2KHz PWM for small motors, Mabuchi FA130. - Electronic Circuits Projects Diagrams Free

blueroomelectronics · 23rd April 2007, 03:09 AM

Many motor controllers use frequencies of around 700Hz for speed control. It appears also 2KHz is a good choice too. The motor is a Mabuchi FA130, Comments?
http://shengyue.en.alibaba.com/produ...130_Motor.html

Sceadwian · 23rd April 2007, 08:11 AM

The only thing that really gives a DC motor a high torque from a dead stop with low driving loss is an absolutly pure DC connection. Since you're likley to have RPM feedback in a controller anyways you could decrease switching loss significantly by using a lower switching frequency at lower RPM's. At dead stop and low RPM's the motor's primary losses are going to be from heat in the coils and the driving circuit itself. You could eliminate this early current draw from the driving circuitry by using no switching at all up until the base low RPM is hit and then switching over to the PWM circuit.
Make sense?

blueroomelectronics · 23rd April 2007, 01:25 PM

Yes it does, and I do have a rotation sensor in the design. The Pololu low voltage small motor controllers PWM between 600Hz to 750Hz.

audioguru · 23rd April 2007, 02:00 PM

I think the motor will have more torque at low RPM because its inductance reduces its current at higher frequencies.

blueroomelectronics · 23rd April 2007, 07:27 PM

Well it's easy enough to drive the motors at 100% PWM (DC) and slow them down the moment the motors begin to turn.
I just thought there was some formula for the ideal PWM frequency for a specific motor type.

jpanhalt · 23rd April 2007, 08:24 PM

There seem to be two schools of thought on the best PWM frequency to use. One school favors relatively low frequencies, as you mention. The other school goes to something like 20 KHz (e.g., 4QD). One rationale for the lower frequencies is that the motor's field and/or armature can keep up with the lower frequency. Those who use the higher frequencies essentially say so what, we are only interested in the average power.

In the few applications that I have made, I went with the higher frequency, namely because you can't hear it. A motor at 2.4 KHz can be a real annoyance. Many of the controllers for small model airplane motors are also going to the higher frequencies. John

bloody-orc · 25th April 2007, 06:48 PM

well I would suggest you get the freq you like

and what is easier to control.
also what kind of PWM you are using. if software one then take lower freq, if Hardware one, then it makes no difference, but lower is still better (less interrupts in the program etc) might make your bot process the data faster. But well... it all depends on the chip you'll be using. PIC I think doesn't care what you use. You are probably using Hardware PWM not a software one (I really Hope at least

.

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23rd April 2007, 03:09 AM	(permalink)
blueroomelectronics	2KHz PWM for small motors, Mabuchi FA130. Many motor controllers use frequencies of around 700Hz for speed control. It appears also 2KHz is a good choice too. The motor is a Mabuchi FA130, Comments? http://shengyue.en.alibaba.com/produ...130_Motor.html __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

23rd April 2007, 08:11 AM	(permalink)
Sceadwian	The only thing that really gives a DC motor a high torque from a dead stop with low driving loss is an absolutly pure DC connection. Since you're likley to have RPM feedback in a controller anyways you could decrease switching loss significantly by using a lower switching frequency at lower RPM's. At dead stop and low RPM's the motor's primary losses are going to be from heat in the coils and the driving circuit itself. You could eliminate this early current draw from the driving circuitry by using no switching at all up until the base low RPM is hit and then switching over to the PWM circuit. Make sense? __________________ "Because I be what I be. I would tell you what you want to know if I could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har."

23rd April 2007, 01:25 PM	(permalink)
blueroomelectronics	Yes it does, and I do have a rotation sensor in the design. The Pololu low voltage small motor controllers PWM between 600Hz to 750Hz. __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

23rd April 2007, 02:00 PM	(permalink)
audioguru	I think the motor will have more torque at low RPM because its inductance reduces its current at higher frequencies. __________________ Uncle $crooge

23rd April 2007, 07:27 PM	(permalink)
blueroomelectronics	Well it's easy enough to drive the motors at 100% PWM (DC) and slow them down the moment the motors begin to turn. I just thought there was some formula for the ideal PWM frequency for a specific motor type. __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

23rd April 2007, 08:24 PM	(permalink)
jpanhalt	There seem to be two schools of thought on the best PWM frequency to use. One school favors relatively low frequencies, as you mention. The other school goes to something like 20 KHz (e.g., 4QD). One rationale for the lower frequencies is that the motor's field and/or armature can keep up with the lower frequency. Those who use the higher frequencies essentially say so what, we are only interested in the average power. In the few applications that I have made, I went with the higher frequency, namely because you can't hear it. A motor at 2.4 KHz can be a real annoyance. Many of the controllers for small model airplane motors are also going to the higher frequencies. John Last edited by jpanhalt; 23rd April 2007 at 11:32 PM.

25th April 2007, 06:48 PM	(permalink)
bloody-orc	well I would suggest you get the freq you like and what is easier to control. also what kind of PWM you are using. if software one then take lower freq, if Hardware one, then it makes no difference, but lower is still better (less interrupts in the program etc) might make your bot process the data faster. But well... it all depends on the chip you'll be using. PIC I think doesn't care what you use. You are probably using Hardware PWM not a software one (I really Hope at least . __________________ Need Help? Press F1 If that doesn\'t help you, ask me... I might know better.