Does this pot exist?

[steamer]

--Howdy! I've been fiddling around with using a pot to position a
"servo". I'm using the teeny weeny one from Parallax that needs to be
turned with a screwdriver. The application is to drive one of those
surplus windshield wiper motors; I'm using the PWM output to send signals
to a Victor motor controller and this is working very well.
--The trouble is determining, with certainty, that the motor is in
"neutral", so to speak. What I'm trying to do is use the motor as a winch
to move a small load up and down on an art car I'm building. The winch
will position the load one way when the vehicle is in motion and in
another when it's parked. Although it's tempting to use a DPDT switch, I'd
prefer to control the rate of the load's position change with a big, easy
to grasp knob on a pot that could be located a few feet from the Stamp.
What's needed is a tactile feedback of some kind so that I know when the
motor is in "neutral", so that the motor isn't creeping. Text and photos
of project to date at: www.nmpproducts.com/artcar.htm.
--TIA,

 

[Tom Biasi]

--Howdy! I've been fiddling around with using a pot to position a
"servo". I'm using the teeny weeny one from Parallax that needs to be
turned with a screwdriver. The application is to drive one of those
surplus windshield wiper motors; I'm using the PWM output to send signals
to a Victor motor controller and this is working very well.
--The trouble is determining, with certainty, that the motor is in
"neutral", so to speak. What I'm trying to do is use the motor as a winch
to move a small load up and down on an art car I'm building. The winch
will position the load one way when the vehicle is in motion and in
another when it's parked. Although it's tempting to use a DPDT switch, I'd
prefer to control the rate of the load's position change with a big, easy
to grasp knob on a pot that could be located a few feet from the Stamp.
What's needed is a tactile feedback of some kind so that I know when the
motor is in "neutral", so that the motor isn't creeping. Text and photos
of project to date at: www.nmpproducts.com/artcar.htm.
--TIA,

--
"Steamboat Ed" Haas : The other night I
Hacking the Trailing Edge! : dreamed about wasabi...
http://www.nmpproducts.com/intro.htm
---Decks a-wash in a sea of words---

Hi,
Say more about the pot that is working now. Is it a multi turn pot?
What resistance? The motor will be in 'neutral' when the voltage across the
motor is zero volts.
Tactile feedback is another story.
Tom

 

[Chris]

--Howdy! I've been fiddling around with using a pot to position a
"servo". I'm using the teeny weeny one from Parallax that needs to be

turned with a screwdriver. The application is to drive one of those
surplus windshield wiper motors; I'm using the PWM output to send signals
to a Victor motor controller and this is working very well.
--The trouble is determining, with certainty, that the motor is in

"neutral", so to speak. What I'm trying to do is use the motor as a winch
to move a small load up and down on an art car I'm building. The winch
will position the load one way when the vehicle is in motion and in
another when it's parked. Although it's tempting to use a DPDT switch, I'd
prefer to control the rate of the load's position change with a big, easy
to grasp knob on a pot that could be located a few feet from the Stamp.
What's needed is a tactile feedback of some kind so that I know when the
motor is in "neutral", so that the motor isn't creeping. Text and photos
of project to date at: www.nmpproducts.com/artcar.htm.
--TIA,

--
"Steamboat Ed" Haas : The other night I
Hacking the Trailing Edge! : dreamed about wasabi...
http://www.nmpproducts.com/intro.htm
---Decks a-wash in a sea of words---

Lookin' good, Ed. The model sitting in the cart in Fig. 2 is very
complimentary to your project -- easy on the eyes, and a definite plus
for the Art Cart team.

Have you considered using a "rocker pot" joystick? You can easily
program in a big enough dead zone for any variability in supply voltage
and pot manufacturing. This will definitely give you a "neutral"
position with feedback -- you just let go of the joystick or let it
spring back to its center position, and the motor stops. You would be
using the pot to determine motor speed and direction rather than
absolute position. You also might just use a couple of microswitches
on the winch to determine end of travel positions (this prevents winch
overtravel and/or overloading the motor). If you were interested in
saving a few clams (and possibly provide some flair of a commercial
sort to your project) you might want to look at some old joysticks (you
can feel if they're just switches by the "click" on end of travel --
stay away from those), and only use the X- or Y-axis (depending on
whether it's going up/down or side-to-side). Many of the older ones
were made to be rugged, have a good plastic/rubber boot over the stick,
and might withstand an onslaught of sand pretty well.

