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How many servos can I connect to one port

Started by Pitpixie, February 17, 2015, 18:54:50 pm

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Pitpixie

I am in the middle of a Stuka build and am a little confused as to how many servos I can y-joint together and plug into one port on my receiver.

I have a 6 channel receiver with 9 servos, the ones I am concerned about are the flap servos as there are 4 of them (2 for each wing) and the aileron servos (1 for each wing) so I will end up plugging 4 into one port and 2 in another...surely this cant be right?

Steve J


I would suggest doing one of two things -

1) Use a nine channel transmitter and receiver.
2) Use a Matchbox on the flaps.

Steve

Pitpixie

Thanks for that, I guess the Matchbox would be the answer for the flaps but would it be ok to y-joint the ailerons? these run mechanically opposite to each other so could run off the same receiver port?

Steve J

It is not uncommon to have the ailerons off the same channel. Personally, I don't as I am rarely short of receiver channels. If you need differential on the ailerons (more up than down or visa versa) then you will find it a lot easier to use two channels for the ailerons.

Steve

Kitten

Just thinking aloud.
I assume you want 4 servos for the flaps because of the split 4 separate flaps on those wings. Even using a match box the power is all drawn from the one reciever channel.
I've looked in the spektrum manuals I have but not managed to find a max loading per channel, so anyone know what the max amp draw isfor a receiver channel at 9.6volts (max for the ar600)

Steve J

Quote from: Kitten on February 17, 2015, 21:06:22 pm
Even using a match box the power is all drawn from the one reciever channel.


A nice thing about the JR Matchbox is that it lets you power the servos that it drives from a separate power source than the receiver.

Steve

Cactus

solder the 4 signal wires together, connect to the signal wire on the rx. then take a seperate supply from the battery ( must be the same one the RX is using ) and connect to the red and black wires.
then you're not using the rx's tiny strip of copper on the board to power anything.
I know you believe you understand what you think i said, but i am not sure you realise that what you think you heard is not what i meant.

Kitten

I stand corrected.
Still be interesting, reassuring to find the numbers though.
A quote from spektrum reciever manual.
"Important: Y-Harnesses and Servo Extensions
Do not use amplified Y-harnesses or servo extensions with Spektrum equipment. Use only standard non-amplified Y-harnesses or servo extensions. When converting an existing model to Spektrum, replace all amplfied Y-harnesses and/or servo extensions with conventional non-amplified versions."
Would the matchbox come under amplified?


PDR

Quote from: Cactus on February 17, 2015, 21:33:49 pm
solder the 4 signal wires together, connect to the signal wire on the rx. then take a seperate supply from the battery ( must be the same one the RX is using ) and connect to the red and black wires.
then you're not using the rx's tiny strip of copper on the board to power anything.


TBH if it's a Spectrum Rx I'd be more concerned about the current capacity of the signal wire than the power wire. The old 35MHz recievers (Futaba, JR, Mpx etc) used to be able to handle a lot of fan-out on the signal pin, but I've heard lots of problems reported with fanning out to much more than two servos with the 2,4GHz receivers (especially specky ones, but that could be just because there are more of them out there) and they all traced back to low voltage levels on the signal wire.

I think it's probably because the 35MHz receivers had a simple CMOS demultiplexer with the full Rx voltage (5v) to drive the servo signal outputs, and they had quite a lot of headroom in current capacity. But in the 2.4GHz receivers the servo outputs come directly from data lines on the processor, and it's a low-power processor that has much less headroom, as well as being only 3.3v to start with.

PDR
There are no shortcuts on the long, hard road to success. But if your dad's rich there could a limo service...

Pitpixie


idigbo

Could you mechanically link the inner small flap to the larger outer one each side? Cutting out the issue completely? Build in a tube into each mating flap end and connect using a length of wire or Bowden cable glued into one section. Works great  :af  What is the Stuka, kit, plan etc etc.

