new to servos

[chrisatpsu]

how do you guys determine what a servo can handle as far as weight of the piece being moved?

i'm new to servos, and the only one I have is the one you get when you get a Parallax Basic Stamp Kit. I'm wondering if i can use that some way.

do you guys get special servos that can be outside? if not, how do you waterproof the servo?

[JonB256]

Servos have Torque ratings. The number of ounces/grams they can move, usually at the farthest hole from the center shaft. Exceeding that value will cause excess wear and eventual failure. Counter-balancing and counter-weighting help a lot, but don't ignore the MASS of an item just because there won't be any apparent weight. The more mass there is, the slower you can move it. (a body at rest ..... )

You could waterproof with brush on Liquid Electrical Tape. Maybe even CorrosionX. But, the shaft will always be open. They may make some with an O-Ring seal, but I've never seen them. These are very low voltage, so water damage will be due to corrosion more than electrical arcs and sparks.

[maffeirw]

do you guys get special servos that can be outside? if not, how do you waterproof the servo?

Most hobby servos are water resistance to a point. Remember that these servos are used in RC airplanes, cars and boats, all which are subject to exterior weather conditions.  As long as the servos are enclosed (in the skull or animated head) you should have no problems.  If the servo is directly exposed to water take a look at the following link.

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[tbone321]

You can actually buy waterproof servos.  Traxxas makes and sells them as well as others.  You should be able to find them at Tower Hobbies and Stormer Hobbes.  They are used in RC monster trucks and many of these have high torque ratings.

[Halstaff]

Thanks for those links!  I use quite a few servos in my Halloween display but those props are inside or under cover.  I may have to try the waterproofing method and try it in the elements
You can check out my newest prototype that uses 7 servos with a 3 axis skull, Picaxe audio driver for the jaw servo and 3 heavy duty servos to provide 3 axis arm movement.
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[rayster]

This is not an endorsement but one place to check out is ServoCity.com they list the servos by types and and the specs, they also show different mounts and ways to take some of the load off the servo and put it on the mount.

Ray

[caretaker]

I just got an email from Servo City and on it they were showing waterproof servos...

[JonB256]

Looked on Ebay for "waterproof servo"

Prices are much better, certainly.

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[rm357]

Usually the rating for torque is something like oz-in which is a simple multiplication of the mass times the distance from the hub.

If we ignore the mass of the arm, a 60 oz-in servo can move 60 ounces at 1 inch from the center of the hub. The same torque would be required for 30 ounces at 2 inches, 10 ounces at 6 inches, 2 ounces at 30 inches... Unfortunately you cannot ignore the mass of the mounting, which makes the equation a little more complex. If you have a dowel rod ( uniform mass distribution), you can figure the entire mass to be concentrated at the halfway point. If you have something complex, like a skeleton arm, you need to consider the mass of each piece at its average distance from the center of the hub.

RM

[typoagain]

Usually the rating for torque is something like oz-in which is a simple multiplication of the mass times the distance from the hub.

If we ignore the mass of the arm, a 60 oz-in servo can move 60 ounces at 1 inch from the center of the hub. The same torque would be required for 30 ounces at 2 inches, 10 ounces at 6 inches, 2 ounces at 30 inches... Unfortunately you cannot ignore the mass of the mounting, which makes the equation a little more complex. If you have a dowel rod ( uniform mass distribution), you can figure the entire mass to be concentrated at the halfway point. If you have something complex, like a skeleton arm, you need to consider the mass of each piece at its average distance from the center of the hub.

RM

Thank you! That actually makes sense even to me.