Robobot MQTT-client - Revision history

Jca at 09:17, 10 July 2026

2026-07-10T09:17:37Z

← Older revision		Revision as of 11:17, 10 July 2026
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	The servo can be controlled by a message directly to the Teensy		The servo can be controlled by a message directly to the Teensy

	topic: "dtubot/~~drive~~/T0", payload: "servo 1 400 200"		topic: "dtubot/cmd/T0", payload: "servo 1 400 200"

	where the topic ''dtubot/~~drive~~/T0'' ~~is a topic where~~ the payload ~~is transferred~~ directly to the Teensy as a ''servo 1 400 200'' command.		where the topic ''dtubot/cmd/T0'' transfers the payload directly to the Teensy as a ''servo 1 400 200'' command.

	The command parameters are ''1'' for servo number one and ''400'' for the position (range is ca. -800 to 800 (us). The third parameter, ''200'', is velocity, the number of values per second. If the starting position is zero and the destination is 400, it takes about 2 seconds to reach position 400.		The command parameters are ''1'' for servo number one and ''400'' for the position (range is ca. -800 to 800 (us). The third parameter, ''200'', is velocity, the number of values per second. If the starting position is zero and the destination is 400, it takes about 2 seconds to reach position 400.

Jca at 09:08, 10 July 2026

2026-07-10T09:08:30Z

← Older revision		Revision as of 11:08, 10 July 2026
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	The commands to the robot, the MQTT messages, are a service function call:		The commands to the robot, the MQTT messages, are a service function call:
	service.send("~~robobot~~/cmd/ti","rc 0.25 0") # go straight		service.send("dtubot/cmd/ti","rc 0.25 0") # go straight
	The first parameter (''"~~robobot~~/cmd/ti"'') is the MQTT topic and indicates that it is a command for the ti (teensy_interface).		The first parameter (''"dtubot/cmd/ti"'') is the MQTT topic and indicates that it is a command for the ti (teensy_interface).

	The second parameter (''"rc 0.25 0"'') is the command, here rc (remote control), forward velocity in meters per second and the turn rate in radians per second (positive is CCW (counter-clockwise).		The second parameter (''"rc 0.25 0"'') is the command, here rc (remote control), forward velocity in meters per second and the turn rate in radians per second (positive is CCW (counter-clockwise).
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	The streamed data is		The streamed data is
	* Wheel velocity (message topic ''~~robobot~~/drive/T0/vel'') in m/s.		* Wheel velocity (message topic ''dtubot/drive/T0/vel'') in m/s.
	* Motor velocity (message topic ''~~robobot~~/drive/T0/mvel'') before the gear. The unit is radians/sec. This stream is probably not needed.		* Motor velocity (message topic ''dtubot/drive/T0/mvel'') before the gear. The unit is radians/sec. This stream is probably not needed.
	* The robot pose (message topic ''~~robobot~~/drive/T0/pose'') is the x,y position and the robot heading as calculated in the Teensy.		* The robot pose (message topic ''dtubot/drive/T0/pose'') is the x,y position and the robot heading as calculated in the Teensy.

	=== Distance ===		=== Distance ===
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	The ''Behave'' block sends a 'remote-control' MQTT message, like:		The ''Behave'' block sends a 'remote-control' MQTT message, like:

	topic: "~~robobot~~/cmd/ti", payload: "rc 0.1 0.5"		topic: "dtubot/cmd/ti", payload: "rc 0.1 0.5"

	where the topic ''~~robobot~~/cmd/ti'' indicates that it is for the ''teensy_interface''. The parameters are a forward velocity of 0.1 m/s and a turn rate of 0.5 rad/s (positive os CCW).		where the topic ''dtubot/cmd/ti'' indicates that it is for the ''teensy_interface''. The parameters are a forward velocity of 0.1 m/s and a turn rate of 0.5 rad/s (positive is CCW).

	The related Python command is		The related Python command is

	service.send("~~robobot~~/cmd/ti", "rc 0.1 0.5")		service.send("dtubot/cmd/ti", "rc 0.1 0.5")

	=== MQTT ===		=== MQTT ===
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	=== Teensy_interface ===		=== Teensy_interface ===

	The ''teensy_interface'' subscribes to all topics starting with ''~~robobot~~/cmd/ti''.		The ''teensy_interface'' subscribes to all topics starting with ''dtubot/cmd/ti''.
	The remote control message values are mixed to a desired ~~velocity~~ for the left and right wheels. The closed loop velocity control block generates a motor voltage sent to the Teensy 4.1 board.		The remote control message values are mixed to produce the desired velocities for the left and right wheels. The closed-loop velocity control block generates a motor voltage sent to the Teensy 4.1 board.

