Position feedback on a modified servo?

It should work, depending on the control alrorithm in the servo. Use a
good pot, and one that matches the specs of the pot internal to the
servo.

(I've not used this approach for a robotic application, and not for a
modified servo. What I did was create a remote-control where turning a
pot moved a small camera that was mounted on the servo.)

The approach must have some merit because someone is trying to patent
this concept, or at least one very close to it. It seems obvious to me,
but I'm not a patent examiner. I make no comment regarding the validity
of the concept as a patentable idea. You can look it up on the uspto.gov
Web site, under patent applications (patents not yet granted). It's
number 20060003865.

In any case, you may find better results by connecting the external pot
to an ADC input, assuming you're using an MCU or something that has a
readily available ADC port. This may provide more overall control.

-- Gordon


Eriswerks wrote:

On rereading, a bit of clarification on this. I guess a servo would be
"modified" if the pot were removed. What I meant was not modified with
the intention of continuous rotation, which my servo didn't do. It
needed only about a 30 degree movement.

My system was a bit more involved, in that the voltage from the pot also
was read by a microcontroller, so that a new setpoint could be made by
manually rotating the camera on the servo (yes, I know it's bad for the
gears!). The idea was to enable someone to manually adjust the position
of the camera, while still allowing the microcontroller to sweep the
camera. In the end we decided it was just as good to use a standard
servo and an external control near the camera.

BTW, is there a reason to use the Traxxas servos? I always thought they
were a bit pricey compared to Hitec and Futaba. Are they better?

-- Gordon

Thanks Gordon and dpa for the helpful posts. I'll try to find a good
match for the servo's 5K pot, or maybe just pull the thing out of the
sevo and mount it externally.

I'm using the Traxxas servos because they have pretty good torque (80
oz-in) even before I gear them down, and because I've been able to find
some good deals on them. People are often selling used ones on ebay,
and I've found them new for US $11 at this site:
http://www.koltenw.com/products.asp?cat"

My application is a smallish robot arm which, with any luck, will be
coming to Burning Man with me this year to autonomously serve drinks.
I'm still debating whether I want to control this thing with a PIC, or
hook it up to a junk laptop and write some control software in Python.
I'm new to both those things, so I'm not sure which would end up being
easier.

Thinking Burning Man, how about an automatic body painter robot arm?
Wait a minute... It's more fun to do it manually!

Good luck with the project.

-- Gordon

Yes, RobotZone. You can get such gearboxes (complete with external pot)
at http://www.servocity.com/  (go under the link for Hitech servos).

And yes, it was obvious to me also.


I like that idea also.
--
D. Jay Newman
http://enerd.ws/robots/

Hi

I have done this very think, I think,  Check out:

<http://www.geology.smu.edu/~dpa-www/robo/servo/servohac>

best
dpa

Eriswerks wrote:

Oops!  URL mangled, should have been:

<http://www.geology.smu.edu/~dpa-www/robo/servo/servohac.htm>

sorry,
dpa

I don't know the date of the patent application, but
I would say that this is prior art.
--
D. Jay Newman
http://enerd.ws/robots/

This requires Dave to have posted the page publicly. The date of the
page is 2000, but this doesn't mean it was publicly available then.

DPA could file an interference if he were so inclined, if he feels this
was originally his idea, and he publicly disclosed it any time before
the patent filing.

However, I will say the patent appears to a combination of two of the
approaches Dave has on the page; that is, the page doesn't explicitly
detail what's covered in the patent. However, it could be argued that
combining the two, as the patent does, is trivial, obvious, and/or
non-novel. Again, could be argued. Not that I am...

-- Gordon

Hi,

Gordon McComb wrote:
...

Oldest reference I can find on the wayback machine internet archives is
August 2003:

<http://web.archive.org/web/20030818211150/www.geology.smu.edu/~dpa-www/robo/servo/servohac.htm>


regards,
dpa

<http://web.archive.org/web/20030818211150/www.geology.smu.edu/~dpa-www/robo/servo/servohac.htm>

The earliest filing of the application is June 18, 2004. The patent I
cited is a later application, based on the 2004 app.

