RED TEAM

Mechanical SpecificationsIntroduction:

Below are the mechanical specifications for MARTHA. All calculations are included in appendix E. These specifications cover all variety of mechanical items that were manufactured in house. Items purchased by Red Team are not included in this section.

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Drive Gear Assembly (P/N: RAD-B00)

Figure 1

Purpose: The drive gear assembly is driven by the motor and connects to the tracks. The gears are essential to connect within the spaces of the tracks and run the vehicle. Motion, differential turning, and speed are dependent upon the integration of this subassembly and the involved design/materials not failing. Specifications such as surface fatigue, bending stress, torque and shear stress were considered. This assembly helps achieve requirements 1 and 10 of necessary requirements list. See Appendix E Gear Assembly for specification calculations.

Specifications:

Material Sut (psi) Sy (psi)Aluminum 6061 45 x 103 40 x 103

Steel 1050 90 x103 50 x103

Table 1

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Gear (P/N: RAD-B03)

Figure 2

Specifications:

Material

Al 6061 chosen because it can be manufactured mechanically with a mill, and has Uncorrected bending strength of 14x103 psi which yields a safety factor above 2 (the accepted safety

factor in machine design) so that the gear will not fail in bending. This gear helps to satisfy necessary requirements 1, 3, 10, and 14.

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Table 2

BendingStress 1532.16 psiStrength 12017.6 psi

Safety Factor 7.84LifeCycles 1.123x106

ReliabilityQuality Index 7Reliability 99.9%Surface Fatigue SquareFatigue Stress 33727 psiFatigue Strength 58760 psiSafety Factor 3.04BacklashGap .001 inTorque Increase 100.4%Stress Increase 101.2%Backlash Stress << Sut? yes

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Gear Shaft (P/N: RAD-B01)

Figure 3

Specifications:

Applied TorqueAlternating 0 lb-inMean 17.5 lb-inApplied Moment Max 31.7 lbfMin 0 lbfEndurance LimitUncorrected 45 kpsiCorrected 20.72 kpsiSafety FactorNsf 9.199Bending StressMax Applied 12.2 kpsiUltimate Strength 90 kpsiSafe? yesShear StressMax Applied 3.4 kpsiYield Strength 50 kpsiSafe? yes

Table 3

Material

Steel 5051 was used due to its high ultimate strength to resist the high bending and torque applied. The safety factor with steel was 9.199, well above the necessary safety factor of 2 to have a safe system.

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Drive Axle Assemble (P/N: RAD-A00)

Figure 4

Purpose: The wheels and axles and springs are essential for requirements 2, 3 and 10 of the engineering specifications document. Music note steel was used for the axle due to its high strength characteristics. The 8-foot drop and bending during the test were considered when making this decision. Extension springs were used to help tension the track, keep the axle in its notch and increase ease of assembly. The Vex/Everbilt wheels were used due to the material being analyzed as “safe” in our vehicle’s conditions and their size for track tension and drive angles. See Appendix E Spring Analyses for specification calculations.

Music String SteelTensile Strength 230-399 kpsiVex Wheels/Everbilt WheelsWheel - ABS PlasticUltimate Strength 4000 psiYield Strength 1400 psiTread - RubberUltimate Strength 2320 psiSpringsTensile Strength 170 – 230 kpsi

Table 4

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Springs (P/N: RAD-A03)

Figure 5

Purpose: The springs help to satisfy “must have” requirement 2 and 10. The track system is tensioned using the springs, which is essential for effective drive and the springs help with the ease of assembly. The springs hold the back axle in its notch and allow a large reduction in tension when putting the tracks on or off.

Specifications:

Safe Working Load Limit 19.1 lbsSpring Coefficient 14.28 N/mmTensile Strength 170-230 kpsiMax Resultant Shear on Axle 85.47 kpsiAxle Tensile Strength 350 kpsiSafe? yesMax Moment 131.11 in-lb

Table 5

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Wheel (In-House P/N: RAD-A01)

Figure 6

Purpose: The wheels chosen are safe within the system they will be operating. The friction coefficients are below 0.62 so they are low enough to provide free rotation of the axle and the wheel without wearing or causing torque issues within the rotation of the track. See Appendix E – Wheels and Axles for specification calculations.

