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MCDESG-125 Design Problems
Assignment 4A
Free Body Diagrams; Amtrak Train Deceleration
MCDESG-125 Page 1
Name: _______________________________________ Team ___________________
Item
ATV Lift Lift table Score Co
ections
1 Top Pad Table /10
2 Idler Lift Arm Idler Frame /
3 Active Lift Arm Active Frame /20
4 Base Assembly Base Assembly /20 Individual Score: (1-6)
5 Cylinder Link Pair - /
6 Amtrak Train Braking Problem /40
7 Free Body Diagram Pipe (Section) /25 Team Score: (7-9)
8 Reaction at Wheel /50
9 Wheel Selection /25
Total Score /200
Total Percent %
Multiplied by 6.00% %
On Time: 0.20% %
Added to Grade %
Hand in ONE cover sheet each person with FBDs
Only one FBD of pipe Support is necessary on one person’s cover sheet
Individual scores apply to the ATV Lift/Lift Table FBDs and Braking Calculation,
everyone gets the same score for the Pipe Support FBD
MCDESG-125 Design Problems
Assignment 4A
Free Body Diagrams; Amtrak Train Deceleration
MCDESG-125 Page 2
MCDESG-125 Design Problems
Assignment 4A
Free Body Diagrams; Amtrak Train Deceleration
MCDESG-125 Page 3
ATV Lift or Lift Table:
Check your Statics book. Remember that a Free Body Diagram (FBD) shows all of the Forces and
Moments on a body - actions and reactions. It must also show the Location and Direction of Forces and
whether a Moment is Clockwise or Counter-Clockwise.
Remember also:
A pin joint cannot sustain a moment and has two unknowns: a force expressed as a magnitude
and direction (or a force separated into two components).
A rigid support can sustain a moment and has three unknowns: a force with magnitude and
direction and a moment.
Cables, ropes, chains, etc. can only have equal and opposite tensile forces whose line of action is
collinear with the cable, etc. Therefore there is only one unknown, the magnitude.
A Link on the other hand is like a cable but can also sustain a compressive force.
Any force bearing on a non-friction surface can only be perpendicular to the surface and also has
only one unknown, the magnitude, as the angle is now known.
Each person on the team select one position of the ATV Lift or Lift Table as laid out in the team’s Layout
Drawing:
o Lift at lowest position
o Lift at a mid-way position
o Lift at highest position
Take angles from AutoCAD Layout. Show to 4 significant figures.
Assume 1500lb in the center of one of the Top Pads in the ATV Lift, or 500lb in the center of the
Lift Table but at one edge. Separate the main constituent parts on AutoCAD and create FBD’s.
Create the entire FBD in AutoCAD.
Use “Quick Leader” (le ) to represent forces. Press Esc to avoid text and
the “landing”
The a
ow on the leader should print at 3/16".
Use “oblique” for the a
ows in the dimensions so that only forces have
actual a
ows
All Dimensions must match your Layout from Assignment 2
MCDESG-125 Design Problems
Assignment 4A
Free Body Diagrams; Amtrak Train Deceleration
MCDESG-125 Page 4
ATV Lift (for Lift table, go to next page):
Make an FBD of the Top Pad. There are three forces: 1500lb
pointing down (gravity) in the center; the Idler Lift Arm (link) at
one end and the Active Lift Arm at the other. What direction is
the force in the Idler Lift Arm? How many forces act on the
Active Lift Arm? Is it a Link? (Hint: No). Name the Forces at the
Pins A & B. Show the forces as magnitude and direction rather
than vertical and horizontal components. Follow this
convention throughout.
ON THE SAME AUTOCAD DRAWING.
o Make an FBD of the Idler Lift Arm. Even
though the piece is “H” shaped, treat it as
though it were two individual links and draw
the FBD of one side only.
o Show it in its actual orientation. If the Link
acts at B, name the force B’ (if at A, then A’).
Follow this convention throughout.
ON THE SAME AUTOCAD DRAWING. Make an FBD of
the Active Lift Arm, again using one side only.
Remember that forces are applied at three places
therefore this is not a Link. Show it in its actual
orientation.
ON THE SAME AUTOCAD DRAWING. Make an FBD of
the Base Assembly again using one side only. The final
supports are wheels against a horizontal surface -
these are the reactions,
what direction must
they be? The
Piston/Cylinder is rigidly
attached to the Base -
will there be a
moment?
