design of lunar backhoe.pdf
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FINAL REPORT
ME 4182 DESI6N
Design of a Lunar Backhoe
Submitted to _r. Brazell
June 3_ 1985
Submitted by:
Brian Hatchell
Jeff KruegerScott LandersSteve DollRob SchenkRick Wilkins
( Team 2 )
(NASA-CR-Id2847) dESIGN OF A LUNAR _ACKriO_
Final Report (Georgia Inst. of Tech.)
129 p
00/37
N90-/1224
w_
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ABSTRACT
This report examines the the design of a backhoe to be used
on the moon's surface. Several modifications had to be made tothe existing conventional backhoe to. make the backhoe suitable
for the lunar environment. Among the problems encounteredinclude dissipating heat, controlling the backhoe in a soundlessvaccuum_ and accounting for the difference between the earth's
and the moon's gravitational fields. This group was left free todetermine its own design parameters for backhoe performance.
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PROBLEMSTATEMENT
Backqround
NASA is currently looking into the feasibility of buildinga lunar base station. Out of necessity_ there is now arequirement that specialized earth moving equipment be designed.This equipment must be able to work in the lunar environment aswell as have the capacity to perform its function on the lunarsoil. This particular team has been designated to design a lunar
backhoe. The design will incorporate some of the basic kinematicand fundamental principles of an analogous earth backhoe.Ho_ver_ there will be modifications to the controlling
(maneuvering) system and power system of the backhoe. This teamhas been left free to set its own design and performancespecifications.
Performance
The backhoe must be able to interface with the given
tractor design. This interface _ill consist of 5_th a physicalcoupling and, in this case_ a hydraulic coupling. The hydrauliclines will be shielded to prevent high heat buildup due to theconstant solar radiation. As a further precaution_ the hydraulicfluid will have a flash point in excess of 400 degrees F ( 205
degrees C). The backhoe will exert high digging forces, which,along with the weight of the backhoe_ will have to be
counterbalanced by the weight of the tractor and outriggers onthe backhoe. This digging forcer as yet unspecified, will be inthe range of 1000 Ibs. as a result of the combined cylinderforces in excess of 9000 lbs. The capacity of the bucket will be
in the range of 7 cu. ft. and the maximum digging depth will bein the range of 120 in. (304.8 cm). The bucket may be equippedwith quick disconnects to allow for the easy installation of
other buckets_ other tools_ etc. The different links will bedesigned to be lightweight_ have low heat capacity, and havehigh strength to prevent bending. This criterion will give rise
to a tube design. The backhoe will also have to be a free
standing unit when not in use.Environmental limitations will necessitate designing aremote control package for the backhoe. These controls may have
a resistant feed back loop so that the operator can feel thebackhoe working_ or a relief valve may be placed in the
hydraulic system. Both of these precautions will prevent theoperator from overloading the system.
Constraints
The main constraint of the backhoe is the lunar
environment. Basically, it is in a vacuum, constantly night orday, with a constant influx of solar radiation and one sixth the
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gravity of earth. This poses several problems for the backhoe.There will be a large heat buildup in any mass put there and theonly means of heat transfer will be by radiation. Thus_ it willbe difficult to dissiPate heat due to friction or heat buildupin the hydraulic lines. Since there is only one sixth thegravity as that on earth, it will be difficult to counterbalancethe digging forces. Due to the vacuum_ it will be necessary forthe operator to wear a spacesuit and this will limit theoperator's maneuverability and his field o vision. The vacuumwill also make it impossible to hear the equipment operating.
The lunar soil is also a limiting factor. The soil is a
cohesionless_ fragmental rock type. It will be very abrasive tothe materials and will necessitate the use of very hard
materials. It is also a powdery top soil which will furtherlimit the operators _ield o_ vision.
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CONTROLS
The open loop control system used to control the backhoe
cylinders consists of a stack of six electro-machanical
servo--valves, a handheld controller/transmitter, and a radiorecei vet.