Specifications:

Wheel StressCompression Stress .255 psi/wheelYield Strength 14000 psiSafe? yesFrictionCoefficient Static .61Coefficient Dynamic .47

Table 6

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Track Assembly (P/N: RAB-000)

Figure 7

Purpose: PVC material was used for the tread of the track in order to get traction on rough surfaces. It also is a strong enough material due to it’s yield strength being 8500 psi so that it will not fail under compression from the applied load of the vehicle since the compressive force is 3421 psi and is much less then the yield strength. The safety factor for separation for the bolted connection of the PVC and 4130 Normalized alloy steel bike chain was 49, which is extremely safe due to having a safety factor of 49 and any factor above 1.5 is considered safe. The tracks satisfy requirement 10. See Appendix E PVC Analysis for specification calculations.

Specifications:

Material: PVCUltimate Stength: 10500 psiYield Strength: 8500 psiYoung's Modulus: 490 ksiForce Applied From Screw Preload: 236.05 lbCompression on PVC from Screw: 3421 psiSafety Factor from Yielding: 1.04Safety Factor from Separation: 49Compression on PVC from Front Wheel: 72.2 psiCompression on PVC from Back Wheel: 108.3 psi

Table 7

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Chassis Assembly (P/N: RAE-000)

Figure 8

Purpose: 6061-Aluminum was used for the chassis material due to its lightweight and low cost. The applied load on the chassis is 2084.9 psi and the yield strength at that point is 40 ksi so that the safety factors against separation between the bolt and material as well as failing under compression are large enough to not need to worry about part or material failure since the safety factor came out to be 28.5 which is much greater than the desired 1.5. There is a shear stress applied to the heads of the screws connecting the side of the chassis being 1051.075 psi, but much too small to cause failure in the screws due to the yield strength being much greater. This assembly helps satisfy necessary requirements 1, 3, 4, 6 and 14. To see specification calculations for the materials reference Appendix E Chassis Analysis.

Specifications:

Material: 6061 AluminumUltimate Strength: 45,000 psiYield Strength: 40,000 psiYoung's Modulus: 10,000 ksiDensity: 0.0975 lb/in3

Force Applied From Screw Preload: 273.54 lbCompression on Chassis: 2084.9 psiStress Applied on Each Screw: 728.43 psiSafety Factor from Yielding: 1.1Safetly Factor from Separation: 28.5Shear Stress applied to Each Side Screws:

1051.075 psi

Force Applied on Screws from Chassis: 285.55 lbTable 8

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Motor Mount Assembly (P/N: RAD-C00)

Figure 9

Purpose: For each screw connection on the motor mount, none of the applied loads on the connections were greater than 2-lb since the total weight supported by the mount from other components is equal to 2-lb. This is not a great enough load in order to cause separation in any connections. This is shown by the safety factor from separation being between 190 and 24480 for each one. The greatest applied stress is on the material for the L-bar bearing connection, which is 12239.75 psi. This is still much less than the yield strength of the 6061 aluminum, which is 40,000 psi. This means that none of the connections in the motor mount are close to failing, giving them very large safety factors. See motor mount analysis in Appendix E for screw connections.

Specifications:

Screw Connections 1 2 3 4 5Safety Factor from Yielding: 1.2 1.08 1.2 4.65 1.1Safety Factor from Separation: 24480 190 48960 1350 207Force Applied from Screw Preload: (lb) 2449.5 283.806 2448.95 284.29 354.465Compression on Material: (psi) 26107 2149.44 12239.8 6216.8 8396.8Stress Applied to each Screw: (psi) 38273.5 10136 3265 3230.55 10125

Table 9

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Shaft and Bearing (P/N:RAD-C04 and RAD-C07)

Figure 10

Purpose: There is a torque applied to the motor shaft and set screws from the motor. The torque is no greater than 20,000 lbf which is not great enough for the motor shaft to fail, giving the setscrews a safety factor of 1.24, which have the lowest safety and would be the first component of the motor shaft to fail. The bearings used give enough support to the motor shaft in order for the shaft not to fail from too much torsion, which is up to 40,000 lbf from the bearing spec. sheet. The power loss in the bearing is very low making it an efficient bearing selection. For specification calculations see Motor Mount Analysis #2 in Appendix E.

