ME490 Feasibility Study Final Version

8/8/2019 ME490 Feasibility Study Final Version

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Manatee Mining Systems

Feasibility Study

Rafael Arndt Jonathan Block Zachary Griffa Michael Riley

David Swanson Michael Varga Ryan Waldmann Eugen Zinn


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1. Awareness

WebCameras

Web Cameras can offer a wide range of visibility for the robot. Currently they are used on space

stations, autonomous robots and other projects by NASA. These cameras can be of great use to an

operator. The operator can used the cameras to navigate the robot through rough terrain, check to see if

certain robotic parts are in position, or even to measure the Lunar Regolith material gathered by a

mining machine. Depending on the quality of the picture, and the refresh rate, the cameras could be

very inexpensive or quite pricey. Regardless of the cost associated with a particular web camera, the

device will not be of much use in a low visibility environment. A high amount of dust will leave the

operator at a great visibility loss if a web camera is used in a low visibility environment. One way to

combat this down side is the variety of ways the camera can be mounted. The cameras can be placed

on almost any stationary part of the robot due to its light weight.

Revisiting the Potential Downfalls of a Typical Web Camera:1. Dust may hinder visibility or damage cameras.

2. Low quality cameras may not provide a reliable picture for the operator.

3. Having many web cameras on the same network could limit the bandwidth available for the more

important applications, such as the robotic motion control system.

Simple experiments could be run with sand and dust to determine the effectiveness of cameras in harsh

environments.

Laser Range Finder System

A laser mapping system could allow for an environment to be seen in 2D by an operator. This would

help the operator to avoid obstacles. This technology has been proven time and time again by

autonomous vehicles such as the infamous National Instruments autonomous SUV or the lowly

autonomous tram system in use by many large manufacturing companies. Currently the Manatee

Mining Systems Team is in procession of a SICK MS200 Laser Range Finder System. has access to a

laser range finder device.

Potential downfalls of a Laser Range Finder

1. The SICK Laser Range Finder is contained in a heavy, bulky enclosure.

2. The system utilizes a serial port as its main method of communication. This could pose a

communications issue.

3. Typically, high level measurement technology such as the SICK Laser finder is very susceptible to

electrical noise. This could pose a problem with multiple motor controllers in the same electrical

circuit.


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Switches

A major portion of the excavation is dumping the contents from the hopper. Knowing exactly when the

right height is reached is very important. Switches could be used to notify the operator when the bucket

or other portions have reached designated locations, or to stop the motion of said parts. Switches can

be very inexpensive, easy to operate, and require very little power to use. There can be some problems

with the switches though.

Potential Problems:

1. Switches dont tell the operator how far the hopper is from the dumping location.

2. If the switch is supposed to stop the machine at a certain point and fails, there is no other failsafe.

GPS

A thesis dissertation I found online combined a GPS system with a laser mapping system for lunar

robotics. The system could accurately pinpoint the location of the robot and allow the operator theopportunity to track the machine through all stages of operation.

Potential Problems:

1. GPS in a confined space would not be as useful as a robot in open lunar terrain.

2. Does not help operator know the initial robot position, just its position related to other locations.

Position Encoders

Using a position encoder, position is measured by a laser reading a passing encoder strip. The encoder

strip is marked in regular increments and provides accurate measurements of position with minimalerror.

Potential Problems:

1. Dust on the encoder strip could cause a misreading.

2. Should the assembly malfunction and move opposite of the direction intended, the operator would

be unaware.

Potentiometers

Potentiometers measure position using electrical resistance. An electrode linked to the moving part

moves across a plate of known resistance and the voltage drop is used to calculate position. Both rotary

and linear potentiometers exist.

Potential Problems:

1. Dust inside the potentiometer could increase electrical resistance or even cause it to stick and fail.

2. If used along a linear actuator, a relatively large potentiometer would be required.


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Position Resolver

Similar to a linear potentiometer, a position resolver employs several input signals to determine

position along two axes. This sensor may be too complex for our purposes.

Strain Gauges

Strain is measured using the voltage drop across a resistance which increases with deformation. A

common device, it can be used to detect potential failures during operation.

2. Structure

The structure of the robot will depend greatly on the excavation method, the hopper design, and the

size constraints imposed by NASA. Determining the correct material, cross-section and geometry for

the a specific part of the structure is largely dependent on the application. At this stage of the design, it

is very difficult to determine the right part without knowing the characteristics of the components that

it is required to support.