The valves are four-position, two way, closed centerdirectional servo-valves that uses a torque motor to control a
spool that diverts the hydraulic fluid into and out of thecylinders. The position of the spool is proportional to the
magnitude of current to the motor. The amount of flow of thehydraulic fluid is controlled by the position of the spool. Atthe null position, no flow passes to the cylinders, and at fullrated current to the motor, full rated flow is driven to the
cylinders. Six valves are used to control the backhoe: one eachfor the shovel, bucket, dipstick, swing, and left and right
outrigger cylinders. One valve is used to control the two swingcylinders.
The valves that were selected are stackable, with one
connection needed for inlet pressure and one for oulet. Full
pressure ( 2500 psi ) is available to each cyclinder. To preventthe operator from overloading the system, relief valves arelocated at the inlet manifold and at each valve stage. Each ofthese relief valves are to be set at 2500 psi. To limit the
maxium force exerted by the cylinders, pressure control valves
are to be placed between the valves and the cyclinders.The maximum temperature under which the valves can be
operated is 100 degrees Celsius using Viton seals. With the
hydraulic fluid heat exchanger, the valves should be suitablefor operating for an indefinite period. Other specificinformation for the valves is located in the appendix.
The valves are controlled by a radio receiving unit that
drives the torque motor with a current proportional to thestrength of the input radio signal. The input signal ismultiplexed to allow for maximum signal reliability. Otherfeatures of the receiver include: environmentally sealed NEMA-4
Junction Box_ internal mountings that permit the unit to bedirectly mounted to the backhoe, a plug in card that mates thereceiver to one sending unit so that several backhoes may be
operated in one area, and ramp output for the proportional
controls for smooth cylinder motion. The receiver requires a 12volt power source, so that the box can be directly connected to
the tractor's battery.The receiver should be mounted on the tractor where it will
not be physically abused and where it can provide clear line ofsight to the operator location. It is suggested that thereceiver be mounted at the rear of tractor near the backhoe
interface. The receiver can be operated at or below 140 degreesFarenheit. Given that the reciever will be stored at 70 degreesFarenheit and that the maximum temperature of the backhoe will
be 250 degrees Farenheit, a properly shielded and insulatedreceiving box could be operated for at least 4 hours under
direct radiation. Material suggested for shielding andinsulating the receiver are the same as those used to protect
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the hydraulic lines.The controlling/transmitting device is a portable handheld
sending unit with 6 spring loaded levers for proportionalcontrol and 8 spring loaded toggle switches for on/off control.Only the proportional controls will be used to control thebackhoe. The sending unit can either be clipped to the spacesuit of the operator or hung around his neck with a neck strap.The controls can be operated with the operator wearing gloves.The sending unit uses a 12-volt rechargeable battery thatprovides 4 hours of continous operation. Other features of thesending unit include: environmentally sealed UHF transmitter_custom label for controls, 2 dead man switches (one of whickmust be depressed to operate the sending unit), and 1/4 mile
line of sight control.A suggested configuration for the control on the sending
unit is provided in Figure I . With the controls set up as
shown, the operator can use the backhoe for digging by squeezing
the dipstick and boom levers together with his left hand. Also,to dump a load of soil, the swing and bucket levers can be
squeezed together with the right hand. This configuration willprovide maximum convenience for the operator, and was suggested
by an actual backhoe operator.The sending unit converts data from the on/off switches and
potentiometers into digitally coded l s and O's. Five bitsprovide for thirty-two possible levels of control where fifteenare for + and -- control each and the remaining t_o levels
provide for control off . Scanning of the switch andpotentiometer positions occurs at a rate of twenty times persecond. ]lle transmitter is capable of providing four different
FM frequencies.The receiver operates at the same frequencies as the
transmitter. An included scanner samples the carrier frequency
continuously for a .15 second period. When data is received itis sent to a shift register where it is compared to a codecard to check for agreement between the code card and sending
code. When the comparisons are checked and confirmed, the datais transferred from the shift register to the a position in
memory. The data is then processed through buffers and relaysfor the on/off switches and digital/analog converters for the
proportional controls. The next digital data is similarlyscanned and if the comparisons are successful, the data enters
memory one twentieth of a second later. Included in the receiverare several fail-safe logics. The sending code must be verified
for each data set, several successive ON commands must be
processed to turn the function on, and valid transmissionoutput will return to zero within one-half of a second ifsucceeding command data is not received.
