Rotation at SerialLink.teach Robotic Toolbox

Question

Im using robotic toolbox to simulate my robot, but i always confused when i see the value of rpy. It always different if i compare with tr2rpy and tr2eul. What kind of rotation used in SerialLink.teach?

a = 40/1000;
b = 81/1000;
c = 130/1000;
d = 18/1000;
e = 166/1000;
f = 31/1000;
g = 95/1000;
%MDH
p = SerialLink([...
Revolute('d',b,'a',0,'alpha',0,'modified');...
Revolute('d',0,'a',a,'alpha',deg2rad(90),'offset',pi/2,'modified');...
Revolute('d',0,'a',c,'alpha',0,'modified');...
Revolute('d',e+f,'a',d,'alpha',deg2rad(90),'modified');...
Revolute('d',0,'a',0,'alpha',deg2rad(-90),'modified');...
Revolute('d',g,'a',0,'alpha',deg2rad(90),'modified');],...
'name','6 DOF')
p.teach([0 deg2rad(90) 0 deg2rad(20) deg2rad(10.8) 0]);
tr2rpy(FK,'deg')
tr2eul(FK,'deg')

• In Simulation = -159.669 -10.142 3.733
• tr2eul = -160 10.8 0
• tr2rpy = 0 10.8 -160

Or what am i missed?

Answer 1

By default teach() displays orientation using XYZ order roll-pitch-yaw angles, since this is compatible with older textbooks on arm robots, eg. Paul, Spong, Siciliano. By default tr2rpy() uses ZYX order. You can pass the 'xyz' option to tr2rpy() to make the two angular representations agree.

Alternatively you can pass the option 'rpy/zyx' to teach().

It's unfortunate that the term roll-pitch-yaw angles is underspecified, many sources just use the term without giving the details. To add to the confusion, different areas of robotics seem to adopt different conventions. Check out the implementation of rpy2tr() to see the difference.