（四）四轴——油门曲线（MWC）

接收的PPM信号为1000~2000ms，为了便于PID控制，需要将信号进行处理。

将ROLL/PITCH/YAW   变为 -500~500范围，将THROTTLE变为1000~2000范围。

MWC具体实现代码为：

1. 先定义lookup函数，用于映射，在EEPROM中；

2. 根据接收的PPM信号进行映射，处理到相应的数据范围。

具体代码如下：

/************************************************************************************//************************************************************************************///set lookuprcRate8 = 90; rcExpo8 = 65;for(i=0;i<5;i++) {    lookupPitchRollRC[i] = (1526+rcExpo8*(i*i-15))*i*(int32_t)rcRate8/1192;}//Motor maxthrottle/* this is the maximum value for the ESCs at full power, this value can be increased up to 2000 */    #define MAXTHROTTLE 1850//Motor minthrottle      /* Set the minimum throttle command sent to the ESC (Electronic Speed Controller)       This is the minimum value that allow motors to run at a idle speed  */    //#define MINTHROTTLE 1300 // for Turnigy Plush ESCs 10A    //#define MINTHROTTLE 1120 // for Super Simple ESCs 10A    //#define MINTHROTTLE 1064 // special ESC (simonk)    //#define MINTHROTTLE 1050 // for brushed ESCs like ladybird    #define MINTHROTTLE 1150 // (*) (**)thrMid8 = 50;thrExpo8 = 0;for(i=0;i<11;i++) {    int16_t tmp = 10*i-thrMid8;    uint8_t y = 1;    if (tmp>0) y = 100-thrMid8;    if (tmp<0) y = thrMid8;    lookupThrottleRC[i] = 10*thrMid8 + tmp*( 100-thrExpo8+(int32_t)thrExpo8*(tmp*tmp)/(y*y) )/10; // [0;1000]    lookupThrottleRC[i] = MINTHROTTLE + (int32_t)(MAXTHROTTLE-MINTHROTTLE)* lookupThrottleRC[i]/1000;  // [0;1000] -> [MINTHROTTLE;MAXTHROTTLE]}/************************************************************************************//************************************************************************************/#define MIDRC 1500  uint16_t tmp,tmp2;  uint8_t axis,prop1,prop2;  dynThrPID = 0;  // PITCH & ROLL only dynamic PID adjustemnt,  depending on throttle value  prop2 = 128; // prop2 was 100, is 128 now  if (rcData[THROTTLE]>1500) { // breakpoint is fix: 1500    if (rcData[THROTTLE]<2000) {      prop2 -=  ((uint16_t)dynThrPID*(rcData[THROTTLE]-1500)>>9); //  /512 instead of /500    } else {      prop2 -=  dynThrPID;    }  }  for(axis=0;axis<3;axis++) {    tmp = min(abs(rcData[axis]-MIDRC),500);    if(axis!=2) { //ROLL & PITCH      tmp2 = tmp>>7; // 500/128 = 3.9  => range [0;3]      rcCommand[axis] = lookupPitchRollRC[tmp2] + ((tmp-(tmp2<<7)) * (lookupPitchRollRC[tmp2+1]-lookupPitchRollRC[tmp2])>>7);      prop1 = 128-((uint16_t)conf.rollPitchRate*tmp>>9); // prop1 was 100, is 128 now -- and /512 instead of /500      prop1 = (uint16_t)prop1*prop2>>7; // prop1: max is 128   prop2: max is 128   result prop1: max is 128      dynP8[axis] = (uint16_t)conf.pid[axis].P8*prop1>>7; // was /100, is /128 now      dynD8[axis] = (uint16_t)conf.pid[axis].D8*prop1>>7; // was /100, is /128 now    } else {      // YAW      rcCommand[axis] = tmp;    }    if (rcData[axis]<MIDRC) rcCommand[axis] = -rcCommand[axis];      //-500 ~ 500  }  tmp = constrain(rcData[THROTTLE],MINCHECK,2000);  tmp = (uint32_t)(tmp-MINCHECK)*2559/(2000-MINCHECK); // [MINCHECK;2000] -> [0;2559]  tmp2 = tmp/256; // range [0;9]  rcCommand[THROTTLE] = lookupThrottleRC[tmp2] + (tmp-tmp2*256) * (lookupThrottleRC[tmp2+1]-lookupThrottleRC[tmp2]) / 256; // [0;2559] -> expo -> [MINTHROTTLE;MAXTHROTTLE]