The control system for the lunar backhoe was designed to beeasy and safe to use, easy to set up and service, and withfeatures to prevent the operator from damaging the system. Radiocontrol was selected over manual control to give the operator
manueverability to compensate for his inherent difficulties with
seeing out of a space suit. Moog was chosen as a vendor for the
radio controls because they were the only company that provideda radio transmitter and receiver that could be used directly
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Figure $
Suggested Control Arrangement for Radio Sending Unit
Left
Swing B
Ri ght
Out
Bu kt El.In
Down
Left Outrigger E
up
hbuttont
Moog
SendingUnit
Out
Dipstick
In
Up
Boom
Down
Down
_ Right Outrigger
Up
i i
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with servo-valves without additional electronic hardware. Theircontroller is by no means the most convenient one that could be
designed for the backhoe operator: a two joystick tummy packwould provide for a system closer to the one on conventional
backhoes. The joysticks would also be easier to use with gloves
on the operator's hands. But designing such a unique system
would introduce complexities that woud require matching manyelectrical components compatible with the chosen servo-valves.The sender/receiver from Moog was specifically designed to becompatible and electrically matched for the servo-valves. Sowith this system, we have a tried and proven system with nocom40atibility problem.
The chosen valves are stackable into a very tightconfiguration for easy mounting on the backhoe. With the relief
valves on the main manifold and for the individual cylinders,the operator or the load cannot easily overload the hydraulic
system. Also, with the pressure controlling valves between thecylinders and the valves, the maximum force exerted by thecylinders can be limited. This will prevent the operator fromlifting the tractor off the ground.
The specification sheets that were provide by Moog for thevalves, transmitter, and receiver are provided in the appendix.
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HYDR_I_LIC SYSTEM - GENERAL SPECIFICATIONS
The hydraulic system is designed to operate using GeneralElectric Versilube F-50 hydraBllc fluid over a temperature rangeOF to 2OOF. Hydraulic hoses and cylinders which can operateeasily under these conditions have been selected and are speclf_ed
in their respective sections. In addition, provision has beenmade for a liquid convection cooling system and shielding againstsolar radiation so that the considerable amount of heat generated
under operating conditions can be dissipated.A_I cylinders are double acting and honed for concentricity
and finish. The piston rods are hlgh-tensile, die drawn steel,
hardened, ground, polished, and chrome plated. Cylinder pistonpackings are of the chevron type. The rod packings are of thechevron type also, but incorporate a viton U seal. The
packing gland supports and retains the rod packing, bearing sleeve,rod wiper, and backup ring. Cylinder pivot and anchor pointsutilize self lubricating bushings. The swing cylinders employ
a connecting hose at the rod ends of the cylinders that permitoil flow between them.
The main control valve is a stack-type assembly consistingof six sections containing spring centered, remote controlledspools which direct high pressure pump oil to the individualcylinder circuits. Each circuit contains a spring loaded check
valve to check the flow from either cylinder port to the valvepressure passage. Also, each section contains adjustable circuit
relief valves to protect against pressure overloading. The maincontrol valve is also equipped with an inlet end cover and an
outlet end cover. The inlet end cover contains the inlet portand the system relief valve. The outlet end cover contains the
return oil port which returns low pressure oil to the reservoir,and the backpressure relief valve. The backpressure relief valveis a simple pilot operated relief valve that functions when the
pressure in the return oil passage is approximately 250 psi great-er than the pressure in the sump oli passage.
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HYDRAULIC FLUID COOLING
Method One
Since the ambient temperature on the moon is high and
the enviornment is a vacuum it is necessary to cool the hy-
draulic fluid. The friction of the fluid will produce much
heat and since there is no air, the heat cannot be transferred
to it. The radiation will be blocked by the shield; however,
the shield will in turn radiate heat to the hydraulic line.
The simplist solution to this problem is to enclose the
whole hydraulic line with a fluid. This fluid will be contained
in the outer hose of a coaxial hose scheme where there are two
hoses, an inner and an outer. The sections of line that are
rigid tubing will then be rigid coaxial tubing.
Th_s coaxial tubing is common and can be purchased from
System Components in Atlanta, Georgia. There seems to be no
manufacturers of coaxial hose and coaxial hose fittings. The
hose can be assembled with the recommended teflon hose inside
a common two inch stainless steel hose. The fittings can be
machined and assembled (see later drawings).
