The Pie's internal controller is based on the same
PCB as the external cruise controller
(more commonly known as the Magic Controller):
Special Features of the controller include:
• Cruise Speed Control
• Programmable via PC to setup motor control parameters
• Motor hall sensor failure redundency (Automatically switch to sensorless control)
• True regenerative braking (only effective when you squeeze the hand brake)
• Other failures redundency (Works with failed throttle and power breaking switches)
• Work with multiple voltages: 24V, 36V and 48V with the same controller
• Support PAS (pedelec for EU regulations)
• Reports failure of components by beeps
• Motor phase self detection and calibration
• Excessive Current Protection
• Low Voltage Protection
• High Reliability
Although the external controllers are advertised as being a 50Amp controller, the maximum current is usually limited to nearer 20 Amps, and there is also a high voltage limit which prevents the controller from operating if the battery voltage is above 60V.
The controller incorporates a temperature operated safety cut out to prevent damage caused by overheating, and has a useful safety feature which automatically prevents the motor from starting if the battery is turned on while the throttle is activated.
This is what the internal controller looks like inside the hub:
The built in controller gives a much neater conversion as there is no need to find addition space to mount a separate controller.
An internal controller is also much less likely to be damaged or removed from the bike
(Stolen).
The biggest problem an internal controller is that it is more susceptible to heat build up within the wheel causing it to cut out if it has been working too hard in high temperature environments, and it is also more involved to remove the unit for replacement if it fails.
That's should be enough information to be going on with for the time being.
Alan 
