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Jaguar/Victor question
So, I'm currently doing a small personal project, and I will need speed controllers.
I'm thinking about using Jags/Victors, but have a question. I know they are PWM based, so if I send a PWM signal to it, will I need to do anything else for them to drive the motors? I'll probably be sending the PWM signal using an arduino, if that makes a difference. |
Re: Jaguar/Victor question
They need power, too. But yeah, they just need a pwm signal to make them work.
If you don't have speed controllers already, and you don't need the high current capacity of the Jags/Victors, you might consider the smaller (lower current) controllers that Banebots sells. They are reversible. They do require you to send them a zero signal before they'll start, which can be either a nice safety feature, or a pain. |
Re: Jaguar/Victor question
As long as you feed them a good PWM signal at 5v levels, they will be very happy and run your motors.
If you miss an update, they will stop your motors. If you are using a Jaguar: Pulse between .8 and 2.2 ms long(I think this is correct) Center is at 1.5 ms long Update at least every 20 ms Update no more then every 5 ms Pulse between 1 and 2 ms Center is 1.5 ms Update at least every 50 ms ish - I dont know this exact time, sooner is better Update no more then every 10 ms All times are in milliseconds. Since you are on Arduino and using unsigned integers, you should probably store the speed value as a uint8 and then scale it to a uint16 (microseconds) for output. Edit: Squirrel beat me to it. |
Re: Jaguar/Victor question
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And yeah, I'll probably need the higher current capacity, I'll be using CIM motors most likely, for my drive train. |
Re: Jaguar/Victor question
Remember that there is a difference between PWM (pulse-width modulation) and PPM (pulse-position modulation). PWM is the ratio of high to low in a signal (25% is X time of the signal is high, and 3X time of the signal low, then it repeats). PPM on the other hand is the servo signal, between 1 ms and 2 ms like described above. The Arduino libraries have a nice structure (class? Is that one written in C or C++?) setup for this in a library, called "Servo". You just have to add the Library in the Arduino IDE. The Servo reference is here:
http://arduino.cc/en/Reference/Servo I'd recommend looking at the "Sweep" example at the bottom, it shows very cleanly how everything is placed. A note on Servo.write(): The "write()" function is designed to take an angle between 0-180 degrees (a typical servo absolute maximum range, most drivers only have 120, so you might get some jitter or mis-calibration around the extremes), but if the number you input is too high to be considered a valid angle, it will consider the value as a time in microseconds and call "writeMicroseconds()". The "read()" function will only return the angle, I believe. Also, if you've never used structures/classes, they act a little like variable types (like an "int" or a "char"). You would declare a specific servo (like "myservo") of type Servo. That's what "Servo myservo;" does under the include statement. |
Re: Jaguar/Victor question
How fast are you running the realtime task on your arduino? If you're running fast enough, you could create you own duty cycle in your algorithm and use a simple H-bridge relay to drive your motors at variable speed and direction.
For example, at 1500Hz you could generate 10 different speed levels at 150Hz. Food for thought. ~ |
Re: Jaguar/Victor question
I've been using Victors for years, and love them. Over seven years we've blown precisely one of them... in our first year... when late at night we hooked three of them up BACKWARDS and ran the robot for many seconds. And we only blew one of the three. Those things are TOUGH.
But the new Jags are worth taking a look at. Our programmer and drivers find they have better low-end response than the Victors, and while we haven't quantified it, I feel it, too, when I try my hand at driving the robot. Even better, though, is that the new "Black" Jags don't require PWM at all... you can communicate over serial and ... using the built-in encoders and limit switches on the speed controllers off-load a lot of your processing to the controller. From what I understand, if you've got one "Black" Jag and some of the "Beige" jags, you can use the Black one to do the RS232 communications and then communicate with the other Jags over the CAN network. The possibility of off-loading PID, limit switch handling and all that to the speed controller is a real paradigm shift for me... it means that anything that can send a serial signal is suddenly a pretty powerful robot controller! Got an old laptop kicking around? Jason |
Re: Jaguar/Victor question
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I believe the motor sensor inputs are just using the CAN bus interface within the Jag to port data back to the controller. They are not handled within the individual Jag independent of a controller. The limit switches do function when using PWM but under the 2010 robot rules, you may only provide limit switches when using the Jag under CAN bus control and then only to port limit data back to the controller. R60 L. If CAN-bus functionality is used, limit switch jumpers may be removed from a Jaguar speed controller and a custom limit switch circuit may be substituted (so that the cRIO-FRC may read the status of the limit switches). |
Re: Jaguar/Victor question
Does <R60> prohibit connecting wheel speed encoders directly to the Jags and using the built-in PID controller in the Jags to control wheel speed or position ?
I was under the impression that some teams did exactly that this year. Could be wrong. |
Re: Jaguar/Victor question
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My guess is that a) somebody messed up at inspection or b) you misheard/misread something. |
Re: Jaguar/Victor question
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The GDC addressed this question in the Q&A forum: http://forums.usfirst.org/showthread.php?t=13757 ~ |
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Re: Jaguar/Victor question
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<R60> doesn't cover connecting custom circuits to a Jaguar. <R68-H> covers the connection of the output of custom circuits to a Jaguar and make them legal (as Ester points out). |
Re: Jaguar/Victor question
Lets avoid quoting rules when we are talking about a small personal project. Okay?
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