Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: xamirx on July 13, 2008, 05:11:18 AM

Title: Cheap Linear Servo?
Post by: xamirx on July 13, 2008, 05:11:18 AM

Hi everyone

I need a linear actuator for my thesis project. I need to implement a robot eyeball system with 'tendons'. the actuators from Firgelli.com would be perfect, the only problem being that they cost about $60 each! Is there a much cheaper alternative? Or is there a way to convert a standard servo to linear motion?

Somebody told me to check out old 3.5 Floppy drives cause they have a linear mechanism of sorts? Are there any other 'scrapyard' type devices where i can salvage a linear servo or actuator?

Thanks

Amir

Title: Re: Cheap Linear Servo?
Post by: dunk on July 13, 2008, 05:26:29 AM

http://www.instructables.com/id/Quick-and-easy-electric-cylinder-prototype-.../?comments=all (http://www.instructables.com/id/Quick-and-easy-electric-cylinder-prototype-.../?comments=all)

dunk.

Title: Re: Cheap Linear Servo?
Post by: BANE on July 13, 2008, 10:03:10 AM

You could use the device in a CD player that moves the laser back and forth,  maybe you could attach a linear potentiometer on it somehow and use a servo h-bridge.

Bane

Title: Re: Cheap Linear Servo?
Post by: Commanderbob on July 14, 2008, 07:17:50 PM

You can always attach control rods to servos. That lets you push/pull with them. Almost every RC vehicle uses them for turning to some kind of motion. Here (http://"http://www.peteronion.org.uk/GeminiBuild/servo2.jpg") is a picture of one.
Justin

Title: Re: Cheap Linear Servo?
Post by: Trumpkin on July 15, 2008, 01:18:44 PM

try ebay.

Title: Re: Cheap Linear Servo?
Post by: emmannuel on July 15, 2008, 02:06:06 PM

OMFG I've been looking for solutions like those that were economical and worked.....

The linear actuator using the DC motor is awesome.. now I feel dumb for never thinking of those ideas :P

Title: Re: Cheap Linear Servo?
Post by: bulkhead on July 16, 2008, 01:04:40 AM

Control rods with servos will probably be the easiest and cheapest way to do it using standard $10 servos.  Look at this picture:
(http://www.rcuniverse.com/magazine/reviews/967/still16.jpg)
The motion of the rod is essentially linear, especially if you just use it to pivot a joint that only has 1 degree of freedom (like a door hinge).  This route will require some careful thought about where the pivot points are because the available pushing/pull force of the servo is a sine/cosine function, where the servo could end up with zero mechanical advantage.  If you go this route go to a hobby shop and look at the steering mechanism on any RC car.  You will need "rod ends" (http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXHGB7&P=7 (http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXHGB7&P=7)) from any hobby shop carrying RC car parts and a ~1/8" threaded rod from any hardware store (cut to the length you need).