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Mile-High Miners Nasa Lunabotics Project (Colorado School of Mines)

For further detail and more images, please refer to attached "Systems Engineering Report_Mile-High Miners.pdf"

Contact Information

University: Colorado School of Mines

Team Members: David Melton, David McQuade, Abe Ng, Cameron Schappell, Theresa Sung, Dane Swanson, Mallory Tayson-Frederick

Faculty Advisors: Paul van Susante, Dr. Chris Dreyer

Email Address:,,

Project Information

Title:  NASA Lunabotics  Excavation  Competition


The goal of this project is to design and build a robot that is capable of traveling across a simulated lunar terrain to a specified site, excavating and collecting lunar regolith simulant, and depositing the regolith at the starting location. The robot will be teleoperated via an 802.11g network and controlled via LabView running on a National Instruments Compact-RIO.


NI 9024 cRIO w/ NI 9133 four-slot chassis

NI 9041 High-Speed Digital I/O (x2)

NI 9201 8-channel Analog Input Module

NI 9403 32-Channel Digital I/O

The Challenge:

In May 2011, the Mile-High Miners will compete in the second annual NASA Lunabotics competition, which requires competitors to design and build an autonomous or tele-operated robot, capable of traveling across a simulated lunar terrain to a specified site, excavating and collecting lunar regolith simulant, and depositing the regolith at the starting location.          The design and construction of the Miners’ rover, MiMi, has spanned two semesters of a Senior Design capstone course, and has included several different phases. Through systems engineering design and analysis techniques, the Miners have developed a successful rover which meets the requirements          of          both          the          Lunabotics competition as well as the Senior Design course.

The Solution:


Formed with the purpose of participating in the 2011 NASA Lunabotics Mining Competition,          the          Mile-High          Miners designed their rover as required by a capstone Senior Design course. The design process behind the systems engineering techniques employed by the Miners is formatted into a Vee Chart as seen below:

Figure 1: Vee Chart

The Vee Chart was clarified using a systems engineering engine, seen in

Appendix H. The capstone course was spread out over a period of nine months where Pre-Phase A, Phase A, and Phase B were addressed in the fall of 2010, and Phases C and D are in progress during spring 2011.

To date, the Mile-High Miners are in Phase D(3); the 2011 rover is currently complete and in the final stages of testing. The design process has included customer needs analysis, brainstorming and ideation, and concept variant analysis. These steps have outlined requirements of the rover that led the Miners to a final design solution. The          following          report          details          the specifications of the competition and consequent robot design constraints. These constraints are translated into a detailed design for the rover, and followed by an analysis of the resulting design components.

A.          Design Methodology

The requirements for the Mile-High Miners’ lunar excavator, MiMi, were developed in four stages. The overriding requirements were set forth by the Lunabotics Mining competition; upon understanding these requirements, the Miners          developed          team-specific expectations to achieve a successful excavator. Next, a reverse engineering analysis of the previous CSM lunar rover, as well as analysis of rovers from the 2010 Lunabotics competition, was done to help drive the requirements for each subsystem. Subsequently,          the          individual          system requirements were combined with the overriding competition requirements to provide a full set of project constraints.

B. Resources

The Mile-High Miners consist of two mechanical engineering students and five electrical engineering students. Aiding the efforts of the team is one faculty advisor and two technical consultants. In addition to personnel, the team has access to a machine

1shop and lab space in the CSM Center for Space Resources. Additionally, the Miners have received financial help through sponsorships: three fabrication companies aided in machining efforts, National Instruments donated a complete control system, and electric motors were offered at a discounted price from the manufacturer. Lastly, the team was funded a total of $16,350 through school and industry sponsorship.

C.          Concept of Operations

At the beginning of this project, the functionality and operation of the rover were analyzed using process, functional, and black box models as well as other ideation techniques (Appendix A). These design methodologies helped the team understand the core operational needs of the competition, and allowed the Miners to identify a competition-specific strategy for the project, which can be seen in Figure 2.

During the competition, the team anticipates that the rover will collect a total of 90 kg by traversing the arena three times, collecting 30 kg each traverse. The rover will have 300 seconds to complete this goal per traverse. When subsystems of the rover are completely tested, these time allotments will be updated to reflect the robot’s true capability. The Miners will then develop a more accurate final strategy to be practiced before the competition.

Figure 2: Concept of operations

D. Prototyping

A key design method used by the Miners for integration of MiMi’s systems was prototyping. Specifically, three prototypes

were built: a marshmallow and toothpick frame, a fully functional 1:3 scale LEGO model, and a full scale wooden mock-up with a functional drivetrain (Appendix B). These prototypes provided vital knowledge about the complex geometries of the rover, as well as confirmation of concepts.