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Backhoe Design
All the materials used in the backhoe are made of an
aluminum alloy 60&&-T&. This alloy contains the strength_workability_ and machinability necessary for the tubular design.
The boom member is of a C-section design to provide space forthe radiator used to cool the hydraulic system. The dipperstickmember is a tubular section since the hydraulic components arenot internal to that member. All members have been designed as aconstant strength beam. This criterion is defined such that thesectional modulus is equal to or greater than the maximumbending moment at a section divided by the maximum allowable
stress in a member. The shape of each member follows the shapeof the bending moment curve closely_ thus defining the taperedsection toward the pin ends. All members are a constant 1/4 inch
in thickness. The bucket to be used will be a standard steel_ 18inch bucket whose capacity is 4 cubic feet (heap capacity wouldbe approximately & cubic feet).The backhoe will be made with a
quick disconnect at the bucket interface thus allowing for adifferent bucket or a different tool to be used. The guide linkand bucket link will also be of aluminum. All pins to be
incorporated in the backhoe will be of a carbon steel alloy. Ateach pin connection there will be a pressed fit sleeve that willabsorb the forces and distribute them evenly to the aluminum. In
this way_ stress concentrations will be greatly reduced in thevicinity of the pin connections.
The hitch_ which is the physical coupling to the tractor_consists of two parts: the pivot hitch and the interfacinghitch. The pivot hitch will be of cast aluminum 6066-T&. This is
where the backhoe connects indirectly to the tractor. Thefunction of this hitch is to produce the swing angle of the
boom. It contains the bore hole about which this hitch pivotsand it also contains the single pin connection to which theswing cylinders connect. The interfacing hitch_ as the namesuggests_ is the direct connection to the tractor. The interface
consists of a hooked bottom and a pin connection at the top;this will allow for easy disconnection and connection. The hitchconsists of a four inch tube stock frame with four 1 1/2 inch
aluminum plates welded and supported to the frame. The swingcylinders are connected in the center of the two sets of plates.
The stabilizer cylinders and legs are also an integral part ofthis interfacing hitch. The connection between the pivot hitchand the interfacing hitch will be time consuming and
complicated. First the pivot hitch is press fitted with a sleeveand inserted between the aluminum plates on the interfacinghitch. Once the bore holes line up_ the sleeve is then linebored and the resulting bore hole is fitted with a pin.
We are assuming that the bearing surfaces used are of a
non-lubricating type. This will eliminate the need for any hightemperature grease or self lubricating bearings.
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Hydraulic Cylinder Specific Vendor Information
Carter Controls, Inc. will custom build h_draulic cylinders tothe dimensions listed for their Roundlin_welded cylinders.These cylinders are capable of extended operation at 450 degreesF and 3000 psi. The required structural specifications weredeveloped in the section on cylinder sizing. Mounting conditionsare shown in the main diagram of the hydraulic system.
Bucket Cylinder Special Requirements
1) Pivot Mount Both Ends, Use Eye RE 2.2) Equip Cylinder with external tubing such that both
connections are at cap end- use 3/4 ' steel tubing with 1 1/16 -12 SAE 37 degree Flared male fittings, facing cap end.
Dipstick Cylinder Special Requirements
1) Pivot Mount Both Ends, Use Rod Eye RE 3.2) Equip Cylinder with external tubing such that both
connections are at center and facing cap end- use 3/4 steeltubing, same fittings as bucket cylinder.
Boom Cylinder Special Requirements
1) Pivot Mount Rod End, Use Rod Eye RE 3. CLevis mount Cap End-RC 3.
2) Equip Cylinder with external tubing subject to sameconditions as Dipstick Cylinder.
Swinq Cylinders (2)
1) Pivot Mount Cap End of both, rod end of one; use CLevis;mount RC3, rod end of other use Rod Eye RE 3.2) No external tubing.
Stabilizer Cylinders (2)
1) Pivot Mount Both Ends, Use Rod Eye RE 3.2) Equip Cylinder with external tubing such that bothconnections are at cap end_ one cylinder with connections atright angle on left, the other cylinder with connections at
right angle on right. Use 3/4 steel tubing_ same fittings asbucket cylinder.
