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Topic: PWM affects only speed or torque as well ? (Read 3296 times) previous topic - next topic

TomGeorge

#15
Mar 19, 2018, 10:18 pm Last Edit: Mar 19, 2018, 10:18 pm by TomGeorge
Hi,
Can you share your code and schematic please?

As this will probably help the OP.

Please read the first post in any forum entitled how to use this forum.
http://forum.arduino.cc/index.php/topic,148850.0.html

Thanks.. Tom.. :)
Everything runs on smoke, let the smoke out, it stops running....


TomGeorge

How about this ? Good stable torque

https://fr.aliexpress.com/item/1-Pcs-N20-DC-12V-100-Rpm-Gear-Motor-High-Torque-Miniature-Motor-Gear-Box-Shaft/32695520982.html
I've  got the 600RPM output ones on order from ebay, shouldn't be long before they arrive.
https://www.ebay.com.au/itm/600RPM-Micro-Speed-Reduct-Gear-Motor-Metal-Gearbox-Wheel-Shaft-DC-12V/323030122621?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2648

Tom.. :)
Everything runs on smoke, let the smoke out, it stops running....

ted

Hi Tom
So you are doing the same project ?

TomGeorge

#19
Mar 20, 2018, 02:52 am Last Edit: Mar 20, 2018, 02:53 am by TomGeorge
Hi Tom
So you are doing the same project ?
No, not really, just looking for some stuff for my brother for his model railway. and me to play around with.


Very relaxing just playing around with stuff.


Tom.. :)
Everything runs on smoke, let the smoke out, it stops running....

ted


fall-apart-dave

V=I*R, so I=V/R

Pi (power in)=I*V


Po (power out) = τ * ω (torque*angular speed)

Torque is calculated by:

τ = (I * V * E *60) / (rpm * 2π) (where E is efficiency)


So you can infer that your current PEAKS will be the same as the constant current were the motor just "on", since PWM is just pulses of 5v and we will say, for ease, that your motor impedance does not change (it does because its a dynamic load but for our purposes here we can say it doesn't)

But your RMS voltage, current and power will all be lower, because any PWM is actually a square wave AC with a bias of 1/2 peak voltage (in other words it stays positive).

So. Your torque will be reduced, as will speed. It can't be any other way. However, if you can get speed to reduce by enough, your torque will increase and balance out.


ted

V=I*R, so I=V/R

Pi (power in)=I*V

You forgot that PWM is not DC and motor is not only R there is a  L.

TomGeorge

Hi Tom
So you are doing the same project ?
Hi, mate
Got my 600RPM motors, really good torque for their size and current at 12V.
Yes, I agree, PWM brings motor inductance into the equation.
Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

ted

V=I*R, so I=V/R

Pi (power in)=I*V


If you like math use this formula; P = U* x I* x cos φ , is good for sine maybe will work for PWM ?

ted

Hi, mate
Got my 600RPM motors, really good torque for their size and current at 12V.
Yes, I agree, PWM brings motor inductance into the equation.
Tom... :)
So you going to have a strong locomotive for Batman

TomGeorge

So you going to have a strong locomotive for Batman
What I am thinking of doing is making a dynomometer to test these cheap and sometimes nasty motors.
Compare linear and PWM performance.
Just a thought. :o :o :o


Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

ted

look at data sheet torque about 2 kg/cm

prayuth01

guideline

Control power output to control devices such as motor strength. The brightness of the LED typically means lower output voltage to the motor. But the pressure is the approach which requires complex circuit is quite tricky. So basically used a technique called Pulse Width Modulation (PWM), which does not reduce pressure. If you use the on / off motor with high speed. The average result of the pressure that has come out is equivalent to change the voltage directly. This technique does not require a complicated circuit. The programming will be more difficult for some.

PWM is typically to generate the square wave (Square Wave) issued by the periodic signal (Period) for a short period, which normally would be of value not exceeding 33 ms (30 Hz) typical for trial. And may be less than 0.01 ms (100KHz) or less in some industrial applications. The key is to adjust the width of the PWM wave in each period. If the pressure wave, it will mean that it is less. And if the average pressure wave would be more valuable. Figure V below average (orange line) will be higher or lower depending on the amplitude of the wave. The amplitude of the wave is called the pulse width or Duty Cycle.

Pulse width will be less than the length of the period is always Duty Cycle Units% of the long period if Period = 10ms and Duty Cycle = 40% means that Pulse width = 10ms * 0.4 = 4 ms and so on. ทางเข้า

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