DC motor

"aman" <aman.bindra@gmail.com> wrote in message
news:1113950521.738636.69580@o13g2000cwo.googlegroups.com...
I can detect a short across the terminals of a DC motor(when I do a
continuity test) before I even connect it. Can anyone tell me what the
problem can be. Do you guys think the motor burnt away or what ?
Click to expand...
Has the commentator ring slipped or are you using brushes that are too
large?

Pull the brushes and test the coils directly at the commentator. You could
have some failed insulation in one of the coils.
 
aman wrote:
This is the motor I am using

http://www.clickautomation.com/PDF/items/GM8712-31.pdf

Anything I can test to see what the problem is ?

What value of resistance did you measure?
Click to expand...
 
aman wrote:

This is the motor I am using

http://www.clickautomation.com/PDF/items/GM8712-31.pdf

Anything I can test to see what the problem is ?

i assume if its much less than 10.8 ohms ! then you must
Click to expand...
really have a short.
because the data that shows does specify 10.5 ohms as the
norm.
 
"aman" <aman.bindra@gmail.com> wrote in message
news:1113951440.881856.112410@l41g2000cwc.googlegroups.com...
This is the motor I am using

http://www.clickautomation.com/PDF/items/GM8712-31.pdf

Anything I can test to see what the problem is ?
Click to expand...
Looks sealed! So no. Since they tested this gear motor at 19 volts to
measure a stall current of 1.76 A. I see no reason you can't connect
it to 12 volt supply and limit the current too a few mA. Slowly
increase the current while observing the voltage. If the motor is
shorted, the voltage will only indicate 0 no matter the current limit.
 
On Tue, 19 Apr 2005 15:42:01 -0700, aman wrote:

I can detect a short across the terminals of a DC motor(when I do a
continuity test) before I even connect it. Can anyone tell me what the
problem can be. Do you guys think the motor burnt away or what ?
Click to expand...
Are you sure it's a "short", or are you just measuring a very low
resistance? They do have a very low DC resistance, you know - the
current flow is limited by what's called "back EMF", which is a
voltage created by the motor's generator action while it's running,
that opposes the applied voltage. You haven't said how big the motor
is, or its ratings, or anything else.

Just for perspective, I've never seen a motor fail short. If it's
busted, it'll fail open or will have already burned up.

How big is the motor, and on what resistance range were you? Did you
zero the meter?

Good Luck!
Rich
 
On Tue, 19 Apr 2005 15:57:20 -0700, aman wrote:
This is the motor I am using
http://www.clickautomation.com/PDF/items/GM8712-31.pdf
Anything I can test to see what the problem is ?
Click to expand...
Get your hands on a 12V power supply and a 10 ohm, 25 watt
resistor.

Put the resistor in series with the power supply and motor:


10 ohms, 25 watts
+12 ----/\/\/----. A
|
[Motor]
|
12V ret. --------' B

Apply power, and see if it runs. The resistor will limit
the current to 1.2A if it's short, which is somewhat less
than the motor's rated stall current (1.76A, from the
datasheet), so even if the motor is a dead short, it will
not burn.

If the motor runs, albeit slowly, then you've got a good
motor.

If not, measure the voltage at point A (the + side of the
motor) relative to point B (the - of the motor). If it's
zero volts, you have a shorted motor. If it's more, I'd
say it's safe to try the 19V supply - first with the
resistor, and if it runs lamely, then leave out the
resistor, because you've most likely got a working motor.

Good Luck!
Rich
 
"Raul" <webmaster@2minclip.biz> wrote in message
news:5902f39f.0412030833.6d9ca8d8@posting.google.com...
First, let me say hello to everyone as I am new to the group. My
question is how can I wire a DC motor to be reversible. Can I use a
potentiometer? It's for a remote control fan. The switch will be
connected to a servo. What I want is: The more I turn to the right the
faster the fan goes clockwise. The more I turn to the left the faster
the fan goes counter clockwise.
If anyone can help that would be great.
Thanks, Raul
Click to expand...
If, as you said this is a motor for an RC race car. A potentiometer will not
be a reasonable way to control speed. Such motors are wound with as few as ten
turns per phase and draw a LOT of current. A solid state controller for that
type of motor may have as many as 6 MOSFET's to switch a PWM for speed control.
Reversing is just a mater of reversing the leads. However it will cause
additional wear on the Brushes.