	The robot.ini configuration file allows you to select many sensor messages available from the Teensy 4.1 board. These messages can be logged for debugging or data analysis.		The robot.ini configuration file allows you to select many sensor messages available from the Teensy 4.1 board. These messages can be logged for debugging or data analysis.
	All messages are further published to the MQTT server.		All messages are further published to the MQTT server.

	Other data can be subscribed directly from the Teensy and ~~are~~ then published ~~directly~~ as MQTT topics.		Other data can be subscribed to directly from the Teensy and is then published as MQTT topics.

	=== Sensor data ===		=== Sensor data ===

	Sensor data in the MQTT client can be used to generate behaviour. Data ~~like~~ driven distance, heading change, line validity, distance sensor, and IMU data can be included.		Sensor data in the MQTT client can be used to generate behaviour. Data such as driven distance, heading change, line validity, distance sensor data, and IMU data can be included.

	== Line drive ==		== Line drive ==
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	The line sensor data from MQTT looks like this.		The line sensor data from MQTT looks like this.

	'~~robobot~~/drive/T0/livn' 1738420382.4767 637 612 649 810 984 872 706 639 136		'dtubot/drive/T0/livn' 1738420382.4767 637 612 649 810 984 872 706 639 136
	'~~robobot~~/drive/T0/livn' 1738420382.4837 638 612 650 812 985 876 710 641 140		'dtubot/drive/T0/livn' 1738420382.4837 638 612 650 812 985 876 710 641 140
	'~~robobot~~/drive/T0/livn' 1738420382.4908 639 613 651 813 985 878 713 642 143		'dtubot/drive/T0/livn' 1738420382.4908 639 613 651 813 985 878 713 642 143

	The topic part ''livn'' is 'line sensor value, ~~normalized~~'. The first value is a timestamp and is ignored.		The topic part ''livn'' is 'line sensor value, normalised'. The first value is a timestamp and is ignored.

	The values are ~~normalized~~ to 1000, where 1000 is the calibrated reflectance for a white tape line. In this case, sensor 5 shows a value of about 980; this sensor sees a tape line. The far-right sensor (8) has a value of about 140; this is not a tape line (0 is black).		The values are normalised to 1000, where 1000 is the calibrated reflectance for a white tape line. In this case, sensor 5 shows a value of about 980; this sensor sees a tape line. The far-right sensor (8) has a value of about 140; this is not a tape line (0 is black).

	=== Line detect ===		=== Line detect ===
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	The servo can be controlled by a message directly to the Teensy		The servo can be controlled by a message directly to the Teensy

	topic: "~~robobot~~/drive/T0", payload: "servo 1 400 200"		topic: "dtubot/drive/T0", payload: "servo 1 400 200"

	where the topic ''~~robobot~~/drive/T0'' is a topic where the payload is transferred directly to the Teensy as a ''servo 1 400 200'' command.		where the topic ''dtubot/drive/T0'' is a topic where the payload is transferred directly to the Teensy as a ''servo 1 400 200'' command.

	The command parameters are ''1'' for servo number one and ''400'' for the position (range is ca. -800 to 800 (us). The third parameter, ''200'', is velocity, the number of values per second. If the starting position is zero and the destination is 400, it takes about 2 seconds to reach position 400.		The command parameters are ''1'' for servo number one and ''400'' for the position (range is ca. -800 to 800 (us). The third parameter, ''200'', is velocity, the number of values per second. If the starting position is zero and the destination is 400, it takes about 2 seconds to reach position 400.

Jca: /* MQTT */

2026-07-10T09:01:55Z

MQTT

@@ Line 220: / Line 220: @@
 All communication is through a network server on the robot's Raspberry PI. The port is 1883.
 The result is that the Python MQTT client can run both on the Raspberry Py and on any other PC on the network with access to the robot.
 === Teensy_interface ===

Jca: /* Behave */

2026-01-20T13:07:05Z

Behave

← Older revision		Revision as of 15:07, 20 January 2026
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	topic: "robobot/cmd/ti", payload: "rc 0.1 0.5"		topic: "robobot/cmd/ti", payload: "rc 0.1 0.5"

	where the topic ''robobot/cmd/ti'' indicates that it is for the ''teensy_interface''. The parameters are a forward velocity of 0.1 m/s and a turn rate of 0.5 rad/s (positive os ~~CCV~~).		where the topic ''robobot/cmd/ti'' indicates that it is for the ''teensy_interface''. The parameters are a forward velocity of 0.1 m/s and a turn rate of 0.5 rad/s (positive os CCW).

