Robots! Part 2

Well it finally arrived, thanks to Robosavvy and the Royal Mail :). The kit comes with the main chassis already built along with the motors and suspension system. All that I had to do was fit the motor axial mounts and the wheels. I left the 2DOF arm off for now, mainly as the chassis is a little bigger than expected and it may have trouble moving around with the arm on. This kit has the 75:1 motor gear boxes and the specification sheets says it will do upto 3km/h. This chassis also has the option of the 34:1 gearbox that will do 7km/h which is a little fast for indoors! Perfect for an outside robot though.

The motors with the Wild Thumper are also quite beefy. Rated at 6VDC (usable between 2VDC and 7.5VDC) with a stall current around 6amps, the Arduino is not going to be able to drive these directly.

Once I started looking around at the various motor shields for the Arduino, one thing quickly became apparent. Motors upto 2A were fine but anything above this was going to require a special motor driver board. The problem was also compounded by the fact the Wild Thumper's motors where connected together in pairs (Both right side act as one, as do the left side). This meant a potential 12amps should the motors stall, on the plus side I could get by with a single or dual motor board.

Pololu seemed to offer a wide variety of motor control boards and after looking around I found the VNH5019 which would control both motors and was an Arduino shield, BONUS! As it was a dual motor driver it also worked out cheaper than buying 2 separate boards. In addition to this Pololu have also written an Arduino library to use with the shield.

The board comes in kit form, where you have to solder the headers and connection block on, but all the other SMD chips are already attached.

The VNH5019 requires external power between 5v and 24v and there is an option to power the Arduino board through the VNH5019 meaning only 1 power supply is required. This is controlled through the blue jumper in the pictures. Jumper present means the Arduino is powered through the VNH5019. When it is configured this way the Arduino can be programmed via USB however NO OTHER POWER can be connected as it will damage both boards. Without the jumper present he Arduino will need its own power source.

Now off to go and look at how to power it all!