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Servo speed specs - what do they mean?

Old 06-26-2011, 04:57 AM
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wessman
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Default Servo speed specs - what do they mean?

Hello,

When a manufacturer says that their servo speed is e.g. (4.8V/6.0V):0.19s / 0.14s they mean really at actual 4.8V and actual 6V OR they mean with 4.8V (4-cell pack that is having 6 volts when fully charged) and 6V ( 5-cell pack that is having 7.4 volts when fully charged)?

Thanks and regards,

Klarm Yai

Old 06-26-2011, 05:43 AM
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BuschBarber
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Default RE: Servo speed specs - what do they mean?


ORIGINAL: wessman

Hello,

When a manufacturer says that their servo speed is e.g. (4.8V/6.0V):0.19s / 0.14s they mean really at actual 4.8V and actual 6V OR they mean with 4.8V (4-cell pack that is having 6 volts when fully charged) and 6V ( 5-cell pack that is having 7.4 volts when fully charged)?

Thanks and regards,

Klarm Yai

No! 4.8 v means 4 cell and 6v means 5 cell.
Old 06-26-2011, 06:47 AM
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Default RE: Servo speed specs - what do they mean?

Wessman,

The measured voltage drops when a load is applied to any battery.

What you measure with your voltmeter is no-load potential differential between the terminals, which is normally as high as 1.5 volts per cell.

The manufacturer has tested the servo with 4-cell and 5-cell batteries (at 1.2 volts per cell normally), measuring the time that a full deflection of the shaft takes.
Note that higher voltage means more torque and speed from the same servo, and also higher Amps consumption in the same time.
That extra flow of electrons leaving the battery is something to be careful about when you decide using 5-cell packs: they need to have higher mAh rating than similar 4-cell pack.

Even more, those specified speeds are at normal mechanical loads which the servo is designed to overcome.

For undersized servos working against huge control surfaces flying at high speeds, that deflection speed would be slower than specified, reaching zero in extreme cases.

That is the reason for which we should use loaded voltmeters to verify the state of the flying packs before each flight.
A non-load measurement can tell you that a battery is full, while in reality, that battery will not be able to stand the demand that loaded servos will create in flight.

This website explains more and better about batteries:

http://www.hangtimes.com/redsbatteryclinic.html
Old 06-26-2011, 09:48 PM
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wessman
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Default RE: Servo speed specs - what do they mean?

Thanks for the replies. Just wanted to know that, as I´m using 2-cell 3000 mAh LiPos with a 10 amp regulator. I can select anything between 5.2V and 7.0V. Since I want to get the 6 volt servo performance of a manufacturer I set my LiPo regulator above 6 volts - actually 6.6 V. This 6.6 volt should be same as a fresh fully charged 5-cell NiMh pack. And reg makes sure that there is no voltage drop when the servos are under the load because my batt pack has more than 8 volts.....

Thanks and regards,

Klarm Yai
Old 06-27-2011, 11:27 AM
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Default RE: Servo speed specs - what do they mean?

Sounds about the same as using A123's, you should be fine.
Old 06-27-2011, 12:50 PM
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Jezmo
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Default RE: Servo speed specs - what do they mean?

I agree with Andy...
Old 06-28-2011, 05:03 AM
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Default RE: Servo speed specs - what do they mean?

I agree with Jezmo

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