	The related Python command is		The related Python command is

Jca: /* Main loop */

2026-01-20T13:06:32Z

Main loop

← Older revision		Revision as of 15:06, 20 January 2026
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	print("% Main Terminated")		print("% Main Terminated")

	The system is set up at the bottom of the code. The main setup parameter is the robot IP. If running on the Raspberry Pi, this should be ''127.0.0.1''; otherwise, it must be the robot's IP as displayed by the robot.		The system is set up at the bottom of the code. The main setup parameter is the robot's IP address. If running on the Raspberry Pi, this should be ''127.0.0.1''; otherwise, it must be the robot's IP as displayed by the robot.

	At the top are the other modules imported.		At the top are the other modules imported.
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	The commands to the robot, the MQTT messages, are a service function call:		The commands to the robot, the MQTT messages, are a service function call:
	service.send(~~service.topicCmd +~~ "ti~~/rc~~","0.25 0") # go straight		service.send("robobot/cmd/ti","rc 0.25 0") # go straight
	The first parameter (''~~service.topicCmd +~~ "ti~~/rc~~"'') is the topic~~. The service module has the system~~ and ~~function part of the topic. Then, "''ti/rc''" is added to indicate~~ that ~~this~~ is for the ''teensy_interface~~'' and a remote-control message~~.		The first parameter (''"robobot/cmd/ti"'') is the MQTT topic and indicates that it is a command for the ti (teensy_interface).

	The second parameter (''"0.25 0"'') is the ~~desired~~ forward velocity in meters per second and the turn rate in radians per second (positive is ~~CCV~~).		The second parameter (''"rc 0.25 0"'') is the command, here rc (remote control), forward velocity in meters per second and the turn rate in radians per second (positive is CCW (counter-clockwise).

	A delay, ''t.sleep(0.1),'' is inserted in the loop to save power and give the processor more time to handle incoming MQTT messages.		A delay, ''t.sleep(0.1),'' is inserted in the loop to save power and give the processor more time to handle incoming MQTT messages.

Jca: /* Behave */

2026-01-20T13:00:09Z

Behave

← Older revision		Revision as of 15:00, 20 January 2026
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	The ''Behave'' block sends a 'remote-control' MQTT message, like:		The ''Behave'' block sends a 'remote-control' MQTT message, like:

	robobot/cmd/ti/rc 0.1 0.5		topic: "robobot/cmd/ti", payload: "rc 0.1 0.5"

	where the topic ''robobot/cmd/ti~~/rc~~'' indicates that it is for the ''teensy_interface~~'' and is a remote-control ''rc~~''. The parameters are a forward velocity of 0.1 m/s and a turn rate of 0.5 rad/s.		where the topic ''robobot/cmd/ti'' indicates that it is for the ''teensy_interface''. The parameters are a forward velocity of 0.1 m/s and a turn rate of 0.5 rad/s (positive os CCV).

	The related Python command is		The related Python command is

	service.send(~~service.topicCmd +~~ "ti~~/rc~~","0.1 0.5")		service.send("robobot/cmd/ti", "rc 0.1 0.5")

	=== MQTT ===		=== MQTT ===

Jca: /* Servo control */

2026-01-20T12:55:58Z

Servo control

← Older revision		Revision as of 14:55, 20 January 2026
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	The servo can be controlled by a message directly to the Teensy		The servo can be controlled by a message directly to the Teensy

	robobot/drive/T0/servo 1 400 200		topic: "robobot/drive/T0", payload: "servo 1 400 200"

	where the topic ''robobot/drive/T0~~/servo~~'' is a topic ~~that~~ is transferred directly to the ~~teensy~~ as a ''servo 1 400 200'' command.		where the topic ''robobot/drive/T0'' is a topic where the payload is transferred directly to the Teensy as a ''servo 1 400 200'' command.