Support Method

Probably the most practical support method would be a four corner vertical beam assembly or a similar

design. Several types of methods could be utilized to strengthen the base support rods, such as

horizontal cross beams, light weight panels such as sheet metal, or gussets. The support beams could

support internal machine components using a variety of different internal beams.

Another method could be to use panels with weaker internal support beams, something similar to

fuselage. Although this method is very impractical since many of the internal components would have

to move in and out of the frame assembly and would require numerous clearance holes which wouldreduce the overall strength of the structure.

Support Beams

Using prefabricated beams takes advantage of very efficient strength per weight ratios. The bar railing

and the channel bar (shown below) have additional accessories that would allow for ease of assembly,

especially in the middle of the beam. Custom beams would allow for limitless design possibilities, but

given time constraints and cost, are mostly impractical for the base support beams.

Figure 1: Possible support beams/bars sources: mcmaster.com, grainger.com


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Connections

There are four types of connections that need to be made to the support beams.

1) Connections between beams

2) Connections between strengthening elements (gussets, brackets)

3) Connections to the robot base.

4) Connections to internal components (hopper, battery)

For most prefabricated beams, all four of these can be achieved using hardware accessories already

manufactured.

Material

The types of material to use are largely dependent on the factors the part is required to endure. The

three most practical materials to use are as follows.

Aluminum:

In general, aluminum is a strong, lightweight material which is useful for frames and brackets that willnot experience large gradients of stress. Aluminum is also very easily to machine, fairly inexpensive,

and easy to find. Aluminum can be welded, but only with a TIG or a specially set up MIG welder.

Potential downfalls of using aluminum:

1. Aluminum has a low modulus of elasticity, thus it easily bends and can warp when machined.

2. Aluminum has a high thermal expansion coefficient making it a poor choice for precision

components that experience a large gradient of heat.

Lexan:

Also known as polycarbonate, Lexan is an industry standard for light weight low-stress components

and safety guarding. Lexan is extremely impact resistant and easily machine-able. It is also relativelypopular and inexpensive.

Potential downfalls of using Lexan:

1. Low heat resistance

2. Low wear resistance

Steel

There are many types of steel available all with varying properties. Steel generally has a much larger

modulus of elasticity making it a must for high stress and shear applications. Steel should be

considered for any shafts, gears and slide rails, as well as fasteners


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3. Excavation

A major part of the lunar excavator is the excavation process itself. To take advantage of the resources

on the moon, the goal is to find a solution to collect lunar regolith. The digging process has to be

efficient due to the limited available energy provided by the battery. Another aspect to consider is the

limited time period available to collect the regolith.

Bucket Wheel

One possible solution is bucket wheel excavating. This technique has been used in surface mining for

years. Bucket wheel excavators use a wheel consisting of a continuous series of buckets to scoop

material as the wheel turns. The bucket wheel is fixed to a boom and is capable of rotating. The

material picked up by the cutting wheel is transported back along the boom by a chute or a conveyor.

Advantages:

Widely used in real world applications

Approved and reliable method

Also applicable for solid material

Disadvantages:

Complex assembly (e.g. a separate conveyor is needed)

Preferred operation for large-scale areas

Figure 3: small Bucket Wheel

(http://www.digitalspace.com/reports/sbir04-phase1-

finalreport/)

Figure 2: Bucket Wheel Excavator

(http://www.reuters.com/article/idUSTRE4AD66L20081125)


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Bucket Chain

Another common possibility is the bucket chain excavator which is similar to the bucket wheel. Instead

of buckets being placed in a ring, they are attached to a kind of a conveyor. Therefore they dig and

transport the material at the same time with one device.

Advantages:Simple construction (low cost assembly)

Widely used in real world applications

Approved and reliable method

Excavating and transporting at the same time (no need for a conveyor)

Disadvantages:

Less applicable for solid material

More power is required due to the forces

Figure 4: Bucket Chain Conveyor (http://www.towercrane-

cn.com/page/chain%20bucket%20conveyor.html)

Figure 5: Bucket Chain

(http://www.informaworld.com/smpp/section?content=a793002

866&fulltext=713240928#references)


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Auger

Device for moving material with a rotating helical screw. This principle is mostly applied in

agriculture. There are many possible solutions.

