Servo Jitter

Oct 30, 2019

@eric.chanussot

Thank you, I will try this and get back to you.

Cheers

Chris Gomersall

Oct 29, 2019

@eric.chanussot

You were right my PWM ranges were initialy wrong I got them from some documentation on a site that sells the servo. But I don't trust them to be correct. It says they use standard PWM range. The Sketch program via the Arduino UNO works well and the servos moved, and responded to the inputs. After following the text prompts from the serial window, The program reported these PWM ranges for the 2 servos. As in my above post.

I'm still not there, I think I have the PWM ranges correct NOW, but the Nybble moves so SLOWLY and the movements are REDUCED in there range. For example in the WAVE or HI behavior. I can see Nybble attempting to wave and his left paw moves up and down but the shoulder position is not moving far enough, and the paw is not moving up and down enough. it just wiggles up and down a small amount.

It looks like I need to increase the range of movement and speed up the movement.

Can I increase the amount of movement per position say in 6 degree increments instead of 5 degree? I'm not sure how to achieve this.

Kind Regards

Chris Gomersall

Oct 29, 2019

Replying to

@Chris Gomersall

I'm also working on this problem, I do not think the problem comes from speed.

Try this sketch!

The servo will position itself in weak abutment, wait and watch the arm of the servo, it is necessary to be attentive.

Press "Send" when the servo starts to move. The start value is captured.

Then the servo arm will move to a high stop, wait and watch the servo arm.

Press "Send" again when the servo starts to move. The end value is captured.

It may be necessary to change the start and end search values (StartLower and StartUpper) to be sure to be in range.

Repeat the test to be sure.

/*************************************

Simple Arduino sketch to find the full pulse width range of a servo.

It does so by starting with a low pulse width and to increase it in small steps. Once

you see movement the minimal pulse width is reached. Press "Send" in the serial monitor to

indicate that to the program.

Note: The code is written in a simple blocking way and not optimized. It's a terrible

startingpoint to use in your own code!

INSTRUCTIONS

- Set Serial Monitor to 115200 baud

- Set Serial Monitor to "Both NL & CR"

- Connect a servo to 'ServoPin' (default: pin 10)

- Press "Send" when the Servo starts moving (for both lower and upper limit)

- When the limits are reached, the servo will alternate between them

- Press reset to start over

*************************************/

#include <Servo.h>

const byte ServoPin = 10;

//Minimal pulse width to try for lower limit (in ms)

const unsigned int StartLower = 500;

//maximal pulse width to try for upper limit (in ms)

const unsigned int StartUpper = 2500;

//Number to increment the pulse width during search (in ms)

const unsigned int StepSize = 11;

//time between increments (in ms)

const unsigned int StepInterval = 1000;

unsigned int lowerLimit;

unsigned int upperLimit;

Servo testServo;

void setup(){

Serial.begin(115200);

Serial.println("Servo pulse width finder sketch");

Serial.println();

Serial.println("Be sure to set Serial monitor to \"Both NL & CR\".");

Serial.println("Press \"Send\" when the servo starts moving during the search.");

Serial.println();

//move servo already to lower end and attach it

testServo.write(0);

testServo.attach(ServoPin, StartLower, StartUpper);

Serial.print("Searching for lower limit");

lowerLimit = sweep(StartLower, StepSize, StepInterval);

printResult("Lower", lowerLimit);

Serial.print("Searching for upper limit");

//minus the 'StepSize' to go the other way

upperLimit = sweep(StartUpper, -StepSize, StepInterval);

printResult("Upper", upperLimit);

Serial.println("Press reset to test again.");

}

void loop(){

testServo.writeMicroseconds(lowerLimit);

delay(2000);

testServo.writeMicroseconds(upperLimit);

delay(2000);

}

unsigned int sweep(unsigned int start, int delta, unsigned int interval){

testServo.writeMicroseconds(start);

delay(interval);

unsigned int value = start;

//stop the search if we receive something on Serial

while(!Serial.available()){

//increase the value to the new position

value += delta;

//stop searching if we go beyond the start positions of the search (= Failed)

if((value < StartLower) || (value > StartUpper)){

Serial.println();

return 0;

}

//otherwise move to new position

testServo.writeMicroseconds(value);

Serial.print(".");

delay(interval);

}

clearSerialBuffer();

Serial.println();

return value;

}

void printResult(char *text, unsigned int value){

//value found

if(value != 0){

Serial.print(text);

Serial.print(" limit: ");

Serial.print(value);

Serial.println("ms");

}

//value not found

else{

Serial.print(text);

Serial.println(" limit not found!");

Serial.println("Press reset to try again.");

//and stop here

while(true);

}

void clearSerialBuffer(){

//clear serial buffer (but do nothing with it)

while(Serial.available()){

Serial.read();

}

Oct 30, 2019

Replying to

@Chris Gomersall

I advise you to search outside Nybble. Make a small assembly (print + arm + servo) to have the real range.

