kylerlaird's profile - activity

Last summer (2015) I used a simple ROS configuration to remotely control a small vehicle (Tractobot00) with Ackermann steering. I only used ROS for the joystick driver and message passing between nodes I wrote. https://www.youtube.com/watch?v=URQXU... I extended the control to navigating using a single RTK GPS with very limited success.

I see that there are cars with ROS interfaces now but I don't see any major development in ROS support for Ackermann vehicles. Is there a simple path to using ROS to control an Ackermann vehicle in a standard way? My initial goal is to be able to drive a large vehicle in a straight line using dual RTK GPS and an IMU. It looks like I could do this easily with APM Rover but I would much rather have the ROS infrastructure available.

[2016.05.29 update]

What did I do? Well...I got really frustrated - both with ROS and APM. Out of desperation, I decided to write my own monolithic Python script. It is amazingly dumb. It does not know about kinematics, vehicle geometry, or even correlation of steering value and steer angle. It does not even use the IMU. It just uses the GPS data for pose, and feeds a steering PID with the difference between the current and desired heading based on cross-track distance. It works surprisingly well for Tractobot01. https://youtu.be/HclgNBaS-Dg

Tractobot01 has been in the shop with transmission problems because it sat unused for decades. I brought it home yesterday and added a solenoid valve for implement control. I hope to have that working next week so that it can drill some soybeans without my assistance.

As my needs become more complex, I often have the urge to return to a ROS-based system. I could certainly port my existing work to ROS but I'd like to start fresh when I return to ROS and do better. I contacted Earle Robotics about continuing to port APM to ROS but it's apparently a bigger undertaking than I expected.

I would gladly pay for someone to port more pieces of APM to ROS and/or help me use existing ROS code to do what I need.

[2016.07.17 update]

It seems that there is interest in this, so here are a few more details on Tractobot01. Also, I'm returning to ROS for Tractobot02 so I'm very interested in porting my work.

Tractobot01 came out of the shop with a repaired transmission, went to the field, and blew a steering cylinder seal. Although I was very late, it did eventually drill about 45 acres of soybeans.

I will describe the guidance in more detail. For reference, here are videos of Tractobot01 in various phases. resuming operation: https://www.youtube.com/watch?v=LhKV-... midfield: https://www.youtube.com/watch?v=fNX1M... headland: https://www.youtube.com/watch?v=XWopH...

Tractobot01 had one capability: follow a line. That meant that it tried to minimize the ... (more)

I have a few PWM input/output pairs connected to my Arduino Nano and defined in an array.

typedef struct {
        char *name;
        byte pin_in;
        byte pin_out;
        unsigned long rise_time;
        unsigned long fall_time;
        byte value_in;
        byte value_out;
        byte state;
} control_t;

control_t controls[]={
     { .name="throttle", .pin_in=3, .pin_out=11, },
     { .name="steering", .pin_in=4, .pin_out=10, },
     { .name="transmission", .pin_in=5, .pin_out=9, },
     { .name=NULL}
};

I want to create a subscriber and publisher for each one so that the input value (from the physical control) is published and the output value (sent to the robot) can be subscribed. I tried using classes but discovered that rosserial doesn't support using class methods for callbacks. So I thought I could have one subscriber callback for all of the controls. It just needs to know the topic used so that it can do a lookup on the control name and set the PWM output of the corresponding pin. For example, publishing 123 to /myrobot/steering/set(?) should put the value 123 on pin 10. (I also welcome help with topic names.)

Is it possible to get the topic name (or ID?) inside the callback? Or is there a better way to handle this?

Thank you.

--kyler

[updates to keep them all together...]

1. There is good info here on how classes are implemented in C++: http://stackoverflow.com/questions/40...

2. boost::bind and boost::function (from #1) appear to do what I want.

3. There is a (partial) Boost library for Arduino: https://github.com/vancegroup/arduino...

4. C++11 can do lambda/anonymous functions. C++11 still seems to be experimental for Arduino.

5. I wonder if I should subclass the rosserial code to make it do what I need.

I'm going to try #4 first. I welcome alternatives.

[...]

I punted and made another option:

1. Use the preprocessor.

I don't like that I have to both define and initialize the controls, but it's otherwise workable and should be easy to extend.

#define CONTROL(n, pi, po, ptmin, ptmax) \
        static control_t control_ ## n = { name:(char *)#n, pin_in:pi, pin_out:po, pt_min:ptmin, pt_max:ptmax, }; \
        void put_ ## n( const std_msgs::UInt8& msg ) { \
                sprintf(buf, "put %s: %u", control_ ## n.name, msg.data); \
                nh.logwarn(buf); \
                control_ ## n.value_out = msg.data; \
                analogWrite(control_ ## n.pin_out, control_ ## n.value_out); \
        } \


#define INIT_CONTROL(n) \
        control_ ## n.next=controls; \
        controls=&control_ ## n; \
        static ros::Subscriber<std_msgs::UInt8> n ## _sub("/" #n "/put", &put_ ## n ); \
        nh.subscribe(n ## _sub); \


control_t *controls = NULL;

CONTROL(throttle, 3, 11, 0, 0)
CONTROL(transmission, 4, 10, 0, 0)
CONTROL(steering, 5, 9, 110, 145)

void setup()
{
        nh.initNode();

        INIT_CONTROL(throttle);
        INIT_CONTROL(transmission);
        INIT_CONTROL(steering);
[...]

(I added support for a min/max range so that I can revert to passthrough mode if a control moves out of the range. IOW, if the steering wheel is moved, full control is passed to the local operator.

I've been a bit concerned about processing several 500 Hz PWM signals but it's working fairly well so far. I need to add at ... (more)