using servo giving error

Hello, I am using the code below to track red object using servomotor and arduino.

clear all;

a=arduino("/dev/cu.usbmodem101","Uno","Libraries","Servo");

s = servo(a,'D4','MinPulseDuration',5.44e-04,'MaxPulseDuration',2.40e-03);

cam=webcam();

for i = 1:300

RGB = snapshot(cam);

size(RGB)

% defining redness of image

r = RGB(:, :,1); g = RGB(:, : ,2); b = RGB(:, :, 3);

% create a binary image (heuristic)

red = (r > 2*g) & (r > 2*b) & (r > 30);

% imshow(red);

% group all red object within 5 pixels of each other as one object

se = strel('disk',5);

red = imclose(red,se);

% delete all objects smaller than 35 pixels in area

red = bwareaopen(red,35);

red = bwareafilt(red, 1);

% getting the centroid & creating bounding box

stats = regionprops(bwlabel(red),'BoundingBox','centroid');

S = vertcat(stats.Centroid);

figure

imshow(RGB) % show original image

hold on

for object = 1:length(stats)

bb = stats(object).BoundingBox;

bc = stats(object).Centroid;

rectangle('Position', bb, 'EdgeColor', 'r', 'LineWidth', 2) % draw bounding box

plot(bc(1), bc(2), '-m+') % mark centroid (x, y) with '+'

a=text(bc(1)+15,bc(2), strcat('X: ', num2str(round(bc(1))), ' Y: ', num2str(round(bc(2)))));

set(a, 'FontName', 'Arial', 'FontWeight', 'bold', 'FontSize', 12, 'Color', 'yellow');

error = bc(1)-320;

x_dist = error*0.06718;

deg = atan(x_dist/30);

deg_map = (deg+0.6)*(1-0)/(0.6+0.6) + 0;

fprintf('DEG %.2f \n', deg_map)

writePosition(s,deg_map)

end

hold off

end

The issue is, whenever the degree is more than 1, it gives an error saying, "Invalid position value. The value must be between 0 and 1." For example:

What can I do to solve this? Thank you!

Answer 1

[Amit Dhakite]

Hi Md,

As per my understanding, you are using "writePosition()" in order to track a red object using a servo motor, but encountering an error.

I would like to draw your attention to the fact that the second parameter in the "writePosition()" is the position of servo motor shaft specified as a number representing the angle from 0 to 1, where 0 represents the minimum angle of rotation and 1 represents the maximum angle of rotation of the servo motor. In your code, it looks like this parameter "deg_map" is out of this specified range.

Try to find out the range of "deg". Let's say it is between "deg_min" and "deg_max", then its mapping would be:

deg_map = (deg - deg_min) / (deg_max - deg_min);

This should help bring the "deg_map" parameter within the specified range of 0 and 1.

To know more about “writePosition()”, kindly refer to the following link: https://www.mathworks.com/help/supportpkg/arduinoio/ref/writeposition.html