Competition Requirements

The general requirements for the Lunabotics competition include designing and constructing an autonomous and/or tele- operated robot capable of excavating at least 10.0 kg of regolith, and depositing the regolith in a one-meter tall container in a time limit of 15 minutes.

Constraints for the design of the robot include a maximum height of 2.0 meters, maximum length of 1.5 meters, maximum width of 0.75 meters, and maximum weight of 80.0 kg. The arena in which the rover will perform is a 3.88 m x 7.38 m sandbox filled with BP-1 regolith simulant.

During competition, the robot must be able to traverse rock-like obstacles 20-30 cm in diameter, as well as craters 30 cm deep and of varying width. The competition’s requirements are summarized in the Specifications Chart below:

Table 1: Competition Specifications Chart

May 2011 NASA Lunabotics Competition Requirements

Time Limit: 15 min

Excavation Min: 10 kg

Max Robot Mass: 80 kg

No Ramps Allowed

Max Dimensions: 1.5m x 0.75m x 2m

Autonomous or Tele-robotic

Latency: None

Deposition Box 1.0m High From Base

Total Sandbox Area: 7.38m x 3.88m

Obstacle Area: 3.88m x 2.94m

3 Rocks, 2 Craters : Placed Randomly


Rocks: 20-30cm, 7-10kg (not buried)

Craters: Less Than 30cm (wide or deep)

Excavation/Mining Area: 3.88m x 2.94m

Collection (Starting) Area: 3.88m x 1.5m

Average 5 Mbps Communication Rate

Emergency-Stop Easy Accessible

Power Off Command Comply

Cannot Chemically Alter Regolith

Moon Processes Only

No Ordinances or Projectiles

No Intentional Harming of Others


Senior Design Requirements

mechanical systems early on in the construction. This will allow for sufficient testing of individual subsystems as well as all integrated systems, another important design requirement.

C.          Design Margins

While designing MiMi, the Miners have built in several design margins.          First, the estimated 300 seconds of total time allotted during competition (as mentioned above) has been divided into the various functions: 15 seconds driving, 200 seconds excavating, 30 seconds dumping. This division allows for a 15 second time margin per round trip.

Second, the Miners have a tight budget for allowable mass of the rover. Each subsystem was given a mass allotment at the beginning of the design, resulting in a 10 kg mass margin.

Finally, margins were created to control the team’s budget and schedule. The budget was given a $400.00 margin, while the schedule was given a generous margin of a month to complete construction and perform full system testing.


The work load of the project has been distributed between the seven team members. The management structure can be found in Appendix D-1.

A. Schedule

To successfully design, construct, and test the rover within the allotted time, the Miners employed several scheduling tools. First, a Work Breakdown Structure (WBS) organized sub-projects and important deliverables. Also, the Miners employed a Gantt chart to produce a detailed schedule for the duration of the project and to manage changes to the project. Both charts may be

A specific part of the capstone course was to analyze customer needs for individual projects; due to the nature of the Lunabotics project, the Miners adopted a non-traditional customer foundation to further evaluate requirements for the rover. Specifically, this included speaking with the stand-in client, Dr. Chris Dreyer, the team faculty advisor, Paul van Susante, and surveying the previous CSM Lunabotics team for suggestions on improvement. In addition to these interviews, the team analyzed successful rovers from the 2010 Lunabotics Competition and from the 2009 Centennial Challenge.

From these analyses (Appendix C), the Mile-High Miners defined several additional requirements for the rover. First and foremost, the Miners found that complete integration of all sub-systems during design and construction was a main requirement.

Next, while analyzing previous CSM rovers, the biggest obstacle noted with the drivetrain was keeping the robot from becoming immobile in the loose regolith. In other rovers, this concern often led to a drivetrain design which employed tracks. A subsequent need discovered was that the electronics and power distribution for the motors and actuators needs to be in a self- contained environment, safe from the hazards posed by the regolith dust. Similarly, it was found that the controls system needs to be integrated into the


viewed in their entirety in Appendix D-2 and D-3.

Throughout the two semesters of this project, the Miners attempted to adhere to the outline schedule as closely as possible. However, several events led to dynamic changes to the timeline. The largest of these events was an underestimation of the time required to design and fabricate the rover’s frame. While the construction of this piece of the rover pushed the entire project back approximately three weeks, schedule margins and active compression allowed the project to finish on time, with slightly less time for testing of individual subsystems.

B. Budget

Currently, the project hardware has cost a little over $6,000, with the majority of the budget being directed at obtaining materials for the final rover assembly. Having used $6,000 thus far for the rover, with projected costs of $10,000 for this project, there is approximately $700 left in the accounts received through industrial monetary sponsorship. Other industrial partners have generously provided in-kind donations in the form of a controls system and machining of complex components; these donations are summarized in Appendix D-4.


