Table of Contents

 alpha = 0.117
 b = [alpha 0]
 a = [1 -(1-alpha)]

 b = [0.0592    0.0592]
 a = [1.0000   -0.8816]

 alpha = 0.117
 b = [alpha 0]
 a = [1 -(1-alpha)]

tmp2 = zeros(size(trq_raw));
for i=2:size(trq_raw,1)
   if abs(trq_raw(i-1)-trq_raw(i)) > 10
      tmp2(i) = tmp1(i-1);
   else
      tmp2(i) = trq_raw(i);
   end
end
y_rc_cl = filter(b,a,tmp2);

Window width 5
Window width 9

The low-pass RC filter considering change limits and the median filter of window width 9 give better results.

In the following experiments, the hip torque is calculated from the button sensor measurements.

1. f_c = 50. The first figure is the raw measurements of the button sensor. The second figure is the hip torque after using this filter.
2. f_c = 20 The first figure is the raw measurements of the button sensor. The second figure is the hip torque after using this filter.

   f_c = 20 comparison The green line is the raw measurements of the button sensor. The blue line is the hip torque after using this filter.

3. f_c = 20 and with change limits . The first is the raw measurements of the button sensor. The second is the hip torque after using the low pass filter. The third is the hip torque after using the low pass filter with change limits. The fourth is the comparison between using the low pass filter with and without change limits.
   Change limits are

       if(fabs(trq_raw - raw[dofNum].trq) > 10){
       trq_raw = raw[dofNum].trq;
       }
   

The low pass filter with cutoff frequency 20 Hz and change limits can be used for the hip torque. Without the filter, we can not set torque feedback gain larger than 50 or it shakes severely. After adding the filter, we can set larger gain for torque control now.

1. gain = 0
2. gain = 40
3. gain = 50 begin to shake
4. gain = 60

Torque control is not good enough. I attribute this to the delay in the control loop. The delay may caused by the communication, sampling, the filter, and response time in high level program. Better torque control may be implemented at the DSP level.

The figures below are for L_HFE_load, L_HFE_curM0, L_HFE_rtrq, and L_HFE_torM0

1. No command is sent to motor driving board
2. Position control
3. position control without button sensor In order to avoid the input pins of AD converter floating, they are connected with an external sensor.

In Fig. 1, no motor commands are sent, the noise is small. In Fig. 2, motor commands are sent during position control, the noise is large. In Fig. 3, motor commands are sent during position control, the noise is still large although the sensor is disconnected.

The noise of button sensor is not introduced by the sensor, the cable between the sensor and DSP board, the movemoents of the leg, but by the DSP board. Filters should be added in the DSP code. Final solution may be a new partition for the DSP board design.