CANJaguar

[Kodiak]

Hello,
I am not new to Java, but I am new to the code for the wpi, so I was looking at the API and was especially looking at CANJaguar. My question is that in order to use CAN, do I make an instance of CANJaguar for each jaguar used, or is it only one instance, and I make an instance of Jaguar for the amount used? Also would I need to use it within the drive train? In the end, I am pretty much asking how to set up CAN withing Java.

[WizenedEE]

The CANJaguar class represents a jaguar. So yes, you need one for each physical jaguar. To set up the drive train, you create all of the jaguars needed and then call the robotDrive constructor with each of the jaguars.

For programming, the only practical difference between CANJaguar and Jaguar is that CANJaguar has more methods (for things like setting PID constants), so if you find a tutorial on how to set things up with normal Jaguars, you just replace the class names with CANJaguar and you should be set.

[Kodiak]

Awesome, that makes it much simpler, also on the ID, its the id you issue the Jaguar when you update the firmware correct? or is in in order they are setup along the CAN

[WizenedEE]

It's the one where you set the number and then press the button on the jaguar (the ID). The order makes absolutely no difference (except for the whole "wire can't be too long" thing)

[Kodiak]

Ha, how can the wire be too long? on such a short distance with data flying at 1mbs and the Jaguars acting as switches. Also I would like your input on this, for Joystick input, would it be best on Periodic or Continuous?

[Bryscus]

Originally Posted by Kodiak

Ha, how can the wire be too long? on such a short distance with data flying at 1mbs and the Jaguars acting as switches. Also I would like your input on this, for Joystick input, would it be best on Periodic or Continuous?

It possibly has to do with loading down the CAN cable driver. I think the total cable length is something like 20' if I remember right. One suggestion was to buy a 20' cable and use it. If you need more, you've used too much.

Read joystick should probably go in Periodic. Continuous will read the joystick as fast as possible. Periodic will read the joystick at precise intervals (200Hz I think). Honestly, in reference to the system response time of "Joystick moved -> Joystick value read -> Joystick value interpreted -> Motor value sent -> Motor starts moving", the moving of the motor is the longest part (by quite a bit).

Running in continuous only makes more requests and sends more control packets (unnecessarily) utilizing more system bandwidth.

- Bryce

[Kodiak]

Originally Posted by Bryscus

It possibly has to do with loading down the CAN cable driver. I think the total cable length is something like 20' if I remember right. One suggestion was to buy a 20' cable and use it. If you need more, you've used too much.

Read joystick should probably go in Periodic. Continuous will read the joystick as fast as possible. Periodic will read the joystick at precise intervals (200Hz I think). Honestly, in reference to the system response time of "Joystick moved -> Joystick value read -> Joystick value interpreted -> Motor value sent -> Motor starts moving", the moving of the motor is the longest part (by quite a bit).

Running in continuous only makes more requests and sends more control packets (unnecessarily) utilizing more system bandwidth.

- Bryce

I agree, and I was looking at the code, and its at 50hz, just in case you where curious, and about the CAN, I guess it can be looked at it just like in Networking, but what I think they may mean about being too long is the distance of wire used between one Jaguar to the next and maybe not meant in total distance, which sounds the same but its not, lol.

[dyanoshak]

Originally Posted by Kodiak

Ha, how can the wire be too long? on such a short distance with data flying at 1mbs and the Jaguars acting as switches. Also I would like your input on this, for Joystick input, would it be best on Periodic or Continuous?

Originally Posted by Kodiak

I guess it can be looked at it just like in Networking, but what I think they may mean about being too long is the distance of wire used between one Jaguar to the next and maybe not meant in total distance, which sounds the same but its not, lol.

Bryscus is correct:

Originally Posted by Bryscus

It possibly has to do with loading down the CAN cable driver. I think the total cable length is something like 20' if I remember right. One suggestion was to buy a 20' cable and use it. If you need more, you've used too much.

It is in fact 20' total, not the maximum between each Jaguar. The Jaguars aren't switches or repeaters, the left and right CAN ports are wired directly to each other on the Jaguar circuit board.

This 20' limitation does have to do with the CAN driver:

When all the Jaguars are responding at the same time to broadcast messages they drive the bus slightly higher than a single Jag would. It takes longer for the bus to return to 'zero' and therefor some Jaguars may not read the bit correctly if the bit hasn't had time to settle.

The time from high to low depends on the termination resistance as well. This is the reason why we also specify a 100 ohm termination resistor. It helps snap the bus back to zero quickly so there aren't any bit timing errors.

We found that 20' of cable, 100 ohm termination resistors, and ~16 Jags on a bus is a good limit for reliable operation. It may be possible to get more Jags, but the cable lengths will have to be shorter.

-David

[Kodiak]

Originally Posted by dyanoshak

Bryscus is correct:



It is in fact 20' total, not the maximum between each Jaguar. The Jaguars aren't switches or repeaters, the left and right CAN ports are wired directly to each other on the Jaguar circuit board.

This 20' limitation does have to do with the CAN driver:

When all the Jaguars are responding at the same time to broadcast messages they drive the bus slightly higher than a single Jag would. It takes longer for the bus to return to 'zero' and therefor some Jaguars may not read the bit correctly if the bit hasn't had time to settle.

The time from high to low depends on the termination resistance as well. This is the reason why we also specify a 100 ohm termination resistor. It helps snap the bus back to zero quickly so there aren't any bit timing errors.

We found that 20' of cable, 100 ohm termination resistors, and ~16 Jags on a bus is a good limit for reliable operation. It may be possible to get more Jags, but the cable lengths will have to be shorter.