Working from an initial concept based on the previously discussed requirements and prototyping, the Mile-High Miners have developed a refined final design for the 2011 rover, which indicates completion of Phases A and B in the systems engineering engine. This design consists of a 2-motor/2-tread skid-steer drivetrain, a lightweight aluminum frame, a single-chain bucket ladder for excavation, a hopper dumping system, and a robust, comprehensive control system. This design includes several

important characteristics which will give the Mile-High Miners an optimum chance of attaining the competition goals.

The chassis and drivetrain designs have been refined from the initial concept to accommodate weight constraints as well as anticipated forces. Square aluminum tubing was chosen to construct the rectangular frame to support the drivetrain, while flat aluminum cross- pieces were added for extra durability and support. The drivetrain itself consists of a set of wheels and tracks obtained from the 2010 rover, but a new tensioning system has been added to provide a strong and stable platform for achieving desired tension in the tread. Motors for the drive system, which will provide both sufficient torque and speed, have been specified based on the competition time constrains and the weight of the overall robot (empty and fully loaded).

For excavation, a single-chain bucket ladder design was chosen which will enable the rover to continuously collect regolith before traversing to the collection bin for dumping. A four-bar linkage system has been designed for mounting the bucket ladder to the rover. This will allow for efficient articulation of the bucket ladder as the rover performs different functions, such as excavation and driving. The articulation of the linkage will be powered by two linear actuators, and the motor to power the rotation of the bucket ladder has been sized using excavation force modeling.

After regolith is excavated, it is collected in the rover’s hopper and stored until it is dumped into the one-meter high collection bin. The Miners’ original concept called for the use of a rack and pinion system to haul the hopper up to the one-meter dumping height; however, as the design became more complicated, it was found that a cable/winch system combined with a skip design used in the mining industry would work better for the application at hand. The original


concept for the tipping mechanism was maintained with the skip design; the hopper is guided along two parallel rails and rotates through these rails near the one-meter dumping height as it tracks a curvature on the bottom set of rails. Using this method, the hopper/dumping system requires only one motor to accomplish motion along two different degrees of freedom.

The electronics system has been defined in a way which will efficiently integrate the mechanical systems of the rover. Analysis of the chosen motors, linear actuators, and communications demonstrated the total amount of power consumed by the rover during the fifteen minute competition. The required power will be supplied by a 24V, 6.8Ah Lithium Polymer primary battery as well as a 5V Lithium Polymer secondary battery. The power will be safely managed by a 120A circuit breaker, a fusing system, and an emergency stop button.

The control system for the rover includes a robust Compact RIO from National Instruments and the accompanying digital and analog I/O modules. Texas Instruments Jaguar motor controllers are included for the drive motors, bucket ladder motor, and hopper/dumping motor. Standard H-bridges have been chosen for control of the linear actuators. Feedback from the rover during the competition will be attained in the form of encoders on each of the four motors, potentiometers on the linear actuators, three Axis network cameras, and limit switches, providing a complete state of awareness for all rover functions.

Finally, a router which broadcasts in 802.11 b/g and a Wireless Access Point (WAP) which receives 802.11 g will be used for communication with the rover. These devices easily interface with the chosen control system as well as the network cameras.

The final design of the rover can be seen in Figure 3, as well as in Appendix E.

Figure 3: Final rover design


A. Chassis/Drivetrain

1)          Specifications and Constraints

The chassis and drivetrain have been grouped together due to interdependent specifications. For a tracked system to turn well, the chassis’ length to width ratio cannot be too large. If this ratio is too small, the robot suffers from front to rear stability issues. The chassis itself needs to be made of strong, yet lightweight material. Tracked drivetrain systems exert horizontal stress on the chassis when turning. This is especially true in the areas supporting the wheels. Therefore, these areas must be able to withstand the incurred bending stresses without yielding. Also, the design of the chassis must allow for fluid integration of the controls, excavation, and disposal systems. Additionally, the drivetrain will need to allow for flotation on top of the loose regolith as well as excellent traction and mobility. The robot must be able to move quickly and turn well without becoming stuck in the regolith. The following is a summary of specific design requirements for the chassis and drivetrain:


The robot shall be able to achieve a speed of 0.5 m/s under full load.

The wheelbase and track width shall be of similar dimensions, so as to exhibit a square shape. This will ensure a proper combination between front to rear stability and ease of turning.

The track tension shall be adjustable using a third tensioner wheel made of lightweight materials.

The entire robot shall not exceed dimensions: 1.5 m long, 0.75 m wide and 2.0 m tall.

The chassis shall allow for easy removal          of          the          drivetrain components.

