@Eugene
I know what you mean that it is deemed most effective to place the IMU as close to the wheel axle as possible. However my thinking was that because the gyroscope measures the angular velocity, I thought it would be most effective if the gyroscope was as close to the top of the structure ie. where the battery is so it would measure any slight variations in angular velocity...
I could be wrong in the this... Let me know your thoughts!
#Eugene
See my github, here a link for the compiled versions of the processing application:
#rob4white
You should put the IMU as close to the axis as possible, as I wrote in my email.
I just built a balancing robot using ATmega328 and Arduino libraries myself. I built it using a toy truck as a base, while not as stable as some other builds it is easy on the wallet. Here is a short video:
You can find more information on the theory and the build on my blog (three parts):
http://www.kerrywong.com/2012/03/08/a-self-balancing-robot-i/
http://www.kerrywong.com/2012/03/14/a-self-balancing-robot-ii/
http://www.kerrywong.com/2012/03/21/a-self-balancing-robot-iii/
Thanks Eugene and Lauszus for the advice, I fully understand now why the IMU should be as close as possible to the axis of rotation.
However, I am quite close to achieving balance with the current setup, I am kinda short on time to move the IMU to the lower deck as the project deadline is fast approaching... Or am I just wasting my time trying to achieve balance with the IMU located where it currently is?? (about 50mm above the axis of rotation in the vertical direction)
My current stumbling block is finding the correct PID parameters.. I am using the original coding as posted by Kas in the initial thread on this topic
Am I correct in thinking that I should tune the terms in this manner. Tune Kp value first then Ki value then the Kd value and finally the "outside" K value? The coding I am referring to shown here:
float K = 1.4;
int Kp = 3;
int Ki = 1;
int Kd = 6;
int last_error = 0;
int integrated_error = 0;
int pTerm = 0, iTerm = 0, dTerm = 0;
int updatePid(int targetPosition, int currentPosition) {
error = targetPosition - currentPosition;
pTerm = Kp * error;
integrated_error += error;
iTerm = Ki * constrain(integrated_error, -GUARD_GAIN, GUARD_GAIN);
dTerm = Kd * (error - last_error);
last_error = error;
return -constrain(K*(pTerm + iTerm + dTerm), -255, 255);
}
I will try to post a video today to show the stage of balancing that I am at! 
Any advice appreciated! Thanks guys!
Hey guys I am thinking about trying to build one of these self balancing robots. I have an arduino r3 motor shield. Im curious if I can find good enough motors that I can control with my shield and not push the 2 amp limit.
Also what do you guys think of this IMU. The goal is to use this on a balancing robot first and if I have success I will move onto a quad copter.
#rob4white
I followed this guide to find the P, I, and D constants:
http://robotics.ee.uwa.edu.au/theses/2003-Balance-Ooi.pdf see page 42:
#Wmgatorfan08
Yes I think it is possible to make a very low cost segway using those parts, but I don't think the performance will be as good, but I will still be a great learning experience and a fun project. Just take a look at AlphaZeta robot: Balancing robot for dummies - #43 by AlphaZeta - Robotics - Arduino Forum
That only cost approximately 20$ excluding the motors!!
I think your forgot to insert the link for your IMU
Sorry here is the link SparkFun 6 Degrees of Freedom IMU Digital Combo Board - ITG3200/ADXL345 - SEN-10121 - SparkFun Electronics
I feel pretty comfortable with this IMU. I have been reading a lot about it and have already found several examples of code to get the data that I need. I have been using arduino for about a year now so I feel pretty confident with my ability to get the board working. I am not as familiar with I^2C as I should be but I am reading and working on it now.
My main concern is the motors. I know that selecting the proper motors and wheels will make or break the project. Ultimately I am thinking I need something with a lot of torque that can respond quickly. I don't think I need high rpm, but it must spin fast enough to catch up with itself when falling.
Possibly this type of motor with the encoders. http://www.robotshop.com/12v-gear-motor-encoder.html
Also correct me if I am wrong, but I am thinking something around a foot to foot and a half tall with the center of mass being around the motors. From what I am reading the IMU needs to be near the top?
