Calling all electronic gurus that use RC rx's! That means you!

[cadconversions]

Ok guys, let me setup the scenario:

I'm getting into flying some larger models and have ran into a problem where the digital servos pull more current than the rx/servo plugs are rated to handle from the rx pack. To compensate for this, they distribute the load over a few empty channels on the rx to enable a more distributed load going into each of the rx/servo plugs on the rx. So a 6 amp load is only 3 amps on each of the two plugs.

My thought is to open the rx case up and to solder wires between each + terminal on the rx and each - terminal on the rx and then run it outside the receiver and terminate it in a higher rated connector like power poles or Deans. This would ample load to the same place on the rx as plugging the batter into a servo port and it would also allow the servos to receive their power from servo ports as well.

This should reduce voltage drop and really work great.

Someone please tell me if this will or will not work. Help me out and we'll split the profits!

[AndyOne]

A better method would to be to use a servo synchroniser which is specially made for large models, it has a separate battery input which I think allows you to run the receiver off its own battery, reducing the load on its connector array.

http://www.futabarc.com/radioaccys/futm4155.html

Andy.

[Andy W]

What you describe yould work "ok" but you'd be modifying your Rx - not desirable if you ever plan to have it serviced.

What Andy (the other one) suggests is better, and you can make your own for not that much effort.
..a

[Acetronics]

Hi, Cadcon,

As you describe it your servos are overloaded ...so the reasonnable solution is to use twin servos, coupled through an as called " magic box "
Another way is to carry the power through large size cables, passing by the receiver connectors , with help from small PCBs to distribute power close to the servos WHICH MUST NOT BE OVERLOADED !!!

Alain

[cadconversions]

Alright, let me give a bit more info...

I'm putting a couple of 1.2 planes together with gas motors. Weight is at a premium so I don't want to add anything like what smart-fly has. I'm just think $2.00 for power poles and some spare 14 AWG wire I have and I'm done with a little soldering.

One plane is the Pitts M12 from Goldberg. It has 7 digital servos in the plane that when moving all together (remember 4 move everytime you move the ailerons) the amp draw momentarily exceeds the rating for the servo plug. If the 7 servos draw 6 amps (plugs are good for 3 amps max) then you have significant voltage drop if you don't completely fry the plug and loose the plane entirely. So why not just have a seperate lead coming out of the rx that you can plug a battery into. Then if each servo draws 2 amps each at the stalled extremes (14 amps total) then you've still not overstrained the plugs and have significant voltage drop.

Another plane is a 87" EF Yak that I'm starting shortly. Again, 4-150 oz/in torque servos, 1-digital throttle, and 1 - 350 oz/in servo requires a lot of juice. More than the plugs are rated for. The HS-5955TG draws 6 amps by itself when completely stalled. Of course, that really wouldn't happen in flight or the servo plug would melt anyway.

As far as warranty on a rx...not really a concern of mine. Must of my rx's are out of warranty anyway and I would probably just buy a new one if it stopped working with as cheap as the FM DC rx's have gotten.

Kevin

[lazy-b]

Cadconversion: if you like to tinker electronics you can make a separate Battery Pack for all your digital servo, and all the digital servo is connected to receiver thru an OPTO Coupler ICs, you might use 4N35......with this configuration, Both your Receiver and Digital use Separate Battery....and there is no electrical connection between your receiver and servo, and you can connect almost unlimitted no. of servo.....I guess this is commercially available...or make your own.....I remember seeing an Article in RCM magazine.

one nice thing about using Optical Isolation, if something happen to ur Digital Servo, it will not affect the Receiver function.

I would not recommend modifiying the existing Receiver.

Ellion

[fhhuber506771]

better solution than modifying the RX or servo(s) if you don't want to buy a "matchbox" or similar... get one aileron extension for each channel. clip the extensions in half. get a PCB "perfboard" and solder up a bussboard such that the red wires of all the servos don't lead back to the RX (it powers from some SMALL battery) and the red+black lead to a heavier guage wire to a heavy duty switch and the higher output battery pack (if dual packs there... you use 2 switches rated for the higher amp load)

It ends up costing nearly as much as one of the commercial power management boxes... (4 to 9 servo leads.. 1 or 2 switches.. circuit board... box to put it in) and all it does is split the power system between RX and servos... but at least if keeps you from melting the stock RX power switch harness.

[adamdb]

A few years ago JR had a receiver with a problem that caused a diode to expire if you put too much current through the RX. I saw a really nice turbine powered jet crash because of this after it had flown, out of control, over the heads of a good sized crowd at one of our events. It's too important to skimp on or trust a home brew design. This has been an issue for a long time due to large models with many servos, so someone has to have a commercial buss-bar device like you are thinking of constructing.

Adam

[vintage1]

I don't think they do, BUT its easy enough to make.

Especially if you can get a ribbon cable and header to plug into the receiver and so elminate all the little servo plugs on the receiver. You only need to carry signal and ground across.

If it were me, I'd probably permanenty hard wire the servos to it anyway, for safety - get rid of all the plugs and sockets, and then just have the receiver unplug - if necessary, but safety might say hard wire that in as well.

[cadconversions]

So vintage, your saying remove the servo plugs from the servos and solder directly to the rx along with the power supply?

