* * *
INSTRUCTOR : As I am, sitting behind the hand controllers, these frames match exactly my body frame.
CANDIDATE 1: And this relates to the internal frame of reference of the latching end effector?
Instructor: Yes.
CANDIDATE 1: In other words, if I want to move along positive X with the lee I am going to push the translational hand controller forward.
Instructor: Yes, that is correct.
* * *
CANDIDATE 2: So if I rotate and then I want to move forward, X is away from me?
Instructor: In the internal command frame, X is always forward.
CANDIDATE 2: Right, but if I rotated the arm?
Instructor: You have to imagine yourself upside down.
CANDIDATE 2: Okay.
Instructor: So if I made this motion, what would that be?
CANDIDATE 2: That is pitching positive.
Instructor: Yes, because my nose is moving up.
CANDIDATE 2: That’s what I was getting at. The frame does not stay fixed in space as I rotate around.
Instructor: Your internal frame stays fixed, like I said, with respect to the lee.
* * *
CANDIDATE 1: You’ll tell us whether we are in the internal frame giving command inputs, or whether we’re making command inputs with respect to the external frame?
Instructor: And which external frame. We only have one internal frame, but there are many external frames, so we’ll have to specify frame 1, frame 2, et cetera.
***
Instructor: What do I do now? I’ll ask candidate 3.
CANDIDATE 3: We are going to have to do a positive Z, so down on the translational hand controller, and then we are going to need to pitch up, so pull the rotational hand controller back.
Instructor: Exactly. Do we all agree with that?
CANDIDATE 1: I understood the pitch, because the dot is down, which means that your end effector is angled like this; you have to pitch up. But I’m not sure I understand the green crosshairs.
Instructor: I like that question, and I’m glad you asked it.
CANDIDATE 1: To me, the green crosshairs suggest the End Effector is too low. Not only is it too low, but it’s pitched down, so that I need to actually move the green crosshairs up.
CANDIDATE 3: If this is purely a translational problem and it’s getting all sorted out, where would that white dot be? Will it be right in the middle?
Instructor: Like the other example we used, it will be right in the middle, slightly high. Candidate 4 wants to say something.
CANDIDATE 4: If you’re using an external frame and you command the rotation, does the centre of the rotation of the end effector —
Instructor: It’s not the camera but the centre of the plane that is flush with the end of the lee.
CANDIDATE 4: Is that for the external frame?
Instructor: Both external and internal. We said that.
CANDIDATE 4: It’s still around this point?
Instructor: For all command frames, this is the centre of rotation.
CANDIDATE 4: Got it.
* * *
CANDIDATE 4: I’m lined up, looking straight down.
Instructor: You’re pretty much looking at it.
CANDIDATE 4: But I think I am like this a little bit.
Instructor: Either you’re like this a little bit, or like this a little bit.
CANDIDATE 4: Okay, I must be translated to the right, so I need to move to the left a little bit.
Instructor: What does the white dot tell you?
CANDIDATE 4: That I am looking straight down.
Instructor: It’s a little bit left, actually. But it doesn’t matter. I mean, it’s never a one-axis misalignment.
CANDIDATE 4: So I need to yaw left and translate left.
Instructor: Well, you want to at least translate left, because it seems that you are misaligned like that, but it is a combination of yaw and translation.
* * *
Instructor: Can we start with the answers? I will start with candidate 5. Internal.
CANDIDATE 5: It’s going to be a roll, and if you go clockwise . . . sorry, that’s going to be negative.
Instructor: From here to there. From here . . . to there.
CANDIDATE 5: Okay, yup, that’s a positive roll.
Instructor: Do we agree with a positive roll, tilt right? Correct. Let’s go with candidate 3 for frame 1.
CANDIDATE 3: Since, again, they’re aligned, it’s going to be the same input — for positive roll.
Instructor: Same thing — a positive roll, tilt right. Candidate 6 for frame 2.
CANDIDATE 6: Now it’s essentially a yaw, a positive yaw, and we are going to twist straight.
Instructor: Do we agree with positive yaw, twist straight?
* * *
Instructor: Candidate 3, frame 2, please.
CANDIDATE 3: Frame 2 is a negative yaw, so that would be a twist to the left.
Instructor: Do we agree with negative yaw, twist left?
CANDIDATE 2: How was the camera again?
Instructor: Like that. This is how I determine my rotation. I start like this and rotate like that.
CANDIDATE 2: Yup.
Instructor: So what does that give you?
CANDIDATE 2: Well, if I’m lying on my back and I want to rotate it like that, that’s a roll.
Instructor: That’s a rotation to your left.
CANDIDATE 2: Oh, sorry, yup. I understand now that’s a yaw. Yeah, I got it now.
Instructor: We agree with negative yaw?
CANDIDATE 2: Yes.
* * *
Instructor: Let’s start with candidate 3, then, for internal.
CANDIDATE 3: We have a positive pitch and a positive yaw, so that is going to be back and twist to the right.
Instructor: Is that right? Do we agree?
CANDIDATE 2: I have a hard time between roll and yaw with these ones.
Instructor: I’m glad you’re asking this now. We are not moving in the roll. It’s a combination of this rotation and that. So although it looks like the roll axis is moving, we’re not rotating around that axis.
CANDIDATE 2: Oh, yeah.
* * *
CANDIDATE 5: Frame 2 should be a negative yaw and a positive roll.
Instructor: That is the correct answer. And what does that mean for hand control input?
CANDIDATE 5: It’s going to be a twist left and a tilt right.
Instructor: Twist left, tilt right, simultaneously.
CANDIDATE 5: Does the rotational hand controller allow simultaneous input?
Instructor: Yes, it does. Negative yaw. And we want this motion.
CANDIDATE 5: That’s the roll, the positive roll.
Instructor: Excellent! One last case, and then we’re done.