I would recommend getting a more suitable motor rated for a somewhat higher
voltage (say 24VDC) surplus, and working with a lower current requirement and a
slower speed due to an already reduced voltage vs. rating.
 
"Raul" <webmaster@2minclip.biz> wrote in message
news:5902f39f.0412030833.6d9ca8d8@posting.google.com...
First, let me say hello to everyone as I am new to the group. My
question is how can I wire a DC motor to be reversible. Can I use a
potentiometer? It's for a remote control fan. The switch will be
connected to a servo. What I want is: The more I turn to the right the
faster the fan goes clockwise. The more I turn to the left the faster
the fan goes counter clockwise.
If anyone can help that would be great.
Thanks, Raul
------
Click to expand...
This depends on how the motor is wound. If it has a wound field- then you
need to get into it to separate the field and armature windings. Then you
can use a reversing switch to reverse either the field or armature. This
requires surgery on the motor. If it has a permanent magnet field then
reversing the connections should do it. Note that often a motor will rn
better in one direction than the other. A center tapped potentiometer could
do it, with the right connections but this is horribly wasteful of energy.
Better to use a reversing switch along with your speed control which could
be electronic rather than a potentiometer.
--
Don Kelly
dhky@peeshaw.ca
remove the urine to answer
 
"Raul" <webmaster@2minclip.biz> wrote in message
news:5902f39f.0412032257.3ef30312@posting.google.com...
I'm also wondering about the parts in your dual powersource drawing.
You have a NPN and a PNP transistor. Will any do or do they need to be
specific?
What do I use for the amplifier? I apologize for my ignorance. I'm a
newbie who builds junkbots, if I don't have the part number, it's hard
for me. This is for a small underwater ROV. The motor will control the
verticle movement.
Raul
Click to expand...
The parts aren't that fussy. The op-amp could be something like a LM741.
What transistor to use, depends on how much current your motor takes to run.
I would use a transistor that could handle the stall current of the motor.
To find the right transistor, I would suggest you go to
http://www.digi-key.com/ and use their search engine. Their search engine is
very good. After you select "transistors", it will give you some parameters
to choose from. Based on that, it will give you a list of transistors to
choose from.
Brian
 
"Brian" <bellis350@comcast.net> wrote in message
news:OMGdnaBD3IpeRSzcRVn-hA@comcast.com...
"Raul" <webmaster@2minclip.biz> wrote in message
news:5902f39f.0412032257.3ef30312@posting.google.com...
I'm also wondering about the parts in your dual powersource drawing.
You have a NPN and a PNP transistor. Will any do or do they need to
be
specific?
What do I use for the amplifier? I apologize for my ignorance. I'm a
newbie who builds junkbots, if I don't have the part number, it's
hard
for me. This is for a small underwater ROV. The motor will control
the
verticle movement.
Raul

The parts aren't that fussy. The op-amp could be something like a
LM741.
What transistor to use, depends on how much current your motor takes to
run.
I would use a transistor that could handle the stall current of the
motor.
To find the right transistor, I would suggest you go to
http://www.digi-key.com/ and use their search engine. Their search
engine is
very good. After you select "transistors", it will give you some
parameters
to choose from. Based on that, it will give you a list of transistors to
choose from.
Brian
Click to expand...
The op-amp should work under the voltages that you are using and supply
enough drive current for the transistors. The transistors need to work with
the voltages being used (I like to have them work with 4 times the max.
voltages required). The transistors must handle the max. current and have
enough current gain for the drive current supplied.

