[fullspool]

Originally Posted by TManiaci

The current makes a loop. We are measuring drop at the half way point, where the demand is, where we make the voltage measurement. The drop from the source to the target is one wire carrying current.

I think we agree, the drop to a servo is no where near 3V. Not even at 17 amps.

The demand would be at the device requiring the power to function, not necessary half way point. Regardless I think the whole 3v thing is bogus!

If I get some time this weekend I will try to make a 20awg extension fail and monitor the current input.

[TManiaci]

Originally Posted by fullspool

The demand would be at the device requiring the power to function, not necessary half way point. Regardless I think the whole 3v thing is bogus!

If I get some time this weekend I will try to make a 20awg extension fail and monitor the current input.

Check that. You are correct. It's the whole loop length, so 2X is correct. Sorry.

[BillFromPerth]

I run a power expander and dual batteries on anything 100cc and over.

[Funboy]

+1,
and a dollar three-eighty to boot.

I have seen and heard of many, many planes being lost due to brown-outs from low voltage. Typically after a snap or a blender. I've seen brand-new 50" electrics (expensive ones with top-quality gear) slam into the ground because the RX browned out, and the owner did not realize a BEC was in order on a model that size, being flown hard. After watching and hearing about several 100cc+ birds crashing from brown-outs I took heed. I'm too paranoid to take risks like that. And too cheap to be replacing airframes! Let alone risking someones life on the ground.


There are many failure points on our GS planes- and slide switches are one of the biggest culprits. Contacts get dirty or worn, or they just get old. Taking an old HD switch out of a 5 year old model and throwing it into a new plane is scary to me, and an unnecessary risk. I have a bag of used HD switches- almost a dozen of them that I don't trust in my big planes. For peace of mind I run dual battery's at minimum, some form of power expander, Fromeco Wolverine switches, Miracle switches, or electronic switches on all my 100cc+ aerobatic planes. In most cases I even cut off the JR/Hitec/Futaba servo connectors and splice in Deans that plug straight into my batterys and power expanders. I even make Deans Y's with multiple servo connectors in my planes that don't have power distribution systems.

Now that I'm flying 2.4 I'm even more aware of brown outs. Both my big aerobatic planes have power expanders- One Smart-fly EQ-10, and a Powerbox Royal. Before that I ran Weatronic units with multiple regulators, dual power inputs, and dual RX's built-in.

I do have a 1/3 scale 100cc Super Cub that runs on one flight battery, one Miracle Switch, does not have an expander, and it draws less than 1/3 the power my of my aerobatic planes. It's not necessary in a plane like that.

Basically- if you're willing to drop $1600 on an airframe, $14-1800 on a motor, and buy a dozen top end digital servo's for over a hundred bucks each, a $200 power expander doesn't seem like a big deal. Especially if you want your $1400 in servo's and $150 RX to function properly.


This is all my opinion- I have no data to back up my position- but I am all for redundancy, and peace of mind. Next to the THOUSANDS we invest in our airplanes, I can't see how an extra $200 is going to break the bank.

Sorry for rambling- I've been programming my Powerbox for the last 2 hours. All my servo's are matched and happy now!

[Dadstoysbg]

The one volt number I was given was a "could be" not all the time and it was on the battery side. It also depended on the quality of the servo connector and wire used.
Which creates more heat volts or amps. I had a electric fence on my farm. the wire carried 5000v but very little amps. Yes did hurt bad if you touched it, but it would not harm you.
The amount of voltage drop it seems can be argued with or without a power system. Still is the drop enough to cause concern.
Yes I have called two of the major radio companies and am still waiting for the return calls.
Horizon did tell me in their testing their servo connectors will melt at 6amp. Nothing was said about wire failure. They also said that their fail safe receiver bus bar was tested to 60amp.
So it seems we have two questions. One is about voltage drop and the other is amp draw.
If there is enough voltage drop to affect the servo performance then there could be blow back on the flight service.
Also we could see slow damage to the switches if we have high peak amp draw. Any kind of harking across the switch that could cause a burn that would get worse and failure of the switch in time.
Hopefully I will get more information from the companies and pass it on. Dennis

[TManiaci]

The Powerbox line uses a remote switch that does not carry any load, it's used to switch solid state switches in the battery sharing circuits.

If you drop voltage to your servo, it will absolutely result in less torque and speed. On my giant 55" DWFoamies Yak, I was getting terrible "blow-back". At any significant speed the Ailerons would only deflect about 20% of full throw. Very mushy performance. I added a UBEC, which supplies 6V to the buss, rather than the 4.8V that comes out of the ESC. The increase in servo performance was huge. Now I get full throw at full throttle, and much quicker response too.

[Dadstoysbg]

This is Tues. and i still haven't heard from any of the companies. I really wonder if they truly know the answers. I suspect JR/Spektrum know this is a issue or they wouldn't have made the powersafe receiver. I have heard (this is second hand) that Futaba receivers bus bars are rated at 10amp, but then again Futaba will still tell you that 6v is not recommended. right now with what little I know I think I'm going to use a power box of some kind.

I'm looking at the Smart Fly Power Expander Pro. It uses a safety switch. I also considered using a JR/spektrum safety receiver but it boils down to money. The jr receiver is $249. which means the $100 receiver i now have can't be used. that really puts the price of the change at over $300 and I still need to replace the batteries. If i use Smart flys system it's $149. and still use my receiver.
Chad who owns Taildraggerrc.com is a friend of mine. I will use his A123's with the heavy wire and deans plugs.

This is my birthday today and it proves you can still learn something new.

I have to admit that after all these years in GS planes I thought these power boards weren't necessary. I know believe they are.


With jets I'm still not sure.
Even with the higher speeds we're not banging the sticks as much and use only one or two flight surfaces at a time very very low rates.

This is still a question to answer. Dennis

[RRRitchey]

The actual voltage drop depends on ohms law, V=IR. Here is a photo of a 24" extension, 6V in, 3A load pulsed at 1KHz. These are very good connectors. This shows that you loose almost 1V over 2 connectors at 3A. At 6A it would be nearly 2V, etc. This does not include the switch drop due contact resistance. I am going to get some JR heavy-duty switches and see how much the contact loss is. Remember, the battery connectors carry the sum of the currents for all servos. In the example I gave Dennis, our 100cc Aeroworks with eight 8711s was drawing almost 18 amps worst case. With 2 leads into a receiver from 2 batteries this would be a drop of around 3V between the batteries and the receiver bus.

[Dadstoysbg]

Thank you ritchey. Now we have a possible 3v drop to the receiver from a123 at 6.6v. Now we have to handle the resistance from the plugs and wire to the receivers. This could be small based on the wire gauge and quality of the plug, but worst case is a 8711 rated a 400+oz at 6v only getting 2.75v. Now what is the amount of torque the servo gives you. Maybe 200oz.

No good answer but you'll see your not getting what you paid for in servo torque. Dennis

[SSG]

Ohms law is tricky for such a simple little equation.

Even after I'd been through a year of avionics school, I know not engineering but still more than a passing familiarity, I thought my dad was full of it when he told me it's important to start the engine on a twin closest to the battery first. I said that doesn't make any sense. You've got that huge 1/0 gauge cable.....how in hell is there going to be a voltage drop across it. At several hundred amps it's simple math. Oh well I was young and thought I knew it all.

This also comes up when people's battery connections become corroded. At no load the voltage will show the same as battery volts. Once the current starts to flow the connection can actually break down to the point it will not crank the engine.

I know this is redundant for a lot of people but perhaps not for others.

It would be really cool if someone with the instruments could do the testing and video tape it for all of us to see first hand.