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PIN CONNECTIONS
All the pin connections will be similar. The description
of one will be demonstrational for the rest. The main problem
is that there needs to be a high strength steel pin connecting
the rod eye of the cylinder to the aluminum member. The alum-
inum member welded up as shown in the drawings, is much softer
than the pin and upon any impact, the aluminum will absorb
the energy since there is going to be some clearance between
them. The solution is to insert an alloy steel sleeve inside
the aluminum member by means of a press fit. Thus the sleeve
will absorb some of the impact energy while redistributing
the remaining energy over a large area of aluminum.
The aluminum member shown in the drawing will be welded
as shown and then line bored to exact tolerances. The pin and
steel inserts will be machined 4340 steel drawn at lO00OF having
a hardness of 50 to _5 Rockwell C scale. The machining
operation will use a cubic Boron nitride tool which is capable
of machine this very hard steel.
The pin will be held in place by the plate coupler on the
end. Grade eight bolts will extend through this coupler plate
deep into tapped holes in the aluminum member.
Bearings that will be used in the pin connections will be
a low speed, non-lubricating bushing type. The bearings are
called _etcar tm high temperature bearings and are capable of a
working temperature of 750F and a maximum temperature of 900OF.
They can be purchased from Metalized Carbon Corporation located
in ossining, New York.
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MATERIALS
In the area of structural materials, there is a need to
minimize weight and maximize strength and toughness. It was
found that high strength aluminum would be the most suitable.
Although some high strength steel alloys have a higher strength _
per pound, the aluminum was found to be more favorable. Three
aluminum alloys were under consideration. First, 7050 T736
has twice the fatigue strength of the others and is commonly
used for die forgings in aircraft; however, it is difficult
to weld. Secondly, 6066 T651 has a UTS of 57000 PSI and is
commonly used as forgings and extrusions for welded structures.
It is difficult to weld with gas but can be welded by arc.
Thirdly, 6061 T6 has a UTS of 42000 PSI and is commonly used
in fabrication because of its ease of fabrication. It has ex-
cellent welding characteristics both for gas and arc.
The GXXX series aluminum alloy contains silicon and mag-
nesium while the 7XXX contains 1% to _ zinc with smaller per-
cents of magnexlum, copper and chromium. The 7XXX series has
by far the best strength characteristics; however, due to its
poor welding characteristics the 6066 T651 and 6061 T6 are the
alloys that are recommended.
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COST ANALYSIS
Description Vendor Part# Quantity Price
Note: all hose is Deutsch Co. Teflon High Pressure with TeflonCore and Steel Braid Cover.
16 Flexible Hose 207220241612
244028
36
5440 ....3624
408032
3/4 Steel Tubing.` 48 .Standard.` Use 1 1/1612 Thread Female
SAE 37deg _ I aredconnections, both ends
Bucket CylinderDipstick CylinderBoom CylinderSwing Cylinder
Stabilizer Cylinder
84A0100012C01684A0100012C02084A0100012C07284A0100012C02084A0100012C024
84A0100012C01684A0100012C01284A0100012C02484A0100012C040
84A0100012C02884A0100012C036
84A0100012C05484A0100012C040
84AO100012CO3&84A0100012C02484A0100012C04084A0100012C080
84A0100012C032
1 $8.00
1 $10.006 $216.001 $10.001 $12.00
1 $8.001 $6.002 $24.00
1 $20.0O1 $14.002 $36.00
1 $27.001 $20.002 $36.002 $24.00
1 $20.002 $80.00
2 $32. OO
2 $20.001 $300.001 $450.00
1 $700.002 $300.002 $4OO.O0
Aluminum Tubing 6066 T6
Manufacturing o_ Materials10 men
12 weeks40 hrs/week
$18/hrPins and SleevesSleeve Insert
Bearings.` high temperature
Metallized Corp.Ossing.` NY
Additional Labor
Hydraulic Lines_ etc.10 men
8 weeks
40 hrs/week3200 hrs
185/hr
900 ibs $2700.00
4800 man/hrs $86400.0021 $882.OO21 $441.0021 $756.00
3200 man/hrs $57600.00
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Coaxial Hose 350Bucket, StandardRod EyesShielding
feet
controlsNote: all parts are provided by Moog Corp.
