Tag: irobot

Part 1 described the hardware portion of this project. TL;DR: the existing microprocessor was replaced with an Arduino.

Part 2 covers the low level robot control and iRobot Create emulation software.

A couple of hardware modifications have been made since part 1 was written:

1. The Arduino Uno was replaced by a Nano. This is not only a lot smaller but also has a couple of extra IO ports.
2. A battery voltage sensor was added in the form of a simple 4:1 resistor divider.

Thearduino pin mapping is now:

μC Pin	Function	Arduino Pin/Dir	Notes
1	Right Bumper	D6 In	HIGH on bump
2	Over current	In	Unused
3
4	Right wheel forward	D10 Out PWM	IN1
5	Right wheel backward	D9 Out PWM	IN2
6
7	Fan & Side brush motor	Out	Unused
8	Wheels up	D11 In	All 3 wheels OR’ed
9	L switch	D12 In	LOW when pressed
10	L switch LED	D13 Out	Active LOW
11
12	M switch	A6 In	LOW when pressed
13	S switch	A7 In	LOW when pressed
14	Green LED	A2 Out	Active LOW
15	Red LED	A3 Out	Active LOW
16	M switch LED	A4 Out	Active LOW
17	S switch LED	A5 Out	Active LOW
NC	Battery Voltage	A0 In	Via 4:1 divider
19
20	GND	GND
21	Left wheel forward	D3 Out PWM	IN4
22	Left wheel backwards	D5 Out PWM	IN3
23	Left bumper	D2 In	HIGH on bump
24	Speaker	D4 Out
25
26	Main brush motor	A1 Out	Unused
27
28
29
30
31
32
33
34
35	Left wheel encoder	D7 In
36
37
38
39	Right wheel encoder	D8 In
40	+5V regulated	5V

 

For the software it was decided to emulate an iRobot Create 2. This has a documented API (iRobot Create 2 Open Interface) so all design decisions have already been made. Also, because this is a popular platform, third party software exists to directly control the robot and a driver for ROS integration is available.

Not all of the Open Interface commands were implemented, just those required for motor control, odometry and common sensors. The source code can be extended as needed. Some constants may need changing.

The code is straight forward in operation:

• The serial port is monitored for any incoming commands. The commands are parsed and executed which results in motors running, sensor data being returned or robot state being updated.
• Wheel encoder pulses are accumulated via two interrupt handlers
• Every 15ms the internal state is updated. Sensor data is streamed out if requested. If the robot is moving, the motor power is updated. In normal driving mode (velocity and radius specified) a PID controller for average velocity is cascaded with another PID controller to keep the wheel speeds in the required ratio for the specified turn radius. In “Direct” driving mode (velocity of each wheel specified), two PID controllers, one for each wheel, are used to keep the velocities at the requested values
• The Arduino PID Library is used with some modifications including bias value support

Full code available on GitHub here.

To verify compatibility the code was tested with the following:

• The Create.1.0.1.2.exe program from here. (If running on Windows 10 need to run as administrator). Local copy here.
• The create_autonomy ROS driver

 

 

 

 

Part 2 (software) now available

I needed a robot platform for a project and bought a Vileda A3 cleaning robot cheaply from ebay, advertised as not working but a new battery fixed that! (Battery for Vileda M-488a fits this A3 model)

Opening it up:

we find the expected motors for the wheels, fan, main brush and edge brush. The wheels are equipped with optical encoders. Other sensors include the left and right bumpers, wheel drop switches and cliff detectors. The top lid holds three buttons and a red and green LED. There is a 360 IR reflector installed but this is not populated with a detector.

There is a self-contained NiMH battery charger board under the top lid:

Rather than totally replace the existing PCB I decided to just replace the microcontroller (an 8051 clone) so I could keep the existing motor drivers, connectors etc

After a bit of reverse engineering I came up with the following PCB pin assignments:

μC Pin	Function	Arduino Pin/Dir	Notes
1	Right Bumper	D6 In	HIGH on bump
2	Over current	In	Unused
3
4	Right wheel forward	D10 Out PWM	IN1
5	Right wheel backward	D9 Out PWM	IN2
6
7	Fan & Side brush motor	Out	Unused
8	Wheels up	D13 In	All 3 wheels OR’ed
9	L switch	D12 In	LOW when pressed
10	L switch LED	D11 Out	Active LOW
11
12	M switch	A0 In	LOW when pressed
13	S switch	A1 In	LOW when pressed
14	Green LED	A2 Out	Active LOW
15	Red LED	A3 Out	Active LOW
16	M switch LED	A4 Out	Active LOW
17	S switch LED	A5 Out	Active LOW
18
19
20	GND
21	Left wheel forward	D3 Out PWM	IN4
22	Left wheel backwards	D5 Out PWM	IN3
23	Left bumper	D2 In	HIGH on bump
24	Speaker	D4 Out
25
26	Main brush motor	Out	Unused
27
28
29
30
31
32
33
34
35	Left wheel encoder	D7 In
36
37
38
39	Right wheel encoder	D8 In
40	+5V regulated

N.B. pin 9 was wired as an 8051 interrupt circuit so I modified PCB to make it a simple switched input (removed C23 and R89 and wired J7 pin 4 directly to μC pin 9).

I didn’t need the cliff sensors so didn’t trace those out.

The motor driver chip is an Allegro A4954 dual 2A/40V h-bridge. Current limit is pre-set. Pins IN1-IN4 of this chip are routed to the microcontroller.

Not much room around the PCB in-situ so I removed the microcontroller, soldered flying leads directly to the PCB and routed them to the indicated arduino pins. I wanted to keep the Rx/Tx pins free so only had 18 pins to play with. It should be possible to multiplex some inputs if needed in the future. Here is the hacked board under test:

and here it is embedded back in the robot:

The PCB is a tight fit and once the main brush motor is removed there is just enough space for the Arduino to sit in its place.

A simple program was written to exercise the main features. Here is a short video showing the response to bumpers and a quick demo routine that cycles through the LEDs, plays a tune and does a little dance.