Chas

My Feedback: (16)

Hi, is 11 standard servos too much to run thru the receiver ? I am using a 6 volt system

Chuck.

dirtybird

My Feedback: (5)

I guess that would depend on the type of servos, the receiver and how you intend to use them

GhostRider32

Possibly. Depends on the size and how many servos are drawing current at the same time and how much current each servo is drawing. What kind of application? I and many others have switched over to A123 cells for battery packs. With that many servos, I simply wouldn't trust anything other than than high current A123 packs. They can sustain 33 to 70 amps continuous depending on battery.

Campgems

Granted the battery will do it, but will the receiver hold up to 30 to 70 amps? My guess is no. That is a lot of current running through the lan patterns of the voltage distribution system of the receiver. I'm perty sure that the little servo pins and contacts are not rated at 70 amps and that is what you would be asking of them if the receiver was your only voltage distribution system.

Don

rmh

The constant duty rating of the servo connectors is 3 amps
Ihave run em under constant 4 amp loads and THAT is all they will tolerate
They will carry higher spikes tho but that depends on the wires and the pins
The ratings you see on servos are NOT constant power just blips.
so 6x3 =18 amps at six volts is about a practical limit on the buss with all six power pins loaded on a six channel setup
You can use a power expander setup and draw larger loads
BUT you are back to what will the seros/leads and connectors really carry
Take yer super duper servo setup and fly the crap out of it then check to see where the actual hot spots are.

GhostRider32

No doubt that the receiver pins are only good for a few amps. I should have mentioned that also.

Campgems

It's susprising the amperage you can poke through a short foil pattern, as there is almost zero resistance and as such little heat is generated. However the pins are another issue. There is quite a bit more resistance, still very small, but still more than a short lan patern. On top of that, the contact area is very small. You have at best, the width of the pin times two (front and back) times an actual contact area of a couple thousandths of an inch. Three or four amps going through that small surface contact area is going to create some heat and as soon as it does, things go bad. One servo isn't the issue as much as the battery input pins.

I used to work computer repair, not PCs but the big monsters. One machine had bus bars from the power supplies to the circut boards. The bars were 1/2" thick x 4" to 6" wide copper bars and they run hot to the touch when the machine was running. The power supply circuits were susprisingly small compaired to those bus bars, and while they required a watter cooled heat transfer, they were up to the to the task. When I ask the power engineers about this they pointed out that the paths were very short and there was no sliding contacts, so there was very little resistance. The big bus bars were the biggest heat producers that were not cooled. All the logic modules, 9 of them, plugged into the board with pins the size of our servo pins. There were 1500 pins to a module and about half were voltage pins though. The whole system was designed for heat transfer and worked very well. Our receivers are no where as well designed in that arena.

Don

P-40 DRIVER

If we are talking about 40 oz standard servos running through an 8 channel receiver using a good power supply such as dual nicads etc. I cannot see that this would be an issue. We would need more info to make a real judgement.

rmh

As long as everthing is in good repair you are fine

Campgems

I aggree. It would be nice if Futaba, JR, and others would publish some numbers. I know I've ask in the past what the current draw on a servo at maximum load was and got a really musshy answer. With the planes we are building today, for example a P-61 I'm building, the number of servos is way more than four, and closer to a dozen. If this wasn't a real issue, things like the JR match box and the Smart Fly systems wouldn't exist. Thank goodnes for the likes of RCUniverse to keep us informed and if not solving a problem for us, pointing out that me may be running into a brick wall.

Don

Chas

My Feedback: (16)

Thanks Guys for the info. The airplane is a twin engine cessna 421. there will be y connectors on the ailerons , flaps, throttles. the receiver is a JR 9 channel pcm 72 mhz. The battery is a 2700 mah Nimh.

Chuck.

BaldEagel

IMO you will have more problems with the Y connections than running 9 servo's off a 9 Channel Rx after all the Rx is designed to take 9 servo's, by using Y connectors you are doubling the amps through one set of pins.

Mike

rmh

That particular size NIMH has shown to be of the later type NIMHwhich really must be correctly "formed" when new
this means NO fast charging for first cycles
then you should do a capacity test .
WHY?
these may show fully charged when only a small charge exists . The situation is caused by not fully exercizing the cells with a 1/10 or less initial charging.
Not trying to scare anyone but having checked a numberof these for friends I found way too many were not operating to full charge - some at les than half.

dirtybird

My Feedback: (5)

I tested several servos and can give you a spreadsheet for the ones I tested.

GhostRider32

Dirtybird,

Would you mind PM'ing me the sheet. I'd like to see the current draws. Thanks.

dirtybird

My Feedback: (5)

I tried to pm the spread sheet but it is not supported by rcu PM.
Here is the current plot of the 8611
The current plot is too large for PM

GhostRider32

Thanks.

Rodney

Dick Hanson in his post said it all. The amount of current you can safely used is a function of the cross section of the printed circuit traces in the receiver. Now most receivers use 1 oz. copper plate which is very thin. As they reduced the size of the receivers, these traces have been made very narrow. You can compute the cross sectional area of the trace and, if you know the thickness of the platting, compute the maximum allowable current. I am quite sure that on many of the smaller receivers, you are flirting with early failure if you exceed 5 amps on any trace - the pins themselves will handle slightly more as long as the connection is not broken during maximum current flow. Remember that the current in that little narrow trace on the power buss will have some section carrying all the current for all the servos combined. On large planes with digital servos, it is almost mandatory to use a power distribution box for maximum reliability if many servos are used.

dirtybird

My Feedback: (5)

Eloy Marez made some tests on the receiver many years ago. He published the results in High Flight or the AMA magazine. I think if I remember the pins and foil were good enough for at least 10 amps.
At any rate, the servos draw less than 4 amps maximum. In normal flying you would never draw more than 1 amp unless the servo were stalled. Then you would probably have other more severe problems

Campgems

As Rodney pointed out though, receivers are getting much smaller and therefor the circuit lands are getting smaller. An example is the Futaba R6014fs. Fourteen servos drawing an average of just one amp would put you over your 10amp threshold. The "many years ago" data may not be valid with todays receivers

It would be interesting to test to failure on a couple dead receivers. IE plug a strong battey on the battery port with an amp meter and then a varaibal load on the other end of the buss and increase the load to the point of either pin contact failure, or lan pattern failure.

I don't have a dead receiver that I could contribute, or I would do it.

Don

dirtybird

My Feedback: (5)

Fourteen servos would not draw 14 amps. I would guess the average current draw of 14 servos in a flying system would be 2 amps. 1 amp is probably the most one would draw for a very short time. Remember most of the servos would not be moving most of the time.
The pins and the lands on the new small receivers are the same size as they have been for the last 30 years.

BaldEagel

The new Futaba 6014HS has the facility for 26 proportional channels and two switched channels, two sets of eight servos off one Rx input using the MPDX-1 system, so I am thinking that the 8 amps statement from Futaba is possibly per output and not the Rx's total safe amperage, admittedly the MPDX-1 system does allow a seperate battery to be used, but the input is still from one Rx output and they do not say you have to use a seperate battery.

Mike

Zeeb

My Feedback: (41)

I wouldn't count on that conclusion, it's my understanding that it's 8 amps total through the rx.....