LeafLabs Garden » Topic: Mac, rev5, and Servo

LeafLabs Garden » Topic: Mac, rev5, and Servo http://forums.leaflabs.com/topic.php?id=871 A place to share, learn, and grow... en-US Fri, 22 Jan 2016 00:23:24 +0000 http://bbpress.org/?v=1.0.2 <![CDATA[Search]]> q http://forums.leaflabs.com/search.php gbulmer on "Mac, rev5, and Servo" http://forums.leaflabs.com/topic.php?id=871#post-5369 Tue, 21 Jun 2011 17:36:25 +0000 gbulmer 5369@http://forums.leaflabs.com/ iRobotGoddard - Assuming your most recently posted program is complete, then it still unlikely to work properly. The posted program does not set the PWM timer cycle time to 20 milliseconds, so it is luck that it might seem to work. My estimate to get a cycle time of roughly 20 milliseconds is to set a timer prescaler of 22, though 20 to 25 is likely to work okay. <a href="http://leaflabs.com/docs/lang/api/hardwaretimer.html#lang-hardwaretimer-setprescalefactor" rel="nofollow">http://leaflabs.com/docs/lang/api/hardwaretimer.html#lang-hardwaretimer-setprescalefactor</a> iRobotGoddard on "Mac, rev5, and Servo" http://forums.leaflabs.com/topic.php?id=871#post-5356 Mon, 20 Jun 2011 12:08:02 +0000 iRobotGoddard 5356@http://forums.leaflabs.com/ thanks @mbolivar! yeah i'm not sure what approach I want to take, there are going to be multiple applications so iGuess I'm going to go with what works with each project. Some will be RC and some will be completely autonomous. I think by hand might work more with autonomous for timing reasons, just to be on the safe side. mbolivar on "Mac, rev5, and Servo" http://forums.leaflabs.com/topic.php?id=871#post-5353 Mon, 20 Jun 2011 11:16:37 +0000 mbolivar 5353@http://forums.leaflabs.com/ iRobotGoddard: why don't you try using the existing Servo library? It's included with Maple IDE. I linked to its documentation in an earlier post. The Servo library has the correct timer configuration for using RC servos, and has easy methods for setting the pulse width, both in microseconds and degrees. If you're not interested in using the library, and want to do servo control "by hand", maybe reading the source code for that library will help you fix the issues you've been having: <a href="https://github.com/leaflabs/libmaple/blob/master/libraries/Servo/Servo.h" rel="nofollow">https://github.com/leaflabs/libmaple/blob/master/libraries/Servo/Servo.h</a> <a href="https://github.com/leaflabs/libmaple/blob/master/libraries/Servo/Servo.cpp" rel="nofollow">https://github.com/leaflabs/libmaple/blob/master/libraries/Servo/Servo.cpp</a> The file examples/test-servo.cpp (part of the libmaple repository) may also be useful to you as an example usage of the library: <a href="https://github.com/leaflabs/libmaple/blob/master/examples/test-servo.cpp" rel="nofollow">https://github.com/leaflabs/libmaple/blob/master/examples/test-servo.cpp</a> iRobotGoddard on "Mac, rev5, and Servo" http://forums.leaflabs.com/topic.php?id=871#post-5352 Mon, 20 Jun 2011 10:20:12 +0000 iRobotGoddard 5352@http://forums.leaflabs.com/ this is going crazy, it's working again... iTried new wires, and it's better now. Now I'm noticing it is running the sweep 6-10 times and then it pauses. I'm thinking this has something to do with the duty cycle. iRobotGoddard on "Mac, rev5, and Servo" http://forums.leaflabs.com/topic.php?id=871#post-5350 Mon, 20 Jun 2011 09:01:10 +0000 iRobotGoddard 5350@http://forums.leaflabs.com/ Ok I must be missing some obvious answer. I had my servo orking over the weekend, and was trying to dampen the motion when transitioning in the sweep program. Now my Servo does not move at all. I've tried different servos, some work and some do not. I thought I blew my servo but I tried it on the old arduino I have and it worked fine. Can someone spell it out for me please, because I am starting to feel elementary. __________________________________________________________________________________________ const int servoPin = 11; void setup() { pinMode(servoPin, PWM); } void loop() { for(uint8 pos = 0; pos < 180; pos += 1) // goes from 0 degrees to 180 degrees { uint16 dutyCycle = 4960 * (uint16)(1.25 * (double)pos); // in steps of 1 degree pwmWrite(servoPin, dutyCycle); // tell servo to go to position in variable 'pos' delay(15); SerialUSB.print("\n CW"); delay(20); // waits 15ms for the servo to reach the position } for(uint8 pos = 180; pos>=1; pos-=1) // goes from 180 degrees to 0 degrees { uint16 dutyCycle = 4960 + (uint16)(1.25 * (double)pos); pwmWrite(servoPin, dutyCycle); // tell servo to go to position in variable 'pos' delay(15); SerialUSB.print("\n CCW"); delay(20); // waits 15ms for the servo to reach the position } } __________________________________________________________________________________________ It compiles, uploads, and seems fine on the serial monitor screen. As I said before it was just working saturday, and now it's stopped working. mbolivar on "Mac, rev5, and Servo" http://forums.leaflabs.com/topic.php?id=871#post-5347 Mon, 20 Jun 2011 01:08:48 +0000 mbolivar 5347@http://forums.leaflabs.com/ iRobotGoddard: Is there some reason the existing Servo library isn't enough for your purposes? We'd be glad to get some feedback on how to improve it. <a href="http://leaflabs.com/docs/libs/servo.html" rel="nofollow">http://leaflabs.com/docs/libs/servo.html</a> iRobotGoddard on "Mac, rev5, and Servo" http://forums.leaflabs.com/topic.php?id=871#post-5335 Fri, 17 Jun 2011 21:50:49 +0000 iRobotGoddard 5335@http://forums.leaflabs.com/ iBrought the servo home with me to work on over the weekend. It seems as if there are simple answers to many of the problems I am having, so I will be "getting to know" the Maple. If anyone has any suggestions please feel free to comment. I will be working on servo control and serial communication, it seems as if they will address many questions for Mac users. iRobotGoddard on "Mac, rev5, and Servo" http://forums.leaflabs.com/topic.php?id=871#post-5334 Fri, 17 Jun 2011 20:25:19 +0000 iRobotGoddard 5334@http://forums.leaflabs.com/ thanks alot, the theory makes complete sense. My issue is calling these functions or defining each perimeter the correct way, or remembering it's necessary if a specific library value/function isn't given. I simply decreased the value "9.1" to "1.25". It's jumping back and forth, so I am working smoother motion. gbulmer on "Mac, rev5, and Servo" http://forums.leaflabs.com/topic.php?id=871#post-5332 Fri, 17 Jun 2011 18:52:55 +0000 gbulmer 5332@http://forums.leaflabs.com/ The cycle time for a servo is 20msec, or 50Hz frequency. So this code: <pre><code>for(uint8 pos = 0; pos < 180; pos += 1) // goes from 0 degrees to 180 degrees { uint16 dutyCycle = 4096 + (uint16)(9.1 * (double)pos); // in steps of 1 degree pwmWrite(servoPin, dutyCycle); // tell servo to go to position in variable 'pos' ... }</code></pre> Will set the duty cycle of the PWM to 4,096 (to 5,274) in 65536. Roughly 1/16th of a cycle. BUT what is the cycle time? It isn't set. I had a quick look at the library code in libmaple, and the timers are initialised to a prescaler (which sets the overall cycle time) to 1. The 16bit counts from 0 to 65536-1 each cycle, So the timer would be running at 72MHz/65536 = 1.1KHz I'd expect the servo to be confused, that is way too fast for it. The frequency at which the timer counts is set by the prescaler, and so the prescaler needs to cause the timer to count from 0 to 65536-1 at 50Hz. The equation is 72MHz/(prescaler*65536) = 50Hz or 72MHz/(50*65536) = prescaler = 21.97 So it needs a prescaler of about 22 to have a frequency of about (close enough) 50Hz. Then the PWM signal would be the servo control signal. Now 65536 = 20mseconds, so: 1.25mseconds = 65536*1.25/20 = 4,096 1.5mseconds = 65536*1.5/20 = 4,915 1.75mseconds = 