I've bought a couple of MCP-4131 digital potentiometers and I've set them up correctly. Setting the SPI transfer value my multimeter shows the values go up then down as expected. So it works.
Equally, my mini motors (http://www.amazon.co.uk/dp/B00LUTF6WC/) when I plug them straight in to the +ve and -ve rails on my breadboard work.
Checking the voltage when the circuit is: arduino -> MCP-4131 (+ve) -> motor -> multimeter -> -ve rail I can see the motor should be at full power, but is not.
Is there a reason for this? Do I need a different kind of chip or motor?