为了更加直观的看出具体的曲线，使用Matlab对其绘制：

（1）lookup函数曲线：

红色为ROLL和PITCH的lookup曲线；

蓝色为THROTTLE的lookup曲线。

matlab代码为：

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%set lookup%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%Roll/PitchrcRate = 90; rcExpo = 65;lookupPitchRollRC=[0 0 0 0 0 0];for i=1:1:5     %1~5    lookupPitchRollRC(i) = (1526+rcExpo*((i-1)*(i-1)-15))*(i-1)*rcRate/1192;end;plot(lookupPitchRollRC,'r');hold on;stem(lookupPitchRollRC,'r');%ThrottleMAXTHROTTLE = 1850;MINTHROTTLE = 1150;thrMid = 50;thrExpo = 0;lookupThrottleRC=[0 0 0 0 0 0 0 0 0 0 0];for i=1:1:11  %1~11    tmp = 10*(i-1)-thrMid;    y = 1;    if (tmp>0)         y = 100-thrMid;    end    if (tmp<0)         y = thrMid;    end    lookupThrottleRC(i) = 10*thrMid + tmp*( 100-thrExpo+thrExpo*(tmp*tmp)/(y*y) )/10; % [0;1000]    lookupThrottleRC(i) = MINTHROTTLE + (MAXTHROTTLE-MINTHROTTLE)* lookupThrottleRC(i)/1000;  % [0;1000] -> [MINTHROTTLE;MAXTHROTTLE]endplot(lookupThrottleRC,'b');stem(lookupThrottleRC,'b');hold off;

（2）使用lookup函数进行数据映射处理：

红色为Yaw的rcCommand曲线；蓝色为Roll和Pitch的rcCommand曲线；绿色的为THROTTLE曲线。

somehow... why the blue beyond it's ...   或许roll和pitch需要constrain一下。不管了，呵呵~

代码如下：

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%rcCommand%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%MIDRC = 1500;dynThrPID = 0;THROTTLE = 4; MINCHECK = 1150;%ROLL and PITCH   //rcData -> rcCommandrcData = 1000:1:2000;tmp = min(abs(rcData-MIDRC),500);tmp_t =floor(tmp/128); % 500/128 = 3.9  => range [0;3]rcCommand_RO_PI = lookupPitchRollRC(tmp_t+1) + ((tmp-(tmp_t/128)).*(lookupPitchRollRC(tmp_t+2)-lookupPitchRollRC(tmp_t+1))/128);  %0~500for j=1:length(rcData)    if (rcData(j)<MIDRC)         rcCommand_RO_PI(j) = -rcCommand_RO_PI(j);      %-500 ~ 500    //when rcData<MIDRC  is '-'    endendplot(rcData,rcCommand_RO_PI,'b');hold on;%YAW   //rcData -> rcCommandrcCommand_YA = tmp;for j=1:length(rcData)    if (rcData(j)<MIDRC)         rcCommand_YA(j) = -rcCommand_YA(j);      %-500 ~ 500    //when rcData<MIDRC  is '-'    endendplot(rcData,rcCommand_YA,'r');%THROTTLE //rcData -> rcCommandTHROTTLE_tmp = max(rcData,MINCHECK);   %[MINCHECK,2000]THROTTLE_tmp =(THROTTLE_tmp-MINCHECK)*2559/(2000-MINCHECK); % [MINCHECK;2000] -> [0;2559]THROTTLE_tmp_t = floor(THROTTLE_tmp/256); % range [0;9]rcCommand_TH = lookupThrottleRC(THROTTLE_tmp_t+1) + (THROTTLE_tmp-THROTTLE_tmp_t*256).*(lookupThrottleRC(THROTTLE_tmp_t+2)-lookupThrottleRC(THROTTLE_tmp_t+1))/256; % [0;2559] -> expo -> [MINTHROTTLE;MAXTHROTTLE]plot(rcData,rcCommand_TH,'g');hold off;