Bundubasher

Hi,
I'm finishing off a new 2.5m Piper Pawnee, installing 8 x JR 591 servos (2 x elevator, 2 x ailerons, 2 x flaps, 1 x rudder and 1 x throttle). I'm using a Spektrum DX7 Tx with a JR RD721 Rx. Power comes from a 6.6 v LiFe PO4 battery.

The 2 x elevator servo's have a "Y" lead with a servo reverser on. The same goes for the 2 x flap servos.

Problem:
Everything powers up and works fine with 6 servo's connected - no problems. However, when I connect the 2 aileron servos (or the 2 x flap servos) , bring the total servo count to 8, the lights on the RD 721 and it's satellite receiver does not come on when switching the system on - everything is dead. However, when I plug them in with the system already switched on, it handles the 8 servos.

It appears that the system don't like 8 servos when it is powering up.

Have anybody had similar problem?, if so, what did you do to solve it?

I'm using 2 "Y" leads with servo reversers on it, how many servo's (maximum), can a DX7 system as per above handle?

Any advice will be appreciated.

Cheers


Bundu

BuschBarber

My Feedback: (2)

if you connect a Wattmeter or a Hangar 9 Current Meter between the Rx battery and the Rx, you should be able to determine how much Current the system is drawing when all servos and moved to the max. It should also measure how much of a Voltage drop there is.

I have used Y Harnesses for many years and they can be a source of problems. I will never again use Reversing Y Harnesses. They drift off Neutral often and require adjustments often. With 72Mhz, they can lead to Interference.

I prefer Channel Mixing or employ the use of a JR Matchbox or Futaba Servo Syncronizer instead of a Y Harness. In your case, you could use a Matchbox for the Ailerons, connect the Elevator servos to Ch3/Ch5 and connect the Flap servos to Ch6/Ch7. Use a separate Programmable Mix for each pair of servos. Aileron, Throttle, and Rudder would plug into their respective channels.

You could use a good quality HD Y Harness for the Ailerons although I would prefer to see you use a Matchbox. The Matchbox allows you to connect up to 4 servos to one channel and Match Neutral, End Points, and Direction, for each servo. In your case, you would only connect two servos to the Matchbox.

Bundubasher

BB,
I've connected the Hyperion Voltage sentry to the system while it is powered on - don't see much drop in voltage - hardly anything at all. That is why I was wondering about whether it might be something else.
Interesting comment you made on the reversing "Y" lead. I'm using the JR ones as I have all JR stuff.

Thanks

Bundu

BarracudaHockey

My Feedback: (11)

JR/Spektrum says not to use reversing Y's and amplified servo extensions with thier 2.4 systems.
http://www.spektrumrc.com/Experience...Practices.aspx

tacx

My Feedback: (1)

One way to check is to remove the Y harnesses with the reversing feature and connect with standard Y harnesses. Of course your servos will not be moving in the correct direction, but it will tell you if the reversing harnesses are your problem.

johnfly

It use to be the standard that about any rx could handle up to 10 amps before the little copper trails go poof !! I haven't had any problems running 5x5625 hitech and 2x517jr in a 1/4 edge 540 with a dle 30 and a 2100 life batt control surface throws are about 35 to 40 deg. so running 8 analog servos i wouldn't think would be too much..... as for the reversing thing.... I prefer to use hitec servos with a programer, then you can reverse the servo, change end points and the center position to the servo. Then you could just run a straight y harness. or as stated.... and i have done both. Use the mix's
I believe there is only 1 mix on the dx7 that will trim the slave servo on a primary control surface.... elevator...... "flaperons are a seperate function"

Bundubasher

Barracuda,
I think you hit the problem spot on, thanks for the link.

To everybody else that have contributed, thanks guys.

Cheers

Bundu