Buzzbot – Wheel Encoders

Now that the Motor Drive Controller has been worked out, (but yet untested)  I needed to make up some encoders for the Left and right Wheels.  After a bit of research I found an excellent program for creating encoders and quickly made two and have just glued them to the inside of the wheels for some rough and ready testing.  I really think I will need to make them more durable, but for the time being they should surfice.  Once I have the encoders and the sensors mounted I will start some testing on the drive system and the PicAxe.

Some quick calculations to see what I get:

Assumptions: 

 Wheel Diameter (D)=50mm
 wheel Circumference (C)= D * 3.14 = 157mm
 Encoder Resolution (Res)= 16

 Distance Travelled Per between encoder Pulses =  C/Res = 9.81mm

So per encoder output pulse width = 4.9mm (~5mm) – Remember the encoder has a resolution of 16 (50% black and 50% white) therefore I need to divide by 50% to get the per pulse distance assuming a nice neat square wave.

I’ve also placed the encoders in the top cover, filed out some slots and hotglued to suit. 

 BuzzBot Encoder Template Buzzbot Wheel encoders Buzzbot Encoder Sensor Placement

BuzzBot Motor Board Schematics

Today I reversed engineered the control board of the RC Buggy and the results are the schematic attached.  I was only interested in the Motor Drive CCT so thats all that is drawn.   It looks fairly straight forward to hook up the PICAXE to this board, although the main Driver Transistors are TO-92L type packages, so I suspect the duty cycle of the drive will not be continuous as there are no heat sinks etc. 

While I was at it I removed the RF Receiver Daughterboard and the decoder chip (U1 in the schematics), so now the board is all ready to go.

Buzzbot Motor Board (Sorry about quality)

Buzzbot Motorcontroller Schematic 

BuzzBot

Introduction 

The Buzzbot idea came to me when i was trying to think what can i do to learn the picaxe uController, something practical, well rather than just flashing Leds and buzz buzzers anyway. What I wanted to do was something robotic that is cheap and easy as I don’t have much of a workshop facility available to me just yet to assemble any bases. 

Recycle 

We had just moved house and whilst doing the spring clean of some toy boxes and throwing alot of my childrens toys into thte “garage sale” box I came across the Buzz Lightyear Remote control buggy.  Basically a 6 wheel buggy with a psycho looking buzz with missile launchers as hands that raises and releases the missiles.  Well the missiles were long lost and what interested me was in using it as the base for my “buzzbot” is that most of the work is already done for me. i.e. I don’t have to build a base and look for motors etc.  I just want to get down to the nitty gritty of interfacing the PICAXE into something and playing around with it. Another thing that I think will work in my favour is that the Left and right wheel drives seem to be independant of each other as this thing from memory could turn on a dime, so therefore there must at least two motors, and the necessary driver circuits in place for me to use.

 BuzzBot Buzz Buggy Side

The Autopsy

Upon dissasembly it looks as though I was right, a gearbox and motor for the left and right drives (front two wheels on each side are geared , while the rear is free wheeling) also a circuit board with a simple RF Receiver and a heap of transistors, which after some initial tracing leads me to suspect are the H-Bridge Drive implementation for the motors, Left, right and the psycho buzz torso aka Missle launcher (he raises up to fire) woohoo, most of the work is already done.

Buzz Buggy InsideBuzzBot Drive Trainbuzzbot control boardbuzzbot -  inside buzz

Man he must be on crack!

buzzbuggy - psycho buzz

Next Steps…..

Ok since I have now dissected the Buzzbuggy it will now be re-assembled back into the “buzzbot”  minus the psycho buzz torso, as I just want to use the base as my test platform for the PicAxe.  I now need to trace through the circuit and see where I can tap into for the motor control, and also add some sensors. 

 Stay Tuned….

Welcome

First post to christen the new site……

Personal Projects underway. 

1)  Learn the PICAXE, a fantastic little uController, http://www.rev-ed.co.uk/picaxe/  I have just got my hands on the PICAXE 18X, so in attempt to learn to use this little beast I am looking at interfacing it with a few sensors and turn my sons discarded “Buzz Buggy” into a little 6 wheeled autonomous “buzzbot”. 
BuzzBot

2)  Also getting pissed off mowing the lawn at home every week, especially now it’s summer in Australia, so have now decided to look at some sort of mowbot.  After some research found someone who has actually implement one over the last few years with some great drawings and details, so will be using this as a starting point http://www.mowbot.org.