Bot balancing without gyros … for a few seconds at least

No gyros, no accelerometers – only a sonar ranger and lots of code.

The motors used are standard servos modified for continuous rotation, sonar sensor is a HC-SR04 as detailed in a previous post

Code ? Well here’s a simplified portion of the PID loop:

int Drive = 0; // PWM value sent to Servos
int Error[5]; // array of 5 Error elements
int P = 0; // proportional term
int I = 0; // integral term
int D = 0; // derivative term

#define Current 0
#define Sum 1
#define Last 2
#define SecondToLast 3
#define Delta 4

int PID() {
Error[Current] = SetPoint – Ptime;
P = Error[Current] * Kp;
Error[Sum] = Error[Current] + Error[Last] + Error[SecondToLast];
I = Error[Sum] * Ki;
Error[Delta] = Error[Current] – Error[Last];
D = Error[Delta] * Kd;
Drive = P + I + D;
Error[SecondToLast] = Error[Last];
Error[Last] = Error[Current];

return Drive;
}

Using an ultrasonic sonar ranger to avoid walls – and people’s feet – before hitting them:

At first I was getting plenty of false readings, so here’s the first run, pausing and verifying before turning:

With faster code, and not stopping:

Improved accuracy, so it detects smaller objects like feet:

Hooked an SR04 ultrasonic sensor to my arduino board – robot eyes !

Ranger sensor uses sonar to give accurate distance measurement to objects or obstacles placed in front of it. They’re surprisingly sensitive / accurate – I was able to reliably measure to a millimeter at 15cm range.

These sensors are also now VERY cheap £2.37 (4$) delivered from HK, and accurate to a few mm.

Added a servo for visual feedback:

Arduino code is basically sending a trigger on one pin, receiving a timing value on another,
which can then be converted into a distance:

pinMode(TP,OUTPUT);
pinMode(EP,INPUT);
Trig_pin=TP;
Echo_pin=EP;

digitalWrite(Trig_pin, LOW);
delayMicroseconds(2);
digitalWrite(Trig_pin, HIGH);
delayMicroseconds(10);
digitalWrite(Trig_pin, LOW);
duration = pulseIn(Echo_pin,HIGH);

Following on from my recent add-ons, here’s a handy plug-in to display latest bbc news headlines.

Instead of opening a tab, this opens a faster mini window on a single click:

So go get the add-on “Latest BBC News” for both firefox and chrome:

V 1.0

Features

• Get all the Latest BBC News headlines with a single click.
• Opens a popup widget with the latest news headlines.
• Links at the bottom to show all sections:
  Technology, Health, Entertainment etc

Get it yourself direct from:

BBC News for Firefox

and for chrome:

BBC News for Chrome
Youtube video

An avid bargain hunter, I often keep an eye on HotUKDeals.com for the latest deals,
and following on from my recent add-on for ebuyer’s website, I thought I’d make a more convenient way of checking the site.

Instead of opening a tab, this opens a faster mini version of the site on a single click:

It also adds the oft-requested feature of page numbers at the top of threads on the main site:

Much better !

So go get the add-on “Top UK Deals” for both firefox and chrome:

V 1.1.0

Features

• Opens a fully functional small version of the HUKD website
• You can
  – sort by date,
  – sort by recently comments

  – view/post comments

• You can even post a new deal direct from the popup !
• Also makes minor edits to the main HotUKDeals site :
• – adds pagination box to the top of the comments page [ 1.,2.3…last]

Get it yourself direct from:

Top UK Deals for Firefox

and for chrome:

Top UK Deals for Chrome
Youtube video