DISCLAIMER!!!!

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DISCLAIMER!!!!
I AM A N00B!
Please do note that everything that I have worked
on is subject to questioning.. in fact.. I
suggest it. This entire project was a learning
experience for me. Ive worked very hard and built
this all from scratch. Many of the things Ive
learned I want to share with you, and any help or
suggestion is good )
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What is a Segwii?
Seg Wii
Seg comes from Segway, which is a product. This
is the self-balancing part (where the real coding
happens).
The Wiimote, aka one of the most hacked products
out there. A bluetooth based controller. Librar
ies out there to interface (almost all open
source).
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Lets talk about the Seg part
How do you balance? Lets start simple.
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Motor pushes the other way based on the angle.
Angle measurement based off the accelerometer
reading.
X
-X
Gain is a constant based on your setup.
Torque anglegain
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Mach 1 (Ghetto bot)
MEMS Accelerometer
H-Bridge
Wiring (AVR ATMega128)
Cheap Lego Motors
Total Cost 130 (could be as low as 80)
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But there is a problem!!
What about how fast you are going at that angle?
How do you account for the angular speed you are
going at a given angle? Gyroscopic sensor, This
will measure Omega, which is angular
velocity. Feed this into your torque!
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X
-X
X /s
X /s
X /s W (Omega)
Torque anglegain angular velocitygain
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Mach 2 (Now were getting somewhere)
Wiring (AVR ATMega128)
H-Bridge
Gyroscopic Sensor
Status Lights (Not necessary but helpful)
Accelerometer
Cheap Lego Motors
Total Cost 230 (could be as low as 180)
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More problems!
Noise and constant assistance needed!
The readings from the accelerometer were very
noisy! This caused the bot to jitter like mad!
Solution Filter the angle reading! But how? and
without putting to much load on the processor?
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Complementary Filter
With many possible filters, this is the most
efficient way to filter the angle without having
to much processing load.
Low Pass Filter
Accelerometer (Angle)
Accelerometer (Angle)
High Pass Filter
Gyroscope (Angular Velocity)
Gyroscope (Angular Velocity)
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Complementary Filter
Angle 90(Angle Angular Velocitydt)
10(Non Filtered Angle)
Previous Clean Angle
Clean Angle
High Pass Constant
Angular Velocity Reading from Gyro
Time Rate of sampling
Low Pass Constant
Raw Angle Reading from Accelerometer
This integration converts angular velocity to
angle.
Low Pass
High Pass
The angle noise is very accurate, but it can
drift after a while.
Gives you a general area of where the angle is.
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One problem left!
Assistance is constantly needed...
The bot may keep itself up for a few seconds but
will keep over shooting the 0 mark.
Solution? PID Proportional Integral Derivative
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PID
Proportional Integral Derivative
Everything is error!
P
I
D
Proportional
Integral
Derivative
Proportional changes torque based on present
information, Directly based on angle error.
Integral changes torque based on past
information, and what has occurred
Derivative changes torque based on future
trajectory.
Iterm (Iterm (angle_error Igain)) .9999
Dterm (angle_error - old_angle_error) Dgain
Pterm angle_error Pgain
How off it is from 0
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One more thing..
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Pterm angle_error Pgain
X
-X
Iterm (Iterm (angle_error Igain)) .9999
X /s
X /s
Dterm (angle_error - old_angle_error) Dgain
AngVelTerm angvelocitygain
X /s W (Omega)
Torque Pterm Dterm Iterm angular
velocitygain
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Mach 3 (Balance at last!)
So now that its balancing! Lets hook it up to a
Wiimote!
Total cost 300 Could be as low as 250
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Wiimote
Using the Wiring or Arduino we can interface
easily with Processing Why? because they are
married! Using the wrj4P5 and WiiRemoteJ
Libraries, communication can be established with
the wiimote via bluetooth.
Wiimote gives computer an angle Computer scales
and sends value to segwii via USB
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Things I hated about this project!
Dont get me wrong, I loved this project.. I just
wish a few things were different!
1) The middle man I say.. cut the middle
man, give the Segwii bluetooth, and write
drivers.
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Things I hated about this project!
2) Segwii Hardware - Gyro and Accelerometer need
a temperature output - Encoders for the motor,
for precise position control - Better motors,
with a properly tuned gearbox - Better
batteries 3) The drivers I wrote - Refining the
drivers I wrote for the IMU 5DOF (Gyro and Acc) -
More precision! - Compensate for temperature, and
add self calibration 4) The Wii part - Based on
the demo, you can see that the controls are quite
crude, and lot of refining is needed. All of
these need time and money...
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Computer Requirements
Segwii GUI is currently available for Mac and
Linux.
Hardware code IDE works on any OS.
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I am Wii, and so can you!
All the code and hardware is now open
source! Help out, donate, or just learn! Code
and Schematics, and additional information and
support can be found here http//www.segwii.com
Questions? Email me arko_at_segwii.com
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DEFCON
Any ideas? - Annoyance bot? - Goon Robot? -
Robot army? - Robot Server/Control me?
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The End