For best results, the IMU needs to be placed near the center of the gravity of your build, wherever that is. Typically, the higher the center of gravity is, the easier it is to balance as the timing becomes less critical.
Yeah I guess that would be true because of the moment of inertia. So ill move the battery toward the top and mount the IMU close to it.
I ordered the 6dof IMU board from sparkfun tonight!
What do you guys think of this motor and encoder setup??
http://www.robotshop.com/cytron-12v-430rpm-15-57oz-gear-motor-encoder-2.html
Sounds like you are thinking building a big one :). They look pretty powerful for sure, just make sure that your battery source can handle the load. Two of these motors will draw around 2A and the stall current will be much higher.
Hi guys, i want to buy this dual driver Pololu - Dual MC33926 Motor Driver Carrier for a 29:1 pololu motor. As regard to you it's ok? Why is necessary this driver? i say this because, this driver it's ok until 9 A, but the motor requires 5 A max. Maybe this http://www.robot-italy.com/product_info.php?cPath=83_30&products_id=2386?
So I am really struggling to pick out the right motor. I really want to stick with my motor shield but it has a max of 2 amps. Most motors that I am finding have low free running current but the stall current exceeds my motor shield. Do these type of bots push the motors to their stall current? I do not see my design pushing the motor anywhere close to its stall current?
I've bought the pololu 29:1 and the relative motor control. So i've a questions: How connect the wires of motor and encoder to arduino and motor control?
Hi all,
Started a project around 2 months ago to build an autonomous robot. The wheels and motors I'm using are as follows: http://www.technobotsonline.com/banebot-wheel-124x20mm-1-2-hex-shore-50.html, Pololu - 30:1 Metal Gearmotor 37Dx52L mm 12V with 64 CPR Encoder (No End Cap).
Although I am able to balance the robot using a PID algorithm, I am finding it tough to control the position of the robot (via the encoders). I have a tilt sensor sending me the angle the robot is at and setting the motorspeed accordingly. To control the position of the robot I have been varying the reference angle to try and move the robot towards a reference point(eg: x = 0) to keep the robot in the same position but I have not had great results.
State space control would be best to control multiple inputs/outputs but I am not sure how this can be done on the Arduino Uno, any ideas?
If state space isn't used how is the best way to approach the problem I am encountering with the position?
The code I am using is as follows:
#include "DualVNH5019MotorShield.h"
#include "math.h"
enum PinAssignments {
encoderPinA = 2, // right
encoderPinB = 3, // left
clearButton = 12 // another two pins
};
DualVNH5019MotorShield md;
int sensorPin = A2;
float setpointang = 501.0;
int oldangle, oldangle_1, oldangle_2, angle, newangle, current_1, current_2, errorpos, a, b, c = 0;
double sumangle, output, oldpos, oldpos_1, oldpos_2, derivpos, integpos = 0.0;
int Kp = 20;
int ZoneA = 2000;
int ZoneB = 1000;
float motorspeed, deriv, error, errorposctrl;
double Kd = 0.3;
float freq = 66.67;
float T = ((1/freq)*1000)-0.5;
float Kp_1 = 1.00 ;
float posScaleA = 500.0;
float posScaleB = 1000.0;
float posScaleC = 2000.0;
volatile unsigned int encoderPos = 0; // a counter for the dial
