I decided to build a balancing robot after stumbling upon a website about this guy who built his own balancing vehicle that you stood up on; his own Segway, at the bottom of his page there was a good selection of links to other websites about balancing robots, after browsing these sites and watching the videos for a couples of hours I was hooked, I had to build my own.
After reading up on the different balancing methods I decided I had to go for an Accelerometer/Gyroscope system, the other methods (distance sensor and potentiometer) require a flat surface for the robot to travel over, I want mine to be able to travel over any surface.
After deciding what method I was going to use I needed to source an accelerometer and a gyroscope, the accelerometer was easy an ADXL202 from Analog Devices bought from RS, the gyroscope was a different matter. I decided what gyroscope I wanted to use an ADXRS150 also from Analog but I needed to find someone who sold it, you can buy from Analogue via there website but you need to be VAT registered, I then contacted Analogue in the UK who put me in touch with one of there distributors Avent Silica, they seem to sell all the different gyroscopes Analog sell. Unfortunately they don't have any in stock so I am currently waiting until the beginning of March for them to become available, until then the project is on hold.

If you do decide to build your own and want to use the Analog gyroscope look at the Evaluation Board ADXRS150EB for the product, the actual chip is in a Ball Grid Array package a 1/4" big which is very hard to attach to anything unless you have surface mount facilities, the Evaluation board has the chip mounted with all the required capacitors on standard size DIL package.
Update 21/02/05
This morning I received my gyroscope, it came in a box about 1m long by about 20cm by 10cm, in the middle of this was my tiny gyroscope.

I have been thinking about the electronics that will make it balance and all I should need is a filter for each device and an amplifier for each device. I do most of my workings out on my tablet so the files can be stored and don't get lost, because of this I am going to upload various documents for this and the Melexis robot, you can view my initial thoughts on the balancing problem in this document

I should be picking up a small PCB today; the board will take my accelerometer which is a surface mount device and convert it into a standard pitch so it can be connected to a normal PCB or Vero board for testing. Hopefully I will be able to put together a design for the balancing system and test the design.
I collected the PCB and have attached the chip I now have the accelerometer and gyroscope in suitable size packages ready to be connected up for testing.

The picture below is of the chassis which will hold the rest of the electronics, you can see that the motors and motor controller has been attached

A photo of the base of the balancing robot

After doing nothing on the robot for 2 months I have decided to make it part of the Melexis project, I am going to build that robot as part of my 3rd year project and during that time I will also try and finish this robot, I can then mount a colour tracking camera on this one and have it follow the Melexis robot, this should impress the people marking the other robot.

I have now decided to make this robot the coursework rather than part of it, I have scrapped the Melexis robot and I will just be construction this.

It's been a while since I have updated this page so 3 months on hears the update.
I have scrapped the balancing idea; I don't have enough time or resources to get this to work. The balancing base I was working with wasn't suitable so I built a new one, it took me a couple of weeks and about £250 and at the end it was useless. I spent £200 on two motors that went powerful enough to move themselves let alone the other electronics to go on the top.
After that fiasco I decided on a different direction for the project

I am still building a robot for my Uni project under the same brief; "Design and build a robot capable of entering and surveying a disaster area" but I have moved up in size. The robot is now constructed from steel and aluminium and has motors that weight about 10Kg each, the whole thing weighs about 20-30Kg and moves slowly but with a lot of power.
Because of the change in direction I am moving this project to a new page.
DARSU (disaster area remote survey unit) – the name of the robot!