More Servo Woes

[Acetronics2]

Hi, Chris

A servomotor has it's own signal limitations ...

from 800 to 2200 µs pulse ( STD ) ... so unpredictable behaviour can occur outside those limits ...

ADCIN 0, B2				' Reads in the PORT A.0 ADC AND STORES THE VALUE IN B2
ADCIN 1, B3				' READS IN THE PORT a.1 ADC AND STORES THE VALUE IN B3

XPRESET	=	B2 + 50

your accelerometer is an analog one, Ok ... but ADCIN can give a result between 0 and 256 ...

so, the servo signal range is not guaranteed to be in the " valid" range.

Now , you read Twice the accelerometer in one cycle ... not really a problem, but it's not compulsory here.

BTW ... Which Pic and Accelerometer do you use ???

Alain

[chrisshortys]

Thanks for all the replies i shall try and go through them now

your accelerometer is an analog one, Ok ... but ADCIN can give a result between 0 and 256 ...

so, the servo signal range is not guaranteed to be in the " valid" range.

BTW ... Which Pic and Accelerometer do you use ???

Alain

Firstly i understand that the ACDIN can give the range from 0-256 how ever the accelerometer is not capable of giving a value of 0-5v, I can't remember the exact voltages as theyre at work but the values i receive on the ACDIN when moving from one limit to the other are 45-128. This is the reason i add a value to the number to try and keep the server centeral(yes i know its not the correct value yet :P ).

The Pic I am using is a 16f876A
and the accelerometer is a prototyping board which i brought from sure electronics http://cgi.ebay.co.uk/3-Axis-low-g-A...1%7C240%3A1318

Hi Chris,
I have only a little experience with servos, and do not have my computer at hand, but the best I remember, if I sent a number to my servo it executed fully before accepting a new value, so I am thinking if you send a count to the servo something like 1500, 1510, 1520 . . . to cause movement you can snuggle an interrupt between the numbers.
EDIT: after reading your code, looks like pretty much what you are doing. I'm empty.

I see no interrupt in your code, Why would you be able to stop it? I never have been able to hijack the count variable in a for next loop, you might try using an interrupt routine and clearing the variable in there, I do not know if it will work though.


Could be latency, could be Breadboard issues where stray capacitance stops the oscillator, could be power supply causing PIC brownout reset, I see no config statement so I assume you are using default config, . . . could be GOTO MAIN at the end of servomove when you used gosub to get there, causing a stack overflow, and eventual reset. . . . On closer inspection looks like you have a return and goto main in there . . . I don't know how that would affect operation if at all since theoretically the code should never go past the return, but who knows? Computers (and PICs) are stupid, but not sloppy, they only do what you tell them to do, whether intentionally or not.
Keep us posted, I would like to see your Final Cut, looks like it would make a cool VR control for a camera in an RC heli.

Yer i think that is the problem the FOR loop is not very interuptable. Thats somthing im going to change once i get time to play with it again.
Shouldnt be a problem with latency as i only ever use veroboard though i havnt placed any capacitors across the crystal so i shall do that asap to see if that helps.
Power supply wise i have tried the circuit on several different powersupplies both at work and at home, the only issue i had there was i had the current limiter at around 100 mA and the servo seems to draw a considerable amount to trip that on its first start up! But hat has now been rectified with a 470 uF across the power rails next to the servo and upping the current limiter.

I shall lso try removing the goto main which was left in from a older attempt but i cant see that command even being looked at but its worth a try!

Orriginally i had planned to make a Pan-Tilt head for a camera but im now looking at making this into a robotic arm kind of setup with possibly strain gauges to detect a hand closing..... i dont know that somthing for later

[Acetronics2]

Hi, Chris

Ok for MMA7260 ... I've got a bunch here , from Elektor magazine. ...


let's then suppose servo pulse kept into the "valid range"

Now, nothing "strange" in the program ... may be you left MMA sensitivy range selecting aside, for the moment.

I'd just recommend you to add :

LOW Servoxyz

just before

PULSOUT Servoxyz

Just to be sure the pulse will be positive. ( not only a view of mind !!! )



Next step to check ... the supply.

Of course, for tests you better use a separate battery for servo powering.

Here you could begin to find success ...

