A few simple questions on programming servos!

Hello, I'm working on a pole climbing robot (
http://img.photobucket.com/albums/v412/Stompy1/climbrobotclimb.jpg) for my individual project at Uni, and its come to the stage where I
must programme it! This, I am not very good at, but I am making some progress. I'm programming in BASIC for a PICAXE microcontroller, if this helps.
I'm at the stage where I can tell a servo to move to a specific postion, I've also been fiddling with microswitches, so a press of the switch causes the servo to do some stuff:
symbol RARM = 2
main: if pin3 = 0 then loop      goto main
loop: servo RARM,75      pause 1000      servo RARM,220      pause 1000      if pin3 = 1 then main      goto loop
(Its a little over-complicated, but only because I'm using it to investigate how it works.)
The two things I would like to know are as follows:
1) How do I programme the servo to move more slowly? 2) I want a microswitch to - when depressed - interrupt the servo's movement, regardless of its position (i.e: on my robot, a microswitch has been mounted at the limit of its arm's gaits. The arm reaches the limit, the microswitch is depressed, which means the servo must go back again.
Many Thanks,
James
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symbol RARM = 2
start = 75 stop = 220 DELAY = speed to move servo
main: if pin3 = 0 then loop ;if button = pressed, then move servo goto main ;otherwise wait for button press
loop:
for i = 1 to 100 servo RARM,start if pin3 = 0 then main pause DELAY next i
for i = 1 to 100 servo RARM,stop if pin3 = 0 then main pause DELAY next i
if pin3 = 1 then main goto loop
You need to read about the servo RARM,stop command for your CPU.. How long does the signal get sent after you give the command?
You might have to use another command if you want to slow the servo down.
R
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I assume you are using standard R/C servos. They are controlled by pulse widths which basically tell the servo which position to go to - and they gother as quickly as they can given the power suply. the make them move slowly, you'd have to know where they already are and then slowly ramp up [or sdown] the pulse width to get where you want to be.
For this type of thing, it _might_ be better to miodify your ervos so you can adjust the resistance in the potentiometer that it uses to 'sense' its position. Thus, you wouild provide a fixed pulse width signal to the servo, but you would bypass the internal pot and use some type of digital pot to fool the servo. This would also allow you to calibrate the servo position with the pot value and you could change it very slowly to get the behavior you need.
You'd still probably wnat your limit switches so you can verify where the servos are.
Good luck.
Jim
PS I wish they had such fun projects when I was in school...
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Thanks to both of you, you've been very helpful!
On a slightly different note, every example I've seen have had servos' extents at 75 and 225, with 150 in the middle. For one of my servos, at least it seems the limits are around 40 and 180? Is it unusual for this, or am I just being an idiot?!
Also, one of my servos seems to be struggling, moving slower, not moving the full distance and making a loud buzzing noise when powered. Is the the sign of a knackered servo, or what?!
Many thanks,
James
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All servos are different... That isn't unusual.
the buzzing struggler sounds like it may be knackered. :-)
Rich
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snipped-for-privacy@gmail.com wrote:

The "180" (I assume 1800 usec or 1.8 milliseconds) is below spec for any servo, so this one is bad. Anything under 1.0 milliseconds, or over 2.0 milliseconds, is extended range that is not part of the standard spec. If your servo handles it great, but if not, you can't complain to the manufacturer because they don't promise a larger range. However 1.8 milliseconds is under range, so I'd consider this one defective.
Is the buzzing servo also the one that only goes to 1.8 milliseconds? Makes sense if they are one in the same.
-- Gordon
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could you tell me how a specific programming language(like Basic) control machines, i m abit new to this field thanks
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There are devices (eg. motors), and controlers (electronic circuits driving (electrically) the devices), and interfaces (electronic circuits allowing the communication between the processor and the controlers).
The interfaces are usually seen from the processors as a set of memory locations: controler registers can be read and/or written as if they where normal memory.
Therefore processor can send commands and parameters to the controlers by writing to some memory location, and can get status information by reading from some memory location.
In a programming language like BASIC, this translates to the PEEK and POKE instructions.
In a programming language like C, you'd just define a pointer to these memory locations:
volatile unsigned char* controler_register=(unsigned char*)0x40000001; /* assuming for example that 0x40000001 is the address of the memory location where the controler register is mapped */ (*controler_register)=0xff; /* send a byte to the controler */
On some processors, the interfaces are seen as "ports", that is, some memory locations in a special plane, accessed with special processor instructions (eg. INP and OUT). Then instead of accessing directly the controler register with a pointer variable, we must use a little assembler function, like PEEK and POKE in BASIC.
--
__Pascal Bourguignon__ http://www.informatimago.com /

Pour moi, la grande question n'a jamais t: Qui suis-je? O vais-je?
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