David's dead reckoning code for the LVBots competition on March 6th. Uses the mbed LPC1768, DRV8835, QTR-3RC, and two DC motors with encoders.
Dependencies: PololuEncoder Pacer mbed GeneralDebouncer
reckoner.h
- Committer:
- DavidEGrayson
- Date:
- 2014-02-23
- Revision:
- 12:835a4d24ae3b
- Child:
- 13:bba5b3abd13f
File content as of revision 12:835a4d24ae3b:
// Robot configuration: // General purpose code: class Reckoner { public: Reckoner(); // Together, cos and sin form a vector with a magnitude close to 2^30 that indicates // the current position of the robot. By definition, when the reckoning starts, // sin is 0 and cos is 2^30. // cos corresponds to the x component of the orientation vector. // sin corresponds to the y component of the orientation vector. int32_t cos, sin; // Together, x and y are a vector that points from the starting point to the // robot's current position. // Units: // * If the units are too big, precision is lost. // * If they are too small, the integers wil overflow. // * For convenience, they should be a power of 2 off from Df (Distance robot moves // forward per encoder tick), so we can just write x += cos >> some_constant. // * Worst case for overflow: our encoders give us a Df of 0.25mm and our robot moves // 5m away from the starting point. Therefore, x and y might need to hold a value // 20000 or -20000 without overflowing. // Overflow condition: x = (1<<31) // 20000*Df < max_dist_x = (1<<31) * U // U > Df * (20000) / (1<<31) = Df / (1<<16) // * Therefore the units we choose for x are Df / (1<<16). // * If we wrote x += cos it would mean the units are Df / (1<<30). // Instead, we write x += cos >> 14 so the units are correct. int32_t x, y; void handleTickLeftForward(); void handleTickLeftBackward(); void handleTickRightForward(); void handleTickRightBackward(); void handleForward(); void handleBackward(); void handleRight(); void handleLeft(); }; extern Reckoner reckoner;