529 replies to this topic

[Bart]

yay for wikipedia

The average value of voltage (and current) fed to the load is controlled by turning the switch between supply and load on and off at a fast pace. The longer the switch is on compared to the off periods, the higher the power supplied to the load is.

The PWM switching frequency has to be much faster than what would affect the load, which is to say the device that uses the power. Typically switchings have to be done several times a minute in an electric stove, 120 Hz in a lamp dimmer, from few kilohertz (kHz) to tens of kHz for a motor drive and well into the tens or hundreds of kHz in audio amplifiers and computer power supplies.

Sounds like what i said .

Yes but how does the MS vary the frequency? Say you want from 20khz to 200khz Thats why i mentioned a variable resistor to vary the frequency

[Bart]

ms doesn't vary the frequency, it vary's how long it holds the switch closed during each cycle.



For (a very poor) example say its set at 5hz (it cycles on and off 5 times a second)

|---|---|---|---|

would provide more current than

|-|-|-|-|

- = time spent grounded
| = switching to ground

Sorry, really really bad example?



So the frequency that it operates is only really important to how smooth it operates, its how long it holds the switch closed that varies the current flow... I could probably use one of the pwm outputs for the idle air control motors, since there just stepper motors. I think it does a 4 wire output for those, I'm guessing so it can change directions rather than me relying on something to return to a position when current is removed.

Ok so it will be a set speed which will go forward and reverse, i confused myself

[76lxhatch]

Didn't mean to sound negative, I just think you should go the whole hog!

What jabba is saying is that it varies (or rather modulates) the pulse width... I still reckon a stepper motor would work fine as long as the load isn't too high

[r2160]

I just thought of a possible problem with using stepper motors.

I have a mate building his own cnc setup. One of the things he has to do is include end stop switches to tell the machine that the stepper motors have reached the end of their travel. Do you have to do this with your possible setup?

That might mean you either have to set it up mechanically or an actuator/solenoid as you have said.

cheers
Glenn

[76lxhatch]

The IAC stepper motor has its steps counted by the ECU, that's why you have to reset it when the ECU has been reset. Once at the correct starting position, the ECU simply demands a certain number of steps (which if the tune is correct will give the correct result). Using that logic would be a great way of controlling the variable intake, you'd just set the number of steps at various RPM/load points. I'm pretty sure its still a PWM output that does it all somehow.

[Bart]

Maybe what I want is a servo motor not a stepper. I was just thinking about my toy helicopter and how it changes the pitch of the blades

That would work well.
Basically you need a stepper/controller to behave like a RC servo.
A potentiometer mechanically moved by the accelerator, the potentiometer moves clock and anti clock wise and the stepper follows. I had a set up exactly like that 10 years ago when I was "into it". I�m sure Jaycar has this setup.
But if you want to use what you have on hand that would be a goes start, I think you would have a "trim" setting which reduces or increases movement of the servos which will be needed I think.

[hanra]

Ive come in a bit late here, but this a Lina Mint car. Personally I would have left it that colour.








This is my good mates 71 GTS.

Edited by hanra, 02 September 2011 - 12:49 PM.

[r2160]

Actually I never thought of that. Try an RC servo, like this

http://www3.towerhob...p?&I=LXLWS8&P=0

So long as it hooks up with your computer, it might be the answer!!

cheers
Glenn

[Bart]

Ive kind of discarded the computer idea

I belueve you will need PWM signal either from your computer or a stand alone system/generator, but you will need to figure how to put that into the stepper controller.
You could use the tacho signal also i think, but for simplicity i think a stand alone system would be better, be it servo or Jaycar kit

Edited by Bart, 02 September 2011 - 02:08 PM.

[76lxhatch]

A stepper motor is just an electric motor that moves in steps instead of continuously, and it is possible to control how many at a time. It stops where it stops, to return to zero you have to turn it backwards again the same number of steps, there is no self-returning or anything like that.

[r2160]

Here we go, assuming the servo route.

servos are controlled with a PWM signal driven to their signal wire. A PWM signal has three parameters that characterizes it: The first is the amplitude (or peak to peak voltage) of the signal. You should use from 3 to 5 volts for your signal, according to it's specifications. The second is the frequency. In PWM, the frequency is usually fixed to a value. For analog servos the frequency is 30-50 Hz, and for digital servos it is 300 to 400 Hz.

This info is on this page http://pcbheaven.com...C_Servos_Works/, I hope it helps

cheers
Glenn

Edited by r2160, 02 September 2011 - 02:25 PM.

[Bart]

http://www.robotmarketplace.com/products/0-PL1390.html

Overkill but wow, that would do it .

Hang it off your engine crane lol