sidgates

My Feedback: (2)

If I apply battery only to the servo, no signal from the receiver, it will randomly change positions from neutral to full throw one direction or the other about every 10 seconds. I have observed the servo for approx. 2 minutes and the random postion changes continue.

dirtybird

My Feedback: (5)

I bought a couple of those servos several years ago. I removed them from use after I got several glitches that I traced to the servos. I think there is a problem with the microprocessor used in that servo.

sidgates

My Feedback: (2)

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dirtybird,
Thanks for your input. I did a search on RCU and am convinced i will change out the servos. My servos are new (but purchased several years ago). I did some more testing this morning and first thought when my work bench lights were out the problem was gone, but no such luck. I am running he servos on LIFE regulated to 6 volts and maybe that exaggerates the problem.

My model is a scratch built proto so not taking any chances.

Zeeb

My Feedback: (41)

5625's were one of the first digital servos produced by Hitec and they've got issues. Even if you do get 'em to stop what you're seeing, they don't center worth a d*mn. Best to follow your plan and change to something else.

pilotpete2

Just for grins remove the regulator, it could be causing noise, switching regulators can do that.
Also, there is no reason at all to use a regulator on a servo rated for 5 cell operation with LiFe. Both 2S LiFe and 5 cell nimh have the same voltage coming off a charge, but LiFe drops down to its nominal faster than the nimh.
Hitec does not publish voltage ratings on their servo, nor do most others. They give the torque and speed of the servos at the nominal voltage of the batteries.
I echo Zeebs feelings on the centering qualities of these servos, but I have a set on a 30cc Yak and they've been fine on 2S A123 for 7 years.
I would also mention that Hitec has new HV versions of the 5625 and 5645 at the same price, I can't remember the first two numbers, but they end in 25 & 45, though I've never tried them, but probably will.
Pete

sidgates

My Feedback: (2)

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PilotPete2,
I have other servos in the plane that I definitely don't trust on more than 6. volts. I have very long leads to the servos and that may contribute to the problem but other servos do not malfunction on the same leads. I have pulled the 5625's and may use them later on a low value project but not in this model. Thanks for the feed back.
Sid

Xpress

The only reason they would be doing that is if they're seeing a stray signal from somewhere. We always recommend to have your Tx on first, followed by your Rx/servos, to keep any stray signals from interfering with the equipment. The HS-5625MG will run on unregulated 6.6V LiFe packs (as will all of our servos with a 6.0v rating). We give you the nominal pack voltage torque ratings so you will know how the servo performs when your battery is under a load.

The HS-5625MG is one of our 5XXX series servos and is not very precise at centering as compared to something like an HS-5565MH or HS-5665MH. Its main intended purpose is trainer or sport models with small control surfaces that don't require a high dollar or high end servo.

sidgates

My Feedback: (2)

XPRESS,
I drafted a reply and had some questions. When I hit post I got a message that said your certificate has expired, hit the back button. My reply was lost and I don't have the energy to reconstruct at present time. Thanks for your response.

RustyUs

For RC buggies and trucks, the HS-5625MG has been a staple in my vehicles for many, many years. I know myself, and others have recommended the servo for many users. I always keep one for back up for my stadium trucks and SCTs. The HS-5625 is one of my all time favorite medium-low priced servos for 1/10 scale RCs. My first one lasted approx. six years during hard running off-road abuse.

sidgates

My Feedback: (2)

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Xpress,
I assume you work for Hitec. I designed and produced servos from 1967 – 1983. I normally would turn on the Tx first and the Rx/Servos second. but I don’t expect a servo to randomly change positions with power on only. Of course we did not build digital servos in those years.

Based on your comments I decided to run some tests. I used a 6 volt LIFE battery and hooked a Oscope to the servo signal in lead. When I applied power to the following: HS-5475HB; HS-5245MH and HS-5625MG the signal lead would go “High”. The HS-5625MG randomly changes position about every 10 seconds. The other 2 did not move in the random manner. Next I hooked up a HS-645MG and a JR DS821HV, the input lead stayed low and the servos are dead quiet.

I am not comfortable using servos that randomly move when power only is applied. Your comments please???

The first three tested all resist being moved by hand when power only is applied. I assume this is some kind of fail safe signal.

Sid Gates

dirtybird

My Feedback: (5)

Are you leaving the signal line open whenyou apply power?

Xpress

Our digitals have a hold function if signal is removed while powered up. What we find is that sometimes the servos are picking up stray signals from the receiver if they are randomly moving if you don't have a signal going to them. If you are questioning the servo, please feel free to send it into us and we'll take a look at it for you.

http://hitecrcd.com/support/warranty-service

sidgates

My Feedback: (2)

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Dirtybird,
The above test was with the Scope on the input lead only. The same thing happens when plugged into the receiver but receiver powered off. I have separate battery for the receiver. I have used this same wiring scheme for at least two years on other planes with no servo problem but I was not using the HS-5625MG in any of these installations.

