The second difference is obviously the price. When considering systems like the HUSKY we are looking at a price of roughly 20’000 Euros, whereas our system costs less than 300 Euros. This makes it very accessible to other research groups and we hope it will serve as a starting platform to future teams.
|3D Parts Ca. 500 gram of Material||40|
|Acryl Glass Material||20|
|Cables/ Safety Switch||20|