High Torque Digital Servo

[skip241]

Just purchased a digital high torque servo for jib trim. When no load is placed on the servo it sits there just fine. When there is no load on the servo it moves just like it should. No chatter. No humming. However, with the least amount of load, the hum or buzz is obvious. Hobby shop and a few R/C car enthusiasts claim the hum is part of the digital servo operation. This is my first digital servo. Any credence to this being a part of a digital servos? Thanks. Skip, Atlanta

[bodacious]

Skip, I have digital servos in my Victorias and also one for my rudder in my EC12s.... they all hum! I thought that they were burning up or something but the one in my #1 Victoria is a DS8411 and it's almost 5 years old!! I believe they have a 3 year warranty.... so just keep the box and the receipt...LOL I think it will be fine! Doug B

[Jim Linville]

I have two HiTec digital servos in my Wheeler, one for rudder, one for backstay tension (can't do backstay with an EC12). They both chirp... I mean they chirp like birds. Weird, I sent them back to HiTec and they told me they're OK, and that all digital servo chirp. They work fine, so I guess that's the way their supposed to act. --Jim Linville

[skip241]

Thanks to both of you for the help. It'll be a noisy day on the lake. [:D]

[Rob Guyatt]

Hey that's a good analogy Jim. Let me extend on that. Analog servos still chirp but it's at a lower pitch. Say, like a crow, you know, like Manuel and Jose for the Warner Bros 'toons. Digital servos chirp like Tweety.

A slightly more technical answer is that it's the frequency of the PWM drive. PWM (Pulse Width Modulation) is where the Voltage to the motor is "chopped" to vary the power to the motor usually in proportion to the position error. Analog servos have PWM drive just like digital servos but at a lower frequency (pitch). The lower pitch of a typical analog servo is less obvious.

Trouble with servos (and winches for that matter) is that they are designed to drive the motor only when changing position. Ideally, the load on the servo is nill once the servo had achieved its desired position. But if the load is such that the servo has not quite made the desired pos then the motor remains powered up. The same applies if the servo achieves its pos but then is wound back by the load. In either case the motor is powered up but stationary because the power of the servo is balanced by the load. It just sits there and chirps its PWM tune.

Bottom line is don't be too concerned about chirping digital servos. However keep in mind that the power that's going to the motor and making it chirp is creating heat. So choose you're extra servo carefully and perhaps check how hot it's getting. I've seen a few servos go bust because of being overloaded. Such as for backstay control.

Cheers

Rob

[Ken S]

For those interested in the differences between Analog and Digital servos here is Futaba's take on it.

http://www.futaba-rc.com/servos/digitalservos.pdf

Down at the bottom left there is a picture of what Bob G. described. Many pulses give you the hum/buzz/chirp you hear when using digital servos. Each one of those pulses is telling your servo where to be, chopping it like this keeps the servo right where you think you want it.

Keep in mind Digital servos use more power throughout the day, so if you find yourself drained sooner then you're used to, its probably because of the digital servos. Is it significant? I haven't found it to be so, but during a regatta I will switch My batteries, during a break, to be on the safe side.

Ken

[ole kistler]

fellow sailors, this is my first response to the discussion page. I just had the misfortune of frying a new digital hitec 5995. It was installed as the Sail Servo for a Soling 1 meter. I found your comments informative on the duscussion page. the noise/chirp info was comforting to know is "normal", but needs to be fixed. Is it possible? the other problem i find is that the servo does not nave a brake when no power is applied. The info about the 3 year warranty will be followed up on. ole

[bodacious]

The servo that I was talking about is a DS8411 made by JR. I don't know if the other manufacturers have as good a warranty.( they now have an 8611.... big pull for a standard size servo!!)