Specifications:

Torque on Motor Shaft: 11513.2 lbfTorque on Set Screw 1: 19777.4 lbfTorque on Set Screw 2: 240,000 lbfSafety Factor of yielding of Set Screws 1.24Coefficient of Friction: 0.004Power Loss in Bearing: 0.006 HPStationary Torque: 0.45 lb-inRotating Torque: 0.8332 lb-in

Table 10

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Rapid Explosive Neutralization System (P/N: RAF-000)

Figure 11

Purpose: The motor, which powers the cutting blade, is a GWS Speed 300 EM350 Motor. It spins at a speed of 27,600 rpm and due to the cutting disc attached having a 3 inch diameter, creates a torque 1.5 times larger than without the disc sticking out. The required force to cut the 22 gauge copper wire is 0.135 lbf, and the motor and blade produce 1.1225 lbf of force making it capable of cutting through the wire.

Specifications:

Motor Speed 27,600 rpmMotor Power 0.0805 HPTorque on cutting blade 1.838 lb-in.Force of cutting blade 1.1225 lbfForce required to cut wire 0.135 lbf

Table 11

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Air/Soil Sampling System (P/N: RAG-000)

Figure 12

Purpose: The soil collector consists of a 4-inch 6061-Al arm connected to the servomotor, which grazes the ground when rotated 180° with 38oz-in of torque. When turned 120°, the arm closes the lid of the air collector, which requires 1.05oz-in of torque to close. The actual torque produced by the servo and arm together is 9.5oz-in so it has more than enough torque to close the lid as well as graze the ground.

Specifications:

Torque from Servo 38 oz.-in.Required Torque to close lid 1.05 oz.-in.Actual Torque closing lid 9.5 oz.-in.

Table 12

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Electronics Specifications

Introduction: Below are the electronic specifications for MARTHA. Included are all circuits designed by the Red Team. Following these are the specifications on purchased electrical components pivotal in the operation of MARTHA.

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Primary Circuit (P/N: RAH-000):

Purpose: The primary purpose of the circuit is to properly and safely distribute power to all necessary components. The wire sizes were picked to properly distribute the amount of current flowing through the circuit. To this end the wires directly transporting current from the battery to the switch and barrier strip used 16-gauge as the circuit was designed to never supply current at a level higher than 22 A. From the barrier strip the wire gauge was 20-gauge as the current is split in the strip and as such no more than the maximum amperage will travel through one wire at once. The rest of the wires used are in areas carrying PWM signals, and low current operations.

The main components of the circuit include the MyRIO, Werker 60 W-hr Battery, Hansen DC Motors, Victor 884 Speed Controllers, Lucky Electronics USB Web-Camera, and Parallax Servo Motors. The entire circuit is controlled a by a master switch that is a rated at 24 VDC and 30 Amps of current. The circuit uses a rated terminal strip to distribute current and a secondary circuit has been implemented to safely regulate the voltage into the MyRIO and distribute current from the battery to the servo motors. Below are the specifications for the circuit and observed power consumption. It should be noted that all wires are chassis-wired and that the run-times are approximate calculations as running the device at stall torque could prove troublesome.

Specifications:

16-Gauge WireMax Current 22 ATensile Strength 75 lbs20-Gauge WireMax Current 11 ATensile Strength 29 lbs24-Gauge WireMax Current 3.5 ATensile Strength 11.5 lbs

Power Consumption (W) Run-Time (hrs)Idle 7.44 8.06No Load 13.44 4.46Contact Torque 60 1.00Stall Torque 97 0.62

Table 13

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Secondary Circuit (RAH-L00):

Figure 13

Purpose: The primary purpose of the secondary circuit is to safely regulate the voltage and current going to the MyRIO to a safe 8.95 V, as well as implement a 5V external power source to power the servo motors. This is done rather than using the MyRIO as the MyRIO is only rated to output 100 mA which does not satisfy the requirements by the loaded servo motors. The resistors were calculated using the following formula (Eq. 1):

