motor speed ( following all my motors question)

[poutpout]

Is there a way to control the speed of a dc motor? Actually, I'm doing it by adding a potentiometer 1k on the red lead but it should exist a small circuit who's doing the job better than that?

I want to control the speed because I need only betweene 3 or 6 RPM speed.

Thanks again and always!

 

[ericgibbs]

Is there a way to control the speed of a dc motor? Actually, I'm doing it by adding a potentiometer 1k on the red lead but it should exist a small circuit who's doing the job better than that?

I want to control the speed because I need only betweene 3 or 6 RPM speed.

Thanks again and always!

hi,
The best way is PWM, a pot is the worst.

You can make a PWM signal with 555's [ or a PIC ]

EDIT: Look here:
**broken link removed**

 

[poutpout]

hi,
The best way is PWM, a pot is the worst.
You can make a PWM signal with 555's [ or a PIC ]
EDIT: Look here:
DPRG: A Simple PWM Circuit Based on the 555 Timer

Many Many thanks again ericgibbs!

 

[audioguru]

An electric motor must use gears or a pulley to reduce its speed to only 3 to 6 RPM or else it won't have any torque.

 

[arhi]

An electric motor must use gears or a pulley to reduce its speed to only 3 to 6 RPM or else it won't have any torque.

Uncle $crooge, can you please elaborate on this

It is clear that set of gears or pulley's will reduce the speed and increase the torque but "won't have any torque" is bit excessive imho I've seen DC motor (no gears, no pulley's) having enough power that I could hardly stop it with bare fingers (ok it was ~200g 5x3x3cm but again, that's not that big, and it is DC motor)?!

I know there is some great experience behind what you just said, and as there is bunch of us willing to learn new things every day, if you have a moment to share the wisdom we are listening

 

[audioguru]

A little motor has torque when it spins at thousands of RPMs. Its speed is slowed with gears or a pulley to allow plenty of torque and a low current. Then you can control its speed by changing its voltage or its current.

If you slow down a motor by loading it then you don't have any speed control.
If you slow a motor to a crawl by reducing its voltage or current then its power is severely reduced so it won't have any torque.

When you can hardly stop a motor with your bare hands then it is working extremely hard and its current is extremely high. It doesn't have its speed controlled.

 

[arhi]

Uncle $crooge, thanks for explaining, well put as always.

 

[poutpout]

The wonderful thing here is ... I don't need any torque! I just need something turning and quiet. Life is great!

 

[audioguru]

The wonderful thing here is ... I don't need any torque! I just need something turning and quiet. Life is great!

I have some cheap little battery-powered fans. I use rechargeable Ni-MH batteries. The fans spin at a few thousand RPMs. Then when the battery runs down the slowest is about 120 RPM which is a lot faster than you want. The motor barely runs at a speed of only 120 RPM because its voltage is low and its current is low. Voltage times current = power, so its power is so low that it won't start running.

 

[Willbe]

It also turns out there is a limit to PWM; current pulses more than 5x steady state demagnetize the little bugger.

 

[poutpout]

**broken link removed**

According to that diagram, is there an equivalent for the IRFZ46N. I have found one on Ebay but it is 8 pounds for shipping! I refuse paying 8 pounds for shipping that little thing!

 

[arhi]

It also turns out there is a limit to PWM; current pulses more than 5x steady state demagnetize the little bugger.

can you explain this a bit for us with cheaper tickets?

what is "steady state"? Can you give some examples?

 

[Andy1845c]

here is another 555 PWM circuit: Pulse Width Modulation 2
uses a transistor in place of the fet in the circuit you posted.

The IRFZ46N is just a power MOSFET. What voltage and current will it be switching? For the little walkman motor you wouldn't need anything too fancy.

 

[poutpout]

here is another 555 PWM circuit: Pulse Width Modulation 2
uses a transistor in place of the fet in the circuit you posted.
The IRFZ46N is just a power MOSFET. What voltage and current will it be switching? For the little walkman motor you wouldn't need anything too fancy.

Thank you! I don't know what voltage and current because I will use a lot of recycling motors, but they are pretty like the motor from the walkman. Yup, I wouldn't need anything too fancy!

 

[jacks]

here is another 555 PWM circuit: Pulse Width Modulation 2
uses a transistor in place of the fet in the circuit you posted.

The IRFZ46N is just a power MOSFET. What voltage and current will it be switching? For the little walkman motor you wouldn't need anything too fancy.

Hi Andy

Is it possible to connect the 555 PWM circuit to this H-bridge circuit with comparators?If it is how will I connect it? Thanks

**broken link removed**

Jacks

 

[saturn1bguy]

Is it possible to connect the 555 PWM circuit to this H-bridge circuit with comparators? If it is how will I connect it?

If you are still using the first LM311 circuit as per your URL, connect your PWM signal directly to one input OR the other. You'll get speed control in one direction or the other. Make sure your 555 circuit is powered from the same supply as the LM311s, or less.

If you wire your H-Bridge up like the second LM311 circuit, i.e. the one with the two LM311s wired together so there is only one direction input, you can wire your PWM signal to said direction input and achieve what's called Locked Anti-Phase control. This is different than Sign/Magnitude control, which is perhaps more conventional.

Sign/Magnitude control requires two inputs, one for direction (sign) and one for speed (magnitude); the latter is where your PWM is applied. Locked anti-phase control uses a single input where both speed and direction are encoded. PWM duty cycles under 50% represent one direction of rotation, signals over 50% the other. (A 25% duty cycle would be half-speed in one direction, 75% would be half-speed in the other direction, and 50% is off.)

Now I don't know how much hysteresis the LM311 H-Bridge has, so you may experience some funky behavior with a PWM signal of around 50%, ±10%.

See the following and download the manual for more info, if desired:

**broken link removed**

 

[jacks]

Saturn1bguy

Thanks once again, and the link you posted has given me a step to the right direction. I really do appreciate it.

I am planning to build what is known as a Decoder for model railways

**broken link removed**

**broken link removed**


I had to make sure the H-Bridge was working and the speed control (PWM)

I have to control the circuit using an eight bit packet specified by

**broken link removed**

Again, you have pointed me to the right direction with the above link.



Jacks

 

[blueroomelectronics]

Why didn't you say DCC in the first place? It's PWM and microcontroller often little 8 pin PICs

 

[audioguru]

I saw a stepper motor in the document. I thought we were talking about a permanent magnet commutating motor.

 

[poutpout]

In the schematic Andy provided Pulse Width Modulation 2
R2 is 120R 0.25W 10% or better. I don' t have that. Can I use a "normal resistor"? Which value then?

Also, I don't have mylar film or ceramic caps, can I use electrolytic instead?