Speed of Motor will be controlled by gain

[qoo]

I have chosen that project for my college. I will use a potentiometer
to vary the resistance and that resistance will vary the gain for the
motor, hence, we will change the speed of the motor by using a
potentiometer.
I think I will use LM741 for amplification. Plz... I want your
comments on that. Thanks

 

[MooseFET]

I have chosen that project for my college. I will use a potentiometer
to vary the resistance and that resistance will vary the gain for the
motor, hence, we will change the speed of the motor by using a
potentiometer.
I think I will use LM741 for amplification. Plz... I want your
comments on that. Thanks

The LM741 is a very old op-amp and is most likely a bad choice.

This is a news group where we discuss designs. You need to make a
start on figuring out what the circuit must do and how to do it before
you are likely to get much help here.

Brush up on your Ohms law. You're going to need it.

 

[Frank Buss]

I have chosen that project for my college. I will use a potentiometer
to vary the resistance and that resistance will vary the gain for the
motor, hence, we will change the speed of the motor by using a
potentiometer.
I think I will use LM741 for amplification. Plz... I want your
comments on that. Thanks

How much power does the motor need? Usually an OpAmp doesn't output the
required power for a motor, you'll need to add a power transistor or a
MOSFET. It depends on your motor type, but if you build a PWM circuit, you
could save big heat sinks. With a MOSFET you don't need an OpAmp any more
and with one or two more transistors you can build the PWM.

 

[Joerg]

The LM741 is a very old op-amp and is most likely a bad choice.

LM324 comes to mind but there should be a transistor between that and
the motor. Possibly a rather big one. Plus some resistors.

This is a news group where we discuss designs. You need to make a
start on figuring out what the circuit must do and how to do it before
you are likely to get much help here.

Yes, and best to post in the s.e.basics group. Also, I'd suggest to get
a copy of "The Art of Electronics", it's all in there.

Brush up on your Ohms law. You're going to need it.

And do it before someone tries to have Ohm's law declared
unconstitutional ;-)

 

[Joerg]

How much power does the motor need? Usually an OpAmp doesn't output the
required power for a motor, you'll need to add a power transistor or a
MOSFET. It depends on your motor type, but if you build a PWM circuit, you
could save big heat sinks. With a MOSFET you don't need an OpAmp any more
and with one or two more transistors you can build the PWM.

Or just use a CD40106 as PWM oscillator and drive a FET with that. If
it's a big one with lots of Cgs use a pair of pnp/npn as buffer. But I
think the OP is just beginning with all this stuff so maybe he should
get his DC circuit working first. Then move on to PWM. Then maybe to a
Blackfin DSP with a nifty PID algorithm in there ;-)

 

[Martin Griffith]

I have chosen that project for my college. I will use a potentiometer
to vary the resistance and that resistance will vary the gain for the
motor, hence, we will change the speed of the motor by using a
potentiometer.
I think I will use LM741 for amplification. Plz... I want your
comments on that. Thanks

As Ken says the 741 is so old, and not really suitable. You could try
the second circuit on this site

http://www.cpemma.co.uk/thermal.html

What test equipment do you have?



martin

 

[Frank Buss]

Then move on to PWM. Then maybe to a
Blackfin DSP with a nifty PID algorithm in there ;-)

A Blackfin DSP would be idle 99.9% of the time with a running PID
algorithm. But it should be fast enough to drive a VGA output and to run a
Linux system. Then you could implement it with Java and a nice GUI, which
should use the Blackfin to full capacity

 

[Joerg]

A Blackfin DSP would be idle 99.9% of the time with a running PID
algorithm. But it should be fast enough to drive a VGA output and to run a
Linux system. Then you could implement it with Java and a nice GUI, which
should use the Blackfin to full capacity

Isn't that what modern operating systems are supposed to do? Generate
tons of work for the processors in order to support sales at the
semiconductor plants ;-)

Oh, and then he'd probably also have to upgrade to 1GB or RAM ...

 

[MooseFET]

LM324 comes to mind but there should be a transistor between that and
the motor. Possibly a rather big one. Plus some resistors.

LT1636 may be a better way to go. LM324s don't pull up very well or
very far and its inputs aren't as robust. When power is removed
suddenly, teh inductive spike from the motor will need some snubbing.

 

[MooseFET]

They already did. The new law is only in effect only on February 29
on odd numbered years. ;-)

At work we often refer to "Ohms opinion". Ohms law often does not
apply in the marketing department.

 

[MooseFET]

How much power does the motor need? Usually an OpAmp doesn't output the
required power for a motor, you'll need to add a power transistor or a
MOSFET. It depends on your motor type, but if you build a PWM circuit, you
could save big heat sinks. With a MOSFET you don't need an OpAmp any more
and with one or two more transistors you can build the PWM.

Use a LM555. You can get the PWM and buckets of base drive.

 

[MooseFET]

A Blackfin DSP would be idle 99.9% of the time with a running PID
algorithm.

It may not be. The OP may want to sample the tach with a 24 bit
converter at 44KHz so that he can handle rapid changes in the load.
He may also want to sample the motors voltage and current and
linearize the torque and move the gain cross over frequency of the
servo loop up to about 5KHz so that he can resond quickly and
accurately to those load changes.

We know that some motors cog as they rotate slowly, at low speeds he
could modulate the PWM operation to remove the torque variations and
produce a smoother rotation.

If there is a CPU, you can bet someone will think of a way to use it
up.

But it should be fast enough to drive a VGA output and to run a
Linux system.

Yes a Blackfin does that nicely.

Then you could implement it with Java and a nice GUI, which
should use the Blackfin to full capacity

No, actually there would still be time left over. You could install a
copy of something like "boch" and install XP on the virtual machine it
makes then all the CPU time would be taken if the user opens one
application.

 

[MooseFET]

As Ken says the 741 is so old, and not really suitable. You could try
the second circuit on this site

http://www.cpemma.co.uk/thermal.html

I don't like that circuit. I would at least add a glitch catching
diode on the motor with its cathode on the positive side and a E-B
resistor on the transistor.

I still think a LM555 would be a better way to go.

 

[Rich Grise]

I have chosen that project for my college. I will use a potentiometer
to vary the resistance and that resistance will vary the gain for the
motor, hence, we will change the speed of the motor by using a
potentiometer.
I think I will use LM741 for amplification. Plz... I want your
comments on that. Thanks

What are you willing to pay to have your homework done for you?

Good Luck!
Rich