Good luck
Chris

 

[John Smith]

I've been lazy and haven't looked at your link.

But...

Have you considered a potentiometer with a built-in switch, like those used
on small transistor radios which control the on-off (switch) AND the volume
(potentiometer)? Should be really easy to get hold of.

 

[steamer]

: Hi,
: Say more about the pot that is working now. Is it a multi turn pot?
--Single turn; maybe 270 degrees total movement; I'll have to
check to be sure tho..
: What resistance? The motor will be in 'neutral' when the voltage across the
: motor is zero volts.
100k ohm, if I read the meter correctly. Yah, that's the
kicker: the motor in "neutral" is still heating up, methinks. However
I crossposted to a robotics group and I found an answer in the form of
a "deadband" that I can program into the Stamp.

: Tactile feedback is another story.
--Yeah; still needed tho...

 

[steamer]

--Re: rocker pot: neat idea! Must remember to put it where it
can't be bumped accidentally tho..

 

[steamer]

: I've been lazy and haven't looked at your link.
: But...
: Have you considered a potentiometer with a built-in switch, like those used
: on small transistor radios which control the on-off (switch) AND the volume
: (potentiometer)? Should be really easy to get hold of.
--Thanks; a viable Plan "B".

 

[Chris]

--Re: rocker pot: neat idea! Must remember to put it where it
can't be bumped accidentally tho..

--
"Steamboat Ed" Haas : The other night I
Hacking the Trailing Edge! : dreamed about wasabi...
http://www.nmpproducts.com/intro.htm
---Decks a-wash in a sea of words---

Hi, Ed. You're right -- accidental jostling of joysticks can result in
big problems.

From quite a bit of experience using joysticks for industrial

applications, I'd like to suggest a "dead man" footswitch or pushbutton
located somewhere else on the control panel. The joystick will only
work while the other button is being pressed. That prevents
inadvertent motion, because the operator has to do "something wrong"
with both hands or one hand and one foot simultaneously.

It's far better to use the "dead man" switch independently of the
processor, rather than just using it as a Stamp input. I would
consider tying the switch/button into the power bus for the motor
drive, using it to drive a relay which does, or using the switch as an
"inhibit" input to your drive.

If you're going with a relay, one good pushbutton choice would be the
All Electronics PB-211 red jumbo pushbutton. You'd recognize it as an
arcade game button, and the switching mechanism is physically separated
from the pushbutton as a microswitch below the plunger mechanism. That
will help with the sand. Somehow, grit always wants to slide in on the
sides of the switch. Another option is to get a pushbutton with rubber
boot, but that will be quite a bit more expensive.

Assuming you've got 12VDC available, you might want to try these for
your Art Cart:

"Rocker Pot" Joystick -- check around -- there are a lot of old ones
available in garage sales and attics. I once got one for free as a
"throw in" with purchase of an old "transistorized" table radio at a
garage sale.

Relay: All Electronics RLY-351 -- $2.40 ea.

12VDC 88 ohm coil, N.O. contacts are rated to switch 30A. Bulkhead
mount, faston-type tab connectors

Switch: All Electronics PB-211 -- $3.75 ea.
With 3 amp SPDT microswitch

http://www.allelectronics.com/

No minimum order at All Electronics -- be sure to sign up for their
catalog mailing list.

Good luck
Chris

 

[Rich Grise]

: Hi,
: Say more about the pot that is working now. Is it a multi turn pot?
--Single turn; maybe 270 degrees total movement; I'll have to
check to be sure tho..
: What resistance? The motor will be in 'neutral' when the voltage across the
: motor is zero volts.
100k ohm, if I read the meter correctly. Yah, that's the
kicker: the motor in "neutral" is still heating up, methinks. However
I crossposted to a robotics group and I found an answer in the form of
a "deadband" that I can program into the Stamp.

: Tactile feedback is another story.
--Yeah; still needed tho...

Look at some Radio Control stuff - I think the transmitters for radio
controlled cars have a small steering wheel with a spring-return to
center. Check out your local hobby shop.

Good Luck!
Rich