Stabilization Table for Accurately Balancing a Loose Element
Critical Design Review
December 13th, 2012
William Brown
Phillip Chen
Eric Huckenpahler
Laura Hughes
Brian Ibeling
Chris Johnson
1

Develop a robust control system that is capable of
balancing a ball at a plate’s origin.

Allow users to control the plate and ball’s position
with various devices.

Integrate interactive games.

Capable of fully autonomous operation.

Operate from AC wall power.
2
3

Constructed physical model to demonstrate
plate and motor interaction.

Communicated and translated touchscreen
data to motor rotation.
4
5

From PDR:
6
7

The motor:
•Sparkfun
•4.8 to 6.0V
•Analog actuation
•Torque around 6kg*cm
•Small Footprint
•$12
•180 degrees of movement

The motor:
•Hitech
•4.8 to 6.0V
•Small Footprint
•Digital actuation
•Torque around 343 oz-in
•$70
•90 degrees of movement

We could have used:
 Ball bearing
 Shaved down hinges
 Fiberglass rod
 Rotating pivot

Or, this nail.

Fiberglass is finally appropriate
 Rigidity issues may force us into aluminum arms

Binding posts were chosen over shoulder
bolts
 Cheaper and easier to find
 Works for both arm-to-arm and arm-to-plate
connections

Bolted it down with the included screws
 Acrylic base needed to secure screws
 Motor arm was imperfect

We could have used:
 Ball bearings
 Gears
 Pneumatics
 Magnets
15

Or, a small hinge:

There are still questions to answer
 How will the second motor affect rotational
stability?
 The motion is software limited, but should we
physically limit this as well?
18

We are strongly considering the use of a
computer PSU to supply the power to our
project
19

Why?
 Integrated/compact design
 Efficiency
 Safety
 Very high quality control
▪ No fried controllers!
20

PSU supplies 12V, 5V, and 3.3V lines

We will need to create a converter circuit on
PCB to supply 6V to motors

PCB will be used for power distribution
21
22

The current control system is fairly
theoretical

Testing will determine whether or not a
different approach to controlling the ball will
be necessary
23




Control based off of second-order physical
system
Forces on the ball were linearized with respect
to angle to simplify system
Using a line of best fit of sin 𝜃 to 30° gave a
good approximation with 𝑅 2 = 0.9994.
Max difference between real and estimated
𝑚
accelerations is 0.01 2
𝑠
24
25

Factoring in rotational inertia, the position of
the ball can be modeled as
𝑋 0.119
=
𝜃
𝑠2

Sanity check: A constant angle input does
cause a constant acceleration
26

For the first design, a simple case was
chosen.
4
𝐻 𝑠 = 2
𝑠 + 4𝑠 + 4

A function that can control this was found to
be
𝑠 4𝑠 2 + 16𝑠 + 16
𝐶 𝑠 =
0.119𝑠 3 + 0.952𝑠 2 + 2.38𝑠 + 1.904
27
28
29

Possible issues:
 This model is highly theoretical. It remains to be
seen if all forms of disturbances can be rejected
▪ If problems arise, a more robust approach will be
needed
 Microcontrollers don’t work in the Laplace
domain!
30
31

Large touchscreen wasn’t accurate enough
32

Smaller touchscreen showed smoother
results
33

We need a more accurate large touchscreen
that will still react to the ball’s weight when
the touchscreen is at an angle
34
35

Simple main file
 Initialize peripherals
 Main loop
▪ Check state and act accordingly

Header file for each peripheral
 More modular
 Keeps code readable
36

Primarily soft interrupts
 Best for an embedded environment
 Easy to set flags which will determine states

Some hard interrupts
 Good for emergency shutoff and other time-
critical tasks
37
38

Hardware interaction with software, requires
careful planning
39
Computer
Cell Phone
User
Input &
ball
feedback
Hardware
Wifi/Eth.
UART
Bluetooth
UART
Joystick
USB
ADC
DI/O
UART
Debugging
Hardware
PMP
LCD screen & 7segment debug
display
PWM
Motor Control
PIC32 Micro
HW Action
Local
Interface
DI/O
UART
Touch Screen
DI/O
ADC

Important PIC32 built in peripherals
 5 UART channels
 1x Parallel Buss
 16 Channel ADC
 5x 16 bit Digital Timers
 8x DMA channels
41

Wireless chip: 1x UART and 2x DMA channels
to prevent the processor from having to wait
for data.
Computer
Wifi/Eth.
User
Input &
ball
feedback
UART
PIC32
Micro
Cell Phone
42

1x UART and 2x DMA channels to keep the
processor from having to wait for data to
arrive.
PIC32
Micro
UART
Debugging
Hardware
43

1x UART and 2x DMA channels to prevent the
processor from having to wait to acquire
data.
Cell Phone
Bluetooth
UART
PIC32
Micro
User
Input &
ball
feedback
44



Flexibility in choice
On-board USB 2.0 On-The-Go host support
with dedicated DMA channels
Extra DI/O and ADC pins for a game port
Joystick.
45

Digital push buttons. Should be triggered by
interrupts to provide highest response rate to
user & button functionality
User
Input &
ball
feedback
Local
Interface
DI/O
UART
PIC32
Micro
46

Fastest operation uses PMP bus to control
parallel port enabled devices.
PIC32 Micro
PMP
LCD screen & 7segment debug
display
47
PIC32 Micro
PWM
Table Control

2x PWM outputs, one for each motor, each
require a 32bit timer to output slow enough.

