Physical AI Lab // Episode 1.1 // Quiz
Coordinate frames and kinematics
Getting a robot arm to reach the cup on the table
01
The camera computes three coordinates for the cup, and the robot reaches using those numbers as they are. It misses by a long way. What is the most likely cause?
The camera's coordinates weren't converted to the base frame
IK has several solutions and it picked the wrong one this time
The cup happened to lie just outside the arm's workspace
Forward kinematics has no unique answer, so the hand wanders
02
In the page's forward-kinematics mode you set the three sliders to some angles and note where the hand is. You move them away, then back to the same angles. What do you see?
The hand may end up at one of several positions
Where the hand goes depends on where the cup is now
You must wait for inverse kinematics to know
The hand returns to the very same spot
03
There is a bottle next to the cup. IK finds two solutions, elbow up and elbow down, and elbow down would hit the bottle. What should happen next?
Average the two sets of joint angles as a compromise
Something is wrong; there can be only one right answer
Pick elbow up: same reach, and it misses the bottle
Declare the cup unreachable and give up this grasp
04
One research robot arm has seven degrees of freedom, more than the three joints of our lab arm. What do the extra joints mainly bring?
Given the angles, the hand's position is no longer unique
More flexible motion that can get around obstacles
Inverse kinematics is left with only one solution
An unlimited workspace that can reach anywhere
05
In the page you drag the cup far away. It turns amber, and the arm stretches out fully toward it but still can't touch it. What does this tell you?
The cup is outside the workspace; IK has no solution
The motors are too slow and the arm hasn't arrived yet
IK has too many solutions and can't choose one in time
The camera can't see that far and has lost the cup
Check