2)          Design Selection

To make the transition from concept to final design, two approaches were taken with the chassis/drivetrain systems. The first was an analysis of the previous year’s rover. This led to the second approach: prototyping. The chassis prototype was constructed out of steel uni-strut, and was used to test the drivetrain system from the 2010 rover. To accommodate the new concept, the tracks were shortened and a third wheel was added as an adjustable tensioning device for the tread. This prototype demonstrated the functionality of the drivetrain concept, and has since been further refined using SolidWorks CAD software. Prototyping of the frame employed the use of toothpicks and marshmallows to visualize where frame members would need to be placed around the various components. This was necessary due the complexity of a seamless integration between control, drive, excavation and dumping systems.

The final chassis shall be made of 6061 aluminum square tubing and u-channel. The chassis will all be welded together with the exception of two pieces of aluminum u- channel used to hold the drivetrain wheels in

place. These need to be separate pieces to allow for easy removal of the drivetrain components. A section of the chassis protrudes from the front end of the rover to allow for installation of the bucket ladder components. Also, the rails for the hopper cart extend upward from the chassis at a 65 degree angle from horizontal.

The drivetrain shall utilize four main wheels to drive the tracks. The front two of these wheels will spin freely while the rear two will be driven by the drivetrain motors. The power is transferred from the motors to the wheels using a chain and sprocket system with a 2:1 gear reduction. The motors have been sized using this reduction and are capable of achieving a rover drive speed of over 0.5 m/s. The tensioner wheels will tension the belt by pushing upward on the inside of the belt, halfway between the two main wheels. This upward movement shall be adjusted using the threaded mounting studs. Nuts on these studs can be turned to change the position of the tensioner wheel. The drivetrain and chassis design can be seen in Figure 4.


Figure 4: Drivetrain design

Engineering Analysis and Testing

Finite Element Analysis (FEA) using SolidWorks Simulation was performed on the chassis of the robot. All analyses assumed a full load of regolith (30 kg). The first two analyses were performed for the robot travelling in a straight line. In the first analysis, the robot was fixed at the eight points where the wheels are attached to the


chassis. Loads were then applied for the hopper, the bucket ladder, the drive motors, and the electronics in their respective locations. The result for Von Mises stress can be found in Appendix F-1. Note that the maximum stress is annotated. The Factor of Safety (FOS) was then found by comparing the maximum Von Mises stress to the material yield strength of 6061 Aluminum. The resultant FOS was 5.7, which is a sufficient FOS considering the analysis was done at maximum load values. The second FEA was similar to the first, with changes made to the fixities. The fixities were placed on only the four outside wheel contact points, assuming a worst case scenario where the outside u-channels would support the entire load. This analysis resulted in a FOS of 3. Although this is not as high as the FOS from the first study, it proves that the chassis will remain unharmed in the worst case scenario. To test the outside wheel supports for loading during turning, another analysis was completed to ensure that the outside wheel supports could withstand the large friction forces exhibited by tracked vehicles during a turn. The resulting FOS was 5.72, proving sufficient design.

B.          Bucket Ladder

1) SpecificationsandConstraints

As a crucial part of the rover, the regolith excavation system must work quickly and reliably. It should be efficient enough in excavation that excessive battery power is not consumed by its operation, and lightweight so that the final robot does not exceed 80 kg. Also, it must not interfere with the workings of the other subsystems, particularly the drivetrain and collection bin. Although not easy to quantify, these constraints translate to the following:

The excavation system shall take no longer than two minutes to fill the collection bin.

The bucket ladder shall be no more than 10 cm away from the collection bin.

The excavation system shall stow at an angle greater than 65 degrees.

The excavation system shall penetrate at least 10 cm into the surface of the arena during excavation.

The length and height of the excavation system shall not cause the robot to exceed the maximum dimensions as laid out by the rules of the competition.

The mass of the excavation system shall be no greater than 15 kg.

2)          Design Selection

The decision to use a bucket ladder for excavation was based on a few key advantages. First, excavating small amounts of regolith at a time consumes less power and requires less force and traction than excavating one large load with a front-end loader. Also, having multiple excavation buckets adds redundancy and reliability to the excavation process. Finally, the mass of the bucket ladder is more uniformly distributed than that of a front-end loader.

To avoid geometric interferences and improve the precision of digging, it was determined that the bucket ladder should be mounted on a four bar linkage, and controlled by linear actuators. The four bar linkage has the advantage of controlling both translation and rotation. By simply adjusting the lengths and pivot points of the bars during the design phase, a myriad of geometries is available. This also allows for precision raising and lowering of the bucket ladder, which ensures that sudden excavation forces will not cause damage to the system.