Alain

PS: http://itp.nyu.edu/physcomp/sensors/Reports/MMA7260Q

[chrisshortys]

Well i carried on with some work before checking back to this forum and i have a much more effective code now although i shall try some of the comments you made last Ace

Ive gone back to using a FOR loop but i have put in a maths calculation so that the servo was nt moving the whole way to the next destination but a 4th of the way before checking the data again. So now i have a fairly responsive system for one servo which seems to keep track pritty well with no more hang ups!

The next thing I intend to address is the speed of the panning of the servo. I intend to have the servo move more quickly when there is a larger change in the accelerometer the faster the servo moves.

If anyone would like to see the code just ask but beware its quite messy atm

[chrisshortys]

Well the speed control didnt take very long at all to implement so I have attached a fully working code below.

Now i have to wait for the servo motors i have ordered to arrive from HK before i move on to having 2 servos in control at once!

any advice on different ways of doing things are welcome.

also sorry for the untidyness of the code but i shall neatn it up in the near future with comments on code

'********************************************************************************
'*	college project to control 2 servo motors from a 3 axis accelerometer   *
'********************************************************************************
'*	04/03/09 		CODE WRITTEN BY CHRIS HAMMERSLEY                *
' FEEL FREE TO MAKE USE OF THIS CODE BUT PLEASE GIVE CREDIT TO WHERE IT IS DUE  *
' V 0.4
' For loop responding to input of ADC
' active ADC inputs displayed on line 2 of lcd
' servo position shown on line 1 of LCD
' removed twitch by adding a minimum movement to adjust servo
' more reliable tracking
' QUICKER RESPONCE TO CHANGES IN AXIS BY REDUCTION OF FOR LOOPS
' SERVO MOVEMENT NOW REPRESENTS DIFFERENT SPEEDS IN MOVEMENT
'***********************************************************************
'** Shows the Connections on the ports of the PIC **********************
'***********************************************************************
'
'A0 = X-AXIS 
'A1 = Y-AXIS
'A2 = Z-AXIS
'A3 = 
'A4 = 
'A5 = 
'
'BO = LCD INTERFACE
'B1 = LCD INTERFACE
'B2 = LCD INTERFACE
'B3 = LCD INTERFACE
'B4 = LCD INTERFACE
'B5 = LCD INTERFACE
'B6 = LCD INTERFACE
'B7 = LCD INTERFACE
'
'C0 = SERVO 1
'C1 = SERVO 2
'C2 = 
'C3 = 
'C4 = 
'C5 =
'C6 =
'C7 =


'***********************************************************************
'****************** DEFINE ADCIN PARAMETERS*****************************
'***********************************************************************

DEFINE ADC_BITS		8		'SETS NUMBER OF BITS IN RESULTS
DEFINE ADC_CLOCK	3		'SET CLOCK SOURCE
DEFINE ADC_SAMPLUS	50		'SET SAMPLING TIME IN US

DEFINE LCD_DREG PORTB 			'Define PIC port used for LCD Data lines
DEFINE LCD_DBIT 4 			'Define first pin of portb connected to LCD DB4
DEFINE LCD_RSREG PORTB 			'Define PIC port used for RS line of LCD
DEFINE LCD_RSBIT 3 			'Define Portb pin used for RS connection
DEFINE LCD_EREG PORTB 			'Define PIC prot used for E line of LCD
DEFINE LCD_EBIT 0 			'Define PortB pin used for E connection
DEFINE LCD_BITS 4 			'Define the 4 bit communication mode to LCD
DEFINE LCD_LINES 2 			'Define using a 2 line LCD
DEFINE LCD_COMMANDUS 2000 		'Define delay between sending LCD commands
DEFINE LCD_DATAUS 50 			'Define delay time between data sent.



