EG112 Design Project for Spring 2013
Overview
You and your teammates have landed jobs as a summer interns with the DWC Elevator
Company. Your assignment is to retrofit an old-fashioned elevator with a modern drive system
and controls.
You will need to replace the old drive system as well as the mechanical controls that were used
with it. An electronic control panel will be installed into the elevator cab so that users can
operate the elevator themselves (a separate elevator operator will no longer be needed).
Unknowns
Due to the plans for the building having been misplaced at city hall (it’s a very old building…),
the prime contractor is unable to tell you at this time where the floors are located. As a result,
you will need to design your control system to dynamically determine when to stop at a floor (as
opposed to knowing the distance beforehand and then simply measuring how far the elevator cab
has travelled).
Deliverables
The objective of this project is to design a lift mechanism and control system for an elevator
which will receive power input from a small DC motor. A single stage gear reduction will drive
a 1.5 inch diameter drum as fast as possible. Students will use SolidWorks to design both the
gears and the gearbox. The lift mechanism must mate to an existing mounting plate – the
specifications of which will be supplied.
The elevator control system has to be programmed to accomplish certain tasks. You will use the
PIC microprocessor in your kit to control the elevator. The first task is that, when commanded to
begin, it will accelerate the elevator cab up from its starting position at the ‘lower floor’ by
increasing the voltage to the motor linearly from zero to 12 volts over a period of one second.
The elevator cab will be equipped with optical switches at its top (the ceiling of the cab) and
bottom (the floor of the cab). These switches will be able to ‘see’ the edge of the building’s floor
(at the side of the elevator shaft) as the switch moves past it. When the sensor at the top of the
elevator cab sees the bottom edge of the upper floor, the elevator will decelerate linearly with
respect to position until the sensor at the floor of the elevator reaches the bottom edge of the
upper floor. The goal is that the elevator has slowed to a speed of 20 inches/minute by the time
the lower sensor sees the bottom edge of the floor, at which point the elevator will continue to
proceed at 20 inches/minute until the floor of the elevator is level with the top edge of the upper
floor. At that point the elevator must automatically stop. The elevator must then return to and
correctly position itself to the lower floor when commanded to do so.
The following steps should be taken to complete the design project, and each should be clearly
described and documented in the final report:
1. Design and build a fixture that provides a direct drive linkage to a 1.5 inch diameter
drum from the motor and generate torque vs. speed data. Create a table to include
weight, speed, angular speed, torque, and power. Create a graph with a linear
regression fit for torque (inch-lbs) vs. angular speed (rpm). Using the torque equation
obtained from the regression fit derive the equation for power and create a graph for
power (watts) vs. angular speed (rpm). Determine the optimal speed and torque at
which the motor will provide the maximum power output. Assuming that a gear with
a 5.5 inch pitch diameter will be linked to the drum, select a pinion that will allow the
motor to run slightly to the right of the Pmax. The elevator with the payload will
weigh approximately 20 pounds. Account for friction losses by assuming they add
70% to the effective weight that must be lifted. Determine the design speed of the
elevator.
2. Explain the use of an involute gear profile to achieve a constant angular velocity ratio
between two gears and why this is important. Generate the (x, y) coordinates with
Excel for an involute curve for the pinion selected above and create the SolidWorks
model. The pinion should have a diametral pitch, P, of 6, a pressure angle of 20, an
addendum of 1.000/P, a dedendum of 1.250/P, a circular tooth thickness at the pitch
circle of  / (2P), and a root fillet radius of 0.0625 inches. The gear will be
manufactured from 3/8 inch Lexan. The center hole should fit onto a 3/8” shaft with
parallel flats 0.290” apart.
3. The 5.5 inch diameter Lexan gear will be linked to the drum. Assuming that the
entire load is carried by one tooth and that the gear tooth would fail by being sheared
off at the pitch circle; determine the shear stress and the factor of safety. Assume that
the yield strength in shear for Lexan (Polycarbonate) is 4500 psi.
4. Design and build the gearbox. Create SolidWorks solid models of all parts and
assemblies. Include working and assembly drawings, and an assembly video.
5. Design a control system that will, in response to the press of a pushbutton, accelerate
the elevator by increasing the motor voltage linearly from zero to 12 volts over a
period of one second. The elevator then continues at full speed (12V) until the top
sensor of the elevator detects the bottom edge of the upper level (floor). At this point
the elevator will begin to decelerate linearly with respect to position. The goal is that
the elevator cab is traveling at 20 inches/minute by the time the sensor at the floor of
the elevator detects the bottom edge of the upper level (floor). At this point the
elevator will then proceed at 20 inches/minute until the sensor at the floor of the
elevator no longer detects the upper level (floor), i.e., the floor of the elevator cab is
now level with the top edge of the upper level (floor). When this happens, the
elevator must automatically stop.