The final design for this subsystem consists of an 84 cm tall single-chain bucket ladder which articulates up and down through the use of a four-bar linkage and is powered by two linear actuators. This subsystem design incorporates many important and ideal features. For instance, the lower struts can be mounted close to the ground and will accept the majority of excavation forces which will then be channeled directly to the chassis. Also, the upper struts will absorb the remainder of the forces generated from the bucket ladder and will reduce the binding issues faced from a single pivot point. The variable excavation depth required will be easily controlled with the linkage system, and the system also allows for a stow position during transit across the arena. Another advantage of this system is that the tip of the bucket ladder moves downward and directly over the collection bucket while excavating, reducing the distance the regolith will need to fall, consequently reducing dust generation. Similarly, the bucket ladder will move up and out of the way of the collection bucket when the collection bucket is raised for dumping. The bucket chain will have a tensioning capability for ease of assembly, and the individual buckets will have a curved design to reduce the excavation forces and improve the overall efficiency of the robot. A model of the bucket ladder system can be seen in Figure 5.

While the stated specifications for the bucket ladder helped construct this final design          for          the          excavation          system, prototyping proved to be an extremely useful method of design methodology. To understand the best geometry for the bucket ladder in relation to the rest of the rover, a 1:3 scale LEGO model was created. With complete functionality, this prototype revealed several dimensional deficiencies in the original concept, and allowed the Miners to create an efficient and functional design.

After creating the LEGO model, the team was able to construct a full scale prototype of the linkage system used to articulate the bucket ladder. This prototype also highlighted several problems with the original concept. For instance, it was found that having two bottom struts and two top struts of different lengths complicated the geometry. The prototype allowed the team to identify problems such as these and account for them in the final design.


Figure 5: Bucket Ladder Design

Engineering Analysis and Testing

Selecting appropriate lengths for the four-bar linkage arms was done using the Microsoft Excel spreadsheet in Appendix F-3. These lengths strike a balance between stress in the linkages, range of motion for the bucket ladder, size of the linear actuators, and the collection bin clearances.

Similar to the chassis, analysis of the bucket ladder design was done using FEA. A number of different load scenarios were considered and tested (Appendix F-4), allowing for an optimal balance between light weight and structural integrity.

The motor which drives the bucket ladder had to be sized to ensure sufficient excavating force without adding too much weight. Using a FOS of 6, the bucket ladder


requires a motor that is capable of 37rpm at about 4 Nm and can handle a peak torque of 12 Nm.

As of now, the bucket ladder has been run extensively, but not yet tested during excavation. Temporary buckets have been installed, and a final bucket design will be based on upcoming excavation testing.

C. Elevator/DisposalSystem

1)          Constraints and Specifications

During the conceptual decision making phase of this project, it was decided that the regolith storage and disposal system would consist of a cart riding on tracks which was able to tip with a purely mechanical action. While translating this concept to design, several constraints were realized. Due to power constraints, one goal was to minimize the number of motors and actuators needed. Additionally, the design must center the bucket directly over the drive-platform in order to obtain a low center of gravity, which is critical for driving the rover across the obstacle area of the arena without tipping over. Also, since the collection bin will be carrying a significant percentage of the robot’s weight and must extend to heights over one meter, a low center of gravity will mitigate the risk of tipping over during dumping. A summary of the specifications for the elevator and disposal system can be seen below:

One motor shall both translate and rotate the collection bucket.

The overall height of the rails and dumping mechanism shall not exceed 2.0 m.

The center of gravity of the system shall be less than 0.5 m above the ground during transit.

The dumping height shall be greater than 1.1 m.

The dumping point shall be greater than 0.1 m from the back of the treads in the direction opposite of the bucket ladder.

The hopper shall achieve a dumping angle greater than 60 degrees from horizontal.

2)          Design Selection

The initial concept for the hopper consisted of a cart on four independent wheels riding on tracks that curve near the top. A single motor would move the hopper along the tracks by means of a rack-and- pinion design. The hopper had a distinct shape which helped keep the center of gravity forward at all times. Another key feature of this design was that the edge of the collection bin—where dumping of the regolith would occur—remained fixed during rotation to ensure that the center of gravity remained in the center of the robot. Though this concept had many positive features, there were also several drawbacks. First, the tracks for the hopper would have required a heavy and complicated framing system. Additionally, the rack-and-pinion design would have created significant challenges for fabrication due to the complexity of gears. Lastly, there would have been a significant risk of binding.

Due to these negative features, the rack- and-pinion design was dropped in favor of a crane/winch system.

Although this change solved some of the previous issues, it was clear that prototyping was necessary in order to prove the concept before any full size construction could begin. A breakthrough in the design of this subsystem occurred while working with the LEGO prototype mentioned above. Instead of four separate tracks, only two rails were needed for the hopper to ride on. The linear system also allowed the hopper to rotate during dumping. By shifting the rotation functionality to the hopper itself, overall


weight of the rover was reduced and binding risks were eliminated.

Another challenge presented itself with this design. The winch system required for the hopper must function properly without interfering with the bucket ladder or the rotation of the hopper itself during deposition of regolith. This issue was quickly resolved by extending the cart’s frame in the direction of the tracks where the cable/rope could then attach to.