The 741 op-amp supplies 0.02 amps of drive current for the transistors. If
the transistors have to supply maybe 0.8 amps to the motor, then the current
gain (Beta) of the transistor has to be 0.8 / 0.02 = 40. So if you are using
a +/- 6 volt supply, under normal working conditions each transitor will
need to handle 12 volts, so choose a transistor that can handle 48 volts,
with a minimum Beta of at least 40 or more.
 
webmaster@2minclip.biz (Raul) wrote:

I got all the parts but it doesn't work yet. I'm sure it's some stupid
thing I'm doing wrong. Here is a shot of the bread board setup. What
do you think the problem is?

http://www.asianhound.com/motor.html

Thanks, Raul
p.s. I must add I can't believe how great the response has been for my
problem. If I could only get people that actually work for me to be
this enthusiatic about stuff.
Click to expand...
You don't identify the op-amp, but whatever it is, you seem to have
several pins unconnected. In fact it looks to me as if you only have
pins 5 and 6 connected! In particular, you have not supplied power to
the opamp. If that's a 741 or similar, +V should go to pin 7, and 0V
(ground, or battery negative) to pin 4. And what is pin 6 connected to
via the red and yellow links? Looks like they just go to strips 18 and
19 of your stripboard, but then nowhere! And what transistors are
those, and what pins are which?

Why not *draw* the schematic, i.e. show what wires connect what pins
etc.

--
Terry Pinnell
Hobbyist, West Sussex, UK
 
On 5 Dec 2004 07:20:52 -0800, webmaster@2minclip.biz (Raul) wrote:

I got all the parts but it doesn't work yet. I'm sure it's some stupid
thing I'm doing wrong. Here is a shot of the bread board setup. What
do you think the problem is?

http://www.asianhound.com/motor.html
Click to expand...
Your schematic should show pin numbers on the op-amp, and should also
show the power supply connections for the op-amp.

I don't see any power supply connections on the breadboard - without
that, it is hard to say what is wrong.

I don't see the feedback connection on the op-amp (output to -input),
and one lead of the pot is not connected.

One of the transistors is inserted in the breadboard incorrectly, I
think. The flat sides should both face the same way, not towards each
other.

--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca
 
On 6 Dec 2004 08:02:02 -0800, "Raul" <webmaster@2minclip.biz> wrote:

Ok, I re-did the board but still no dice. Here are pics of how it sits
now.

http://www.asianhound.com/motor.html

If I swap the transistors the motor runs but one of the transistors
gets really hot.

Now what am I doing wrong?
Click to expand...
---
Probably nothing, since if the motor runs, one of the transistors
_has_ to get hot! The transistors just look like variable resistors,
and since you're dropping some of the supply voltage across and
allowing current to flow through the one that's running the motor, the
amount of current flowing through the resistor multipled by the
voltage dropped across the resistor will be equal to the power it's
wasting in order to slow the motor down.

Unfortunately, there's not a lot you can do with the motor even if you
do get it to run back and forth, since at low speeds you'll get very
little torque out of it and there'll be a pretty wide "dead band"
around the center of the pot's range where the motor won't do anything
except sit there.

The best way to do what you want to do is to pulse-width modulate the
motor, which means that if you want it to run slow you turn it all the
way on but only for a short time every once in a while, and if you
want it to run faster you leave the switch on a little longer every
once in a while. The slick thing about doing it that way is that
since the switches are only ever either all the way on or all the way
off they don't get very hot. I'm working on a simple circuit to do
that, and I'll post it when I'm done if you're interested.

--
John Fields
 
On 6 Dec 2004 07:57:55 -0800, "Raul" <webmaster@2minclip.biz> wrote:

Ok, I re-did the bread board but still no dice. Here are pics of the
current setup.

http://www.asianhound.com/motor.html

If I swap the transistors the motor runs in one direction but one of
the transistors gets really hot.

Thanks for all the help.
Raul
Click to expand...
You have the negative sides of the two batteries connected together,
so you have two positive supplies, not one positive,m and one
negative.

Please show pin numbers for the op-amp on your schematic. As far as I
can tell, the op-amp is not connected corretly - it appears that you
misunderstand how the pins are numbered, but without pin numbers on
the schematic, it is hard to say how you think the pins are numbered.