MCDESG-125 Design Problems
Assignment 4A
Free Body Diagrams; Amtrak Train Deceleration
MCDESG-125 Page 5
Lift Table:
Make an FBD of the Table. Put the 500lb
centered on one edge. Note that the Idler
frame is not a link, so you do not yet
know the direction of the force at that
pin. What direction is the force at the
oller on the Active frame? Name the
forces A & B. Show the forces as
magnitude and direction rather than
vertical and horizontal components.
Follow this convention throughout.
ON THE SAME AUTOCAD DRAWING.
o Make an FBD of the Idler frame. Even though the piece is
“ladder” shaped, treat it as though it were two individual sides and
draw the FBD of one side only.
o Show it in its actual orientation. If the frame acts at B, name the
force B’ (if at A, then A’). Follow this convention throughout.
ON THE SAME AUTOCAD DRAWING. Make an FBD of the Active
Frame, again using one side only. Forces are applied at four
places. Show the angle of the Piston/Cylinder line to four
significant figures. Show it in its actual orientation.
ON THE SAME AUTOCAD DRAWING. Make an FBD of the
ase Assembly, again using one side only. Forces are applied
at three places plus reactions at the wheels. Show the angle
of the Piston/Cylinder line to four significant figures.
MCDESG-125 Design Problems
Assignment 4A
Free Body Diagrams; Amtrak Train Deceleration
MCDESG-125 Page 6
Pipe Support:
Make a FBD of a cross section of the 18" Sch 80 pipe at the support. Is the support ca
ying half
a length of pipe, L/2, or a full length, L? Estimate a distance (10', 15', 20' ?) between supports
and show the value of the weight on the FBD.
Solve for the reactions at the wheels. You can use Σ?? = 0 ??? Σ?? = 0 (you should find
that this acts as a “particle”) or draw a vector diagram in AutoCAD. Label everything as though
you are in Statics!
Go to http:
www.mcmaster.com/# (or other source if you prefer) and select a wheel that can
handle the load. Select a wheel which is either Nylon/Phenolic/Plastic throughout or metal with
a Nylon/Phenolic/Plastic tire. Be a little cost conscious - don’t select a $100 wheel because it’s
pretty when a $20 would work just as well. Be sure there’s enough room in your design to
accommodate the diameter and thickness.
If your results aren’t satisfactory, can you change the distance between supports?
Print your final selection from McMaster-Ca
’s website (or other) and include with your calculation.
http:
www.mcmaster.com
MCDESG-125 Design Problems
Assignment 4A
Free Body Diagrams; Amtrak Train Deceleration
MCDESG-125 Page 7
Braking Problem:
An Amtrak train bound
from New York City to
Savannah, Georgia
derailed south of
Philadelphia on 3rd April,
2016. According to the
news article, it was going
at 106mph (the speed
limit on this section of
track is 110mph) when
the engineer saw a
ackhoe on the track and
put the train into
emergency
aking with
about 5 seconds to go.
Problems:
Braking will be approximately constant deceleration and
dependent on the friction between the rims of the steel wheels
and the steel rails.
How far away was the backhoe? In other words, how far would the train travel in 5 sec at
106mph (and not
aking)?
If the train were to stop before hitting the backhoe:
106mph to zero in the distance that you figure
above, what would the deceleration need to be?
If this stop were to be possible, what would the
coefficient of friction () need to be?
The coefficient of friction for dry steel on dry steel is usually taken as 0.15. What is the
maximum possible value of deceleration?
At this deceleration, how fast was the train going at impact (in ft/sec and mph)?
At this deceleration, what distance would have been needed to avoid collision?
How much time would this be?
Use a different equation to check your values of a, s & t
See next page for a list of
elevant equations (which you
have memorized anyway).
If the train is slowing down, does it still
take 5 seconds to reach the backhoe?
Hint: No
MCDESG-125 Design Problems
Assignment 4A
Free Body Diagrams
MCDESG-125 Page 8
Equations used in Constant Velocity
s = v t, i.e. a = 0
Equations used in Constant Acceleration
? = ?0 + ??
Where:
s = distance
v = velocity
v0 = initial velocity
a = acceleration
5,280 ft = 1 mile
mph x 22/15 = ft/sec
Use consistent units!
? = ?0? + ½??
2
? =
(? + ?0)
2
?