The final design realized for this subsystem incorporates many important and ideal features, and can be seen below in Figure 6. First, the required framing structure can be reasonably small and lightweight. Second, the entire functionality of the subsystem is accomplished by a single motor. The collection bin’s stow position is directly over the drive-platform, allowing for a low center of gravity during transit and reducing the length of the bucket ladder. Forces pulling the cart linearly and rotating the collection bucket do not create serious concerns of binding. The center of gravity remains as far to the center of the rover as feasible to minimize the risk of tipping over. Finally, the angle of the rails allows the collection bucket to achieve a dumping angle greater than 60 degrees.

Figure 6: Elevator/Disposal System

3)          Engineering Analysis and Testing

To estimate the torque and power that will be required by the hopper motor, a simplified model of the system was analyzed. This model was broken into two

free body diagrams (FBDs) – one for the cart and one for the pulley which are depicted in Figure 7.

Due to the relative simplicity of this calculation, the main variable affecting the performance are the weight and speed. These values would specify the torque and power needed. Based on a weight of 50 kg, and a speed of 0.25 m/s, the motor requires atleast23Nm,and115Wtoallowa dumping time of 15 s.

The hopper/dumping system was heavily influenced by the interface between the bucket ladder and the chassis/drivetrain. To ensure these systems functioned together properly at the interface, the geometry was determined from the Microsoft Excel sheet provided in Appendix F-3.

Thus far, a complete test of the hopper/dumping system has not been performed. However, a functioning concept has been demonstrated on the 1:3 LEGO prototypes, and the full-scale mock up. Additionally, the cart has been built and successfully tracks the rails on the frame. The final piece remaining to build and test is the rail cap and motor assembly.

Figure 7: Cart and Pulley Free Body Diagrams

D. Controls

1)          Specifications and Constraints

While the choice to employ a National Instruments control system was a


relatively simple one, several design constraints accompany the use of the cRIO and its supporting architecture. Because the cRIO is so comprehensive, it is prudent to choose components which can easily be integrated with the NI system. This requirement translates to the use of Luminary Micro Jaguars.

Although the NI control system is elegant, it is much less useful without feedback. Therefore, it will be necessary to equip all four motors with quadrature encoders of a high resolution. Based on the capabilities of the cRIO Digital I/O modules, the encoders can have a resolution of up to 10MHz, or 10 million pulses per rotation. For additional feedback, potentiometers will also be required on the linear actuators. Standard ranges of potentiometers for this application are 10 kΩ, which is sufficient for the necessary feedback. Other mechanical feedback will be required in the form of switches and sensors. Finally, visual feedback will also be required. The number of cameras on the rover is limited by the data rate constraint, 5Mb/s and the number of ports on the Wireless Access Points (WAPs), which is four. A summary of these constraints and requirements is:

Each motor (4) shall be equipped with quadrature encoders which require less than 10 MHz.

Each linear actuator (2) shall be equipped          with          a          10          kOhm potentiometer.

The rover shall utilize multiple switches and feedback sensors.

The rover shall utilize three cameras for visual feedback.

The rover shall be controlled using a gaming device and a laptop, and shall communicate with the rover wirelessly.

2)          Design Selection

The rover’s control infrastructure was chosen for several reasons. First of all, the cRIO is a rugged, embedded real-time controller. The use of swappable I/O modules allows it to communicate with many different sensors and devices. Specifically, the cRIO itself is composed of a High Speed Controller (NI 9024) and a four-slot chassis (NI 9133); it operates with voltages between 9V to 35V and consumes 35 Watts. The controller has an 800MHz processor, 512MB of DRAM, and 4GB of storage, making it one of the most powerful controllers NI offers. This allows the controller to perform multiple calculations in real time, which is necessary for the applications of the rover. Additionally, the controller has a USB port for memory devices, an RS232 port for serial communications, and an extra Ethernet port for any supplementary communications. The cRIO chassis will accept four modules, determined to be sufficient for this application. Communications with the cRIO are through an Ethernet port, which allows for simple interfacing with the competition required 802.11g protocol.

The task of actually controlling the rover using this architecture is accomplished through the use of a control station, which consists of a laptop, a D-Link DIR-655 Wireless router, and a Logitech Gamepad F310 computer gaming controller. The laptop runs LabVIEW 2010 and is connected to the Wireless router through a CAT-5 cable. The gaming controller is connected to the computer through USB 2.0, and was chosen because LabVIEW provides pre-made VIs for the device.

