NEED HELP TWO SERVOS DYING AT THE SAME TIME?

[tom galdys]

Need some help and an explanation. I had 2 servos quit on me at the same time,rudder and throttle. They were both Hi-tech servos an HS 77 BB and an HS85 MG. I use the Futaba FHSS system and the receiver is a R603GF. They were newer servos that never got wet and the radio box was high and dry. I use a 4.8 volt Hydramax ultra 1600 battery pack that is brand new. The voltage at the time was 4.86 and with a load was 4.79 volts. The receiver is good as I hooked up servos from 2 different boats to it and they performed fine. Tried 2 other battery packs and 2 other receivers and the servos did not work. The result after trying all combinations was it is servo failure. Switch is also good. The servos,all connections and switch were all corrosion free. My local Hobby Shop owner,who KNOWS HIS STUFF said I had some sort of power surge that started in one servo and jumped to the other. He said I got lucky because that sort of thing usually takes out the receiver also. Any comments or suggestions to prevent this in the future would be greatly appreciated.Nobody at the race could help out and even Joe Petro was baffled. Please Help. Thanks Tom Galdys

 

[Grimracer]

What radio.. is it futaba and its is in HRS mode?

Grim

 

[tom galdys]

The radio is a Futaba sport 2.4GHz FHSS 2PL-2.4G and what is HRS mode? Thanks Tom

 

[Tony Jacuzzi]

Tom those are non digital servos you need to set the radio to PPM mode or else the HRS mode will fry the non digitals. I am guessing they both smelled burned up? I have done the same thing

 

[tom galdys]

Tony, Thanks but no the servos did not smell or look burnt. Now my ignorance, how do I set the radio to PPM mode and all my radios are the same along with the servos and receivers. Thanks Tom

 

[SayMikey]

Tom there is no ppm/hrs adjustment for your radio. Id suspect the rec for the failure

 

[ALLAN YUEN]

h34r: watch out did you change " High or Norm" Mode for 4PL? If you use non digital servo and set up " norm" or use digital servos and set up " high" will you learn on lesson and read manual book!

 

[NITROSNIFER]

Easy solution....Stop using hitec servo's. I've had several issues with the same ones you are using. Switched to futaba and have not had one fail since.

 

[tom galdys]

Will have to change to Futaba servos. The radio is a 2PL so there is no high or low settings

 

[Neil LaGarry]

Tom I used the Traxass waterproof servos on the rudder and Hitec makes a waterproof servo. I like the less weight of the Hitec 225 Mg on the .21 riggers

 

[Blackout]

Hi Tom,

Have you tried a 6.0 volt rx pack? I always run 6.0 volt NiMH or 6.6 volt LiFe packs. Just a thought.... In theory 4.8 v should work....

 

[tom galdys]

Hi Craig,I've tried it all,6 and 4.8 volts Everything works but the servos. Receiver works great with other servos. They just cra**ed the bed at the same time. No good explanation. I can't buy the power surge idea that my hobby shop talked about,don't know how it could happen. The receiver is not cooked and servos look and smell fine.No corrosion.

 

[Blackout]

Well, I guess switching to Futaba would be logical then. I run both. I run Futaba as much as I can, but you can't beat the selection and price that Hitec has over Futaba. Not sure if you go to Dan's Craft and Things, but I picked up a std. nylon. JR servo for around $15 for use as a throttle servo on my last build. Not sure the part number off hand. But if you need a small servo metal gears are important.

 

[Justin Wray]

Did they die on the bench before the boat got run? What size boat is it? The HS 77 does not have a lot of torque especially at 4.8 volts. The HS 85 will not tolerate being over driven for any length of time so I would question end points. Also the Hitec servo connectors do not have alignment tabs for the RX if they got plugged in backwards they will pop a circuit on the board and never move. It also will not smell burned up.

 

[tom galdys]

Thanks Justin for a decent answer. The boat is a 21 size aero cat. This happened during the third heat of the day and it was on the water with one lap in. The end points,that could be the problem as it was not the connectors. They were in properly as I never re-opened the radio box from the start of the day. What circuit board are you speaking of? In the servo or receiver? Receiver still works. Thanks Tom

 

[Justin Wray]

The board that would fry is in the servo, but that would only happen if they were pluged in backward. I would lean toward endpoints on the HS 85. It is possible however rare that the HS 85 was being over drawn on amps and took out the HS 77 or vis versa. Do you remeber if the throttle or rudder could be put into a bind?

 

[tom galdys]

Justin, i can't remember but I don't think there was a bind on either servo. Today, the 88 has a very slight motion when 1st plugged in but there is no resistence moving the servo horn. Thinking about it, the 77 was acting up a bit I think as all of a sudden the boat would hook(3 times) under the normal settings on the trans.So the 77 could have had a problem that jumped to the other servo. Tom

 

[Kez]

but there is no resistence moving the servo horn.

Even if the servo is not powered, there should be a lot of resistance when you try to turn the servo horn because of the gear reduction. One of the reasons that you do not feel resistance moving the servo horn is that the gears are stripped; especially the final output gear.

kez

 

[tom galdys]

Hi Kez, No,the gears aren't stripped.they turn very smoothly and upon inspection they are in perfect shape. On a good servo that is powered up,you can't turn the horn. These you can which means the power board must be burned out because everything else truly checks out OK. The servos just don't work and the question is,what was/is the cause of BOTH going at the same time. Still baffled but the servo power boards aren't working, Even with the servos apart and plugged in the motor does not work. Thanks Tom

 

[Kez]

Hi Tom,

The servo gear train has very high ratio to generate the torque. It will take a lot of force at the servo arm to overcome the motor drag (magnetic drag from an electric motor)at the input end. If the gears aren't stripped, maybe the motor is fried?

kez