Log in

I forgot my password

RDMFC Social Media
RDMFC Facebook Page
Latest topics
» 2019 Llanfair TH Village Fete
Digital servos Empty2019-07-12, 18:53 by Rich

» Proposals for Model aircraft flying ( CAA registration) April 2019
Digital servos Empty2019-05-08, 17:49 by Gary M Jones

» Police crash
Digital servos Empty2019-04-14, 15:36 by Roy

» Bit of indoors
Digital servos Empty2019-04-13, 16:49 by Roy

» For Sale
Digital servos Empty2019-03-03, 23:44 by Charles E Cornes

Saturday 7/7/18

2018-07-07, 21:07 by Gary M Jones

I was at the field today between 14:00 & 15:00 all on my own , good flying too. There is a dead sheep along the fence line towards the gate from the pits, I saw the farmer so reported this to her. I hope no one had plans for a BBQ Smile .

Farmer …

Comments: 1


Digital servos

Go down

Digital servos Empty Digital servos

Post by Brian Colclough on 2010-07-04, 14:21

Someone on another forum I frequent posed the question " are digital servos worth the extra cost compared with their analogue counterparts?" Then someone else posted this useful link to a PDF file which explains the differences http://www.futaba-rc.com/servos/digitalservos.pdf I found it interesting hope you do too Wink

Brian Colclough

Posts : 3238
RDMFC Bonus points : 4736
Join date : 2008-11-17
Location : Rhuddlan

http://www.imacuk.co.uk/   http://www.rdmfc.org.uk/

Back to top Go down

Digital servos Empty Re: Digital servos

Post by PDQ on 2010-07-04, 19:58

Useful info, nice quick guide.

The screeching noise from digital servos in bigger models is so dfistinctive. What makes the noise?
PDQ
PDQ
RDMFC Member

Posts : 658
RDMFC Bonus points : 773
Join date : 2009-03-05
Location : Prestatyn

Back to top Go down

Digital servos Empty Re: Digital servos

Post by Tim on 2010-07-04, 21:56

Im not sure thats the servos, I always assumed it was the control surface/hinge line/airflow pressure thingy ??

_________________
Experience often wins.
Tim
Tim
Committee Member

Posts : 2968
RDMFC Bonus points : 3235
Join date : 2008-11-18
Location : Tim Mackey lives in Deganwy

Back to top Go down

Digital servos Empty Re: Digital servos

Post by Andy Sayle on 2010-07-04, 22:03

It's the motor that makes the sound. to keep it short, it is the sound of the motor being switched on and off very quickly by the control electronics, to maintain the position demanded....

Andy

_________________
Chicks dig slop free linkages....
Andy Sayle
Andy Sayle
Club Chairman

Posts : 4739
RDMFC Bonus points : -487569787
Join date : 2008-11-16
Location : Abergele, North Wales

Back to top Go down

Digital servos Empty Re: Digital servos

Post by Brian Colclough on 2010-07-04, 22:16

I think the noise Paul means is the screech found on composite models which is air being forced over the open end of the composite ailerons on high deflections, you still get it with analogue servos Wink

Brian Colclough

Posts : 3238
RDMFC Bonus points : 4736
Join date : 2008-11-17
Location : Rhuddlan

http://www.imacuk.co.uk/   http://www.rdmfc.org.uk/

Back to top Go down

Digital servos Empty Re: Digital servos

Post by Tim on 2010-07-05, 09:40

Yahooo - I was nearly right...more righter than Andy for sure Digital servos Icon_biggrin

_________________
Experience often wins.
Tim
Tim
Committee Member

Posts : 2968
RDMFC Bonus points : 3235
Join date : 2008-11-18
Location : Tim Mackey lives in Deganwy

Back to top Go down

Digital servos Empty Re: Digital servos

Post by Andy Sayle on 2010-07-05, 11:23

I blame an ambiguous question, and the thread starting off being about digital servos........ Wink

The whisltely noise you get on composite aircraft is mainly due to the hollowness of the wings around the hingeline. Because most composite hinges are "skin" hinges, or "live" hinges, where the wingskin itself acts as the hinge (Usually on the top surface of the wing), when the control surface is deflected upwards, the bottom wingskin is opened up to the airflow. The opening and chamber now act exactly the same as a whistle, resonating at a frequency that is dependant on the size of the chamber (and a few other minor things).

Smaller composite models do it as well, it is just that the smaller sized chamber has a much higher resonant frequency, and therefore the whistle pitch is much higher pitched. Also the smaller size is not as loud....

The fact that the wings are usually hollow moulded, means they alos act as giant soundboxes, effectively amplifying the sound, which makes it so noticeable on the bigger models.