The VIs used for the gaming controller translate the controller’s actions to signals for the motor controller. The Black Jaguar motor controller accepts an RC Servo signal with a period of 20ms and a pulse width ranging from 0.67ms to 2.33ms, with 1.5ms


being neutral/stop. Therefore, the cRIO will output a PWM with a frequency of 50Hz and a duty cycle between 3.35% and 11.65%. The H-bridges accept any PWM signal with a duty cycle between 0% and 100% accompanied with a second input to switch between forward and reverse for control of the two linear actuators.

3)          Engineering Analysis and Testing

In order to test this interface, the Miners set up a development station, as shown in Figure 8. With this configuration, the individual control schemes, such as interfacing with the gaming controller or creating a PWM signal, were first developed. When these schemes were fully developed, they were integrated together. This integration was simple thanks to LabVIEW’s VI structure; one VI was created for interfacing with the controller and another for creating a PWM signal, afterward they were simply connected together.

Figure 8: Controls development station

Thus far, the Miners have been able to wirelessly control multiple motors with the gaming controller. Although multiple motors have not been run simultaneously, it is known that the robot will drive correctly due to verification that the motor controllers are receiving the correct signal. In the time ahead, sensors and other feedback devices will be integrated into the system.

E. Communications

1)          Specifications and Constraints

By considering the competition rules, the specifications for the communications were determined and are listed below. In addition to these competition constraints, a four-port WAP was deemed necessary for the purpose of synchronizing the cameras to the rover’s network. These summarized requirements are:

The average data rate used for communications with the rover shall not exceed 5 Mbps.

The communications system shall use the USA 802.11 b/g standard. Single channel communications shall

be employed. The rover shall use channel 1 or

channel 11 for communications, and all communications shall be encrypted using WPA.

The communications range shall be at least 50 ft.

The WAP employed on the rover shall have at least four ports; one for cRIO communications and three for visual feedback (cameras).

2)          Design Selection

The          equipment          chosen          for communications meets the requirements stated above. A router which broadcasts in 802.11 b/g (D-Link DIR-655), and a Wireless Access Point (WAP) which receives 802.11 g (D-Link DAP-1522) will be used for communications. The WAP was chosen because it has 4 Ethernet ports, one port which will receive/send information to the cRIO and three ports which will receive/send the camera images. The integrated Ethernet ports of the DAP-1522 will allow for simple implementation of a network for the three cameras and the cRIO.


Both the router and the WAP will allow for WPA encryption.

The USA 802.11 specification in and of itself meets many requirements. The standard will broadcast with a 150 ft range, at 19 Mbps, and on selectable channels 1 through 13, with no overlap between channels 1 and 11, as per the competition requirements.

3)          Engineering Analysis and Testing

Analysis of the communications system design included ensuring that all standards and rules were followed.

To test the communications system, the cameras and cRIO were connected to the WAP, and accessed wirelessly from the control station laptop. This test was successful, communications with the cRIO and cameras were established wirelessly.

F. Power

1)          Specifications and Constraints

While the competition requirements do not specifically address the power subsystem, there were still constraints that had to be met. These were:

The rover shall be completely internally powered.

Major electronic components shall be appropriately fused.

The power source(s) shall be able to fit in the protective case with the other electronic components.

An emergency stop button shall be implemented to cut all power to the rover.

The power system and electronic components shall weigh no more than 10 kg.

2)          Design Selection

A single 24V, 6.8Ah Lithium Polymer battery was chosen to power the entire

machine. LiPo is a fairly new technology for batteries, and compared to lead-acid and others, it is very lightweight and compact for the amount of power it can produce. The battery was chosen primarily for these properties. Figure 9 shows the single-line diagram for power distribution. The red box represents the protective plastic housing.

It was decided to fuse the major control components, namely the DC motor controllers and the cRIO. Due to the environment of the competition, and after analyzing previous teams’ experience, there is a possibility of getting stuck or jammed on some sort of obstacle. When a DC motor is stalled, it is prone to damage from the abnormally high levels of current running through it. While the rover was mechanically designed to minimize this possibility, it still must be accounted for electrically, which was done through fusing of the individual motor controllers. Also, in order to keep wiring simple and organized, a terminal block with eight integrated fuse holders was chosen.

Figure 9: Power distribution diagram

3)          Engineering Analysis and Testing

In order to ensure the battery does not die mid-competition, some analysis had to


be done on the power usage of the rover’s electronics. By breaking the system down into the individual components and determining the time each is in use for a specific task and the average current being drawn during said time, the required amount of energy in amp-hours was determined. This came to be a total of 3.8Ah, just under half of the available 6.5Ah in the LiPo battery being used. A second battery has been purchased in order to have a backup battery available at all times.

The most extensive testing done so far occurred during an all-day outreach event at which the rover was on display and demonstrated intermittently. At the time, the drive motors, linear actuators, and bucket ladder motor were fully functional, and were being activated for approximately one minute on five-minute intervals. Throughout the whole day, the battery lost only 10% of its charge. However, this testing was done under no load conditions, and further tests will be performed under loading.


