Kinematics

JamesNewton edited this page Nov 24, 2018 · 3 revisions

Kinematics

Convert XYZ to Joint Angles for J1, J2, J3, J4, and J5. Dexter follows the common convention is that Z is up / down, X is right / left, and Y is out / back. (see picture below)

In DDE we can move_to(X, Y, Z, direction, config) where

  • X, Y, and Z are the destination in meters,
  • direction is an array of unit vectors [X, Y, Z]. e.g. [0, 0, -1] is straight down,
  • config is an array of boolean options [right_arm, elbow_up, wrist_out]. See below for more.

Dexter also directly supports the 'M' and 'T' oplets which take the same parameters, but the X, Y, Z units are integer microns, aka "micrometers", or a millionths of a meter (1/1,000,000 meters).

config For most points within the reachability of Dexter, there are multiple ways in which Dexter can get there. For example, This picture shows all the ways Dexter might get to the same point (on the sloped face of the grey cube). There is also a (really big) version that shows them all seperated. config helps you specify your preference as to how Dexter configures its joints to get to the indicated x, y, z. There are 3 independent boolean values to determining this configuration. They are:

  • base-rotation right_arm: LEFT or 0 means J1, the base joint has a negative value, ie it is to the right if you are facing Dexters front. Looking down from the top at Dexter this would mean its rotated counter clockwise. The opposite direction is RIGHT, or 1 which is clockwise, to the left facing the robot.
  • J3-position elbow_up: Joint 3 can be thought of as Dexter's elbow. The elbow can be either UP i.e. away from the table or DOWN, closer to the table.
  • J4 Position wrist_out: Joint 4 / 5 can be thought of as Dexter's wrist. It can be pointing either IN, towards the base, or OUT, away from the base.

Direction controls what direction the last part of the arm is pointing. It will be at X, Y, Z, but should it be pointing straight down? [0, 0, -1] does that. Or should it be pointed out? [0, 1, 0] does that. Or maybe you want it pointed in? [0, -1, 0]. You can also use an array of 2 values in DDE, which will be used as pitch and roll angles, but be careful not to use 90 as both of the angles because it will cause a "singularity"

Singularity "A point at which a function takes an infinite value" In many cases, there are more than one way to get to the target. If you specify [90,90] for wrist pitch and roll, there are an infinite number of ways to get to that direction.

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