unsigned int lastReportedPos = 1; // change management
static boolean rotating=false; // debounce management
// interrupt service routine vars
boolean A_set = false;
boolean B_set = false;
void setup()
{
Serial.begin(115200);
md.init();
TCCR1B = TCCR1B & 0b11111000 | 0x01;
pinMode(encoderPinA, INPUT);
pinMode(encoderPinB, INPUT);
pinMode(clearButton, INPUT);
// turn on pullup resistors
digitalWrite(encoderPinA, HIGH);
digitalWrite(encoderPinB, HIGH);
digitalWrite(clearButton, HIGH);
attachInterrupt(0, doEncoderB, RISING); //CHANGE
}
void loop()
{
angle = analogRead(sensorPin);
if ((angle < 300) || (angle > 700))
{
md.setM1Speed(0);
md.setM2Speed(0);
}
else if ((current_1 < 6000) || (current_2 < 6000) )
{
//PID
oldangle_2 = oldangle_1;
oldangle_1 = oldangle;
oldangle = newangle;
newangle = (setpointang - angle);
deriv = ((newangle + (3*oldangle) -(3*oldangle_1) - oldangle_2)*(freq/6));
error = (Kp*(newangle) + Kd*(deriv));
//Translating PID output value to a value within the range of the motor driver
motorspeed = ((error/511)*400);
//Driving the motors
md.setM1Speed(motorspeed);
md.setM2Speed(motorspeed);
//---------------------------------------------------------------------------------------------------------------------------------------------------------------Angle Control End
//Serial.println(analogRead(A3)); //to plot
if (lastReportedPos != encoderPos) {
if (motorspeed < 0)
{
errorpos = errorpos - (lastReportedPos - encoderPos);
}
else if (motorspeed > 0)
{
errorpos = errorpos + (lastReportedPos - encoderPos);
}
lastReportedPos = encoderPos;
}
errorposctrl = errorpos;
Serial.print(" errorposctrl: ");
Serial.print(errorposctrl);
float a = (errorposctrl/posScaleA);
float b = (errorposctrl/posScaleB);
float c = (errorposctrl/posScaleC);
if (abs(errorposctrl) > ZoneA)
{
setpointang = setpointang - (a);
}
else if (abs(errorposctrl) > ZoneB)
{
setpointang = setpointang - (b);
}
else
{
setpointang = setpointang - (c);
}
Serial.print(" a: ");
Serial.print(a);
Serial.print(" b: ");
Serial.print(b);
Serial.print(" c: ");
Serial.println(c);
//
current_1 = (analogRead(A0)) * 34;
current_2 = (analogRead(A1)) * 34;
//Serial.print(" errorpos: ");
//Serial.print(errorpos);
//Serial.print(" encoderPos: ");
//Serial.println(encoderPos);
//delay((int)T);
}
}
//// Interrupt on A changing state
//void doEncoderA(){
// encoderPos += 1;
//}
// Interrupt on B changing state, same as A above
void doEncoderB()
{
encoderPos += 1;
}
Thanks in advance,
MAAhelp
MAAhelp:
Hi all,Started a project around 2 months ago to build an autonomous robot. The wheels and motors I'm using are as follows: http://www.technobotsonline.com/banebot-wheel-124x20mm-1-2-hex-shore-50.html, Pololu - 30:1 Metal Gearmotor 37Dx52L mm 12V with 64 CPR Encoder (No End Cap).
Although I am able to balance the robot using a PID algorithm, I am finding it tough to control the position of the robot (via the encoders). I have a tilt sensor sending me the angle the robot is at and setting the motorspeed accordingly. To control the position of the robot I have been varying the reference angle to try and move the robot towards a reference point(eg: x = 0) to keep the robot in the same position but I have not had great results.
State space control would be best to control multiple inputs/outputs but I am not sure how this can be done on the Arduino Uno, any ideas?