Now, I have no problem with entrepreneurs who innovate, but I do get
concerned if someone obtains a patent for what we've been doing all
along. Rather than innovation it leads to a stiffling of progress. I
know that I have built exactly what is described in the patent as early
as 1991, but I did not publicly disclose it.

Bear in mind the above is not a legal analysis, is not legal advice, and
it is not a professional (or otherwise) judgement on the merits of the
patent claim. It's merely a layman observation.

-- Gordon

Hi

I found an older reference to the same article on the Seattle Robotics
Society Encoder web page, from 2000:

<http://www.seattlerobotics.org/encoder/200010/servohac.htm>

I tend to agree, and the fact that you and I (and who knows who else)
came up
with this independently is highyl suggestive that it is a common
practice.

So, who do we send the link to?

regards,
dpa


Gordon McComb wrote:

<http://web.archive.org/web/20030818211150/www.geology.smu.edu/~dpa-www/robo/servo/servohac.htm>

wayack machine internet archive has the SRS Encoder page archived on
January 26, 2001:

<http://web.archive.org/web/20010126202100/http://www.seattlerobotics.org/encoder/200010/servohac.htm>

dpa

Well, one way to do it is do nothing. The patent may not be granted. The
official procedure is to file an interference, but my non-lawyer
understanding is that this is usually done by people with conflicting
interests in an invention. I'm not sure what the process is for if
you're just a concerned citizen. I'd think it's more of a concern for
Hitec, Futaba, and the other servo makers. Let them make the effort.

Even if the patent is granted, if these previous disclosures are indeed
cogent, then the patent is unenforceable anyway (NON lawyer opinion),
and whoever the inventor is wasted a lot of time and money. The Wayback
Machine is often used for this sort of thing, and I'm surprised a search
of prior art didn't turn up these pages. Even Google would have found
something.

It's not like this field is wildly lucrative, and frankly I'm perplexed
anyone would bother with the expense of a patent. You have to be
prepared to lititagate it, and that can costs hundreds of thousands.

-- Gordon

Yeah, October 2000 in the Encoder seems to be a pretty good hallmark.

Last week, I happened to pick up a magazine from an old stack sitting
around. Forbes ASAP [now defunct, I think] mag from Summer 2002.
Most of the issue was devoted to the mess that is the USPTO. In 2001,
344,717 patents were applied for and 187,822 were granted, almost
"double" on both counts from the year before. An examiner typically
devoted about 20 hours to each patent, including searches on prior art.



be resolved in court, not by the USPTO. I think the system is setup for

the benefit of the lawyers. They make money on both ends, writing up
the patents and litigating them afterwards. The article termed patent
litigation as a "growth industry".













I'm not sure what the process is for if

From what I gather, filing can be really cheap. This gives them the "patent
pending" marketing tool at little expense.

On an off-side, do you recall the debalce with servo city, aka Brian Thomas
robotics, regarding anonamously posting in forums about how great servo city
was?

Mike

No expense at all. Patent Pending only means you intend to seek a
patent. You have a year from first commericalization to file then
protected.


Yes, I remember. Faux Pas extraordinaire as I recall.

I (and some of my attendies) openned a servo and picked off the wiper
signal and measured it in a public class in 2001 during our "Arm in a
day" project. Does that mean I have former art?

--
Randy M. Dumse
www.newmicros.com
Caution: Objects in mirror are more confused than they appear.

In this case they did file, and through an attorney, who I assume
charged the usual fees. So I'm sure it was at least a couple of grand.

Is the market big enough to even bother with "patent pending" marketing?
Is this a product people are falling over themselves to use? I think a
couple of people have asked about the idea here last year. For folks who
need such a thing it's great to have, but you'd think if there was a big
enough market to patent the idea that servo makers would already be
providing ready-made products with these specs. Servo makers have for
years made units with 3-4 turn rotations, and high outputs for things
like sail winches.


I don't remember that one. I'm sure I was here, but probably shilling
for my book, and too busy to notice! <g>

-- Gordon