Advantages:

Simple assembly

Less power required

Several application possibilities (e.g. flexible auger Archimedes screw)

Disadvantages:

Not used or only a few real world applications for collecting solid material

Issues with large rocks due to the diameter of the tube

Figure 7: Auger with enclosed tube

(http://www.brockgrain.com/products.php?product_id=204)

Figure 6: Auger with U-Profile(http://www.usairfiltration.com/parts/auger_conveyor

s.htm)

Figure 8: Auger perpendicular to direction of motion

(http://www.freepatentsonline.com/4912862.pdf)


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4. Hopper

For the hopper a few considerations must be addressed right away. The lunar regolith has a very high

packing efficiency and fills the shape of the container that it is placed into. Because of this the hopper

should be as flat and smooth as possible to prevent build up, possibly adding fillets to the edges tofurther prevent packing. The other consideration is that when dumping there will need to be some kind

of process or action to help in releasing the regolith so that it can be placed into the collection box.

Options include applying a vibration to the material to aid its release into the collection box, or simple

motions such as shaking or hammering.

While ensuring ways the regolith will remain loose and unpacked while in the hopper is important, the

actual process of the material being transfered from the hopper to the collection box is essential to a

successful excavation. Common designs include a simple rotating hopper that is rotated or tilted until

the force of gravity begins to cause the material to fall out. This design is completely feasible and is

seen in many robotic excavators today, as well as in other applications such as dump trucks and

bulldozers. Issues with this design however include the presence of additional moving parts,

opportunities for the mechanism to get stuck or hung up on something during function, as well as

designing the extent at which the machine and its parts will be rotating.

Another feasible option is a hopper that will not rotate or tilt but instead have a removable bottom that

will open or close remotely when needed. This will allow the material to fall straight down into the

collection box. This design is based off a simple funnel or reservoir with a controlled output. Many

design options are available in terms of how the hopper releases its bottom. These include hinges that

allow the doors the swing open perpendicular to the floor, or screw drives that slide a single slabparallel with the floor. This hopper design is advantageous because it typically provides a more

controlled dump because it is falling straight down. It also alleviates the concern of dealing with the

challenges involved with rotating a large load. On the contrary, issues regarding the structural rigidity

of the excavator arise when trying to extend the hopper over the collection box linearly as opposed to

rotating. Another obvious concern of this design includes the very real possibility of malfunction in the

various mechanisms used to control the release.


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5. Controls

For our system we will be using last year's Labveiw control board, so the only obstacle will be learning

the interface, but it will be feasible.

6. Mobility

For our design we are using last years track system which has been proven to be effective in the field.

No further analysis on this will be necessary at this time.

7. Stability

The stability of the excavator was examined on a static and dynamic basis in a worst case scenario. In

this scenario, the hopper is higher than its current design. The hoppers centroid is assumed to move

toward the edge of the hopper as it is dumping, so the upper edge is assumed to be the centroid. The

centroid of the excavator is also assumed to be higher than the current design would suggest. Lastly,

the hopper is loaded with 50 kilograms of regolith, more than the current design allowance.

For static stability, a weighted average of the weight of the hopper and the excavator was taken to

determine the overall centroid. The overall centroid must be within the excavator itself for the total

assembly to be stable. Even in this worst case scenario, the overall centroid is 0.88

meters, within therequired 1 meter.

For dynamic stability, a moment was taken at point A to determine the ratio of gravity required for the

excavator to become unstable. The ratio was determined to be 0.13, which under normal conditions

should not be problem, since when the excavator is moving the hopper will be within the excavator.

When the hopper is within the excavator the ratio becomes 0.35, which might become an issue if there

is a large acceleration. Lower centroids and smaller loads in the hopper would reduce this number.


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Figure 9: The system used to calculate the excavator stability

( 80 )(0.5 ) ( 50 )(1.5 )0.88

( 80 ) ( 50 )

0

( 80 )(0.5 ) ( 50 )(0.5 ) ( 80 )(0.5 ) ( 50 )(1.5 ) 0

( 30 )(0.5 ) (80 (0.5 ) 50 (1.5 ))

0.13

A

A

Static

g kg m g kg mm

g kg g kg

Dynamic Hopper extended

M

g kg m g kg m x kg m x kg m

g kg m x kg m kg m

x g

Hopper retracted

M

!

!

!

!

!

0

( 80 )(0.5 ) ( 80 )(0.5 ) ( 50 )(1.5 ) 0

( 30 )(0.5 ) (80 (0.5 ) 50 (1.5 ))

0.35

g kg m x kg m x kg m

g kg m x kg m kg m

x g

!

!

!

!

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ME490 Feasibility Study Final Version