	The command parameters are ''1'' for servo number one and ''400'' for the position (range is ca. -800 to 800 (us). The third parameter, ''200'', is velocity, the number of values per second. If the starting position is zero and the destination is 400, it takes about 2 seconds to reach position 400.		The command parameters are ''1'' for servo number one and ''400'' for the position (range is ca. -800 to 800 (us). The third parameter, ''200'', is velocity, the number of values per second. If the starting position is zero and the destination is 400, it takes about 2 seconds to reach position 400.

Jca: /* Line detect */

2026-01-20T12:52:40Z

Line detect

← Older revision		Revision as of 14:52, 20 January 2026
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	A forward velocity of zero will end the line drive.		A forward velocity of zero will end the line drive.

	Other detections are probably needed to achieve smooth line-following. The provided code uses only 8 values, from -3.5 to +3.5, ~~in steps~~ of 1.		Other detections are probably needed to achieve smooth line-following. The provided code uses only 8 values, from -3.5 (left) to +3.5 (right), with a step size of 1.

	== Servo control ==		== Servo control ==

Jca: /* Line detect */

2026-01-20T12:52:02Z

Line detect

← Older revision		Revision as of 14:52, 20 January 2026
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	=== Line detect ===		=== Line detect ===

	~~There is a (basic)~~ line ~~detect~~ function ~~that uses~~ the centre of gravity ~~for~~ the bright part to determine the position of the tape line.		A line-detection function could use the centre of gravity of the bright part to determine the position of the tape line.
			Note that this is not the way the provided code works; it estimates the left and right edge positions.

	[[file:bode_set_a6_720_124.png \| 500px]]		[[file:bode_set_a6_720_124.png \| 500px]]
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	The red curves show steady measurements, and the blue shows a situation with more variation.		The red curves show steady measurements, and the blue shows a situation with more variation.
	Sensor level 0 is black (no reflection). In this case, the background is about 600, i.e., rather bright but not as bright as the tape line (calibrated to 1000).		Sensor level 0 is black (no reflection). In this case, the background is about 600, i.e., rather bright but not as bright as the tape line (calibrated to 1000).
	The vertical lines show the ~~detector's estimate~~ of ~~the line~~ position.		The vertical lines show the "centre of gravity" position.
	Note the variation in measurements on the floor (a wooden floor with some variation).		Note the variation in measurements on the floor (a wooden floor with some variation).

	The line position is zero if the tape line is centred below the robot, between sensors 4 and 5. The value is the number of sensors away from the centre. The red line position measurement is about -0.6, and the blue is about +0.7.		The line position is zero if the tape line is centred below the robot, between sensors 4 and 5. The value is the number of sensors away from the centre. The red line position measurement is thus about -0.6, and the blue is about +0.7.

	For ~~every~~ update of the line sensor data, a new turn rate is calculated and published on the MQTT server~~, which~~ controls the wheels.		For each update to the line sensor data, a new turn rate is calculated and published to the MQTT server that controls the wheels.

	A forward velocity of zero will end the line drive.		A forward velocity of zero will end the line drive.

	Other detections ~~can be added~~, ~~such as line crossing~~ to ~~one side or line edge~~.		Other detections are probably needed to achieve smooth line-following. The provided code uses only 8 values, from -3.5 to +3.5, in steps of 1.

	== Servo control ==		== Servo control ==

Jca: /* Command line parameters */

2026-01-20T09:17:33Z

Command line parameters

← Older revision		Revision as of 11:17, 20 January 2026
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	=== Command line parameters ===		=== Command line parameters ===

	The app has defined a few command line parameters, among these help:		The app has defined a few command-line parameters, among these is help:

	python3 mqtt-client.py --help		python3 mqtt-client.py --help
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	'' -s, --silent Print less to console		'' -s, --silent Print less to console
	'' -n, --now Start drive now (do not wait for start button)		'' -n, --now Start drive now (do not wait for start button)
			'' -m, --meter Drive 1 m and stop
			'' -p, --pi Turn 180 degrees (Pi) and stop
			'' -u USESTATE, --usestate USESTATE
			Set mission state to this value

	The command line options include ~~some~~ sensor calibration. The distance sensor calibration is missing (but needed, see the [[Robobot_teensy_firmware]]).		The command-line options include sensor calibration. The distance sensor calibration is missing (but needed, see the [[Robobot_teensy_firmware]]).

	=== Main loop ===		=== Main loop ===