The documentation states on page 12:
A Drive command with a
positive velocity and a positive radius makes Room
ba drive forward while turning toward the left. A
negative radius makes Roomba turn toward the right.
Special cases for the radius make Roomba turn in
place or drive straight, as specified below
The radius value is documented this way:
Radius (-2000 – 2000 mm)
Special cases:
Straight = 32768 or 32767 = 0x8000 or 0x7FFF
Turn in place clockwise = -1 = 0xFFFF
Turn in place counter-clockwise = 1 = 0x0001
Obviously supply different values if you are not trying to achieve any of those special cases, like in the example that follows:
Example:
To drive in reverse at a velocity of -200 mm/s while
turning at a radius of 500mm, send the following
serial byte sequence:
[137] [255] [56] [1] [244]
Explanation:
Desired value -> two’s complement and convert to hex -> split into 2 bytes ->
convert to decimal
Velocity = -200 = 0xFF38 = [0xFF] [0x38] = [255] [56]
Radius = 500 = 0x01F4 = [0x01] [0xF4] = [1] [244]