Continuous vs. Modified

[airman00]

Whats the difference between buying a continuous servo and a modified to be continuous servo. I'm talking about the servos which are manufactured to be continuous not the ones that are modified by the seller.

Is there some big difference why they charge 20 bucks more for a continuous one then for a modified one?

[airman00]

I was reading The robot Builders bonanza and have some questions.

In the book it says:

Modifying a servo for continual rotation carries with it a few limitations, exceptions, and
?gotchas? that you?ll want to keep in mind:

The average servo is not engineered for lots and lots of continual use. The mechanics
of the servo are likely to wear out after perhaps as little as 25 hours (that?s elapsed time),
depending on the amount of load on the servos. Models with metal gears and/or brass
bushing or ball bearings will last longer.

The control electronics of a servo are made for intermittent duty. Servos used to power a
robot across the floor may be used minutes or even hours at a time, and they tend to be under
additional mechanical stress because of the weight of the robot. Though this is not exactly
common, it is possible to burn out the control circuitry in the servo by overdriving it.

Is it really true that if I modify my servos they'll last only 25 hours??? And if the robot is driving across the floor then will it really break so soon???

,Eric

[Steve Joblin]

I'm not quite sure exactly where the "25" comes from, but yes, servos are not meant to be continuously driven, so don't plan on them lasting forever.  Typically, the more you spend, the better the quality, and the longer they will last.  That said, I've been into robots for about 8 years now and my first robot (a Parallax BoeBot) is still running just fine!!

[airman00]

Did you include a modified servo into your parallax boe bot?

Also, if I purchase a continuous one over a modified one, will the continuous be better?

[Steve Joblin]

The Parallax BOEbot has two Futaba-S148 servos that I modified for continuous rotation.

The reasons you would want to buy a continuous servo are:
1.  You are not mechanically inclined and are afraid to take the servo apart
2.  You don't have the correct tools to make the modification
3.  You are "sloppy" and are concerned that your modifications to the gears won't be good

If you take your time, follow the instructions, and are careful, you won't have any problems and should have the same "performance".  One helpful hint is to add a bit of extra gear grease to all the moving parts before you reassemble the servo.  Bottom line is that for small, light-weight robots, you won't know the difference.

[airman00]

Thanks Steve.


 

[annoyin_kid]

is 25 hours an extreme prediction or does it really die in 25 hours sometimes? any idea how long a futaba s3003 (just a standard servo) would last?

[Steve Joblin]

It all depends on how long it is being driven and how hard it is being driven.  I would assume that a modified servo being driven at 5 volts with no load will last much longer than one being drive constantly at at 7 volts with a heavy payload attached.

[Admin]

I have never had a servo break except when I abused it (high torque and repeated direction reversals).

If you treat the servo well, it will last years.

[airman00]

so basically what the book said was wrong...

[Steve Joblin]

My gosh!  There is way too much time being spent on this topic... Relax, have a nice cup of green tea and just enjoy your robots!  The point is that you should not plan on incorporating a modified servo in a commercial product or in any product that is related to sustaining life (that is, don't use a continuous servo in a heart/lung machine) since that is not what they were designed for; however, they are a very reliable and easy to use product for hobby or research robotics.

[creedcradle]

so basically what the book said was wrong...

I reviewed more or less than ten robotic books but most of them talked about personal bias and experiences of the authors

books are made by humans, not made by Gods, so it is not perfect at all
that is why errata exists...

[Admin]

yeap what creedcradle said is right . . . you have to break quite a lot of servos (of the exact same type) to know how reliable it really is . . . then do a probability distribution . . . . something i doubt the author did . . .

Steve Joblin, Im all out of green tea so I had to reply

[Admin]

Call/email the manufacturer

I'd be willing to bet its hand modified by a monkey . . .

And keep your related posts together! grrrrr