6. A rotary optical encoder (128 pulses/ revolution, quadrature encoding) will be
provided to measure the rotation of the drum axle. An interface will be provided to
sensors on the top of the elevator and on the floor of the elevator cab that will sense
the “floor” of the building as it passes each sensor. Specifications will be provided to
you for all of the sensors used in the elevator system. Specifications will also be
provided for interfacing to the sensors mounted on the elevator cab.
7. An Innovation-First Victor 883 ‘blue’ motor speed controller will be supplied for you
to use in controlling the lift motor. Specifications for the speed controller will be
supplied. Your control program will need to generate the PWM signal that is the
input to the speed controller – you will learn how to do this in class.
8. The LCD display of the control system for your elevator must clearly display to the
operator what is happening at each stage of operation. You will learn how to write
messages to the LCD display during class. You may additionally use any of the other
components in your EG112 electronics kit as you see fit. For example, you may wish
to use LEDs or the speaker to indicate the status of the system (in addition to the LCD
display). You may use the temperature sensor included in your kit to monitor the
motor temperature (that is worth extra credit – see below).
9. Operation of the elevator (i.e., the ‘test’) will be initiated by pressing a momentary,
normally-off (NO) pushbutton switch on the control panel. The microprocessor must
respond to the pressing of this switch by illuminating the LED under the switch and
then starting movement of the elevator. A multi-pin ‘header’ will be the interface to
the control panel switches and LEDs (specification to be provided). The electrical
system will also include a master power cutoff switch which will control 12V power
to the motor. The cutoff switch will be used in the event of any unsafe/runaway
operation of your control system.
10. A separate momentary (NO) pushbutton switch (‘Reset’) will be used to return the
elevator cab to its starting position. This switch will be made available through the
same header as the ‘test’ switch. This switch also has an LED underneath it which
must be illuminated once the switch is pressed. A third momentary (NO) pushbutton
switch and LED on the control panel will be available through the same header. This
switch and/or LED may be used at your discretion, but may play no role in
controlling the movement of the elevator.
11. The speed of operation of your elevator system will be measured independently of
your control system. We will use various Pasco sensors from the physics lab along
with Data Studio to perform these measurements. You do not need to concern
yourself with how these measurements will be made.
12. Test your design. Prepare a Power Point presentation of your project. Include digital
video.
13. Extra Credit: Continuous monitoring and display of the motor temperature is
desirable and worthy of extra credit. If this is done, the motor temperature must be
able to be displayed on the LCD display in degrees Centigrade or degrees Fahrenheit
at the push of a button. In other words, pressing and holding down the pushbutton
will cause the temperature to be displayed in degrees Centigrade. When the button is
released the LCD must go back to whatever it had previously displayed. A
subsequent press of the pushbutton will cause the temperature to be displayed in
degrees Fahrenheit, and so on alternating the temperature display units used with each
press of the button.
14. Safety is paramount. Deductions will be made for such things as poor or unsafe
machine shop practices, electrical wiring, system operation, etc.
Project Milestones:
(Note that each team will submit regular Microsoft Project progress reports. Save a copy of each progress
report for inclusion in the appendix of your final report. Also, an accurate record should be kept of the
work of each team member.)
2/6
Present design of motor test fixture to include exploded and collapsed assembly
views and working drawings and assembly video. ( /10)
2/22
Microsoft Project Report ( /4)
2/22
Complete construction of motor test fixture and testing of motor. ( /10)
3/6
Present table to include weight (lbf), speed (inches/sec), angular speed (RPM),
torque (in-lbf), and power (watts). Create a graph with a linear regression fit for
torque (inch-lbs) vs. angular speed (rpm). Using the torque equation obtained from
the regression fit derive the equation for power and create a graph for power (watts)
vs. angular speed (rpm). Present and explain selection of the pinion so that the
motor will run slightly to the right of Pmax and the corresponding design speed of
the elevator. Include a solid model of the pinion. Present shear stress calculation
on gear tooth and factor of safety. Submit an electronic copy of your presentation
as well. ( /20)
3/22
Present completed SolidWorks elevator lift assembly. Include working and
assembly drawings and an assembly video. ( /20)
Submit draft of the mechanical aspects of your final report. ( /20)
Microsoft Project Report ( /4)
3/29
Submit flowchart and functional specifications. ( /10)
4/8
Present completed physical assembly. Test with manual motor control box. ( /20)
4/12
Submit preliminary test code including high-level subroutines and test plan. ( /10)
Submit draft of the control aspects of your final report. ( /20)
4/19
Microsoft Project Report ( /4)
Submit final code for review and initial testing. ( /20)
4/24
Final testing of code complete; data has been gathered for final report. ( /20)
5/2
Project presentations. ( /30)
Submit final report. ( /120)
Construction/Quality/Initiative ( /40)
Web Page ( /30)
Total – ( /412)