V out=V ref (1+ R 2R 1 )+ I adj R 2 Eq (1)

Where the reference voltage was 1.25V and the adjustment current was 50 μA. Below are the specifications for the components in the circuit:

Specifications:

LM338TMax Current 5AMin Current 10 mA1.0 k 2x)Power Rating 1/4 WTolerance 5%333 Power Rating 1/4 WTolerance 5%LM323TMax Current 3 AMinimum Voltage In 7.5 VPower Dissipation 30 WVout Range 4.8-5.2V

Table 14

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Tertiary Circuit (RAH-M00):

Figure 14

Purpose: The primary purpose of the tertiary circuit is to control the GWS motor. The circuit operates off of MOSFET theory, and when given a +5V input the gate will open and complete the circuit so that the motor will rotate. The resistors are included as pull-down resistors so that when the team shuts the circuit down the current will immediately drain off. Below are some specifications for the IRF746n transistor and the resistors included. Note the transistor is a power transistor and can handle massive amounts of current.

Specifications:

IRF746nMax Continuous Drain Current 53 AGate-Source Voltage 20 VPeak Operating Temp 175 °CPower Dissipation 107 W1 MPower Rating 1/4 WTolerance 5%10 kPower Rating 1/4 WTolerance 5%

Table 15

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MyRIO Specifications (In-House P/N: RAC-000)

Figure 15

Purpose: The MyRIO (figure 2) houses a dual-core ARM Cortex-A9 real-time processing microprocessor along with a Xilinx FBGA customizable I/O interface. The device has a plethora of onboard devices, such as an accelerometer and is used in this project as the microcontroller governing all onboard electrical systems. Below are listed specifications (table 1) as well as a chart relating the voltage versus current characteristics (figure 3).

Specifications:

Ideal Supply Range: 6-16VMinimum Voltage Necessary: 5.25VMaximum Power Consumption: 14 WIdle Power Consumption: 2.6 WDevice Weight: 6.8 ozMaximum Current Output (Per pin): 100 mAMaximum Voltage Ouput (Per Pin): 5.25 V

Table 16

0 2 4 6 8 10 12 140

0.050.1

0.150.2

0.250.3

0.35

V-i Characterisitcs of myRIO

Voltage In (V)

Curr

ent D

raw

n (A

)

Figure 16

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Werker 12V – 5 A-hr Battery (In-House P/N: RAH-A00)

Figure 17

Purpose: To provide power to the primary and secondary circuits.

Specifications:

Voltage Output 12VCapacity 5 AHWeight 4.39 lbsMax Discharge Current 15.0 A

Table 17

Figure 18(Courtesy: Powerstroke Electronics)

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Hansen DC Motor Specifications (In-House P/N: RAD-C06)

Figure 19

Purpose: The above DC Motor is Hansen Model number: 116-41216-48-C. The motor features an included capacitive encoder that is capable of transmitting the count of motor revolutions. Inside the main spur box are gears to maximize the output torque. The motors are controlled and regulated by the Victor 884 Speed Controllers. Below in Table (18) the specifications for the motor are listed. Attached are the Voltage vs. Current Characteristics for no-load (figure 20) and the torque applied vs. current drawn (figure 21).

Specifications:

Gear Ratio 48:1Nominal Voltage 12 VNo Load Speed 60 RPMNo Load Current 0.2 ALoad Speed 33 RPMLoad Torque 280 In-OzLoad Current (Max) 1.6 AStall Torque 672 In-OzStall Current 4.0 A

Table 18

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0 50 100 150 200 250 300 350 4000

1

2

3

4

5

6

7

8

f(x) = 0.0161211512717537 x + 0.823373493975904R² = 0.98291643115873

Current Drawn due to Applied Torque

Current DrawnLinear (Current Drawn)

Torque Applied (oz-in)

Curr

ent D

raw

n (A

)

Figure 20

0 1 2 3 4 5 6 7 8 9 10 11 120

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

V-i Characteristics of the DC Motors (No LOAD)

Voltage In (V)

Curr

ent D

raw

n (A

)

Figure 21

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Victor 884 Speed Controller (In-House P/N: RAH-B00)

