Hello,
I'm attempting to run a dc motor using PWM, but when the values get lower the motor becomes more and more noisy. I can manage this with an RC filter (10k ohms and a 100uF cap). The issue is that after this resistor I'm not getting nearly enough voltage to move the motor. I'm thinking I could use an amplifier to boost the signal from after the low pass but are there better ways of achieving this?
Note: The power supply is 9v from an SN754410 H-Bridge
The usual method is to use a suitable (and commercially available, and inexpensive) motor driver module (circuit board) to drive the motor. And, if the PWM signal has a time-averaged value (eg. over 1 cyclic period) that falls below a certain amount, then it is not going to move the motor - due to "motor dead zone". In that case, the method is not to amplify the signal. Instead, just keep the PWM level ABOVE that 'certain amount'. That is.... don't fall below some minimum PWM level.
TheNimaj:
Hello,I'm attempting to run a do motor usuing PWM, when the values get lower the motor becomes more and more noisy. I can manage this with an RC filter (10k ohms and a 100uF cap). The issue is that after this resistor I'm not getting nearly enough voltage to move the motor. I'm thinking I could use an amplifier to boost the signal from after the low pass but are there better ways of achieving this?
Note: The power supply is 9v from an SN754410 H-Bridge
You don't low-pass filter power PWM, it goes straight into the motor where the winding
inductance does all the filtering needed. Assuming a reasonable PWM frequency for the size of motor.
MarkT:
You don't low-pass filter power PWM, it goes straight into the motor where the winding
inductance does all the filtering needed. Assuming a reasonable PWM frequency for the size of motor.
The motor is one attached to a 100mm fader (slide pot). Im relatively new to this sort of thing but I tried changing the PWM frequency with no success. The issue is that it's too noisy at low duty cycles (sub 50%) but I've found I needed to go this low to make accurate movements.
Southpark:
In that case, the method is not to amplify the signal. Instead, just keep the PWM level ABOVE that 'certain amount'. That is.... don't fall below some minimum PWM level.
That was my thought too: if you up the voltage after reducing it with PWM, then you might as well not have taken the PWM voltage so low anyway.
JimboZA:
That was my thought too: if you up the voltage after reducing it with PWM, then you might as well not have taken the PWM voltage so low anyway.
I think I was unclear. Using PWM causes the fader to move in jittery and noisy steps, I came to the conclusion that a lp filter would remedy that. Simply putting a capacitor in parallel helped to an extent. However, the resistor used for the RC circuit drops the voltage to an unusable level. This is the problem I'm trying to solve OR a better solution to smooth the voltage (and therefore allow the fader to move slowly and relatively quietly).
Adding an RC filter after a pwm output would be like using a programmable DC voltage supply. You will still face motor deadzone. In this case... the same idea applies. Don't fall below a particular pwm level when the motor is moving. Know in advance what minimum pwm level is needed to move your motor shaft.
Right, and programmable DC output is what I'm after assuming it'll solve the noise problem. The motor dead zone is not an issue. I've played with enough values to find out about how much of a duty cycle I need to get the motor going (and keep it going). Perhaps I'm misinterpreting what you're trying to tell me?
Edit: I think I see where your comment is coming from. I'm saying that even if I provide a 100% duty cycle, the resistor drops the voltage too low to move the motor. I've tried lower resistor values just for the sake of testing (down to several 220 ohm resistors in parallel ).
TheNimaj:
I've played with enough values to find out about how much of a duty cycle I need to get the motor going (and keep it going).Edit: I'm saying that even if I provide a 100% duty cycle, the resistor drops the voltage too low to move the motor.
If you have found out the required duty cycle needed to get the motor going...... then that's great. But it is contradictory to then say that the motor won't move when you apply 100% duty cycle.
In any case...... use a motor driver circuit that provides your motor adequate power.
The problem was never getting the motor to move. The problem is getting it to move quietly. I am using an H Bridge to supply enough voltage. At this point the motor runs and I know how to run it. Now I want to make it quiet.
So, as my original post states, I've added an RC filter AFTER to h bridge attempting to achieve this programmable variable dc output. The resistor (from the RC ) drops the voltage to a level where no matter what duty cycle I apply, the motor will NEVER move. This is why I ever suggested boosting the signal. (PWM -> H Bridge -> RC Filter -> Signal Boost).
What is an example of a motor driver circuit because my understanding is that an H Bridge is one but perhaps not? Will this allow me to supply a steady variable DC Voltage to my motor to allow it to run quietly at lower speeds? If not then this is not a solution to my question.
What motor?
What PWM frequencies have you tried?
The datashheet for the fader(and motor) http://www.alps.com/prod/info/E/HTML/Potentiometer/SlidePotentiometers/RSN1M/RSA0N11M9A0K.html
I've tried all of the frequencies based on the links/articles I've found around the forum and the web on how to change the PWM frequency. By that I mean I've tried with every divisor.
A video with sound?
TheNimaj:
The datashheet for the fader(and motor) http://www.alps.com/prod/info/E/HTML/Potentiometer/SlidePotentiometers/RSN1M/RSA0N11M9A0K.htmlI've tried all of the frequencies based on the links/articles I've found around the forum and the web on how to change the PWM frequency. By that I mean I've tried with every divisor.
Lets try again shall we: What PWM frequencies have you tried? That's a question requesting some
numbers, not a vague description that could mean many things.