Andy


_________________
Chicks dig slop free linkages....
Andy Sayle
Andy Sayle
Club Chairman

Posts : 4739
RDMFC Bonus points : -487569787
Join date : 2008-11-16
Location : Abergele, North Wales

Back to top Go down

Digital servos Empty Re: Digital servos

Post by PDQ on 2010-07-05, 21:44

Thanks Andy, I think your first explanation was nearly right. I wasn't thinking of composites and the whistling musical wings you describe, but the the bigger built up models I've seen at the shows which squeal violently at every flick and twist.
I did find though this web page just now
http://www.servocity.com/html/digital_servo_faq.html

In particular it shows
Are there disadvantages to digital servos?
A-1. If there is any disadvantage to using digital servos it is power consumption. To obtain the high standing torque and quick response, digital servos require more from the power source than standard servos. By using a larger capacity battery and heavy duty harnesses, you will ensure proper servo performance.

A-2. Digital servos also create a high frequency pitch or squeal.
That's nearer to being the answer that matches the question I arsked.(posh for asked)

I was also surprised to find that conventional pots and brushed motors are used in digital servos. It's the Mosfet and high speed processor that makes all the the difference.
PDQ
PDQ
RDMFC Member

Posts : 658
RDMFC Bonus points : 773
Join date : 2009-03-05
Location : Prestatyn

Back to top Go down

Digital servos Empty Re: Digital servos

Post by Andy Sayle on 2010-07-06, 10:20

PDQ wrote:
I was also surprised to find that conventional pots and brushed motors are used in digital servos. It's the Mosfet and high speed processor that makes all the the difference.

That's the important bit. Just because servos are "digital" doesn't automatically mean they are good. Generally, you get what you pay for with servos, and there are old style analogue servos out there, that are much better quality (and performance) than some digitals. It's about the whole package, not just the control electronics inside Smile

Speaking of conventional pots, Hitec have got an encoder based servo listed on their website now. Which is interesting (and bound to be damn expensive!)....

Andy

_________________
Chicks dig slop free linkages....
Andy Sayle
Andy Sayle
Club Chairman

Posts : 4739
RDMFC Bonus points : -487569787
Join date : 2008-11-16
Location : Abergele, North Wales

Back to top Go down

Digital servos Empty Re: Digital servos

Post by Guest on 2010-07-06, 12:52

I guess your talking about the one with the magnetic position sensor. IMHO its about time the historical servo cct was scraped and the digital positional info sent by the Tx (as a digital number) was used directly and not converted back to a pulse width time devision multiplexed information stream. 'Discuss'

Guest
Guest


Back to top Go down

Digital servos Empty Re: Digital servos

Post by Brian Colclough on 2010-07-06, 13:18

I have come across just about every type of digital servo of all types at shows and comps and have yet to hear one emit a screeching noise audible from the ground, the only such noises I've heard are from the ailerons of composite models be they gliders or power models. Richie's Yak does it as does my Wasabi glider tongue

Brian Colclough

Posts : 3238
RDMFC Bonus points : 4736
Join date : 2008-11-17
Location : Rhuddlan

http://www.imacuk.co.uk/   http://www.rdmfc.org.uk/

Back to top Go down

Digital servos Empty Re: Digital servos

Post by Andy Sayle on 2010-07-06, 13:54

You can hear the wing servos chuntering away on my big glider on a slow and low pass.... That's with the motor off mind....

Andy

_________________
Chicks dig slop free linkages....
Andy Sayle
Andy Sayle
Club Chairman

Posts : 4739
RDMFC Bonus points : -487569787
Join date : 2008-11-16
Location : Abergele, North Wales

Back to top Go down

Digital servos Empty Re: Digital servos

Post by Tim on 2010-07-06, 14:06

Ah but chuntering is not screaming like the noise under discussion.

_________________
Experience often wins.
Tim
Tim
Committee Member

Posts : 2968
RDMFC Bonus points : 3235
Join date : 2008-11-18
Location : Tim Mackey lives in Deganwy

Back to top Go down

Digital servos Empty Re: Digital servos

Post by Andy Sayle on 2010-07-06, 14:14

That's only because the motor is off though. Motor off, they chunter with content, but they start screaming in pain when I open the throttle.....

Andy

_________________
Chicks dig slop free linkages....
Andy Sayle
Andy Sayle
Club Chairman

Posts : 4739
RDMFC Bonus points : -487569787
Join date : 2008-11-16
Location : Abergele, North Wales

Back to top Go down

Digital servos Empty Re: Digital servos

Post by Tim on 2010-07-06, 14:17

Come to mention it, I dont think I have ever heard a chunter screaming anyway - which raises the question.... can they scream at all? - or indeed just a few Digital servos Icon_rolleyes
I better go now.

_________________
Experience often wins.
Tim
Tim
Committee Member

Posts : 2968
RDMFC Bonus points : 3235
Join date : 2008-11-18
Location : Tim Mackey lives in Deganwy

Back to top Go down

Digital servos Empty Re: Digital servos

Post by Sponsored content


Sponsored content


Back to top Go down

Back to top


 
Permissions in this forum:
You cannot reply to topics in this forum