Requires 4 of the 5 16bit timers.

Needs to be updated at 50Hz to maximize
control systems abilities.
48
User
Input &
ball
feedback

Touch Screen
DI/O
ADC
PIC32
Micro
2x ADC pins
 Need to be triggered to sample at a steady frequency
in order to calculate velocity. Will likely involve the
use of the 5th timer.


2x DI/O pins
Needs to update at highest rate TBD. Hopefully
100-200Hz
49
Hardware
Number Available
Number Used
UART
5
3
Parallel Buss
1
1
ADC’s
16
2-4
16 bit digital timers
5
5
General Purpose DMA
channels
8
6
General DI/O
Lots
+-12

Knowing this information, need to carefully
program our processor otherwise system will
fail to meet hard deadlines.
50
Hardware
Number
Pins/Feature
Number Used
UART
2
6
Parallel Buss
11
11
ADC’s
1
2-4
16 bit digital timers
1
2 required PWM signals
General DI/O
Plenty
+-12
Total:

+-35 pins
Using a good number of the available I/O pins
as well.
51
52


Need some scheduler to deal with multiple
demands made on processor at a time:
Various demands should only be ignored so
long before being addressed
53

If only one demand is made at a time,
scheduling is simple:
 Deal with the demand and wait for another one

Problems arise when multiple demands arrive
at the same time or arrive during another
demand:
 How should we pick which demand to address
first?
54

Simple Priority Based Scheduling:
 Easy to code and debug
 Provides minimal control over scheduling and
ignores deadlines completely—can lead to
starvation
Why am
I always
last?
55

Variable Priority Based Scheduling:
 Some difficulty debugging
 Provides extensive but unintuitive control over
scheduling and can indirectly address soft
deadlines
Sometimes the world
appreciates me as I
deserve
56

Time Slice Based Scheduling:
 Provides extensive and intuitive control over
scheduling and predictable deadlines
 Difficult to code and debug
 Increased context switching inevitably leads to poorer
performance
 Poor design could lead to insufficient processor time
being given to demands
57

More complex systems yield better results
but are more difficult to implement

Use simpler systems to begin with and then
upgrade to more complex system if simpler
system is insufficient for our purposes
58
59
User
Interaction
User
Interface
Desired
Position
Control
System
Parse Input
(joystick)
User
Input
Parse Input
(tablet/phone)
Desired
Position
Control System
Standard Mode
Interface
Physical
State
Game Mode
Art Mode
61

Multiple methods of manipulating and
viewing the same control system: Model View
Controller
62
63

Ball’s speed and weight too great
 Non-steel ball with higher frictional coefficient

Dual motor interaction and locking
 Ball joints rather than door hinges
 Redesign motor arms
64

Parallel processing for touchscreen, UI
devices, and motor actuation
 Optimize code
 Split responsibilities over 2 processors

Noisy PWM signal for motors
 Filter signal output
 Split responsibilities over 2 processors
65

Unable to meet deadlines for data analysis and
plate actuation
 Adjust control code to predict ball behavior
 Optimize code for faster runtime operation
 Faster processor
 Split responsibilities over 2 processors
66
Task
Brian Ibeling
Laura Hughes
William Brown
Motor Control
S
P
S
Mechanical/
Structure
P
S
S
Power Board
S
S
P
ADC Board
S
S
P
Command and
Data Handling
TouchScreen
Control
User Interface
Control
User Interface
Device Comm
Documentation
Phillip Chen Eric Huckenpahler Chris Johnson
S
P
S
S
S
S
P
S
S
S
P
S
S
P
S
S
S
P
S
P = Primary
S
S = Secondary
67
Item
Unit Price Quantity Unit Total
Mechanical
Servomotor
$77
4
$308
Aluminum (0.5” x 0.5” x 6”)
$20
4
$80
Plexi-glass Plate
$40
1
$40
External Case
$50
1
$50
Steel Ball
$10
1
$10
Electrical
Microchip PIC32
Development Board
$70
2 Sampled
Power PCB Creation
$45
3
$135
AC AC Transformer
$20
3
$60
6V Regulator
$15
3
$45
3.3V Regulator
$15
3
$45
Touchscreen Sensor
$50
1
$50
Joystick
$20
1
$20
LEDs
$0.15
100
$15
Breakout ADC Board
Creation
$45
3
$135
Touchscreen Driver
$7
2
$14
Misc. Dev Components
(Resistors, Caps, headers)
$50
1
$50
Net Estimated Budget
$1057
68
69




Structure fully developed
Basic control algorithm implemented
Rev 1 Power PCB developed and tested
Testing plans implemented
70





System integration complete
Fine control algorithm actuating
Rev 2 (3 if needed) Power PCB complete
Aesthetics fully developed
Documentation complete
71




Capcakes = capstone + cupcakes
Fully functional system
Games implemented and available to guests
Aesthetically pleasing system and
presentation
72
73
74
75
Yes
Ball
Centered?
No
Ball resting at
origin
Touchscreen
senses ball
movement
Ball’s offset
and speed
calculated
Motors and
plate actuated
76
Ball resting at
initial position
UI device sends
data
No
Ball at
final
position?
Yes
Plate tilt or ball
offset
calculated
Complete
Motors and
plate actuated
77