Proportional Electrohydraulic Directionalvalves for dipstick, boom
and swing cylinders A65-20-3-W-L-250valve for the bucket
cylinder Ab5-20-3-W-L-250
Inlet Manifold AssemblyOutlet ManifoldSending UnitProportional Plus
On/Off ControllerTranmitterBattery PackJunction Box
A31094-2-250A31102-1V
130-180125-104128-103
Prototype ProductionTesting
2500 man hrsRemodification
121
Control Valves
3
I
113
1
$1750.00
$480.O0$210.00$1000.00
$75O.0O
$25O.OO
$100.00
$101.00
$100.00
$I00.00
$200.00$200.00$200.00
$45000.00
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HAZZARDS
The biggest foreseeable hazzard is the hydraulic fluid.
The one specified is able to withstand extremely high tem-
peratures. The high temperatures combined with its high
pressure, could cause extreme harm to someone if there was
a failure in the hydraulic line.
Another hazzard might be in the area of materials. Six
thousand and seven thousand series aluminum anneal at 775OF
in about three hours. The beginning annealing temperature
would be less than that. It is clear that the temperature
of the aluminum, when setting in direct sunlight should not
exceed a temperature limit well below this 775OF. If the
material were allowed to anneal, it would loose its heat
treated strength and this might fail under load.
Physical hazzards to the operator do not exist since he
is removed from the backhoe.
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FORESEEABLE DESIGN PROBLEMS
The main area of failure would have been in the area of
hydraulic line heat transfer; however, this problem has al-
ready been solved by methods previously discussed. The method
used to cool the fluid as it returns to the tractor has not
been considered since it is not our responsibility.
The power source that drives the hydraulic pump was never
specified. We simply assumed that it existed and were not con-
cerned with the problems that would arise because of it.
The bellypack controls will be very awkward to the operator
since the operator will be somewhat removed from the work area
and will not have a good view. He will not be able to tell
how deep the hole is nor the angle that the bucket is cutting.
We have not made any provision for the mobility of the
tractor. When the trench is dug in the area that is specified,
the tractor will need to move forward to dig the next portion.
It will be almost impossible for the operator, which is removed
from the tractor, to get it in the correct location, assuming
that there are the appropriate controls added to his bellypack.
The only foreseeable solution is to install a computer
guidance system that would have the trench coordinates already
preprogramed in it. Then when the trench has been dug up to
the base of the tractor, the computer would then advance it
ten feet so that the trench could continued to be dug.
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If a computer were to be incorporated into the backhoe
system, it should include the actual backhoe operation. It
would be ideal to be able to specify the depth of cut and
cordinates of the trench and let the computer do the rest.
A backhoe like this, compared to the one we have designed
is like comparing complexity to simplicity.
In my opinion, the backhoe designed with controls con-
tained on a bellypackis not feasibla, and the computerized
backhoe is the only way to solve the problem of the operator
being removed from the machine.
D
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CONCLUSIONS
The lunar environment introduces numerous obstacles to be
considered when designing a backhoe or the moon. The lack of
air, heat dissipation_ soil mechanics, and gravitational fieldall add to the complexity of creating a machine that willefficiently dig foundation trenches for a lunar base.
Heat dissipation appears to cause the greatestdifficulties. Not only does the heat fail to convect in thelunar environment_ but the electronic equipment is not designedto withstand temperatures encountered on the moon. The limited
time for the electrical component's usage could be overcome byfurther detailed design in the electronic components used.
Continuous operation of a hydraulic system in such anenvironment is indeed possible using commercially availablecomponents as long as a heat sink is available. The most
important considerations are preventing heat entry by radiationand providing an adequate amount of surface area for heat
dissipation to the cooling fluid. These areas are critical sincethe backhoe is a dynamic implement and must be designed suchthat there is a minimum of bulk and weight. We are sure thatfurther_ more detailed analysis of the problems will yield
designs that are much more efficient and effective_ yet we feelthat our design is a credible first approximation.
