Alabama Lunabotics in Hawaii!
We decided to do a complete re-design of our robot because of the change in dimensions after last year's competition. Our competition robot from last year is used for outreaches as an educational tool. We carried several of the concepts over from last year, one of them being a sweeping wheel design. One of the problems with driving on an extremely powdery and soft surface, such as the moon, is traction. Conventional steering styles pose problems on this terrain since they dig into the driving surface when they turn. Skid-steering, like a tank, is exceptionally bad with this, especially when your vehicle has a large mass. Since this competition revolves around mining and transporting, we are almost guaranteed to have high mass scenarios. We chose to operate each wheel independently and sweep them so that we can turn in one spot (or even drive sideways) while maintaining a positive driving style. Here is a model of our base showing possibilities with this driving style:
Along with the sweeping wheels, we also carried over our modular robot approach. The reason behind NASA's Lunabotics Mining Competition is to gain knowledge, ideas and innovation to use towards real-life moon mining missions. In order to accomplish real world missions, NASA has several restraints that we do not have at the competition. We have decided to take on these constraints and incorporate them into the spirit of our project even if it can put us behind other participants who follow only the competition rules. With our modular approach, we design and build a base which provides three main components: locomotion, power, and communication. On top of the base will sit a module that provides all of the mining collection, storage, and dumping operations. With this we have the option to design multiple modules (or even multiple sub-modules) and choose which one is best for the competition. This fits with our real world goals since NASA could send one base with multiple modules to accomplish different tasks. Whether they need to mine, transport, or just have a robotic platform for various sensors, NASA would only have to choose the appropriate module to accomplish the task at hand. This is a key component when you think about the enormous cost it takes to send a payload to the moon.
The base was designed to be able to carry upwards of 205kg (~450lbs) so that no matter what module we design, the base can support it. A common mounting interface, as well as a common communication interface, provide mating between the base and module. Above is a picture from some early strength testing using last year's wheels on the new base.
Alabama Lunabotics sneak-preview video spotlighting "The Base".
In order to support this strength and power electrically, we choose to use an 18v system utilizing www.banebots.com RS775 18v motors. In all there are eight of these motors on the base alone. Four for driving the wheels and the other four run the worm-gear setup which allows our wheels to independently sweep. Each of these motors have a 130A stall current so 60a/120a (60 amp continuous, 120amp peak) motor controllers were chosen for the high-torque applications. The sweeping systems do not require very much torque so they were given 25a/50a motor controllers to save power, space, and still be strong enough to power a drive motor in the event of a failure with no replacements. Failures were one of the most thought out pieces of this season's robot. We use the same RS775 motors all over the robot to make the number of spares needed as small as possible. Also this allows us to sacrifice motors from low priority areas and move them to high priority areas of the robot. In order to support this amount of current we chose to use 6AWG, 8AWG, and 12AWG wire as our primary wire gauges. This also helps us to reach our goal of supporting any module despite the weight or power requirements. All of this current comes straight through our batteries, through circuit breakers, into a 500amp relay, through our 500amp current measuring circuit and then is distributed to the base and module through bus bars and high current connectors. If there is ever a situation that the on-board 20ah Li-Po batteries are not able to run the entire system for the 10 min competition cycle, we have wired our safety kill switch so that we can have an additional relay on the module for it's own power source. This allows a very safe and clean "kill" no matter the module that is attached.
It has been very busy getting ready for and competing at the event! The following video shows a system overview with the base and the bucket wheel excavator. Due to the layout of the points at the competition we used our front end loader module instead of the bucket wheel excavator.
This video shows the developement of our front-end software over the last semester.
Here are our two competition runs which earned us 2nd place in the digging category. They are followed by the SpaceX launch we were able to attend!