Model Boat Mayhem - Forum

Technical, Techniques, Hints, and Tips => The "Black Arts!" ( Electrics & Electronics ) => Topic started by: sailorboy61 on April 30, 2011, 06:45:38 PM

Title: Digital Servos
Post by: sailorboy61 on April 30, 2011, 06:45:38 PM
Does anyone have any experience of these?

I am at the stage in a build of putting in my steering servos, and whilst I already have several traditional 'analogue' servos handy, I was considering a couple of digitals. The build is a twin Kort tug, so may possibly benefit from any better control these servos may provide.

Thanks
Title: Re: Digital Servos
Post by: john s 2 on April 30, 2011, 06:58:12 PM
For Model boating use their not really needed.They take more power and the extra speed and accuracy are
not needed for a tug. If youve got some spare fine use them , but as said not needed. John.
Title: Re: Digital Servos
Post by: sailorboy61 on April 30, 2011, 07:00:27 PM
Thanks John, I guessed they probably weren't worth the extra expense for a boat when I already have standard ones in my box. Cheers.
Title: Re: Digital Servos
Post by: Nordsee on May 09, 2011, 04:43:31 PM
I bought a digital servo last year, an impulse buy, they were very cheap so I bought one. I don't use it though, it is very twitchy and hunts for neutral the whole time, also far too fast for a boat, so out it came and in went an old Futaba, much better!
Title: Re: Digital Servos
Post by: red181 on May 09, 2011, 09:42:39 PM
I suppose it depends on the application, I changed over 2 of my fast  boats to digital metal gear servo for rudder, faster and more presice than the futaba 3000 I was using, but on  a tug I dont think its needed, you dont need the servo speed or torque
Title: Re: Digital Servos
Post by: malcolmfrary on May 11, 2011, 10:56:55 AM
I bought a digital servo last year, an impulse buy, they were very cheap so I bought one. I don't use it though, it is very twitchy and hunts for neutral the whole time, also far too fast for a boat, so out it came and in went an old Futaba, much better!
Sounds like its missing the neutral point with a level of precision that only digital devices can hope to achieve.  Some designer somewhere is in need of a good slap over the head.
Title: Re: Digital Servos
Post by: Subculture on May 11, 2011, 03:33:37 PM
The funny thing is that most 'analogue' servos, are in fact digital these days. Years ago servos used specific IC's for control, but nowadays most are using microcontrollers like Atmel or PIC programmed to emulate them.
Title: Re: Digital Servos
Post by: malcolmfrary on May 12, 2011, 11:28:39 AM
The funny thing is that most 'analogue' servos, are in fact digital these days. Years ago servos used specific IC's for control, but nowadays most are using microcontrollers like Atmel or PIC programmed to emulate them.
Back in the olden days, there suddenly appeared on the market "electronic" washing machines.  They had pretty much the same innards as their predecessors, but the motor switching was done by a semiconductor device and small contacts in the control box rather than big contacts on the control box.  It was cheaper to do and they could charge more for the product.
In much the same way, so-called digital servos are different in that they have a stepper motor (i.e. brushless) and the appropriate output stage.  The input signal is called "digital", because it is in one of two states at any one time - on or off.  Its just as analogue as it ever was because the information consists of the length of time the signal is "on".  It doesn't really matter what is in between, discrete components, a hybrid chip or a PIC, all we are interested in is whether it works.
No doubt before long there will be a fully digital system, probably using a derivative of USB for connection and as a signal protocol, along with something really clever as a position sensing device, and I cannot help but wonder what the marketing people will call it, having used all of the appropriate words on the preceding stuff.
Title: Re: Digital Servos
Post by: Subculture on May 12, 2011, 12:08:22 PM
Futaba S-bus?

Digital servos are mechanically the same as analogue servos, it's just that they are pulsed at a higher rate, so can deliver more torque, they also tend to have narrower deadband. They do not use stepper motors, although some very high end servos now use brushless motors.
Title: Re: Digital Servos
Post by: PMK on May 12, 2011, 12:17:01 PM
And probably just a matter of time before they replace the humble gimbal potentiometer with a rotary encoder.
Title: Re: Digital Servos
Post by: Subculture on May 12, 2011, 12:51:39 PM
A chap in Switzerland did that with replaced with some hall effect sensors. There are benefits for servos, for robotics applications where the servo swings backwards and forwards a lot.
Title: Re: Digital Servos
Post by: sailorboy61 on May 14, 2011, 09:05:28 AM
Thanks all for the info.