(C-D) Turning
The programs in the section show different ways to
make Multi-Bot turn. Working through the examples in order will
help you learn the different options for motor control.
Basic Turning
(Downloadable programs are available only on the
CD "LEGO MINDSTORMS NXT 2.0 by Example").
|
Program |
Description and Observations |
Attachments |
| C1-MoveCurve |
|
 |
|
This
program uses the Steering option of the Move block
to make the robot drive in a gradual arc turn.
When Steering is used on a Move
block, the Power and Duration apply to the outside
motor (the one travelling the longer distance), and the inside
motor will go a lesser speed and distance that is calculated
based on the amount of steering. |
(none required) |
| C2-MoveTurn |
|
|
|
This
program uses uses the Steering option of the Move
block with the Steering slider at the second to last
position, which will produce a turn with the inside wheel
approximately stopped.
Although similar to turning with only one
motor (see below), these turns with the Steering option
are usually significantly less accurate. |
(none required) |
| C3-MovePivot |
|
|
|
This
program uses uses the Steering option of the Move
block with the Steering slider at the last position
(tightest turn). This will produce a turn where both
wheels move with the Power and Duration specified,
but the inside motor moves in the opposite direction, producing
a very tight "pivot" turn. Although this
is the easiest way to create a tight "pivot" turn, it is usually
less accurate than a pivot turn created by controlling the two
motors separately (see the Turning - Advanced) section
below. |
(none required) |
| C4-1WheelMove |
|
|
|
This
program uses the the Move block with only one motor
selected to make the robot turn by moving one wheel while
keeping the other stopped.
Although similar to the turn produced by the
C2-MoveTurn program (Move
block with Steering), these turns are typically much more
accurate. |
(none required) |
| C5-1WheelMotor |
|
|
|
This
program uses the Motor block to make the robot turn by
moving one wheel while keeping the other stopped.
Although similar to the
C4-1WheelMove program (Move
block with one motor selected), you will notice that the
Motor block maintains the selected power throughout the turn
rather than slowing down at the end. This may result in a
more accurate turn for heavier robots. |
(none required) |
| C6-LetterN |
|
|
|
This
program uses five Move blocks to make Multi-Bot move in
an "N" shaped path in a simple but reasonably accurate way
(using only motor for the turns). |
(none required) |
| C7-PathNTest |
|
|
|
This
program is an extension of the C6-LetterN program that retraces the N-shaped path in
reverse afterwards, so that the robot should end up
approximately where it started. You can
use this program to test how accurately a robot design turns and
drives. It is possible to design a robot that is
significantly more accurate than Multi-Bot. Give it a try! |
(none required) |
Advanced Turning
(Downloadable programs are available only on the
CD "LEGO MINDSTORMS NXT 2.0 by Example").
|
Program |
Description and Observations |
Attachments |
| D1-Pivot |
|
|
|
This
program shows one simple way to do a pivot turn (wheels turning
opposite directions) using two Motor blocks instead of
the Move block with the Steering slider all the way to
the side. Unfortunately, similar to the
B2-Motors program above which goes
straight, the Brake option will not work if selected on
the first motor (both motors use Coast in this example),
so the end of the turn will not be accurate. |
(none required) |
| D2-PivotWait1 |
|
|
|
This
program fixes the braking problem with the
D1-Pivot program by measuring
rotations separately with a Rotation Sensor and then
using a Stop to brake both motors.
However, a remaining problem is that the
rotations on motor C are not being measured, so it possible that
motor C may travel fewer or more than the desired rotations. |
(none required) |
| D3-PivotWait2 |
|
 |
|
This
program is a more complete variation on the D2-PivotWait1 technique that
stops only after both motors have completed the full
rotations required. Now both motors are
guaranteed to travel the required rotations. However, it
is now possible that either motor may travel more than
the desired rotations. |
(none required) |
| D4-PivotSeq |
|
 |
|
This
program shows a more accurate way to do a pivot turn using two
Motor blocks, by using two sequence beams.
Compared to the D2-PivotWait1 program, this
technique measures rotations independently on both motors, so
both motors are told to stop when they finish.
However, one subtle problem remains.
Because the program will stop when the main sequence finishes,
if motor C gets hung up for some reason (try stopping or slowing
it by hand), it may not finish the requested rotations. |
(none required) |
| D5-PivotSeq2 |
|
|
|
This
program solves the subtle problem with the D4-PivotSeq
program by using a block wired between the two sequences to
force the main sequence to wait for the second sequence to
finish before continuing.
Now the program will sound the tone and then
end (or continue if there was another motion after the turn)
only after both motors have completed their rotations.
|
(none required) |
Using My Blocks to Turn
(Downloadable programs are available only on the
CD "LEGO MINDSTORMS NXT 2.0 by Example").
|
Program |
Description and Observations |
Attachments |
| D6-PivotBlocks |
|
 |
|
This
program does a left and right pivot turn using two My Blocks
named PivotLeft and PivotRight. These My Blocks
make it easy to reproduce accurate pivot turns using parallel
Motor blocks (instead of the Move block) internal to
the My Blocks. Note that the fix for the
two Motor block pivot turn included in the
D5-PivotSeq2 program is not
necessary in these My Blocks, because a My Block with multiple
sequences will wait for all of the sequences to complete before
finishing and returning to the main program. |
(none required) |
| D7-PivotAngleBlocks |
|
|
|
This
program does a left and right pivot turn using two more advanced
My Blocks named LeftPivotAngle and RightPivotAngle,
which are extensions of the simple PivotLeft and
PivotRight My Blocks. The
LeftPivotAngle and RightPivotAngle My Blocks allow
the program to specify the amount of robot heading angle
desired in the turn, rather than the amount of motor rotation.
This makes it significantly easier to do, say, a "90 degree
turn" by simply specifying 90 degrees of robot heading angle.
|
(none required) |
| D8-PathBlocks |
|
|
|
This
program is similar to the C6-LetterN
program, which drives the robot along an N-shaped path, except
that it uses the My Blocks Forward, LeftPivotAngle,
and RightPivotAngle, and it is currently configured for a
robot with treads. If the three My
Blocks are already written, the main program is easy to create.
Comparing the program to C6-LetterN,
note how straight distances in centimeters and turns in
robot heading angle make the program even easier to write
and understand compared to using motor degrees. The
program can also be easily re-configured for Multi-Bot using
wheels vs. treads. |
(none required) |
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