driving 16 servos
Lee Marshall
Posts: 106
hi, I want to control 16 servos, and PWM control 8 LEDs whilst receiving commands from a 19.2KBaud serial line
I thought: "This is a job for the parallax propeller"
I want to use the counters in 2 cogs to do the servo control, but i am concerned about the latency caused by polling the counters(to complete the servo pulses), which would probably be about 100-200ns.
latency in servo pulses seems to me like a bad thing.(i still think the prop 2 could benefit from some kind of interrupt system).
is a 200ns possible variation from one pulse to the next really going to make the servo shake around? or is it too small to noticably affect the servo?
im using analog servos and ill be controlling them with a resolution of 16usec.
Post Edited (Lee Marshall) : 10/19/2008 10:39:33 AM GMT
I thought: "This is a job for the parallax propeller"
I want to use the counters in 2 cogs to do the servo control, but i am concerned about the latency caused by polling the counters(to complete the servo pulses), which would probably be about 100-200ns.
latency in servo pulses seems to me like a bad thing.(i still think the prop 2 could benefit from some kind of interrupt system).
is a 200ns possible variation from one pulse to the next really going to make the servo shake around? or is it too small to noticably affect the servo?
im using analog servos and ill be controlling them with a resolution of 16usec.
Post Edited (Lee Marshall) : 10/19/2008 10:39:33 AM GMT
Comments
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Cheers,
Simon
www.norfolkhelicopterclub.com
You'll always have as many take-offs as landings, the trick is to be sure you can take-off again
BTW: I type as I'm thinking, so please don't take any offence at my writing style
ah, i still have my head in a PICMicro.
i forgot that when you are running parallel, you can waste time for a certain task and not have to design everything else around it.
on beau's servo controller:
now THAT is damn tight.
methinks im gonna use that.
the prop really has turned uC programming upside-down for me, shame it doesn't have more ram...
the alternative for this task was like 5 PIC16f628s..
now, the only problem is that ive gotta build this thing in time for halloween.(it's a computer controlled LED lighting cluster)
thanks for the help, guys.
EDIT: there is something else - is it possible to hand-solder the QFP44 prop relatively easily(in comparison to other smts)? it's just that the DIP40 is big, and needs holes in the PCB and doesn't look as cool.
Post Edited (Lee Marshall) : 10/19/2008 12:28:10 PM GMT
to speed up help from the forum there are three rules:
1.) give a DETAILED descrition of what you want to do
taking 10 minutes more to make it detailed will pay back
in 10 hours less time finding the solution
2.) Ask CONCRETE questions
if somebody has to ask back you will loose minimum some hours
3.) Attach your COMPLETE code using the archive-function of Proptool
and the attachement.manager of this forum site
manual for this is here
"...why do i need a 4k7 resistor between the prop and each servo?" - The resistor is to help·attenuate any inductive issues that may occur within the servos or long distance wire runs greater than 6 inches, something I have noticed in my experiments.· With a resistor physically close to the controller, and a capacitor across power·physically close to the servo itself, I have achieved·steady servo control·over 20 feet away.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
For low power applications I use roughly 50uF per foot... so at 20 feet I used a 1000uF cap as close to the servo power as possible.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.