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Servo Voltage

Old 09-15-2007, 08:39 AM
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Darkbird
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Default Servo Voltage

Having a problem with a pair of Futaba s-3003 servos. When I set up the plane I used a 4.8v pack to set centers and such and had no problems. During final setup of the aircraft, I found I needed quite a bit of weight in the nose, so I went to a much larger 6v pack. I prefer to carry battery rather than lead. Problem is when I checked the radio system, I had no aileron control. Have changed recievers, tried changing the way they were plugged in(different channels and such) and one or two other things but the only thing that helps is going back to a 4.8v pack. Can anyone tell me why I'm have this problem? the only thing I have changed about these servos is to install longer leads due to one have a bad lead when I got the plane.
Old 09-15-2007, 09:50 AM
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Rodney
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Default RE: Servo Voltage

The long leads are defective or not properly plugged in.
Old 09-15-2007, 07:10 PM
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Darkbird
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Default RE: Servo Voltage

The long leads are brand new and soldered directly to the board inside the servo. Also, they work fine when on 4.8v, just not on 6v. Thats the part thats got me stumped.
Old 09-15-2007, 07:29 PM
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bruce88123
 
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Default RE: Servo Voltage

The S3003 is rated to be used at 6 volts but are the RX's that you are using rated for that voltage too? Are there any other servos plugged in that are working? Have you tried a different "model" of RX? What RX are you using.
Old 09-16-2007, 02:11 AM
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NikolayTT
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Default RE: Servo Voltage

The problem might be that when you think you have 6V battery, you might have more. If you use NiMH then it is for sure
lot more than 6V. NiCd batteries have quite stable 1.25V per cell while NiMH has its sells in fully charged status even
about 1.4V per cell i.e. 5x1.4 = 7V and that is something your system might not like. I am using a voltage stabilizer
circuit for 6V and 8(eight!) cells of NiMH in order to have 6V whole the time, even during very cold winter we have
when the temperature is lot below the freezing point. NiCd batteries are better and you might do well with 5 cells
but make sure that they are fully charged and then load them with small 5W car bulb for about couple minutes
prior you connect them to the Radio, becaue when fully charged they might have 1.3V per cell and some radios
and servos just do not "like" that. Why did I use NiMH ? - I got a lot of them almost for free and that is the only
good reason.
Old 09-16-2007, 09:37 AM
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Darkbird
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Default RE: Servo Voltage

The problem is servo specific and only occurs when i use them with the 5-cell pack. Rest of the servos/channels work fine(including another s-3003) and channel swapping the problem servos doesn't help. No-load voltage on the RX pack in question is 6.4v and is an 1800mah 5-cell NiCd pack. The only thing different about these two servos is that they have about 36" leads on them that i installed due to the installation issues with this plane. Don't know why that would affect them on 6v only though. They work fine at 4.8v.
Old 09-16-2007, 05:14 PM
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bruce88123
 
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Default RE: Servo Voltage

Did they work on 6.4 before you changed the leads??
Old 09-17-2007, 08:50 AM
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dirtybird
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Default RE: Servo Voltage

They should work on 6 volts if they work on 4.8. In fact they would probably work OK on 8 volts. You will know if you used too much voltage if they start to smoke when you turn them on.
Old 09-17-2007, 09:45 AM
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Darkbird
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Default RE: Servo Voltage

Don't know what they did b4 changing leads. One was new, the other was used but had a bad lead anyway. I know they should work on 6v if they work on 4.8v, but they don't. All they do is twitch when I turn on the power and don't respond after that. Put the 4-cell pack back in and everything works normally. Yes I've changed recievers and done everything else I can think of. Each servo is even plugged into different channels(1 and 6). I may just change both servos to avoid having an inflight failure. Just means that the plane won't fly till next season.
Old 09-17-2007, 10:17 AM
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NikolayTT
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Default RE: Servo Voltage

Then seems clear, that your servo has over-voltage protection which blocks the whole
operation if the voltage exceeds 6.00V. That is simple to do and maybe done on most
servos by many reasons. If it is said that servo is 6V, then you may have no chances
to make it working on any voltage equal or bigger than 6.1 V. And that is different
from servo-to-servo; they are not so simple things as someone might think and place
even 8V [sm=drowning.gif]