Oct 29, 2019

@Rongzhong Li

@eric.chanussot

Hi There,

I used the Sketch code you provided with my Arduino UNO to get the PWM ranges of the two servos:

Shouldder servos K-Power DMC809 = 283 - 2080 replaces MG92B

Knee Servos Power-HD HD-1810MG = 490 - 3100 replaces MG90D

Uploaded modified sketch code to cat.

Then recalibrated.

Cat performs all behaviors VERY SLOWLY and with LIMITED RANGE OF MOTION

Should I change the constant in the code ?

#define MG92B_RANGE 150 to #define MG92B_RANGE 180

#define MG90D_RANGE 150 to #define MG90D_RANGE 180

Is there a way to speed up the servo movement? at the moment it is very slow?

Thanks for your support and help.

Kind Regards

Chris Gomersall

Oct 22, 2019

@Chris Gomersall

Hello,

Have you calculated the minimum and maximum pulse values of your DMC809 yourself? or did you find them somewhere?

In your October 12 message, you say you use the values: 1000µS at 1500µS.

It seems that the right values are: 900µS at 2100µS.

Source:

https://french.alibaba.com/product-detail/k-power-dmc809-coreless-servo-high-speed-3kg-torque-micro-digital-servo-for-450-rc-helicopter-60778400736.html

Maybe your problem is there?

Good cordiality

Oct 18, 2019

Yes, imagine you are the cat and the joints are arranged as clockwise spiral from body to limbs.

Oct 18, 2019

@Rongzhong Li

The index of the servos is the same as that of the representation below?

Oct 18, 2019

@Chris Gomersall

If you own an Arduino UNO.

Try this test sketch with the Servo library to see how your

servo responds to different settings, type a position

(0 to 180) or if you type a number greater than 200 it will be

interpreted as microseconds(544 to 2400), in the top of serial

monitor and hit [ENTER], start at 90 (or 1472) and work your

way toward zero (544) 5 degrees (or 50 micros) at a time, then

toward 180 (2400).

#include <Servo.h>

Servo servo;

void setup() {

// initialize serial:

Serial.begin(9600); //set serial monitor baud rate to match

servo.write(90);

servo.attach(9);

prntIt();

}

void loop() {

// if there's any serial available, read it:

while (Serial.available() > 0) {

// look for the next valid integer in the incoming serial stream:

int pos = Serial.parseInt();

pos = constrain(pos, 0, 2400);

servo.write(pos);

prntIt();

}

void prntIt()

{

Serial.print(" degrees = ");

Serial.print(servo.read());

Serial.print("\t");

Serial.print("microseconds = ");

Serial.println(servo.readMicroseconds());

}

Oct 18, 2019

then use the corresponding servo index after the ‘m’

Oct 18, 2019

That is a good idea, however I still have the Original servos' for the Head pan and tilt and the Tail.

I change the servos over for some testing.

Oct 18, 2019

On the cat, try to use the ‘m’ token to check the angle range. For example, “m0 -45” and “m0 45” should make the cat pan it’s head by 90 degrees. You can also use it to check the max angle ranges on Botha sides.

Oct 18, 2019

I've uploaded the altered code, and the cat is performing the behaviours strangely. The movements are shortened and the limbs don't extend fully

The wave for example. Nybble doesn't sit properly, and her front legs don't extend fully.

Maybe I need to alter the angle range of the servo's for the shoulder and for the knees?

Unfortunately I don't have any servo range testing equipment.

I must admit I feel a bit out of my depth here. Any further help is appreciated.

Cheers

Chris G

Oct 17, 2019

It’s the angle range of the servo. The tolerance is actually quite wide.

Oct 17, 2019

@Rongzhong Li

What is the value of 150 (MG92B_RANGE) located in: OpenCat.h \ // servo constants?