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Topic: What is Dead Band Width? (Read 12429 times) previous topic - next topic

jack1992

Hello to everyone.I have the MG995 Servo and on the specs says Dead Band Width 4usec
What is dead band width?If anyone knows please reply.Thanks in advance.

septillion

That's the amount the signal is allowed to change without affecting the output/servo arm. It's a error tolerance :)
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polymorph

To further explain, if you did not have a band where a change in pulse didn't cause a reaction in the servo, the servo would keep hunting constantly just due to noise. This could run down your batteries very quickly.
Steve Greenfield AE7HD
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jackrae

The website data sheet for that model actually states 5us but that still permits a signal resolution of 1 part in 200 or 0.5% of full scale width which is still pretty good.

MarkT

Deadband in the input signal is not the same thing as hysteresis in the control loop.  The servo will
always work hard if you have a varying load torque it is working against.

Hysteresis in the input signal is pointless for control, but it will stop a lightly loaded servo from
jittering if the servo pulse source itself is jittery - ie the Servo library has jitter due to the other
interrupts (timer0 interrupt that drives millis() for instance), having deadband in the servo will
reduce the chattering of that servo, but will also reduce the accuracy of that servo.

If you have a jitter-free servo controller such a dead-band isn't helping you, but it probably is
a reasonable compromise for the Servo library, and for analog RC control.
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KayakDiver

Does anyone know if the Deadband of a Hitec digital servo can be changed programmatically, in other words, on the fly by talking to it over the PWM connection to it within a program and betweeen setting the desired pulse width?

Southpark

So is it like an input 'resolution' thing? A purposely 'designed' resolution.

Eg. If the pulse width is set to 1.5 millisecond (for the moment), then the servo won't do move until the pulse width changes to a value that is either larger (or equal to) approximately 1.5 millisecond PLUS 4 microsecond......  less than (or equal to) approximately 1.5 millisecond MINUS 4 microsecond.

That's assuming that the dead band 'width' specification is 4 microsecond.

polymorph

Southpark: Yes, that describes it pretty well. Except a deadband width of 4us means +-2us.

It also means that the servo will stop moving when it is within that 4us deadband, so it may reduce the positional accuracy if you were to use a large deadband.
Steve Greenfield AE7HD
Drawing Schematics: tinyurl.com/23mo9pf - tinyurl.com/o97ysyx - https://tinyurl.com/Technote8
Multitasking: forum.arduino.cc/index.php?topic=223286.0
gammon.com.au/blink - gammon.com.au/serial - gammon.com.au/interrupts

Southpark

Southpark: Yes, that describes it pretty well. Except a deadband width of 4us means +-2us.

It also means that the servo will stop moving when it is within that 4us deadband, so it may reduce the positional accuracy if you were to use a large deadband.
Thanks for that explanation polymorph. That's definitely clear now. Glad that you added that comment. It really helps a lot.

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