65536*1.75/20 = 5734 As all the arithmetic can be 32bit the calculation might be: <code>uint16 dutyCycle = 4096 + (91 * pos)/10; // in steps of 1 degree</code> iRobotGoddard on "Mac, rev5, and Servo" http://forums.leaflabs.com/topic.php?id=871#post-5328 Fri, 17 Jun 2011 16:09:36 +0000 iRobotGoddard 5328@http://forums.leaflabs.com/ iApologize that was completely wrong. I am trying to transfer test code over from old arduino to the new maple, and am not sending what was updated. In either case I did not place the calculation in, but I did enter new values but they were in the range of 16 bits. Here is my code with the updated information, but the servo will not do a sweep....it only completes it once and never again while the strings print back and forth between "CW" and "CCW". ________________________________________________________________________________ const int servoPin = 11; void setup() { pinMode(servoPin, PWM); } void loop() { for(uint8 pos = 0; pos < 180; pos += 1) // goes from 0 degrees to 180 degrees { uint16 dutyCycle = 4096 + (uint16)(9.1 * (double)pos); // in steps of 1 degree pwmWrite(servoPin, dutyCycle); // tell servo to go to position in variable 'pos' delay(20); SerialUSB.print("\n CW"); delay(20); // waits 15ms for the servo to reach the position } for(uint8 pos = 180; pos>=1; pos-=1) // goes from 180 degrees to 0 degrees { uint16 dutyCycle = 4096 + (uint16)(9.1 * (double)pos); pwmWrite(servoPin, dutyCycle); // tell servo to go to position in variable 'pos' delay(20); SerialUSB.print("\n CCW"); delay(20); // waits 15ms for the servo to reach the position } } ________________________________________________________________________________ robodude666 on "Mac, rev5, and Servo" http://forums.leaflabs.com/topic.php?id=871#post-5327 Fri, 17 Jun 2011 15:52:39 +0000 robodude666 5327@http://forums.leaflabs.com/ The <code>pwmWrite</code> function's second argument is a 16-bit value that represents a 0 - 100% duty cycle. You can't simply write an angle to it like that. You need to convert the angle to 16-bit duty cycle. For example: <pre><code>/* About PWM: <a href="http://leaflabs.com/docs/pwm.html#pwm" rel="nofollow">http://leaflabs.com/docs/pwm.html#pwm</a> 0 Degrees - 1.25 ms - 4096 90 Degrees - 1.50 ms - 4915 180 Degrees - 1.70 ms - 5734 */ for(uint8 degrees = 0; degrees < 180; degrees++) { uint16 dutyCycle = 4096 + (uint16)(9.1 * (double)degrees); pwmWrite(servoPin, dutyCycle); delay(20); } for(uint8 degrees = 180; degrees > 0; degrees--) { uint16 dutyCycle = 4096 + (uint16)(9.1 * (double)degrees); pwmWrite(servoPin, dutyCycle); delay(20); }</code></pre> -robodude666 iRobotGoddard on "Mac, rev5, and Servo" http://forums.leaflabs.com/topic.php?id=871#post-5326 Fri, 17 Jun 2011 15:12:58 +0000 iRobotGoddard 5326@http://forums.leaflabs.com/ Trying to run a sweep program, but the servo will not repeat the sweep. The code switches back and forth, observed through the serial monitor, but the actual motor will not operate accordingly. I am running a sample program from the arduino but I have translated the minor things. Here's my code. _________________________________________________________________________________________ const int servoPin = 11; double pos = 0; void setup() { pinMode(servoPin, PWM); } void loop() { for(pos = 0; pos < 180; pos += 1) // goes from 0 degrees to 180 degrees { // in steps of 1 degree pwmWrite(servoPin, pos); // tell servo to go to position in variable 'pos' delay(15); SerialUSB.print("\n CW"); delay(20); // waits 15ms for the servo to reach the position } for(pos = 180; pos>=1; pos-=1) // goes from 180 degrees to 0 degrees { pwmWrite(servoPin, pos); // tell servo to go to position in variable 'pos' delay(15); SerialUSB.print("\n CCW"); delay(20); // waits 15ms for the servo to reach the position } } _______________________________________________________________________________