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DC motor

R

Raul

Jan 1, 1970
0
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
 
I

Ian Stirling

Jan 1, 1970
0
Raul said:
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.

Are you sure it's a simple DC motor?
Most small fans are not, and cannot be reversed.
 
C

Clarence

Jan 1, 1970
0
Raul said:
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

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.
 
B

Brian

Jan 1, 1970
0
Raul said:
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

You didn't give any voltage or current ratings. If it is a low power DC
motor, I drew up something that would probably work for you. Check it out at
http://www.fncwired.com/MotorExample/
Brian
 
R

Raul

Jan 1, 1970
0
-"You didn't give any voltage or current ratings. If it is a low power
DC
motor, I drew up something that would probably work for you. Check it out at
http://www.fncwired.com/MotorExample/"

I'm sorry, it's a small DC I bought at a shop. It's 6v. I might change
it to a 3v because physical space limitations. Thanks for the drawing,
I'll see if I can get it to work.

Raul
 
D

Don Kelly

Jan 1, 1970
0
Raul said:
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
------
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.
 
R

Raul

Jan 1, 1970
0
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
 
R

Raul

Jan 1, 1970
0
Yes, by switching the leads the motor will run either clockwise or
counter clockwise. So I guess I just need a switch to swap the
voltage. That's good. I can have the servo connected to the switch and
the speed control at the same time. That might be the easiest way.
Thanks, Raul
 
B

Brian

Jan 1, 1970
0
Raul said:
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
 
B

Brian

Jan 1, 1970
0
Brian said:
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

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.
 
R

Raul

Jan 1, 1970
0
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.
 
S

Steve Evans

Jan 1, 1970
0
Yes, by switching the leads the motor will run either clockwise or
counter clockwise.

that's your main problem solved. some motors only run one-way whatever
the polarity attached (automobile starter motors, for example).
So I guess I just need a switch to swap the
voltage. That's good. I can have the servo connected to the switch and
the speed control at the same time. That might be the easiest way.
Thanks, Raul

you want a power mosfet in to drve the motor with a PWM signal; that's
most efficeint. there are some simple and really cheap circuits out
there that you can use. just do a search on the web.
 
T

Terry Pinnell

Jan 1, 1970
0
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.

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.
 
P

Peter Bennett

Jan 1, 1970
0
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

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
 
R

Raul

Jan 1, 1970
0
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
 
R

Raul

Jan 1, 1970
0
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?
Thanks for the help.
Raul
 
T

Terry Pinnell

Jan 1, 1970
0
Raul said:
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?

Several things, including my suggestion that you *draw* the schematic
so that we can be clear what you are doing. It doesn't have to be a
work of art. Just identify all connections clearly, and photograph
*that* instead of your breadboard.

Also, if that's 3V you're using for the 741, it's too low a voltage.
 
R

Roger Johansson

Jan 1, 1970
0
Raul said:
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.

You are still only using 2 connections on the op-amp chip.

It needs at least 4 connections, input, output, plus power and minus
power.

The power connections are not shown in some schematics, but the op-amp
always need power to work.

One wire from the pot is not connected to anything..?

Your pictures are very good, and they make it easy to help you. It is
easy to see how the circuit actually is connected.

You need to check all connections of all components on the schematic and
in the real breadboarded circuit.
 
J

John Fields

Jan 1, 1970
0
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?

---
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.
 
P

Peter Bennett

Jan 1, 1970
0
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

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.
 
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