Servos Power draw

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Fly-n-Low

Active Member
I have a hydro that I want to put back into service. It has a .90 nitro motor and has a huge rudder and rudder servo. Analog I am sure. Will a Spektrum ground RX be up for the task?

Or will it draw too many amps? We are talking about a 90mph boat here...

The Spektrum worked fine for my Revos... this is a bit different?
 

Boats - I built it for nitro but

It is a super light 40 size mono. The deck came off one mono and the hull from another. I built it when I was working for Youngblood. I built so many monos I couldn't count them all, and this is the only one I have... Plus the hydro. So I was thinking about electric... Although it is rigged...
www.rc-help.com www.rc-help.com
 
A .90 nitro... is referred to as an engine and doesn't draw amps... if on the otherhand you do mean electric motor, that will draw amps and you just have to have a big enough ESC to handle it.

Also an RX ( receiver ) doesn't pull that many amps no matter if they are made for air or ground... its the servo's and the number of them that would add up on how much power is used. For that info, you'd refer to each make/models servo's spec sheet since a micro will draw less than a standard or larger servo. I would expect you'll need a larger servo for the steering but it's outside of any experience I've had ( all air ) although if you ran boats back in the day with a nitro engines, that power requirement would not have changed.
 
I know the nitro engine/motor doesn't draw amps. :twothumbsup: And if you look up the definition, they interchange, but that is an argument for another day. That was NOT the purpose of my query. I was trying to establish a basis for it. A .21 boat will not nearly have the stress on the rudder servo that a .90 boat will.

The rudder is my main concern, hence my question. I'll have to get a better look and some numbers... But it is twice the size of the other servos, at least. And we aren't talking micro either. Logic tells me it would use more power....?

The RX that I used 30+ years ago seemed to be more robust than they are now. "Seemed".
 
The motor/engine part was more of a CYA just in case you had posted incorrectly about what/which you were using.

The RX is a negligible part of the equation of power usage. While they do use a certain amount depending on what power level they are set for ( country dependent since the laws for the allowed power levels differ ), it isn't a big amount. Since different makes/models will likely differ slightly, it would be a spec you'd want to look up for the specific one you are using.

Servo's are also going to be unique on the amount of draw they are capable of which is why I said you'd want to look that up based on the make/model you are using. Even similar sized ones have different torque and/or speed values and therefor will also have different power draws. This is why I said this is the part you want to look up and pay attention to.

The part I forgot to bring up would be how the power is supplied and what it is capable of. I'm not even sure why/how I overlooked that part. Direct from a battery pack and what it can supply, will differ from an ESC ( irrelevant since you aren't using a motor, just included for others that may read this later ) can provide vs a BEC. I think most of the BEC's I've seen specs on list having either 3A, 5A or 10A of current and of course there are now different voltages they can provide with the advent of high power servos being a thing now.
 
Thanks Randy. I really appreciate your input. Using 6V pack for power. I have to take it apart. All the rubber bellows need to be changed. Pretty sure the servos are Futaba.

The rudder servo
 

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Looks like a standard size servo. if it's several years old it will be analogue so wont have very high power requirements.. maybe 0.5A or so. Just make sure you fit a decent Rx battery and you should be good. The receiver doesn't really factor into the equation as far as power supply to the servo, that's all about the Rx battery.
 
Well on my cars, trucks, boats, etc I use relays to lighten the electrical load. That is all I was thinking of. Over thinking I guess.

STD size? It is bit over 2" long. I figured the other two were standard... ? Pic of throttle and mixture servos 1.5" long:

So analog takes less power? I was thinking the other way around... Learn me something!!! :arms:

So it doesn't matter having analog servos with a newer RX, TX, etc, right?
 

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The physical size of the servo can only hint at the possible power draw... it's about it's torque and speed. You need to look up the specs to see what it can pull if you want to know. I've seen micro servo's pull as much as a standard simply because they had similar torque and speeds.

I suspect that digital servos pull more because they are newer designs and can have more torque and speed than the older model of servos... again, going by type or size isn't how you'd estimate it... look at the specs. Everything else is a generalization and isn't telling you anything specific.
 
Fly-n-ow.. actually you are correct in that the servo is larger than standard size.. but this doesn't make any difference. The receiver still doesn't provide power to the servo as such, the receiver is basically a 'pass-through' from battery to the servo. The 'weak link' as far as being able to pass enough current is either the battery or the servo plugs. Standard servo plugs can only do about 4A continuous so in most cases the plug would fail before the receiver did.

Bottom line is that if it used to work ok with whatever old receiver you had fitted then it will be fine with a new receiver. The new receiver may be physically smaller but that says nothing about the size of servos that you can operate from it.
 
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