The control system that was designed is simple in form. The
components used were chosen for compatibility and for simplicityof the overall system. While closed loop feedback using loadsensing transducers was not used, the open loop system we chose
is a workable one_ with many measures to insure that the systemwould not be overloaded by the operator. The backhoe can besafely controlled by an operator in a space suit_ but noteasily. The sending unit chosen has rather small turn controls
making it difficult to operate two controls at once with one
hand. Certain measures were taken to overcome this problem, andthe unit has been used to control a three degree-of-freedom
forklift, but the operator will probably find operating thebackhoe a little tedious.
The mechanical layout of the backhoe is a design that willachieve the project objectives. The C-section of the boom was
neccesary to provide space for the radiators in the hydraulic
circuit. Such a section will require that the boom be internallybraced to prevent floppyness.
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Recommendations
It is recommended that an alternative to a backhoe beconsidered for the earth-moving requirements_ such as using a"Ditch Witch". The "Ditch Witch" potentially has severaladvantages over the backhoe: its rate of soil removal is greaterthan that of the backhoe, it can collect loose dust as itremoves the soil to prevent a visibility problem for theoperator, and it can be programmed to dig a ditch without anoperator being present. Other specific recommendations for eachsection of the backhoe follow below.
Hydraulic System
Since each side of the piston displaces a different amountof fluid _ the flow rate of fluid to one side of the cylinderand out of the other is not the same. To balance the flow rate
between sides of the cylinders, it is recommended thatcounter-balanced flow rate control valves be used in the
hydraulic circuit. Also_ it is suggested that the design of a
pneumatic backhoe be considered. Since air has no flash point_ apneumatic system would ease the maximum temperature constraintof the working fluid in the circuit.
Controls
It is recommended that the controller be redisigned toinclude two joysticks to allow for easier two--hand operation.Load sensing feedback control could be incorporated into the
control system to provide for better system protection. Also_ acomputer could be used to control the backhoe in certain
standard operations_ such as in digging a ditch.
Mechanical Desiqn
It is recommended that an existing design be used for thedimensions of the boom, bucket, and dipstick. With such a
design_ the kinematic calculations have been carried out_ andthe design has already been optimized. With backhoes of manydifferent specifications curently available_ one should be able
to choose a design that would meet specific needs. Given such adesign_ more effort could be concentrated into the areas of heattransfer and material selection.
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ALTERNATE DESIGNS
Although the backhoe is functionable, it is very inefficient.
The purpose of it was rather ambiguous; however, now to our under-
standing, it is to dig the footings of a building to be used as
a lunar base. If this assumption is correct, a backhoe is the
wrong machine to use. It is unnecessarily large, heavy, and
clumsy. It is capable of digging holes ten feet deep which
are not needed. It has a hard time digging a trench with a
constant depth due to the controls. If the purpose of the
machine is to dig trenches then the machine to be used is a
trencher, since it would be simpler to make and also to operate.
It would be composed of two rotating wheels each with
teeth about them. The two wheels would be rotating in opposite
directions thus almost eliminating the horizontal digging forces.
The only force of significance would be the vertical force push-
ing down and would be limited by the machine_ weight. This
force could easily be increased by accumulating the soil being
dug into a large container until the desired vertical digging
force is reached.
The machine would not have wheels but rather bulldozer
type tracks to assure good traction.
This machine would be much easier to be computer controlled
compared to the backhoe since it has such a simple design com-
paritively.
The first drawing shows the two rotars having their height
controlled by hydraulic cylinders. For regular trenching, the
depth of the first rotar (dl) is half of that of the second(dE).
2d I = _
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Weekly Progress Reports
Design Section: Rob SchenkRick Wilkins
Week Proqress
2
3
4
5
Picked team members
Picked study topic- soil mechanicsPicked design topic-- BackhoeGroup meeting
Divided up study topic into sub-topics: books_ technicalreports_ abstacts_ govt. documents.Group meeting
Organized material for progress meeting.Progress Meeting
Suggeted a photocopy list of all material for centralinformation file.
