Channel Expander? - Page 5 - RC Groups
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Dec 12, 2012, 12:32 PM
I run 12awg on all of my setups. I know that my 33% Extra 260 with 7 JR8711 servos pulls about 230ma sitting idle and peaks of over 60A when doing a snap to snap maneuver. People don't realize that servos draw 2-5 times their stall current during a direction change... albeit for a brief period of time, it still happens and can cause a lockout of systems that can't handle low voltage situations.
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Dec 12, 2012, 02:46 PM
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theKM's Avatar
Quote:
Originally Posted by JimDrew
You won't need a regulator as this has one built in (500mA), and the Nano needs about 20mA max. You could use 2.5v to 25v for the input, but that voltage gets passed to the servos. I think pads are the way to go. I will just fill them full of vias (through holes) to prevent copper delamination. I will also use 2oz double pour (top/bottom) for power and ground to the servo pins.

Now, the question is, how many outputs per channel. I guess with the Nano, since you can do all of the servo reversing/matching in it I would only need a single output for each channel. Thoughts?
Wasn't too worried about the Nano as it can take 16v as it is... more that people will solder switches and regulators to power the servos, cuz that's simply what they do.

If there were 16 outputs total, and could configure each pin to be the channel you want... that would allow 16 separate channels, or grouped channels as needed. needing more than 16 outputs to me seems like a pretty cool excuse to get a second expander. I have yet to see a full smartfly pro.

Servo matching in the Nano isn't capable enough for the giant aerobatic crowd... need to match end points and have some way to make settings changes with the servos powered and driving. Hitec's kinda-sorta give-the-servo-a-little-power is enough, but matchboxes are nicer to program as the servos have full power and driving as if they were flying; easier to use the ammeters, etc.

For the big expander, my thoughts would be that whatever makes it most useful for non-XPS receivers will help spread the XPS love overall. Reading S-bus or the Spek satellite, get the rx part up and out of the way, super setup for servo power and output value-adds... is wunderbar. Smartfly are bringing out a box that the 14 channel Futaba Rx simply plugs into that connects all the pins on the receiver, and is just a power expander. It's going to be expensive. But the xps expander would allow their full range 6/8 channel s-bus receivers to be up wherever, snorkel style like the Nano, and still get all the channel outputs and power expanding... this will save $100 for the Futaba dudes on the price of just the receiver let alone the expander.

...being able to snorkel the receiver is pretty sexy, but sales to the non-XPS crowd will be mostly about a sexy matching solution. Even just using an app on the PC to inc/dec values for any channel while the servos are driving would be a huge win.
Dec 12, 2012, 03:59 PM
Registered User
E_ferret's Avatar
Quote:
Originally Posted by theKM
...being able to snorkel the receiver is pretty sexy, .
I don't quite understand the advantages of using a miniature diesel to power the receiver.
Dec 12, 2012, 05:21 PM
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theKM's Avatar
snorkel is a much more amusing word than "remote" or whatever... the system needing a snorkel in order to breathe clean less-RF-noise air
Dec 13, 2012, 02:59 PM
Registered User
E_ferret's Avatar
Quote:
Originally Posted by theKM
snorkel is a much more amusing word than "remote" or whatever... the system needing a snorkel in order to breathe clean less-RF-noise air
I understand your train of thought; snorkel, diesel, submarine, torpedo, explosion,
ship, sinking, into the deep, bathycaph, James Cameron, remotes, Jim Drew,
XPS, 2.4GHz, receivers, Nano, single antenna, RF, noise, rejection, wife, ... but I digress.
Last edited by E_ferret; Dec 13, 2012 at 03:15 PM. Reason: syntax
Dec 21, 2012, 03:04 PM
Barefoot Birkinsomething
rcbirk21's Avatar
this sounds like a pretty cool idea, would definitely like to see pics when the time comes and see how a setup procedure would go
Dec 21, 2012, 05:25 PM
There is a picture of the original design on the 2nd page of this thread.
Dec 21, 2012, 05:44 PM
Registered User
Quote:
Originally Posted by JimDrew
There is a picture of the original design on the 2nd page of this thread.
Really ?? Do you expect people to actually read these threads ?? That would be a novel idea !!!
Dec 21, 2012, 10:45 PM
Registered User

RF filter use?


Quote:
Originally Posted by JimDrew
The great thing about 2.4GHz is that it is immune from virtually any type of noise, such as from ignitions, metal to metal contact, etc. The servos, however, are not. So, an opto-isolation circuit will offer no benefit.
Hi Jim, Does this mean that the RF Filters, such as the ring style JR PA029 that the esc wire wraps around several times at the rx end are not needed with 2.4 systems? If so, I've wasted a lot of money. Thanks, Bob.
Dec 22, 2012, 12:10 AM
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theKM's Avatar
Quote:
Originally Posted by flyingfever
Hi Jim, Does this mean that the RF Filters, such as the ring style JR PA029 that the esc wire wraps around several times at the rx end are not needed with 2.4 systems? If so, I've wasted a lot of money. Thanks, Bob.
not really wasted because the servos are not immune to that noise... receiver is fine, but that doesn't matter if the noise is making other components go crazy.

The problem with the other bands like 72mhz was that some of the noise was being picked up by the receivers and was turned into servo output commands... at least with 2.4 it means that the junk isn't turning into an actual servo command, but servos still have to deal with the junk on its own merits.
Dec 22, 2012, 12:00 PM
Correct... the servos still can be affected by the noise, although good digital servos should not be - analog servos definitely will be.
Dec 22, 2012, 01:28 PM
Registered User

filters


Thanks guys, I'll keep using them. Not much weight gain, and maybe a little insurance.
Dec 27, 2012, 11:16 AM
Just an update... I finished the design for the new separated RF section. I am not sure what to call this yet. The unit can be bound using either a command from the servo port side (not sure what to call that yet either) or via the push button. This way you can bury the RF portion in the fuse and you don't need access to the button to bind it later. The RF portion can output a XPS, Spetrum, Futaba S-Bus, or PPM data stream. The servo portion will retain the failsafe, channel mapping, reversing, etc. information. This allows you to simply remove the RF portion and put it in a different airplane without having to change all of the settings again. The RF portion is what sends the telemetry data, but the servo portion will be the interface to the telemetry devices.
Dec 27, 2012, 01:36 PM
Barefoot Birkinsomething
rcbirk21's Avatar
Quote:
Originally Posted by JimDrew
Just an update... I finished the design for the new separated RF section. I am not sure what to call this yet. The unit can be bound using either a command from the servo port side (not sure what to call that yet either) or via the push button. This way you can bury the RF portion in the fuse and you don't need access to the button to bind it later. The RF portion can output a XPS, Spetrum, Futaba S-Bus, or PPM data stream. The servo portion will retain the failsafe, channel mapping, reversing, etc. information. This allows you to simply remove the RF portion and put it in a different airplane without having to change all of the settings again. The RF portion is what sends the telemetry data, but the servo portion will be the interface to the telemetry devices.
that sounds cool. so are you saying the servo extension that would connect this channel expander can be used for binding as well?

Would you even need to bind it if plugging into a nano rx?

and i am assuming you are not far enough along to know this, but how long of an extension can you you use?
Last edited by rcbirk21; Dec 27, 2012 at 01:43 PM.
Dec 27, 2012, 02:16 PM
Registered User
How robust is the RF link regarding number of antennas and diversity? And what is the maximum distance between the antenna and the RF section?


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