DML Quizzes and HW
select the appropriate tap drill size for tapping 1/4-28 thread in steel
#1 0.228
torque vs. speed curves for electric motors are:
linear
Which of the following statements are true?
brushed motors can easily control speed and torque without the use on an electric speed control ESC unit brushed-type motors are compatible with the control box used for the course project brushless-type motors are compatible with the control box used for the course project
Which of the following statements are true?
brushed-type motors are less efficient than brushless motors the rotating portion of an electric motor is called the armature or rotor
which of the following rules apply when turning on the milling machine
check speed range before turning on, check tool clearance before turning on, check tool direction when turning on
fasteners are primarily designed to do what
clamp parts together
key elements to decision matrices
clearly defined and weighted objectives justified magnitude assignments with traceable supporting data always try to use linear score assignments highest scoring concept wins unless there is a packaging incompatability
plastic
constructing hoppers and ball sorting mechanisms, which see no significant loading can be cast, pressed, extruded and machined easily
rack and pinion
convert rotational motion into linear motion steering, scales
Calculation of required fastener tightening torque depends on two variables:
desired preload and fastener diameter
which of the following statements are true?
differential steering is less complex than rack and pinion steering for best maneuverability the steering wheels should be positioned closer to the items being manipulated
proportional control can vary the __ and __ of a motor
direction speed
when operating a lathe the tool bit should always be positioned:
directly on the spindle centerline
when operating a lathe the tool bit should typically be positioned:
directly on the spindle centerline
what are three things that can cause calipers to measure inaccurately
failure to zero the calipers before each use debris, chips or burrs on measured surfaces failure to hold the jaws perpendicular to the measured surfaces inadequate or excessive closing pressure
it is acceptable to temporarily leave dial calipers and parallels out of their storage boxes while working on the equipment in the shop
false
manufacturing time is an example of a qualitative assessment
false
milling is a metal cutting process used primarily for the generation of cylindrical surfaces
false
turning is a metal cutting process used mainly for the generation of rectangular surfaces
false
what information is required to properly denote fasteners in assembly BOMs for this course
fastener thread specification, fastener head type, overall fastener length
list three common methods of sorting balls:
funnel, grate, wire mesh
plastic on concrete has a friction coefficient that is roughly __ that of rubber on concrete
half
which of the following are common components of an engine lathe
headstock, cross slide, tool post, tailstock
which of the following is a common work holding method on a lathe:
holding in a chuck, holding between centers, holding in a collet
which of the following is the most common work holding method on a milling machine
holding in a collet
what is the structural benefit of bending sheetmetal edges/ flanges
increase rigidity, faster than machining
Why are separate evaluation matrices created for separate functional subunits of a design?
isolate each part and evaluate it separately will make the best whole robot
which of the following qualifies as an industry-standard clearance hole size for a 3/8 fastener
it is 0.375 so all are greater for clearance but only 0.386 and 0.397 count for standard hole size
common types of milling machines include:
knee and column mills, bed mills
spur
most common type of gear with straight teeth and gears mounted on parallel shafts electric screwdriver
the following rules apply when using the milling machine:
never bring anything within 6'' of the cutting zone while the spindle is running always remove parallels after clamping the workpiece in the vise always lock the quill in the uppermost position before changing tools always adjust the spindle speed while the spindle is running always ramp gently into contact with the workpiece
it is okay to leave the cutting tool or workpiece rotating when making a measurement under the following circumstance
none
steel
often used as structural support in buildings its high ductility, strength, and weldability make it suitable for making rigid parts with moderate mass
aluminum
often used in aircraft, automobiles, and bicycle frames has a high relatively machinability among metals
wood
often used in boats, furniture and flooring naturally occurring composite that can be used for moderate loads
80-20
often used to construct robot frames and prototyping highly modular material that makes rapid prototyping structures and mechanisms convenient
relay control is either __ or __, meaning it can cause a motor to rotate __ or __ at the rated speed of the motor
on off CW CCW
the maximum allowable material which can be removed in a single pass on the mill or lathe is:
one hundred thousands of an inch (0.100) too high cutting forces damage the tool
gearing can be used to increase motor torque at the expense of what?
output speed
which of the following should be present in assembly BOMs created for this course
part numbers, part quantities, part descriptions, unique item numbers matching the balloon numbers on the assembly drawing
list two advantages of keyways and/or pin joints
positive mechanical engagement - has to fail in shear allows disassembly without damaging components easy to machine pin joints
when transferring torque using set-screws, why is it important to use D shaped shafts with small flats cut into them and what is it called
positive mechanical engagement, doesn't only rely on friction because there is more surface area of engagement
list three considerations when designing motor hubs
power transmission/torque transmission attaches a wheel, gear,arm to a motor attach hub to device
advantages of splines include
provide positive mechanical engagement easy removal without damaging components
circle the design action that results in a more stable robot geometry:
reduce the CG height maximize the distance between the CG location and the roll axes increase the mass of the robot
explain the difference between relay and proportional control
relay is like a light switch that is either on or off, proportional is the speed and direction are controllable
list five benefits to using 80/20
reusable, good for prototyping, relatively inexpensive, lightweight, strong
linear actuators use screw-type mechanisms to convert __ electric motor output to __ motion
rotational linear
list three required items you must bring every week to your laboratory session
safety sheets, closed toed shoes, long pants
which is the most common type of wheel for lighter weight robotic platforms, like those built in this course?