The dimple on top of the IC is close to pin 1, and the pin numbers run
counterclockwise from there - just as shown on the pinout drawing.

You appear to have the output (pin 6) connected to V- (pin 4), and the
wiper of the pot connected to V+ (pin 7)

You still don't have any power supply on the op-amp, so it won't work.


--
Peter Bennett VE7CEI
email: peterbb4 (at) interchange.ubc.ca
GPS and NMEA info and programs: http://vancouver-webpages.com/peter/index.html
Newsgroup new user info: http://vancouver-webpages.com/nnq
 
Raul wrote:
Ok, I put up some more images. I don't know the pin numbers for the
op-amp on the schematic. I didn't draw it. A guy named Brian did when I
first posted my problem. I'm a novice. I just make bugbots from books
as a hobby. The schematic shows three connections to the the amp. So
I've got three. That's probably the problem, he assumed I knew
something... My wife does that sometimes also.

Raul
Click to expand...
Your basic problem is that you are confusing the + and - inputs with the
power supply. Pin 7 should go to the highest voltage (the + terminal of
the positive side battery pair) and pin 4 should go to the lowest
voltage (the - terminal of the negative side battery pair). These are
the POWER SUPPLY pins. The things marked - and + on the triangle in the
schematic are really the 'inverting input' and 'non-inverting input',
respectively.

Thus, your opamp needs 4 inputs, two for power, and two for the + and -
inputs. The output goes to bases of the transistors.

Also, your connections for the two transistors look wrong. They should
be like this (view with fixed-space font):

+
|
e b c 2N3904
| |
motor---o o-------- ctl
| |
e b c 2N3906
|
-

With this picture, they should both be flat-side 'down', towards
negative. Look at the datasheet for the transistors on
http://www.fairchildsemi.com/ds/ if you are confused by this.

One final thing: if you take the feedback to pin 2 from the emitters of
the transistors (they are connected together) then your opamp will
compesate for any wierdness in the push-pull circuit, making the
transition much smoother (otherwise, there will be a big spot when the
output is at ground)

One other final thing: If you use two similar circuits, and hook them up
so one goes up as the other goes down, you will be able to make the
motor go much faster. There is a simple op-amp circuit to do this:

VCC
----------------
| |
.-. |
| | R2 |
| | | R1
'-' | ___
| .----|----|___|--.
| | | |
| R1 | | |
| ___ | |\| |
Input ----|--|___|--o--|-\ |
| | >----------o-Inverted Output
o------------|+/ With respect to
| |/| Ground
| |
| |
.-. |
| | R2 |
| | |
'-' |
| |
----------------
-VCC
(created by AACircuit v1.28 beta 10/06/04 www.tech-chat.de)

Thus, using an LM324 and two more transistors, you could double the
voltage range across the motor.

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.
 
Raul wrote:
I'm sorry to say Robert it still doesn't work. I don't know what I'm
doing wrong. Am I supposed to have two power supplies? Here are the
lastest pictures if you want to have a look.

http://www.asianhound.com/motor.html

I you guys feel like I'm wasting your time just let me know and I won't
bug you anymore.

Thanks, Raul
Click to expand...
Still wrong. The + sign inside the triangle amplifier symbol refers
to pin 3, the noninverting input, and the - refers to pin 2, the
inverting input. After you move the connections on those pins,
connect pin 7 (V+) to the positive side of the battery and pin 4 (V-)
to the negative side of the battery.

This design needs two batteries connected in series, so that the
middle point between them can serve as the ground point for the
motor. That way, if the upper transistor turns on, the upper battery
drives the motor one way and if the bottom transistor turns on, it
allows the bottom battery to drive the motor the other way. I would
start with two nine volt batteries, to make sure the op amp has enough
voltage to function. There are opamps that work on less, but this one
needs at least 6 volts total, before it can swing its output much at
all.
--
John Popelish
 
"Raul" <webmaster@2minclip.biz> wrote:

I'm sorry to say Robert it still doesn't work. I don't know what I'm
doing wrong. Am I supposed to have two power supplies?
Click to expand...
You have two supplies, two battery units.
Connect plus from one with minus from the other to get your ground.

