Servo connections direct to battery

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Postby tim070872 » Thu Sep 04, 2003 12:26 pm

I have the XS-6 FM digital sender and a BEC receiver.....
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Postby NilsThorell » Fri Sep 05, 2003 6:49 am

What I mean is that: Have anybody really measured the actual voltage at the servo? With oscilloscope and digtal voltmeter? If so, what did you gain by rewiring? How many millivolts?
Somebody said that the power pins are already wired together in the receiver. So, I doubt that you will gain 1.2 volt as somebody said.
And I would guess that a Multiplex jumbo servo would typically draw 1 amp, which is not a lot. But correct me if I am wrong.

I am more concerned about all the thin wires. And all the tiny connectors in the receiver.
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Postby Tony » Fri Sep 05, 2003 9:00 am

its not a matter of gaining millivolts, the potential gain is indeed 1.2V, this will only be noticed if you are using a BEC Rx, as they are designed to accept an input of 7.2V and reduce it to 4.8 for the servos etc, this goes back to the old electric days when you used to have a 7.2v pack and 4AA's to power the servos etc.

with the better modern non BEC Rx, as supplied with the 3VC set, there is no such circuit, if you put 6v into the batt socket then 6 volt will be supplied to the servos, what is the issue though with this set up is that during testing I managed to record a figure of nearly 3 amps current draw when all 3 servos in my car where in use, ie simulating full braking while turning into a corner, this is in my opinion far too much for the small tracks on the PCB and also the SMD in the Rx.

on another website is a thread from a guy that just plugged his servos into the Rx as normal and then proceeded to blow 3 in as many weeks, now seeing as the one I use is something like £80 to replace, I am not going to worry about spending £5 on extra leads to protect the Rx and it circuitry.

as further evidence, have a look around the track and try to find someone with a tonegawa plugged into the Rx for its power!!!, the reason behind this is the current that they draw, this is the same principle that is being applied by use of the Y leads etc...

also the difference is visually noticable, especially with the Hitec servo that I use, you can see that it is quicker with the 6v, and also their own data sheets fully detail the spec difference between 4.8V and 6V
hope this helps

Tony
just as I thought there was a light at the end of the tunnel, I realised it was just my boss with a torch and more work for me!!!
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Postby NilsThorell » Mon Sep 08, 2003 4:15 pm

This is the reply I got from Futaba:

"We do not have voltage drop ratings for receivers. It is not a
necessary statistic in the R/C realm. One amp will be fine for the RX,
but not much more current. You could run a batt straight to the servo
but you won't see much of an increase in speed, more so you will notice
your batteries lasting longer since the 1amp servo has its own dedicated
power supply."
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My wiring...

Postby Viper » Wed Sep 10, 2003 11:02 pm

Hey there,

just wanted to share my wiring system. Most only run the steering servo's directly from the battery, or have 2 powered lead running to the receiver. ine has only one power-cable to the receiver (on the batt. connection) and all 4 servo's (dual steering & 1 gas/front brake + 1 rear brake) directly from the battery.

It can be found here: gallery/image_page.php?album_id=79&image_id=178
Two things are universal - Hydrogen and Stupidity
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Postby Lone_Ranger » Thu Sep 11, 2003 12:28 am

NilsThorell wrote:This is the reply I got from Futaba:

"We do not have voltage drop ratings for receivers. It is not a
necessary statistic in the R/C realm. One amp will be fine for the RX,
but not much more current. You could run a batt straight to the servo
but you won't see much of an increase in speed, more so you will notice
your batteries lasting longer since the 1amp servo has its own dedicated
power supply."


Hi Nils

The main reason for wiring the servos directly to the battery is not really to gain any more speed although in some cases with older BEC (Battery Eliminator Circuit) receivers they were set to allow only 4.8Volts to the receiver and also to the servos, this was originally for the electric cars that used a 7.2Volt or 8.4Volt pack so the main battery could also be used to power the receiver without the high voltage damaging the receiver.

The high current (Amperes) drawn by the more powerful servos like Digital types, big HiTech types and the Tonegawa can cause damage to the receiver so wiring the servos so they can draw the high current they need direct from the battery is a safegaurd for your receiver!

Some receivers will happily carry the high current without damage (KO Propo is one) so if you don`t have a problem with damaged receivers then there is no need to wire the servos direct it is only for extra protection really!!
Rob Lochier
ALRO Racing Systems
Engine Tuning/Repairs/Servicing

Quote:- "It`s only Toy Cars really"!!
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Postby rodders47 » Sat Oct 18, 2003 5:37 am

Hi All, well I have read and re-read this article and I am wondering if we all are not getting a bit confused here...

Can anyone explain WHY the red/black wires from the battery cannot be connected to the same colour wires of ALL the servos, then supply the Rx with a red/black wire ( for power) and just use the "SENSING wire ... white or yellow) from the RX to the servo. I had a servo fail the other day and upon opening it up I found the SENSING white wire had become disconnected from the circuit board. Power was still applied to the servo but it failed to operate because it never had the "POSITIONING' instruction from the RX
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Postby Lone_Ranger » Sat Oct 18, 2003 7:31 am

rodders47 wrote:Hi All, well I have read and re-read this article and I am wondering if we all are not getting a bit confused here...

Can anyone explain WHY the red/black wires from the battery cannot be connected to the same colour wires of ALL the servos, then supply the Rx with a red/black wire ( for power) and just use the "SENSING wire ... white or yellow) from the RX to the servo. I had a servo fail the other day and upon opening it up I found the SENSING white wire had become disconnected from the circuit board. Power was still applied to the servo but it failed to operate because it never had the "POSITIONING' instruction from the RX


Only some are confused, yes if you wanted to you could cut all the red/black wires and connect them together and run a supply for the receiver, my diagrams are done for use with "Y" leads so no wire cutting is needed. The white wire you refer to is called the "signal" wire as it carries the "signals" or "commands" to the servo!!
Rob Lochier
ALRO Racing Systems
Engine Tuning/Repairs/Servicing

Quote:- "It`s only Toy Cars really"!!
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Postby rodders47 » Sun Oct 19, 2003 6:17 am

Thanks Rob. it is , in my opinion, much easier to use the gold plated multi connection units for the Pos/Neg wire connection to all the servos and then just couple the "Signal" wire from RX to each servo.
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Postby Daytona7 » Sun Nov 09, 2003 3:28 pm

I have a question that might seem dumb but.....
I have an FG F1 that I have installed front hydros as shown in their diagram. Only problem is with the servos and their connections. Have a Hitech for throttle and rear inline brake and another for the hydro's. Radio and reveiver is 3 channel Futaba PCM. If I set my hydro servo as shown in the FG diagram and give the throttle a squeeze, the servo for the hydros applies the brakes. If I reverse the servo, the hydro boot is on top of the servo horn connection. I do not have a book for the radio nor servos. Any help and or a diagram for reverse wiring of the hydro servo would be greatly appreciated. Can mail to
"aenglishspringer@earthlink.net"
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