semi-rigid wheel
based on last week's sheetmetal demonstration, the lab has the following sheetmetal capabilities
shear, brake, punch press for creating round holes
which of the following statements are true:
sheetmetal refers to workpieces with a high ratio of surface area to thickness sheets are defined as less than quarter inch in thickness plates are defined as greater than quarter inch in thickness
the following personal items are dangerous to wear when operating powered equipment
shorts or open toed shoes, long hair which is not securely tied back, jewelry on your hands or wrists, loose fitting clothing
which of the following is an advantage of press fits
simple to fabricate, they self-loosen
the purpose of gears is to exchange __ for __ or vice-versa
speed torque
list the four common ways to transmit torque through a hub from strongest to weakest
splines keyway/ pin joint set screw press/interference fit
fastener threads should always be loaded in __ and should never be loaded in __
tension shear
weldability
the ability of a material be permanently joined to a separate piece of identical material using the application of intense heat
machinability
the ability of a material to be machined to particular tolerance and surface finish requirements
ductility
the ability of a material to deform before fracture by tensile stress
strength
the ability of a material to withstand an applied stress without failure
cost
the amount of money required to purchase and manufacture a particular part
what rotates on a lathe
the chuck, the material and workpiece
what rotates on a milling machine
the cutting tool, the spindle
density
the ration of a material's mass per unit volume
stiffness
the resistance of an elastic body to deformation by an applied force
proportional controls are often used for:
the robot's drive wheels
which of the following statements are correct about ball hoppers?
the two common types are fabricated and prefabricated buckets and plastic containers are examples of prefabricated hoppers fabricated hoppers can be designed to meet exact geometry and strength needs a good designer considers the time and cost necessary to manufacture a custom hopper
which of the following statements are correct about ball/bucket manipulators?
the two common types are fixed and moveable manipulators/grippers moveable grippers require an extra motor to control the moveable part of the mechanism fixed grippers require more accurate/ sensitive positioning on the part of the driver
which of the following statements are true?
three wheel platforms possess the fewest wheels required for balance without a complex systems of sensors and logic simple four wheel platforms without complex suspension systems can experience traction issues three wheel platforms do not three wheel platforms offer superior stability at higher speeds
what is the purpose of tolerances and when should they be used?
tolerances note the allowable margin of error for each dimension; they should always be used on final part drawings because manufacturing dimensions without tolerances are useless; tolerances are not necessary in conceptual sketches
after creating a decision matrix, the concept with the highest overall value should be selected for use in the final design
true
decision matrices are used to unbiasedly evaluate different ideas based on a weighted set of objectives the design team decides are important for solving the problem
true
decision matrix objectives are weighted because not all objectives are of equal importance
true
once the spindle completely stops, it is still dangerous to remove cutting chips by hand because they can easily cause lacerations
true
the speed range on the mills or lathes should be set before the machine is turned on
true
when changing spindle speeds on the milling machine the spindle must be running
true
you must provide detail drawings for all off-the-shelf OTS parts used with your project, with the exception of fasteners; however, fasteners must appear in the assembly drawings/ BOM
true
the control box must attach using __ mounting flanges and cannot be used to __ other parts of the robot
two support
bevel
typically used for changing the direction of a shafts rotation car differentials
worm
use when significant gear reductions are required, like on conveyors conveyor system
equation for linear velocity
v = pi x wheel diameter x motor shaft speed x efficiency
caster wheels have their own mounting axle and are typically free to pivot about a second, nearly __ axis
vertical
it is acceptable to leave a machine running
when touching off on the work piece
Based on the over- versus under-tightening example, properly torqued fasteners can withstand how many more force application cycles before failure?
~1000 times
How much radial clearance does a close fit hole for a 1/4" bolt leave?
0.0035''
what is the thread pitch for a 10-32 fastener
0.0313
list 4 features of CNC machines that possess that allow increased productivity
1. automatic part probing to locate datums 2.automatic tool changing 3.high pressure coolant 4.stiffer structures and more powerful motors
based on HW#2, list ten items a proper detail drawing should contain
1. dimensions needed to locate every part feature 2. appropriate tolerances for every dim on dwg 3. units specification inches, mm 4.material specification- aluminum, steel 5.quantity of parts to be made 6. surface finish specifications for every surface 7.appropriate hole and thread notes for every hole 8.unique part name and or number 9.designer/drawer's names 10.additional info about breaking sharp corners, etc
list the first four steps of the design process
1. recognize the need 2.define the problem 3.gather information/background research 4.concept generation
what power source do the laboratory control boxes use?
12 VDC
the definition of horsepower is
1hp = 550 lb-ft/s
the laboratory controllers provide __ relay and __ proportional channels of control
3 2
which of the following statements are correct about design project/ process used in DML?
DR1 is where each student researches and presents their best individual ideas for solving the design problem DR2 is where each group compares their members' individual concepts and selects the best of each for their final design DR3 is where most of the detailed design and analysis work are performed to figure out how to make the selected concept work DR4 is where we take an unbiased look at how your group's design performed during the course competition
last semester several robot designs were unable to traverse the ramps leading into the arena. these would help the traction problem:
add weight to their robots to increase the normal load on the drive wheels choose drive wheels materials with higher friction coefficients
what keeps a bolted joint tight
adequate torquing/stretching of the bolt
when should the lathe chuck key be removed from the spindle
after clamping the workpiece
the following rules apply when using the lathe:
always make sure the spindle is rotating CCW- looking toward the spindle always turn the spindle off before measuring or inspecting the workpiece allow the machine to stop completely before switching spindle directions ramp gently into contact with the workpiece always file left handed so your wrist is never close to the rotating chuck jaws
which statements are true about installing/removing tools on the milling machine
always perform root changing above the plastic covers on the table always raise the spindle to the uppermost position using the quill handle always secure the quill/spindle in the upper-most position using the spring loaded lock
helical
angled gears for gradual engagement of teeth car transmissions