Group meeting
topic is finished- have lists typed upGroup meetingGathering of all typed material for fianl listing in
information file
progress meetingturned in soil mechanics material
started backhoe designBrazell gave us a starting pointSplit up into groups- controls
hydraulicsdesign
Vendor informations obtained- Vermeer
meeting with Jeff Kreugerdiscussed kinematic problems and design ideas
group meeting- Rob Schenck- more info on catepillarSteve-check out lunar atmosphereScott and Brian- controlsRick- lunar soil
continued with kinematic initial designProgress meetingdiscussed syllabus for remainder of quarteravailability of IBM- 3erry Insilia
Word Processing for writing reportProblem statement due 5/2
Group meetingDiscussed hydraulic line problems and design
Posed problem statement for review_discussion_ revision_ etc.
Determined capacity and digging depth
final form of statement to be typed up Wednesday-BrianRob-talk to Catapillar representative-get details on
interface for hitch_ hitch design initiated.Controls info received
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&
7
8
9
Progress meetingTurned in problem statement, revised digging forces.Concentrated on hydraulic lines_ shielding temperature
limits, etc.Discussed purpose of VSMF catalogConsult this for Vendor informationcontrols group interface with hydraulics.Group meetingMore vendor info- FordDesign is complete, meet with Brazell to determine
member sections.More work on controls and valves for hydraulic system.Consult VSMF standards to determine position for digging
forces.Progress meetingearly meeting with _r. BrazellMethod for determining section modulus in backhoe
sections.
Quick disconnect idea is discussed.Control problem discussed- flow rates proportional toforces which in turn determines cylinder sizes.
Looked at buckling problems.Materials for suitable use is suggested: low emmissivity.
low reflectivityStill need final details on hitch.
Stabilizers and swing ranges and sizes.
Choose digging forces to initiate sizing of system.Materials chosen. Aluminum 6066 T-&
Modified hitch to incorporate labor intensive work.
Progress meeting.Initial hitch design complete- modify for swing cylinders
Dig Forces- take individual cases to determine reactionforces, don_t add
interface-- choose design.design complete, finish sections
Initial design has to be changed- bending momentsdidn't work out in boom member.
Final changes made in hitch
final drawings competed.Backhoe final drawings done.Force analysis complete.
Choose section modulus to incorporate cylinders andheat exchanger.
Change from original tube section to C-section.
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Weekly Progress Reports
Controls Section: Brian HatchellScott Landers
Week Proaresq
1
2
3
4
5
6
7
?
Had organizational meeting to determine individual dutiesfor research assignment: Hatchell, technical reports
Lenders, government reportsSearched microfiche, journals, and government reportsrelevant to soil mechanics.
Continued searching library material for soil mechanicsliterature relevant to project. Wrote down findings tobe compiled into class data base.
Researched TomCat for vendors involved in remote control,
radio control, and electro-mechanical hydraulic valves.Considered alternative designs to relieve the operator'sinherent vision problem. Decided that radio control wasthe safest solution to the problem.Worked on problem statement, and researched Tomcat foradditional vendors that might be needed.Wrote letters to 15 prospective venders and called 3others in the areas of hydraulic valves and radiocontrol.
Wrote up problem statement, typing.Called up Moog for servo valves.
Researched library for textbooks that could help insetting up the control system. Selected 5 books thatwere moderately helpful. Read these books and learnedabout the specific kinds of valves that would be needed
to complete the system. Learned about overall hydraulicsystem.
Group meeting.Looked over the vendor information that we received
and determined that we probably had information on allthe components that we wouZd nemd_ except for a radioreceiver and a transmitter. Called up the Moogrepresentative for the Atlanta area and he said thatMoog had a radio receiver and transmitter that wouldprovide the proportional control of servo-valves that
we would require. He agreed to send us the informationthat we would need to set the system up.
Given the hydraulic information from Rick and Steve,we were able to determine the valves that would be
required. Luckily, we had a stackable control valvethat could be easily set up on the backhoe. The sizesand accessories that would be needed were determined.Considered cross-port verus regular relief valves anddecided that the regular relief valve was the best forour application.
Went out to the Ford tractor place and looked at a
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backhoe similar to the backhoe that we were dssigning.Because the Moog representative failed to mail us theinformation that we asked or_ we drove out to hisoffice. We talked with him for about 45 minutes about the
system that we Nere designing. He suggested severalalternatives including position and load feedback
control. These measures would require additionalelectronic hardwarep and we decided that using reliefvalves and pressure controlling valves would be asimpler, but still adequate solution.Completed the overall design of the control system.
Worked on typing up the report.
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