Author Topic: Servo pulse logic level  (Read 4052 times)

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Offline jsmokerTopic starter

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Servo pulse logic level
« on: April 03, 2009, 12:35:15 PM »
If a servo is supplied powered at 5V, will a 3.3V PWM work to control it?

Thanks
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Offline galannthegreat

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Re: Servo pulse logic level
« Reply #1 on: April 03, 2009, 02:54:48 PM »
What model servo are you using? Because you can usually find the information in the datasheet on tolerances for the PWM signal.
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Kurt

Offline jsmokerTopic starter

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Re: Servo pulse logic level
« Reply #2 on: April 24, 2009, 11:29:27 AM »
I'm using a Traxxas 2065 submicro servo.
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Offline galannthegreat

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Re: Servo pulse logic level
« Reply #3 on: April 24, 2009, 11:48:32 AM »
I would guess that it would work, try breadboarding the circuit, and with your findings report it on the forum, this would be pretty helpful info.
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Kurt

Offline jsmokerTopic starter

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Re: Servo pulse logic level
« Reply #4 on: April 24, 2009, 12:08:47 PM »
I just tried it out.  When I first posted I didn't have a function generator, so I figured I could get easy answer online, but now I do and with PWM output to bat.  It worked.  I supplied 5V to the power leads and then applied the 3.3V as the PWM.  I got it down to 2.5V before the servo went jittery.  Also, fyi, you all might have known this but I found that ramping that 5V power supply keeps the servo from jumping initially as opposed to an immediate 5V supply that always makes the servo jump. 

This leads me to another question.  If ramping is not a possibility can one supply the PWM first before turning on the power to try to keep it from jumping?  Will that mess up the servo?  How do commercial servo controllers do it?  They never seem to jump (other than jumping into place).
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Offline galannthegreat

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Re: Servo pulse logic level
« Reply #5 on: April 24, 2009, 12:17:02 PM »
Nice, that will come in handy later on :)
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Kurt

Offline Soeren

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Re: Servo pulse logic level
« Reply #6 on: April 24, 2009, 08:01:48 PM »
Hi,

Quote from: jsmoker on April 24, 2009, 12:08:47 PM
[...] can one supply the PWM first before turning on the power to try to keep it from jumping?  Will that mess up the servo?
Not knowing the innards of your servos electronics, I'd recommend against it.
Unless you know for certain, that a given circuit is safeguarded against it, applying input voltage before the supply has stabilized, will often result in currents going places that it shouldn't.
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Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
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Offline Admin

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Re: Servo pulse logic level
« Reply #7 on: May 25, 2009, 06:15:43 PM »
The reason servos jump when you turn the system power on is simply just noise. Slowly ramping power to the servos will/should prevent that from happening.

However, slowly ramping power to a microcontroller can cause problems, so it'd force you to have separate power supplies.

PWM'ing a non-powered servo won't break/do anything.
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