i have 2 new hi-tec digital servos,they work fine alone ,but when hooked up to a y-harness ,they stop working.why?i'm using an 1800 mah ni-cad pack .

Best guess is that together they are sinking too much current on the signal lead for your receiver to drive. Using a Futaba 149DP receiver by any chance?

I have seen the same thing happen when using a JR RX too. I think that the Y is creating some sort of feedback loop between the servos and generating lots of RF. Personally I would never run a Y cord in any of my airplanes.



Shawn

I have 2 Hitec digitals on a Y-harness to drive split elevators on a Seagull Harrier .90.
I use a Hitec Supreme 8 receiver and an 1800mAh NiMh 5 cell battery (6V). I have not seen any problems in this configuration. Not sure what's up with your setup.. Just thought I'd let you know that I'm running a similar setup successfully. Oh the Y-harness is a 'buffered' harness (i.e. uses some battery power to reconstruct the servo signal to each servo independently)... Have you tried to buffered Y-harness??

I had 2 5945s on my rudder on a y-cable, and had no problems.
It was a Futaba PCS reciever, and Fromeco batteries/regs.

What model servos are these.?

tower part number LXXA48 its a futaba dual extension/heavy duty. I use this with for all my Y-harness aplications. When I got my first giant scale plane (it was used) I imediately replaced the servos as what was in it was standard. Anyway I striped a servo just setting up linkages becasue the servo was so confused with the long leads and long y's, they were jumping everywhere when I turned the switch on. At first I thought that the cheaper high torque servos were the problem so I sent them back and got good futaba's, same problem only I got the switch off before something tore up in those sevos to. Went and did some reading and decided my problem was to small of wire and to long of y'harnesses. I use the futaba dual extension and Hobbico pro leads, they are one guage heavier than most other servo extensions on the market. I read somewhere that on a JR matchbox you are only supposed to use the extension that comes with it thus keepeing the matchbox relatively close to the reciever and then run your main extensions from it. People talk about filters, chokes and other things. I look at it like a aircompressor here on the farm, if its needed in the hay barn it will start up but real slow, it doesnt turn right on like normal and thats if your using 2 good quality cords, it doesnt work if you round up 2 or 3 regular duty cords even though the distance is the same. If its needed out past that forget it because with the addition of another cord it just wont start the motor, it just hums and burns up an extension cord. Even if you dont use futaba you can slice off the "J" part of the conector.

The hitec digitals sometimes need a y harness w/ built in choke/amplifier (Available through MPI) when used with futaba reciever (especially pcm- lower signal voltage) nothing wrong with them, they just need maintained signal voltage, and long leads and y's dont help. the choke/amp should solve your problem. Also, always watch your battery voltage - with digi's the more mah the better (easier to stay on the safe side) It has more to do with the servo not 'hearing' the signal than just getting a little tired.

hope this helps,
Ted

Hitec is aware of the y-harness problem with some of their servos. I believe they have fixed the problem with their latest versions. Contact Hitec and they will probably exchange them for you

I have two 5645's set up in a 27% on the elevators with a Y harness. I stuck an Expert reversing Y harness on it for centering. The receiver is a 127 futaba. No troublels a'tall