Ian.
THIS MAN KNOWS NOTHING AND SHOULD NOT BE LISTENED TO OR TRUSTED!!   -  Forum admin.

itsnoteasy

Quote from: idigbo on February 19, 2015, 13:16:22 pm
Could you mechanically link the inner small flap to the larger outer one each side? Cutting out the issue completely? Build in a tube into each mating flap end and connect using a length of wire or Bowden cable glued into one section. Works great  :af  What is the Stuka, kit, plan etc etc.

Ian.


  The above will work fine  as most of my set ups use that system ,, However I too use spectum for & many years now run 4 analog servos on flaps @ 6v  on a scale Hawker Hurricane without problems.

FrankS

Quote from: itsnoteasy on February 19, 2015, 16:27:47 pm
   However I too use spectum for & many years now run 4 analog servos on flaps @ 6v  on a scale Hawker Hurricane without problems.


All plugged into one receiver socket? It's not the power to servos that is the issue, but if one signal output has the capability of providing the signal current to 4 servos. I know somebody who could get a set of EFlite tricycle retracts to work until he used the splitter lead they came with instead of a couple of Y leads he had.

kinverflyer

Quote from: Pitpixie on February 17, 2015, 18:54:50 pm
I am in the middle of a Stuka build and am a little confused as to how many servos I can y-joint together and plug into one port on my receiver.

I have a 6 channel receiver with 9 servos, the ones I am concerned about are the flap servos as there are 4 of them (2 for each wing) and the aileron servos (1 for each wing) so I will end up plugging 4 into one port and 2 in another...surely this cant be right?


The concern I would have in plugging four flap servos in to one port is the load exerted on to a flap servo when in flight, this is then transmitted back in to the receiver in the form of higher amps and you could end up overloading the receiver, there is one way to improve this situation mechanically is when thew flap is fully deployed the servo arm is a flat as possible.
I would go with a 9 channel receiver and spread the load.
SM Services used to do a nice little unit that would take the load off the receiver, unfortunately they have ceased trading, you might pick one up second hand, they are a lot cheaper than alternate units.

JohnMac

I was just going to make a reply to this thread but I see PDR has made it before me. I would recomend a larger Rx with the correct number of ports. Signal charge deficiency is a real problem with some modern Rx's, especially if you are using older servos.
This route also ensures that you can easily fine tune your flaps from your Tx.
John

FrankS

Quote from: JohnMac on February 20, 2015, 08:54:34 am

This route also ensures that you can easily fine tune your flaps from your Tx.
John


Providing your Tx has more than 6 channels, allows you to have 4 flap servos and lastly you can program it  ;) I have friends who don't even put aileron servos on separate channels because they find programming daunting.

itsnoteasy



Or you could just Use Bellcranks & a High torque servo  as done in the days before  computer tx's.
 

PDR

Ah, yes - mechanical mixers, Dodson linkages, jumpers for goal posts...

Used to fly a 63", 61-powered Spitfire with both ailerons driven by pushrods and belcranks to a single Futaba FD-16 (1kg-cm), with the airborne system (including retracts & flaps) running form a single 4-cell 500mAh DEAC. And we'd get a day's flying out of that, but in those days we knew how to do it without brute force...

PDR
There are no shortcuts on the long, hard road to success. But if your dad's rich there could a limo service...

SteveBB

Quote from: FrankS on February 20, 2015, 13:24:21 pm
Providing your Tx has more than 6 channels, allows you to have 4 flap servos and lastly you can program it ;) I have friends who don't even put aileron servos on separate channels because they find programming daunting.



Exactly. And it depends if the Tx has the 'mixing' capability to run 9 servos by dodging it. Personally I'd dump the Tx and invest in a Tx that can handle it, and get the rx to suit. I've run 8 channels from a 7 ch MPX Cockpit SX, but; a) it had the mixing ability to do it and b) I used a Y lead for spoilers and a second battery for the retract and tow release. I wouldn't have attempted to try and run 9 or 10 channels.
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