-David

Awesome, great information! thanks for the clarification.

[kingkurry]

How do we know if we have regular jaguars or CAN jaguars? Also, if we use jaguars does this mean we actually need to declare 4 jaguar instances to drive the robot? Can we do something like

public void robotInit() {
RobotDrive robot = new RobotDrive(1,2,3,4);
Joystick left = new Joystick(1);
Joystick right = new Joystick(2);

}
public void teleopPeriodic() {
robot.tankDrive(left.getThrottle(),(-1*right.getThrottle())); 

}

or do we need to actually need to create jaguar instances and use them to drive the robot. If so, how would we do this?

[Kodiak]

Originally Posted by kingkurry

How do we know if we have regular jaguars or CAN jaguars? Also, if we use jaguars does this mean we actually need to declare 4 jaguar instances to drive the robot? Can we do something like

public void robotInit() {
RobotDrive robot = new RobotDrive(1,2,3,4);
Joystick left = new Joystick(1);
Joystick right = new Joystick(2);

}
public void teleopPeriodic() {
robot.tankDrive(left.getThrottle(),(-1*right.getThrottle())); 

}

or do we need to actually need to create jaguar instances and use them to drive the robot. If so, how would we do this?

All jaguars both gray and black can use CAN, it is a diffrent way of sending information to them, instead of using the PWM cables you use a phone like cable. Both get the job done, just more accuracy and additional information about the controller while its running comes with the CAN.

And what I did with the jaguar is create an instance for each jaguar outside of any of the Init's. Then on the RobotInit(), I initialized them along with the drive train.

public class Team3325 extends IterativeRobot {

    CANJaguar leftCANJaguarTop;
    CANJaguar leftCANJaguarBottom;
    CANJaguar rightCANJaguarTop;
    CANJaguar rightCANJaguarBottom;
    Joystick inputJoystick;
    int leftCanTop = 1;
    int leftCanBot = 2;
    int rightCanTop = 3;
    int rightCanBot = 4;
    RobotDrive mechanumDrive;

    public void robotInit() {

        try {

            leftCANJaguarTop = new CANJaguar(leftCanTop);
            leftCANJaguarBottom = new CANJaguar(leftCanBot);
            rightCANJaguarBottom = new CANJaguar(rightCanBot);
            rightCANJaguarTop = new CANJaguar(rightCanTop);

            inputJoystick = new Joystick(1);

            mechanumDrive = new RobotDrive(leftCANJaguarTop, leftCANJaguarBottom, rightCANJaguarTop, rightCANJaguarBottom);

        } catch (Exception e) {

            System.out.println(e);
        }
    }

    public void teleopPeriodic() {

        try {

            mechanumDrive.mecanumDrive_Cartesian(inputJoystick.getX(), inputJoystick.getY(), inputJoystick.getThrottle(), 0.0); //TODO <-- Fix Gyro to proper Param.


        } catch (Exception e) {

            System.out.println(e);
        }
    }
}

The code is a little dirty, but it works for testing purposes and can hopefully help you. In your case, if you didn't use CAN, you would have to replace CANJaguar with Jaguar and fix a few of the params respectively.

[CodeYeti]

Besides variables going out of scope, the code you have posed there would do ok. To answer your question about creating Jaguar instances, you can create a RobotDrive both ways

RobotDrive(int frontLeftMotor, int rearLeftMotor, int frontRightMotor, int rearRightMotor);

/* OR */

RobotDrive(SpeedController frontLeftMotor, SpeedController rearLeftMotor, SpeedController frontRightMotor, SpeedController rearRightMotor);

And whether you have CANJaguars or regular Jaguars all depends on how you have them hooked up. chances are, you have normal Jaguars. If you are using a PWM cable to hook the Jaguars to the digital module/sidecar, then you have regular Jaguars for sure.

EDIT: Also, its more common to use the y axis of each joystick to control motor speeds than it is the throttle, but obviously you can do whatever you wish.

[Mike Copioli]

Originally Posted by dyanoshak

Bryscus is correct:

We found that 20' of cable, 100 ohm termination resistors, and ~16 Jags on a bus is a good limit for reliable operation. It may be possible to get more Jags, but the cable lengths will have to be shorter.

-David

David,

I have to disagree with you on this. According to CAN spec IS0 11898:1993(E) Table 15, the maximum cable distance for 1Mbit/second is 40 Meters not 20 feet.

We have also tested at distances much greater than 20 feet without issue using 120 Ohm's of termination on each end of the BUS.

FYI a termination resistor of 100 ohms is outside of the spec. Teams using 120 ohms resistors should have no issues related to signal reflection.

[Bryscus]

Originally Posted by Mike Copioli

David,

I have to disagree with you on this. According to CAN spec IS0 11898:1993(E) Table 15, the maximum cable distance for 1Mbit/second is 40 Meters not 20 feet.

We have also tested at distances much greater than 20 feet without issue using 120 Ohm's of termination on each end of the BUS.

FYI a termination resistor of 100 ohms is outside of the spec. Teams using 120 ohms resistors should have no issues related to signal reflection.

From the getting started guide:

Total Cable Length
(maximum)
20 ft / 6.1m Tip: Start with this length of bulk cable and cut all
segments from it to ensure compliance.

Termination Resistance 100 At each end of the network.

Just quoting specs.

- Bryce

[Kodiak]

Total Cable Length
(maximum)
20 ft / 6.1m Tip: Start with this length of bulk cable and cut all
segments from it to ensure compliance.

Termination Resistance 100 At each end of the network.

Just quoting specs.

Hmm, it may be that 20 feet is the best length for the best outcome, but if you need more it may not be THE limit.