SERVOY 		VAR	PORTC.0
SERVOX 		VAR	PORTC.1

YAXIS		VAR	WORD
XAXIS		VAR	WORD
ZAXIS		VAR	WORD

XPRESET		VAR	WORD
YPRESET 	VAR	WORD
ZPRESET		VAR	WORD

B0 		VAR 	WORD
B1 		VAR 	WORD
B2		VAR 	WORD
B3 		VAR 	WORD

STEPPING 	VAR 	WORD


TRISA = %00000011			'SETS INPUTS/OUTPUTS FOR BANK A
TRISB = %00000000			'SETS INPUTS/OUTPUTS FOR BANK B
TRISC = %00000000			'SETS INPUTS/OUTPUTS FOR BANK C

ADCON1 = %00000110			'SETS THE ANALOGUE/DIGITAL INPUTS TO BANK A

PORTA = %00000000			'SETS THE INITIAL VALUE OF BANK A
PORTB = %00000000			'SETS THE INITIAL VALUE OF BANK B
PORTC = %00000000			'SETS THE INITIAL VALUE OF BANK C


'**************************************************************************
'				CENTER THE SERVO
'				****************
' Pause for one second to allow initalisations
' Clear the LCD display
' Center Servo 1 and then servo 2
'
'**************************************************************************

PAUSE 1000
LCDOUT "STARTING"
pause 1000
LCDOUT $FE, 1

CENTER:					'NEW SUBROUTINE FOR SETTING THE SERVO
	FOR B0 = 1 TO 100		'MOVES THE SERVO FROM ITS 0 TO ITS 100 MARK
	PULSOUT SERVOY, 150		'
	PAUSE 20			'
	NEXT	

	FOR B1 = 1 TO 100		'Pans the servo from 0 to a halfway point of 100
	PULSOUT SERVOX, 150		'
	PAUSE 20			'
	NEXT

			


'**************************************************************************
'				setup ADC
'				*********
' reads the ADC ports and sets the initial values for calculations
'**************************************************************************
STARTUP:				

ADCIN 0, B2				' reads in the ADC on PORT A.0 and sends it to memory location B2
ADCIN 1, B3				' reads in the ADC on PORT A.1 and sends it to memory location B3

STEPPING = 1

gosub LCDUPDATE

'**************************************************************************
'				Servo calculations
'				******************
' 
'
'**************************************************************************

MAIN:

gosub LCDUPDATE

ADCIN 0, B2				' Reads in the PORT A.0 ADC AND STORES THE VALUE IN B2
ADCIN 1, B3				' READS IN THE PORT a.1 ADC AND STORES THE VALUE IN B3

XPRESET	=	B2 + 50

If Xpreset > B0 then
goto positiveone
endif

if xpreset < B0 then
goto negativeone
endif

'*******************************************************************
'			SERVO MOVEMENT
'			**************
'
' CONTROLS THE OUTPUTS TO THE SERVO
'
'********************************************************************
positive:
	FOR B0 = B0 TO XPRESET STEP STEPPING
	PULSOUT SERVOY, B0
	PAUSE 20
	gosub LCDUPDATE
	NEXT

goto main



negative:
	FOR B0 = B0 TO xpreset STEP - STEPPING
	PULSOUT SERVOY, B0
	PAUSE 20
	gosub LCDUPDATE
	NEXT

goto main


'******************************************************************************
'			MOVEMENT CALCULATIONS
'			*********************
'
' THIS SECTION COMPARES THE INPUT TO THE CURRENT LOCATION AND DECIDES WHETHER A 
' POSITIVE OR NEGATIVE MOVEMENT IS REQUIRED
'
'*******************************************************************************


positiveone:

	xaxis= xpreset - B0

	if xaxis > 3 then
	goto positivetwo
	endif
STEPPING = 1

goto main



negativeone:
	xaxis= B0 - xpreset
	
	if xaxis > 3 then
	goto negativetwo
	endif
STEPPING = 1

goto main

'**************************************************************************************
'			SERVO SPEED CONTROL POSITIVE
'			****************************
'
' THIS SECTION LOOKS AT THE INPUT DATA AND DECIDES HOW FAST TO MOVE THE SERVO DEPENDING
' ON THE VALUE OF THE CHANGE BETWEEN THE INPUT AND THE CURRENT POSITION
'
'***************************************************************************************


positivetwo:

IF XAXIS > 18 THEN
STEPPING = 6
ENDIF

IF XAXIS > 15 THEN
STEPPING = 5
ENDIF

IF XAXIS > 12 THEN
STEPPING = 4
ENDIF

IF XAXIS > 9 THEN
STEPPING = 3
ENDIF

IF XAXIS > 6 THEN
STEPPING = 2
ELSE
STEPPING = 1
ENDIF

'**************************************************************************************************************
' THE FOLLOWING CODE DIVIDES THE CHANGE VALUE BY 4 SO THAT THE FOR LOOP ONLY CHANGES A 4TH OF THE VALUE BEFORE 
' RECHECKING ITS INPUTS
'**************************************************************************************************************

if xaxis > 20 then
xaxis = xaxis / 4
XPRESET = B0 + XAXIS
ENDIF

goto positive

'**************************************************************************************
'			SERVO SPEED CONTROL NEGATIVE
'			****************************
'
' THIS SECTION LOOKS AT THE INPUT DATA AND DECIDES HOW FAST TO MOVE THE SERVO DEPENDING
' ON THE VALUE OF THE CHANGE BETWEEN THE INPUT AND THE CURRENT POSITION
'
'***************************************************************************************

negativetwo:

IF XAXIS > 18 THEN
STEPPING = 6
ENDIF

IF XAXIS > 15 THEN
STEPPING = 5
ENDIF

IF XAXIS > 12 THEN
STEPPING = 4
ENDIF

IF XAXIS > 9 THEN
STEPPING = 3
ENDIF

IF XAXIS > 6 THEN
STEPPING = 2
ELSE
STEPPING = 1
ENDIF


'**************************************************************************************************************
' THE FOLLOWING CODE DIVIDES THE CHANGE VALUE BY 4 SO THAT THE FOR LOOP ONLY CHANGES A 4TH OF THE VALUE BEFORE 
' RECHECKING ITS INPUTS
'**************************************************************************************************************

IF XAXIS > 20 THEN
XAXIS = XAXIS / 4
XPRESET = B0 - XAXIS
ENDIF

GOTO NEGATIVE

'
'
''*******************************************************************************************************************
'			LCDUPDATE CONTROL
'			*********************
' MOVES BOTH SERVOS FOR BOTH X AND Y MOVEMENT
' CREATES THE NEW X AND Y PRESETS FOR THE CALCULATIONS
' UPDATES THE LCD DISPLAY
'*******************************************************************************************************************
LCDUPDATE:


ADCIN 0, B2				' Reads in the PORT A.0 ADC AND STORES THE VALUE IN B2
ADCIN 1, B3				' READS IN THE PORT a.1 ADC AND STORES THE VALUE IN B3



LCDOUT $FE, 2				' SENDS THE COMMAND TO THE LCD TO MOVE TO THE START OF THE FIRST LINE

LCDOUT "Servo Pos= ",DEC3 B0		' SENDS THE DATA FOR THE X AXIS TO THE LCD ON THE FIRST LINE

LCDOUT $FE, $C0				' MOVES THE CURSUR OF THE LCD TO THE START OF THE SECOND LINE

LCDOUT "Y = ",DEC3 B2, " X = ",DEC3 B3		' SENDS THE DATA FOR THE Y AXIS TO THE LCD ON THE SECOND LINE

RETURN					' RETURNS TO THE PREVIOUS BLAAAAAAAAAAAAAAAAAAAAAAH


'GOTO MAIN



END*

[flipper_md]

positivetwo:

IF XAXIS > 18 THEN
STEPPING = 6
ENDIF

IF XAXIS > 15 THEN
STEPPING = 5
ENDIF

IF XAXIS > 12 THEN
STEPPING = 4
ENDIF

IF XAXIS > 9 THEN
STEPPING = 3
ENDIF

IF XAXIS > 6 THEN
STEPPING = 2
ELSE
STEPPING = 1
ENDIF

'************************************************* ************************************************** ***********

Hi Chris

I am looking to do something similar (soon I hope) and as I was scrolling thru your code, I saw that this whole section could be resumed by this.

STEPPING = XAXIS /3

and maybe add a IF statement for low values of xaxis..

IF XAXIS < 5
STEPPING = 1
END IF


I don't know if that can make the whole thing more reponsive...since all the IF have to be processed.

anyhow, thanks for sharing your code!

[chrisshortys]

Cheers for that flipper, I shall try that when I get back from the business trip I'm on.
Anything to make it simplier will help with the two servo motors!