How long is too long?
 

Since the tomcat is back on the building table :(, I think im going to redo some stuff and I was wondering if having my robbe battery backer in the very front with very long sbus leads to the tail is bad? I know its a common problem on very large aircraft with long servo leads which causes a drop in torque. The leads the battery backer uses are very thick but i was worried about torque loss to the stab servos. I could move the battery back back about 12 inches but thats about it.

Keith, look at the length of the stock leads they give you with the battery backer... Easy 7-8'! Doubt they would give it to you if it wasn't ready. Now if you overloaded that strand with 10-12 servos???????

Well you can get leads for the battery backer that are 12 feet long so I'm guessing I'm good since they f14 is under 100inches

Fenderbean,

Have you flown your Rebel Pro?

What is your operating voltage? In giants I typically use 7 - 8 VDC (2S LiPO) and then use HV servos that give me the torque I need at say 6 VDC.

Digital servos are power hungry. They can all be moving at the same time. I calculate how much current the entire system needs and verify that the power system can supply that + 50%.

In Giants I stick with HD servo leads and power wiring. Also, every servo has its own power supply line.

May be a bit over kill. But when we are using a plane where there are spectators stuck in their chairs, we can not have a large plane land in their lap(s).

David, I have not flown it yet, with the crash and then holidays I havent had a chance. I heard you guys are having a jet fly on the 2nd? I thought about coming down and trying it then but thats in the air as well since I may have to take a trip to south alabama that day to check on my house. It really blows not having a flying site here, I need to just join the bowling green club and go there.

Todd, yeah im using 7.4 volts to the stabs/rudders, I have two of the large leads going to the tail, its a big overkill since one would suffice but I have two servos on each lead and each wing has its own lead as well.

Keith I wouldn't worry too much about it. 10 to 12 inches will add next to nothing in the wire resistance.

You are using 7.4v going to a servo that will perform with loads of torque down to 6 volts.

Agreed. That being said, the best way to minimize voltage drop over long distances is with larger wire. I have a roll of heavy duty servo wire that I make all of my leads out of. It takes a couple of minutes to make a wire, and it will be exactly the length you need. Shops that cater to the giant scale crowd typically carry HD servo wire and ends.

Scott

Thanks yeah the leads that come with the battery backer are much larger than the th heavy duty servo wire you buy.

What Pylonracr said. To expand a bit:

If the wire is fat enough, the operating voltage low enough, and the amp draw low enough, then there is practically no loss due to longer leads. Play with the calculator in the link below and you will see that even at 10 FEET, the voltage drop on a 7.4 volt 18ga line drawing 3 amps is less than 1/2 volt.

In in other words, use good fat wire and there are no worries.


http://www.calculator.net/voltage-dr...res=60&x=0&y=0

Keih
You will be fine. The HD servo wire is sually 18ga, depending on brand. If your wire is larger, and you ran 2, you have the capacity to carry more current than you will be able to use.
Scott