A.          Final Rover Construction

Construction of the rover began with the aluminum frame. The chassis was welded into a single rigid piece using 6061 material. The          hopper          elevation          system          was constructed out of aluminum U-channel, while the remaining pieces of the chassis are aluminum square tubing. All tubing used for the chassis has a 0.125 in wall thickness. The outside U-channel pieces holding the drivetrain together are removable and attach using bolts.

Next to be assembled was the drivetrain. The rear wheels of the track system are driven while the front wheels simply allow the tracks to contact the ground. The third tensioner wheel pushes on the inside of track

and is adjusted by turning nuts on the four mounting bolts to obtain vertical movement. Slots in the frame allow for movement of the motor mount to obtain the desired chain tension, a necessity for a chain driven system.

Construction of the bucket ladder began with the ladder frame. The main frame of the bucket ladder was broken into two pieces to allow for tension adjustments in the chain. The large bottom piece of the frame houses the driven sprocket while the top piece acts as a motor mount and houses the driver sprocket. These two pieces have flanges that were bolted together. The adjustability of the chain comes from the distance between these two flanges which is controlled using plastic spacers.

The hopper for the elevator disposal system was constructed from a single aluminum sheet and pivots on the cart using two bolts. The cart itself is constructed of aluminum tubing and rides on the diagonal rails via cam-rollers. The fins, which force the hopper to tilt, are made out of layered plastic pieces which reduces weight while maintaining rigid functionality. The winch system that elevates the hopper uses two 3.0x3.0 in pieces of square tubing which slide over the diagonal rails. One of the pieces is used as a motor mount and the other has a simple polymer bearing. Round 1.0 in aluminum bar stock is spun directly by the motor and is supported on the opposite end by the bearing. The winch cable is wound about this bar stock, elevating the hopper. To make the system less flexible, pieces of aluminum strips have been run from one piece of square tubing to the other.

After construction of the mechanical systems was complete, the electronics enclosure was mounted at the hopper end of the chassis, and wired accordingly to the four motors, linear actuators, switches, and cameras.


B.          Testing Procedures

Robot testing shall take place in environments simulating the Lunarena. The drivetrain will be tested to its fullest potential on local dirt roads located on the CSM campus. This testing will include speed and turning tests under full load, and will determine the power needs of the drive motors.

The driving, excavation, and dumping processes shall also be tested in a sandbox filled with Portland cement. This mix will cheaply and effectively allow for operations in a similar environment to the Lunarena. Testing of the bucket ladder will be iterative. Iteration shall involve changes in the bucket ladder motor speed, as well as the speed of the drivetrain motors. This will let the team to find the most effective combination between bucket ladder rotation speed and the robots rate of forward movement. Testing will also allow for the determination of the proper excavation depth and drive speed. This depth shall be changed by altering the lengths of the linear actuators attached to the bucket ladder, and the settings will be recorded for competition.

The test for the dumping process will occur in the same sandbox following excavation of the concrete-sand mix. Testing will determine the maximum angle that is needed for the regolith to slide out of the hopper. The test will also prove the capabilities of the motor that acts as a winch for the hopper.


The constructed robot closely resembles the final design as very few changes had to be made during building. The chassis, bucket ladder and drivetrain have all been built according to design. Discrepancies, however, can be found in the elevator/

disposal system. Designs called for the fins to be made out of 0.25 in aluminum plate, but polycarbonate was chosen to save weight. Originally, the winch system to elevate the hopper was constructed using a single strip of aluminum. The two piece system using two 3.0x3.0 in tubing was chosen instead to save weight and increase strength.

Although the Miners consistently chose strength over weight for design assessment, the robot is less than 80.0 kg. This requirement, as well as dimensional requirements and communication requirements, have been met with the final constructed robot. The robot is expected to last for six months so that next year’s team will be able to conduct a complete analysis of this robot.


The Mile-High Miners have worked to create a specific and robust design based on the concepts developed in this project. The team has been able to successfully prepare a design that meets the requirements of the competition and satisfies the specifications put forth by concept choices. The Mile- High Miners will continue putting forth their fullest efforts in producing a quality robot to represent the Colorado School of Mines at the Lunabotics Mining Competition in May 2011.

NI Employee (retired)

Hello there,


Thank you so much for your project submission into the NI LabVIEW Student Design Competition. It's great to see your enthusiasm for NI LabVIEW! Make sure you share your project URL with your peers and faculty so you can collect votes for your project and win. Collecting the most "likes" gives you the opportunity to win cash prizes for your project submission. If you or your friends have any questions about how to go about "voting" for your project, tell them to read this brief document (


I'm curious to know, what's your favorite part about using LabVIEW and how did you hear about the competition? Nice work!!


Good Luck, Liz in Austin, TX.