Figure 22

Purpose: The Victor 884 Speed Controller is used to regulate the current into the Hansen DC Motor allowing for speed adjustment. This is achieved through the use of the field effect transistors. The speed controller is controlled using an input square wave. The team used a 50 Hz square wave with duty cycle ranging from 0.0375 to 0.1125 with 0.075 as the middle point. Below in figure (23) is the calibration curve showing the encoder count compared to the duty cycle from the motor. As can be seen the curve approaches full forward at a nice exponential curve. The current drawn by the speed controllers is directly inputted into the motors with nominal amounts being used to power the transistor and cooling fan. Further the current required to generate the PWM pulse can be considered nominal.

0.0375 0.0475 0.0575 0.0675 0.0775 0.0875 0.0975 0.1075

-25000

-20000

-15000

-10000

-5000

0

5000

10000

15000

20000

25000

Speed Controller Calibration Curves

Encoder Count (Right)Encoder Count (Left)

Duty Cycle

Enco

der C

ount

Figure 23

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20.0 MP USB Web-Camera (In- House P/N: RAH-K00)

Figure 24

Purpose: To meet the first optional requirement a camera is installed through the USB ports on the MyRIO. The camera has capability of displaying video and audio. Interfaced with LabVIEW this data is captured and recorded. The camera price was relatively inexpensive to help maintain must requirement 14.

Specifications:

Video Format 24bit RGBInterface USBFrame Rate 30 frame/secS/N Ratio 48dBFocus Range 3cm-infinityCurrent Drawn (w/ LED) 0.2 ACurrent Drawn (w/o LED) 0.15 A

Table 19

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Parallax Servo Motor (In-House P/N: RAF-A03)

Figure 25

Purpose: To achieve must engineering requirement 13 and 7, these servo motors are used to operate a soil sampling device along with the wire cutting device. Below are the specifications for the torque requirements. The servo motors are controlled using the same pulses that control the Victor 884’s. It should be noted that the maximum torque for the servo motors could not be calculated as the team did not want to damage the motors. The current when in use will vary with torque applied.

Specifications:

Max Torque (No-Load) 38 oz-inMax Current (No-Load) 140±50 mAMin Current to Hold 15 mARequired Voltage 4.8-6 VPWM Required: 20 ms off

0.75-2.25 ms onTable 20

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GWS Speed 300 EM350 Motor (In-House P/N:RAF-C00):

Figure 26

Purpose: To achieve engineering design requirement 7 another, smaller, high RPM DC motor was required. The motor is a brushed motor and as such does not require a speed controller for operation. The team installed a tertiary circuit seen above in figure (14 ) to control the motor. Below are the specifications for the motor, along with the Current Drawn to Input Voltage and the estimated stall current draw.

Nominal Voltage 12 VNo Load Speed 30500 RPMNo Load Current 700 mALoad Speed 33 RPMLoad Torque 280 In-OzLoad Current (Max) 1.6 AStall Torque 8.3 In-OzStall Current 30 A

Table 21

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0 1 2 3 4 5 60

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Current Drawn vs Input Voltage

Current Drawn

Volage In (V)

Curr

ent D

raw

n (A

)

Figure 27

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2-0.2

0.8

1.8

2.8

3.8

4.8

5.8

f(x) = 2.576 x − 0.212R² = 0.988294951959738

Stall Current vs Input Voltage

Stall CurrentLinear (Stall Current)

Voltage (V)

Curr

ent D

raw

n (A

)

Figure 28

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Control System Specifications:

Introduction: Below is the control system front panel used to control MARTHA. The language primarily employed by the Red Team was LabVIEW, with some MATLAB Code. The section provides an image of how the vehicle is controlled and a visualization of the path to be followed. Please see Appendix E for the MATLAB calculations.

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Primary Control System:

Figure 29

Purpose: The above control system provides an operator with a user friendly experience whilst controlling MARTHA. The panel displays all necessary information for operation, including the GPS coordinates, calculation results, video image display and wireless control set up. Additionally errors are displayed if the program runs into one. Below in figure 30 is a visual representation of the path the vehicle follows. Included in Appendix E are the angle calculations used to determine how much to rotate for turning.

Figure 30

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