RC India

Guys,

A servo is only connected to receiver right? In the sense there is no external connector to the battery. If that be the case, then specs of the servo goes like this "peak load of 3amps" whereas the operating current of a Rx is in miliamps. So where does the extra amp come from?

Am I missing something?

Pankaj

I am not sure where you got that information, but the current that the receivers can handle is multiple amps (3A, and much higher in most cases).

For example, see the Futaba's answer to this question (the last question on the page below), which points out the bigger issue of voltage drop.

http://www.futabarc.com/faq/faq-receivers.html#q878

BTW, you should get an award/prize for asking the right basic questions that any beginner should ask  {:)}  ;D 

Also, the typical operating amp draw of servos (unless they are stuck or something) is well below 3A, in fact, typically they are in the 0.25A range even for the full size servos.

The rx becomes the conduit thru which the current to the servos are given. Any momentary surges upto 3amps per servo due to the start and stop of a digital servo or because of the load may be acceptable, provided no other actuation occurs at the same time.
 You are right, there is a max'm current capacity. If the servo in question has to have higher current requirement, then it is better to connect only the signal wire from the rx and connect the battery separately to the servo(s).
One effect of having high current discharges thru the receiver is to have the copper tracks on the rx board heat up and disrupt normal operation of the rx (Futaba 2.4ghz FASST Rx  .... Chan's crash investigation)

Saju

Anwar,
I was actually browsing the hobbycity site, came across a spec of Corona Rx which seemed to be the only one with a amp rating. The link is given below

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=8527&Product_Name=Corona_2.4Ghz_6ch_Receiver_(V2_DSSS)


The main specs given are

Spec.
Size : 46mm*25mm*16mm
Voltage : 4.8 V - 6V
range : more than 2100m
Operating current : 30 MA
Sensitivity : -100dbm
Latency : 22ms

Personally, I think the operating current is 30mA and not 30MA which makes it 30 milliamp.

 In the servo section of the same site, for a metal gear 16gm servo (http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=8761&Product_Name=BMS-385DMAX_Digital_Servo_(Metal_Gear)_4.2kg_/_.15sec_/_16.5g)

one of the line in the description says that "MOS-FET motor driver chips that can handle 7A peak loads".


Now it is logical to assume that no would put in a mosfet to handle 7amp if the operating current is <= 30 miliamps.

Also in the site, I did not see that there are receivers marked for bigger servos, so  I am assuming it would be the same receiver. Also, it is natural that to hold on to a larger torque, more current would be required.  The question originated from this comparison.

As for my asking the right question – I guess thats age for you ... :-)

Pankaj

What the Corona RX specs mention is the amps drawn for its own operation.  But an RX also allows battery power to pass through it to the servos (as a conduit), that is different from the "operating current" mentioned. 

It sort of becomes a question about the overall current handling capacity of the materials/components used in the RX (as compared the amps drawn by the RX itself).