Here are the
lastest pictures if you want to have a look.

http://www.asianhound.com/motor.html

I you guys feel like I'm wasting your time just let me know and I won't
bug you anymore.
Click to expand...
I don't think you are wasting anybodies time, you do a lot to explain
your situation, and your pictures are very helpful.

I have reloaded the web page to get the latest version.
In the first picture I see the faulty numbering of the pins is still
there.

The pins marked V- and V+ in the second picture, are the power
input pins, not the op-amp input pins. The inputs are marked Inverting
input and non-inverting input.

In the schematics you still have only 3 connections on the op-amp.
This has led you to the faulty use of the pins.

Start by adding vertical line into the op-amp triangle, from the top
side, write V+ beside it. Add vertical line into the op-amp from the down
side, write V- beside it. Erase these symbols from where you had earlier
written them. These arrows you have drawn point to the op-amp inputs,
often marked with - or +. But not with V+ and V-, they are the power
connection labels.

Now you have an op-amp with 5 connections.
Make sure you mark and use them correctly.

On the breadboard, in reality, you have connected the battery pack to the
power rails, that is good. But you should add a wire between the minus of
the upper battery pack to the plus of the lower pack. That wire and the
rows of holes connected to it, is your ground.

I have not checked the rest of the circuit, you need to fix these big
problems to begin with.



--
Roger J.
 
Raul wrote:
I'm sorry to say Robert it still doesn't work. I don't know what I'm
doing wrong. Am I supposed to have two power supplies? Here are the
lastest pictures if you want to have a look.

http://www.asianhound.com/motor.html

I you guys feel like I'm wasting your time just let me know and I won't
bug you anymore.

Thanks, Raul
Click to expand...
Here is a better schematic, that shows everything including pin numbers:

http://home.comcast.net/~rcmonsen/raul/motor1.GIF

note the batteries, which are 9V. Your 3V batteries may not work, as JP
pointed out. I bet the 741 can't get closer than about a volt to the top
rail.

Here is a schematic for the circuit I proposed, that gets you twice the
voltage across the motor

http://home.comcast.net/~rcmonsen/raul/motor2.GIF

Here are some fuzzy pictures of the second circuit, which is using an
LM324 opamp instead of two 741s:

http://home.comcast.net/~rcmonsen/raul/circuit1.jpg
http://home.comcast.net/~rcmonsen/raul/circuit2.jpg
http://home.comcast.net/~rcmonsen/raul/circuit3.jpg

Here is a circuitmaker input file of the circuit:

http://home.comcast.net/~rcmonsen/raul/circuit.ckt

Good Luck.

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.
 
Ok, I changed the schematic to add in the voltage. I also changed to a
higher voltage as suggested incase that was a problem. I have it wired
as the new schematic shows and the motor turns. Yea! Only one direction
though. The 3904 resistor get very hot very quickly so I have to unplug
the power. Atleast I'm making progress. Here are the new pics.
http://www.asianhound.com/motor.html

Thanks, Raul
 
Raul wrote:
Ok, I changed the schematic to add in the voltage. I also changed to a
higher voltage as suggested incase that was a problem. I have it wired
as the new schematic shows and the motor turns. Yea! Only one direction
though. The 3904 resistor get very hot very quickly so I have to unplug
the power. Atleast I'm making progress. Here are the new pics.
http://www.asianhound.com/motor.html

Thanks, Raul
Click to expand...
It only goes one direction because one side of the motor is grounded.
You could just get rid of the 2N3906, because it will never do anything
with this hookup.

If you want it to go in both directions, you could use dual batteries,
and connect the other side of the motor not to the negative rail, but to
the point between the batteries. See the schematic I posted in another
area of the thread.

Note that your transistors aren't going to be able to take much current.
The 2N3904 is limited to something like 200mA, and 650mW.

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top