To find out you can do the following: - Visit the local Radio/TV/Phone repair shop
and tell the story to the guys there. My suggestion is to ask them to power your Radio and
servo from their laboratory power sourse with smoth posibility of increasing the voltage
and with continuous mA metter. Then increase the voltage from 5V till 6.5V in steps
of 0.1V (or even 0.025V better)and look at the current. If there is a sharp change(glitch)
in the current increase around 6.05V then all is clear, there is a smart protection in the
servo and you cannot overrun that.
Old 09-17-2007, 11:28 AM
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Default RE: Servo Voltage

The S3003 is less than $10 each. Not worth the aggravation. Chuck them IMO. No warranty at the LHS once modified.
Old 09-17-2007, 01:21 PM
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NikolayTT
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Default RE: Servo Voltage

That is true, I am using 3004 and that is better than 3003 and still cheap one. At the end, the only Metal Gears
servos are the ones which last and worth money, especially if they are digital, that seems as good use of the money.
I.e. the Cheap servos come Expensive at the end, as many other things indeed.
Old 09-17-2007, 03:32 PM
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dirtybird
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Default RE: Servo Voltage

At $10/servo I am sure they don't have overvoltage protection.
Old 09-17-2007, 05:07 PM
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bruce88123
 
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Default RE: Servo Voltage

All it would take is a 20 cent Zener diode but I doubt it's got protection either.
http://www.americanmicrosemi.com/tutorials/zener.htm
Old 09-17-2007, 06:06 PM
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Darkbird
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Default RE: Servo Voltage

I will probably pull them and find them homes in less critical applications. Used them because one was in the airframe when i got it along with a 148 on the other aileron. Changed out the 148 so that I would have matching servos on the ailerons. I'd rather ground the plane than lose it to a servo that suddenly stops working even at 4.8.
Old 09-17-2007, 10:55 PM
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NikolayTT
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Default RE: Servo Voltage

ORIGINAL: bruce88123

All it would take is a 20 cent Zener diode but I doubt it's got protection either.
http://www.americanmicrosemi.com/tutorials/zener.htm
Well, as far as the cost goes, the microchip in the servo seems to be the cheapest thing inside.
Maybe the chip cost in total 50 cents and the rest is Motor+Gears+Box etc, all multiplied by 300%
proft margin at least ... well those guys got to eat something ... You can trust me a "bit" more since
I am in that business about 30+ years or more.
If it was a zenner diode, ti would just limit the voltage to 6V and the only trouble would be higher
curret drain trough the Zenner diode till the battery voltage drops to 6.0 V. That is why I suggested
to be measured the current consumption in a Laboratory.

Most likely the "protection" alike behaviour comes from the Feedback Electronic Circuit which monitors
the position of the Potentiometer attached to the servo arm. That potetniometer "tells" to the circuit that
the rotation angle has been achieved or not, and from there comes the signal to stop or continue
running the el.motor inside. That feedback system is also designed to operate at Wide Range
of Battery Voltages and Temperatures and if one exceed that Battery range, then the system
gets "dizzy" and wander what the "H..." is going on now.

Voltage stabilizer in the Servo is also a bit trouble to do because that takes space for heat sink and
more importantly is would affect the Speed. Since almost all servos with price difference of 10x the
speed is usually increasing with the Voltage increase from 4.8 to 6.0 volts, that shows that most
likely inside there isn't voltage stabilizer.

That is why I found more efficient to add it for my(!) needs outside. Below is the Electric Circuit
one can use.

But make sure that you have not less than 7 cells in order to allow the voltage drop over the
regualtor, which is about 2V. Of course, as mentioned, I needed this in order to be able to
have exactly(!) 6 volts and also use NiMH Batteries in temperature range -25 to +40 Deg. C.
That is a bit overkill indeed and costs some time to solder all those wires. No problem if your
side hobby (or profession) is electronics.
Attached Files
File Type: pdf
Ec88453.pdf (60.6 KB, 2 views)
Old 09-17-2007, 11:16 PM
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dirtybird
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Default RE: Servo Voltage

Lets see 0.2 X 100000 = $20000 I'd say thats significant. A ball bearing costs less(in quantity) and it increases the price of the servo nearly $5.
When you are looking at high prduction runs a savings of 0.1 is very significant.

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