TFF

I think your experience and curiosity can be a hinderance as much as help. I would have tossed it if it did not act normal at all, in a second.

sidgates

My Feedback: (2)

TFF,
If I knew for sure it is the servo I would just replace it too. Today more testing and I found out my electronics skills are a little rusty. I hooked up the scope to the signal lead and applied power to the servo. The servo lead is approx. 80in long in the model. All servos I have been using for test were quiet, no random movement.
Next I plugged the servo lead into my power bus system which is located right near the receiver. All the Hitec digital servos randomly moved and a negative going pulse appeared on the scope. The pulse goes negative about 1 1/2 volts from full deflection of 6 volts. The pulse is approx 2ms long and repeats approx every 20ms. I have trouble syncing on the negative pulse so these numbers are not 100% accurate.
Tonight I hooked up the Hitec servo programmer to make sure the servo failsafe was turned off. With the failsafe off the servo stills does random movements. I hoped that turning off failsafe also turned off the "hold" feature but no such luck.
None of the analog servos or the JR digital I have move randomly when plugged into my power bus. Right now I conclude that the problem is the combination Hitec digitals plugged into my power bus. I am not saying it is the servos fault, I just can't use them in this model.
Thanks for all the input.
Sid Gates

dirtybird

My Feedback: (5)

My personal opinion is if you can live with a 13 usec deadband you are better off with analog servos.
I have friends that tell me they had servos burn up. I have never had one do that.

sidgates

My Feedback: (2)

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I am replacing the 3ea 6525's with analogs. I have never lost a servo in the air either. I have a hard time accepting digitals buzzing a lot and I never run servos over their rated voltage.

Len Todd

He did say the signal line was NOT connected. That makes it an antenna for any stray RF buzzing around. Unless you have a scope capable of seeing UHF, you would never even know the signal was getting on the line, other than seeing the servo's reaction.

Why would anyone even test a servo with the signal line disconnected? Even if your splitting off the power from the Signal, the Signal line still has to be connected to some component in the same ground plane. Otherwise you risk getting what you are seeing.

sidgates

My Feedback: (2)

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Len,
The signal lead I was talking about is at the end of an 80" servo extension. The servo is on the other end.

If you hook the red and black wire of a Hitec digital servo (the 3 I checked) the signal lead goes to plus supply voltage or nearly so. There was no noise on the line and the servo is quiet. Next I plugged the servo extension into my home made power bus and then the pulse I describe earlier appears and the the servo starts random movements.

If I then turn on the receiver the servo operates normally but I sure wouldn't want the signal lead from the receiver to the power bus to open, then the servo starts this random movement.

TFF

80" servo extension adds to the puzzle. Is the extension braided or is it ribbon flat. Pretty long without a ferric bead or at least braided.

sidgates

My Feedback: (2)

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The long leads are twisted. I haven't mentioned I have two other servos with the same long leads. They never move with power applied only. The one with the problem is the rudder servo. I can drive the rudder servo normally with either the receiver or with a servo signal generator. I see no noise or pulses on the signal line except the normal control pulse when either the Rx or the Servo Sig Gen is plugged in and powered up

I will replace the servo tomorrow. Not worth any more time. I am comfortable using different brand servo or Hitec analog, They don't created the problem when using my "power bus".

chuckk2

This is a lulu!
Anyway, with the long leads, I'd add a capacitor to the servo power leads towards the servo. I'd also connect the servo control wire via a 1K to 10K or so resistor to the common (Black) lead.

Pulses going below common can indicate serious problems.

sidgates

My Feedback: (2)

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Chuckk2,
This comment today is my last chapter on my problem. I know long leads can sometimes be a problem. Today I plugged a Hitec digital servo directly into my home made power bus, 10in lead. Applied battery to power bus and the digital servo was perfectly quiet. Next I hooked the rudder output of the receiver to the servo on the power bus using a 2in long cable with negative and signal lead only, the pulses appeared in the scope trace and the servo started its random movement. The receiver is a Weatronic Micro 12ch. No power was applied to the receiver. By the way I looked at other receiver servo outputs and there were no pulses ocuring on the other outputs.

My conclusion is that the problem only occurs if I turn on power to the servos with receiver output connected but the receiver turned off and it only occurs with Hitec digital servos.

Four Stroker

Hey Sid;

Your "power bus" should have some pull up / down resistors on the signal lead.

Recall that Hitec servos have always had problems with some receivers - like the Futaba 6014FS. They have their own ideas about signals and how to drive them. For stuff coming from the aether, ferrite "beads" work especially if you wind the wire several times. Futaba used to make some filtered extensions back when everyone was crashing the 5014 receivers.

Xpress

With an 80 inch extension, there is a large margin for signal degradation. From what you have been describing, it sounds like the cure to your issue is 1. Use a signal booster to ensure the signal does not degrade through the extension, and 2. Make sure your receiver is turned on.