Algorithm to find the inclination of rotating component

I need a freelancer to collect some data and to write an algorithm to find the inclination of the crank of a bicycle with an IMU (possibly less than 3axis gyroscope and 3 axis accelerometer) on the crank, with an accuracy of +/-2 degrees. The bycicle will have several confunding motions in addition to the rotation of the the crank as moving up and downhill road, lateral inclination of the bicycle, linear accelerations, ...
So we need to start thinking at all these aspects but initially study a simplified situation (for example just the rotation of the crank) .
I have seen a bosch sensor or inversesense but still available to changes. I would probably will need the scripts in C++ but you can use mathlab and maybe start with a simulation.