RC Servos

[tuppetsdad]

The cheapest servos to buy are the ones used for remote control cars, boats and planes - "RC servos".

They are a very nice package as you get a servo motor, gearbox, position sensor (usually a potentiometer) and control unit in one package. A 3 wire interface is standard - Power supply (6-12 volt typical), Common and control input. The control input receives a pulse each 20 msec from whatever controller is used and the width of the pulse determines what angle the servo shaft output moves to. Typically the pulse length is 1-2 msec long.   

RC servos are designed for controlling the angle of parts and so the output of the servo typically moves 0-90 degrees. They are rated based on the speed they can move (0.15 msec per 60 deg is fast and 0.5 sec per 60 deg is slow) and the output torque (5 N cm is small and 40 N cm is big).

A great site to read up on RC servos is

http://www.horrorseek.com/home/halloween/wolfstone/Motors/svoint_RCServos.html

There are two types Analogue and Digital but the interface is the same. The difference is the internal switching frequency for the motor. For analogue it is typically 50 Hz and for digital 300 Hz so digital is more responsive. Digital servos are typically 2 x the price of similar rated analogue ones. As you move to larger digital servos the interface changes to various proprietary digital buses.

Tuppet purchased a few servos today from Little Bird Electronics in Sydney and paid about $15 each for them.

http://www.littlebirdelectronics.com/

Most control boards for RC servos are not so suited for lighting applications but many are available for animatronics applications.

Suppliers of DMX RC controller cards include:
http://lasershowparts.com/store/index.php?_a=viewCat&catId=35      Single Channel $70
http://northlightdmx.com/DMX512toRCservo.htm       8 Channel $49

For those that want to make their own board and examples is here
http://www.hoelscher-hi.de/hendrik/english/servo.htm

[David_AVD]

Servos are certainly fun to play with.  I made a little PCB with 8 pin PIC a while ago that moved a servo between two preset (via trim pots) positions at the flick of a switch.

[Tabor]

As Bruce has pointed out servos are particularly useful for small motion control.

One of my motion control projects this year is actually a dmx to servo controller.
However thats not all.

For my own use I wanted  a servo controller, but I also wanted a few extras.

Heres what I am hoping to have on the controller.
8 Channel Servo control
18 channels low current led control

Options:
Wireless / Wired
Battery power, LIPO / Mains

I want it in a very small form factor.
So what do I want a board like this?
I want to build my daughters costumes, elf/fairy.
They love the lights each christmas and are constantly wanting to go and stand around with the other people out there.
My eldest daughter has started rattling the tin at the viewers so I thought this could be a great way to do something different.

Well thats the plan.

Tabor

[XDU]

Sounds great T... looking forward to seeing it

[cenote]

How easy is it to build a PCB to control a servo that would for say do a waving motion as long as it was powered? I know a wiper motor sometimes is easier to use, but may have an idea for 2012 that servo motors would be better applied, and would be a waste of sequencing using a servo channel.

[tuppet]

How easy is it to build a PCB to control a servo that would for say do a waving motion as long as it was powered? I

Answer: very easy. A friend of mine just completed a circuit using a 555 timer and some potentiometers so he could manually change the limits of motion. Making it go slowly enough to look like a wave is a little trickier, but can also be done (I'm just starting to play with slowing servo motors down, I'll let you know once I've figured it out).

I've been buying cheap servos from dealextreme.com, cost between $4-12 AUD shipped (less if you buy more than 3). They aren't naturally waterproof, but that can be overcome (people do use RC servos to drive model boats, so they can need to be submersible) - google search brings up lots of possible methods.

[ѕυρєямαη]

I'm interested in making the servos travel slower. I've managed to build a couple of stand alone servo controllers to have a automatic windscreen wiper motion between 2 or 3 points using 555 timers and a few other components. I Brought 10 standard servos from china to play with under $60 delivered http://www.aliexpress.com/snapshot/100989094.html

[ѕυρєямαη]

How easy is it to build a PCB to control a servo that would for say do a waving motion as long as it was powered? I know a wiper motor sometimes is easier to use, but may have an idea for 2012 that servo motors would be better applied, and would be a waste of sequencing using a servo channel.

If you cant find any schematics on the internet let me know and i'll flick you some

[David_AVD]

This "SR518 robot Digtal metal servo" on eBay looks interesting.  Also some the same on Alibaba:

They appear to use a serial protocol instead of a standard RC servo stream.  I'm sure they can be controlled by DMX with the help of some electronics though.