If state space isn't used how is the best way to approach the problem I am encountering with the position?The code I am using is as follows:
#include "DualVNH5019MotorShield.h"
#include "math.h"
enum PinAssignments {
encoderPinA = 2, // right
encoderPinB = 3, // left
clearButton = 12 // another two pins
};
DualVNH5019MotorShield md;
int sensorPin = A2;
float setpointang = 501.0;
int oldangle, oldangle_1, oldangle_2, angle, newangle, current_1, current_2, errorpos, a, b, c = 0;
double sumangle, output, oldpos, oldpos_1, oldpos_2, derivpos, integpos = 0.0;
int Kp = 20;
int ZoneA = 2000;
int ZoneB = 1000;
float motorspeed, deriv, error, errorposctrl;
double Kd = 0.3;
float freq = 66.67;
float T = ((1/freq)*1000)-0.5;
float Kp_1 = 1.00 ;
float posScaleA = 500.0;
float posScaleB = 1000.0;
float posScaleC = 2000.0;
volatile unsigned int encoderPos = 0; // a counter for the dial
unsigned int lastReportedPos = 1; // change management
static boolean rotating=false; // debounce management
// interrupt service routine vars
boolean A_set = false;
boolean B_set = false;
void setup()
{
Serial.begin(115200);
md.init();
TCCR1B = TCCR1B & 0b11111000 | 0x01;
pinMode(encoderPinA, INPUT);
pinMode(encoderPinB, INPUT);
pinMode(clearButton, INPUT);
// turn on pullup resistors
digitalWrite(encoderPinA, HIGH);
digitalWrite(encoderPinB, HIGH);
digitalWrite(clearButton, HIGH);
attachInterrupt(0, doEncoderB, RISING); //CHANGE
}
void loop()
{
angle = analogRead(sensorPin);
if ((angle < 300) || (angle > 700))
{
md.setM1Speed(0);
md.setM2Speed(0);
}
else if ((current_1 < 6000) || (current_2 < 6000) )
{
//PID
oldangle_2 = oldangle_1;
oldangle_1 = oldangle;
oldangle = newangle;
newangle = (setpointang - angle);
deriv = ((newangle + (3oldangle) -(3oldangle_1) - oldangle_2)(freq/6));
error = (Kp(newangle) + Kd*(deriv));
//Translating PID output value to a value within the range of the motor driver
motorspeed = ((error/511)*400);
//Driving the motors
md.setM1Speed(motorspeed);
md.setM2Speed(motorspeed);
//---------------------------------------------------------------------------------------------------------------------------------------------------------------Angle Control End
//Serial.println(analogRead(A3)); //to plot
if (lastReportedPos != encoderPos) {
if (motorspeed < 0)
{
errorpos = errorpos - (lastReportedPos - encoderPos);
}
else if (motorspeed > 0)
{
errorpos = errorpos + (lastReportedPos - encoderPos);
}
lastReportedPos = encoderPos;
}
errorposctrl = errorpos;
Serial.print(" errorposctrl: ");
Serial.print(errorposctrl);
float a = (errorposctrl/posScaleA);
float b = (errorposctrl/posScaleB);
float c = (errorposctrl/posScaleC);
if (abs(errorposctrl) > ZoneA)
{
setpointang = setpointang - (a);
}
else if (abs(errorposctrl) > ZoneB)
{
setpointang = setpointang - (b);
}
else
{
setpointang = setpointang - (c);
}
Serial.print(" a: ");
Serial.print(a);
Serial.print(" b: ");
Serial.print(b);
Serial.print(" c: ");
Serial.println(c);
//
current_1 = (analogRead(A0)) * 34;
current_2 = (analogRead(A1)) * 34;
//Serial.print(" errorpos: ");
//Serial.print(errorpos);
//Serial.print(" encoderPos: ");
//Serial.println(encoderPos);
//delay((int)T);
}
}
//// Interrupt on A changing state
//void doEncoderA(){
// encoderPos += 1;
//}
// Interrupt on B changing state, same as A above
void doEncoderB()
{
encoderPos += 1;
}
Thanks in advance, MAAhelp
It seems that the problem I am currently encountering could be easily solved by just adding the integral term with regards to the PID control I am currently trying. Does this make sense?
I have this motors:
http://www.robotshop.com/world/solutions-cubed-ezr-5.html
And this Motor board controller:
http://www.sparkfun.com/products/9670
I would like to know if you think this hardware is possible to build a robot of this type?????
#aasanchez
Yes I think is possible, but the motors are not that powerfull (only 3.6 kg-cm torque), so start out by making a small version first.
For instance I used these motors from Pololu: Pololu - 30:1 Metal Gearmotor 37Dx52L mm 12V with 64 CPR Encoder (No End Cap) which has a torque of 8 kg-cm.
Also I think it is weird, that the peak current is not listed on the website or in the pdf (http://www.robotshop.com/world/PDF/rbsol03_manual.pdf), but if think the motor controller will be okay - if it get's very how, then add a heatsink.
Regards
Lauszus