[lazy-b]

I guess, Vintage is right, without spending a single centavos, and If you want it to be permanent, Just HARDWIRE it directly....Connect all those Red and Black wire together and connect it Directly to the SWITCH directly, and all those WHITE SERVO SIGNAL wire goes to the receiver.......This is the most reliable way to do it, this will eliminate LOOSE CONNECTION problem.

[cadconversions]

How would you power the rx?

[lazy-b]

The Receiver power connected directly to the SWITCH......we just re-route all those SERVO POWER CABLE directly to the SWITCH.

our main purpose here is to connect all servo power cable and Receiver power cable to MAIN BATTERY SUPPLY, to avoid voltage drop....I am assuming you have a main power switch.

To add reliability, you might eliminate the SWITCH, just use a DEANS Connector 30 AMPS (This is use by most RC Electric Car/plane/Heli)....Connect all those Servo and receiver power cable directly to the DEANS CONNECTOR.

I have encounter a SWITCH failure, due to long time of not using it, I guess the switch contact might have corroded, Fortunately, I have not take-off the Helicopter, and notice the servo is not responding.

If you Want to add a switch, I suggest add a two of more switches connected in parallel, to add reliability.....inspite our FUTABA SWITCH is a DPDT (its 2 switches connected in parallel), I also encounter a switch failure.

[cadconversions]

Ok, let's see if I understand....

Take all red/black wires from servo (+ and -) to a battery pack. Only run the signal wire to the rx's plug. Between the battery and servos be sure to have a switch present. I guess it would need to be a heavy duty w/ larger AWG wire than typical switches to handle the potential load. I like the idea of just plugging the battery into the wired together servos for a switch.

Seperate battery for the rx plugged into a normal port on the rx?

Thanks guys. I plan on cracking open a rx soon to take a look inside the case.

[vintage1]

Oh dear.

I had a drawing somewhere.

What you need to do is to get some verobaord or something, and use two strips to solder all the reds and blacks together from all the servos. Bring the receiver battery into those as well via a switch.

Now you have to take ONE red, ONE black and ALL the signals from there to the receiver.

I'd be tempted to use a bit of ribbon cable to do it and remove teh reciver connector wires. In fact, if it were me, I'd get a reciever DIY KIT with a separate decoder board and build the whole back end myself.

Can you etch a simple PCB? Are you preapared to do a little electronics?

Havbe you got a smashed receiver you can cannibalise for the connecors?

[cadconversions]

I don't know enough about electronics to etch my own boards. I can solder and I did make my own interface cable for FMS when I was starting out. Outside of that, you can forget it. I've just got more of an idea in my head.

I did take a rx apart last night. All of the + leads go to one etching on the PCB as well as the - leads. I plan on using my voltometer and using a battery check where the positive and negative feeds go between the two boards. If I connect the power at that point in the circuit would it have any effects vs. power coming from the connector point?

Also, why can't I just solder and heat shrink some wire to the battery post and bypass the servo type of connector completely or would I need to distribute the load across the entire PCB post? I'll try to take some pics today of what I'm talking about.

[lazy-b]

I think soldering the wire directly to battery post is much simpler.....using a PCB will just make it look nice......use a GLUE GUN to hold the wire and protect it from vibration.

[fhhuber506771]

Ok, let's see if I understand....

Take all red/black wires from servo (+ and -) to a battery pack. Only run the signal wire to the rx's plug. Between the battery and servos be sure to have a switch present. I guess it would need to be a heavy duty w/ larger AWG wire than typical switches to handle the potential load. I like the idea of just plugging the battery into the wired together servos for a switch.

Seperate battery for the rx plugged into a normal port on the rx?

Thanks guys. I plan on cracking open a rx soon to take a look inside the case.

The - lead as well as the signal lead have to connect from RX to servo. The red lead can be split to have the RX powered by one battery and the servo(s) by another.

If you build the board to do the split for all servos.. then you might also want to incorporate "glitch busters" into the board especially if you have long leads.

The Glitch buster (noise trap) can be found here::
http://www.uoguelph.ca/~antoon/gadgets/gadgets.htm
(actually here:: http://www.uoguelph.ca/~antoon/gadgets/noiserx.htm but the site's rules say link the main page instead of the individual pages)

******

The gadgets site can help you understand a lot about how the RC systems work...

[cadconversions]

Let me ask everyone this...

If I just solder the wires directly to the post then it will still provide the amperage needed in high drain situations becuase the small servo plug isn't restricting the flow any longer. Correct?

Otherwords, if I eliminate the plug that's only rated for 2.5 amps and solder directly to the rx, that solves the problems right?

[Zeta Phoenix]

Let me add another idea, using a glitch buster issolate the + power to the sevos there so u do not need to modify the RX. Let me try and draw this.

Ok, Sorry if it is hard to see.

You have a regular servo plug going to the Glitch buster (powering the buster) and a seperate bat for the servos. This could be done on one borad and would porblay weigh less than 1/2 oz.

-Jon

[cadconversions]

I'm not an electronics guy and although I've drawn electronics stuff as part of my training in college 9 years ago...I've forgotten almost all of it. I was really just looking for a simple idea to provide enough power for the 23-27% gassers out there without paying another $100 for smart-fly stuff and adding undue weight.

The great thing is that someone is going to read this and try a lot of these ideas and get something simple and easy for the masses.