Potato sprinkle recording

[gary]

Hi Gary i am using a 5 pin unipolar that looks like a 4 or 6 pin bipolar ,i do have a few of those about as well....have to say that is a simple circuit saves a lot of electronics .

Unipolars can be run as bipolars normally but a 5 wire unipolar has the centre taps tied together and as far as I am aware can only be run in unipolar mode, so yes that is a problem.

Does it just work off 12volts bet the stepper gets hot ?

Harry the higher the voltage the better because it helps to overcome the inductance of the coils, however if the voltage used causes the maximum current to exceed the motor's rated current, the current must be limited somehow. There are a number of ways to do that but the easiest by far, and the way I do it, is to use a high wattage series carbon resistor, or, as I do in my CNC machine, a car light bulb (it's fun watching them light up).

The series resistor is calculated using ohms law - just measure the resistance of the coil and use ohms law to determine what series resistance is needed to limit the current I = V/(Rcoil + Rseries).

I would like to emphasise it is very good to have a higher than rated voltage - however if you have a transformer just the right voltage then give it a go and see.

What governs the speed Gary the line frequency?

The speed is indeed determined by the frequency according to that formula I posted earlier in this thread.

could you use say instead of just line Ac transformer a 555 timer at that frequency feeding a mosfet perhaps also turning that square wave to a sine wave before the trany sounds like a simple way to get speed control out of a stepper?

Well that's more-or-less what Steve and I have been discussing - using a 555 is fine provided it gets turned into a true AC sine wave (true as in bipolar swing - the shape can be a little rough but not too rough).

It's sounds simple until you realise you have to turn it into a bipolar sine wave (i.e. the voltage swings sinusoidally from +V to -V (NOT +V to 0V).

It sounds simple and I have done it in a few ways but it isn't all that simple and can be expensive. A single mosfet won't cut it - you are probably familiar with a H-Bridge motor driver? It's something like that but for sine waves rather than square waves.

The simplest way is to use a push-pull amplifier with a dual power supply.

OTOH f you have a high power stereo amplifier you can press into service your work is done. (Note that is just what Albert did for his Edikow - it is exactly the same principle).

I suggest you try and stick to just the transformer and cap for now if it is suitable.

Just an extra point though, because I can literally hear the gears in your head turning, if you are thinking in terms of high speed (e.g. 750 RPM) then a high driving voltage is essential and the speed needs to be ramped up to speed to avoid the resonances that occur in the motor. That becomes a bit tricky but I have done it and it works well.

[Harry Dalek]

Thanks for the reply there Gary darn not as simple as it seemed .
I have a few bibolar motors i will test today with your circuit see if i can find that cap looks like its not an electronic sounds like a big cap then i should have that some where in my junk box .

I'll have a go and try it with the transformer see what happens i know failed last time i tried but i must not have hooked it up correct that time .

let you know what happens .

[gary]

Doesn't have to be a huge beastie, but remember non-polarised. A motor start capacitor is what I used I think - lots of those around scrap yards etc.

[gary]

I should own up here and say the main reason I say the driver is non-trivial is basically because I am a miser. I just can't come at building some thing for less than $10 and then having to buy a $60-$80 transformer to power it. I have heaps and heaps of transformers around but not one that has the required VA AND a centre tap.

Once you have a beefy dual power supply the problem reduces to a couple of complementary power transistors (say tip41/42) - more-or-less anyway.

And a PC is an excellent source of the two sine waves BTW (obviously to the input of the power amp).

There are many ways of attacking the problem - maybe someone else has an idea?

[Harry Dalek]

Doesn't have to be a huge beastie, but remember non-polarised. A motor start capacitor is what I used I think - lots of those around scrap yards etc.

I think i have a few of those but i think they are biggish...i should have something that will work ...i found a 3 and 4.7 non polarised so far .

[Harry Dalek]

I should own up here and say the main reason I say the driver is non-trivial is basically because I am a miser. I just can't come at building some thing for less than $10 and then having to buy a $60-$80 transformer to power it. I have heaps and heaps of transformers around but not one that has the required VA AND a centre tap.

Me too I don't buy any resistor and cap and if i have a scrap ic or trany on and some times an old circuit board with an ic i will do that ,only thing tend to buy is LEDS lasers and panel pots and ics i don't have .

Yes the centre tape transformer is rare here to ,i tend to just scrap those for pot luck what i find at the reuse shop from some old electronic thing.

The main reason i would rather power this from 12 volt 5 volt supply is i just use that old pc power supply i test every thing with saves me ever making a power supply.

But it is worth it if the transformer works for this project .

Once you have a beefy dual power supply the problem reduces to a couple of complementary power transistors (say tip41/42) - more-or-less anyway.

And a PC is an excellent source of the two sine waves BTW (obviously to the input of the power amp).

There are many ways of attacking the problem - maybe someone else has an idea?

[/quote]


SO your better off with a sine wave oscillator to start with and a push pull amp ...then your sine wave drive setup.

[gary]

SO your better off with a sine wave oscillator to start with and a push pull amp

Not sure what you mean by better off, certainly if you want to vary the speed yes that is basically what you need - there are just many ways of doing that.

...then your sine wave drive setup.

If I understand you correctly, no, you don't need the transformer then. If you use a source of 2 sine waves, one 90 degrees out of phase with the other (as you would get with a PC) you don't need the cap either - there would be two push-pull amps - one for each coil.

Just to be clear all you are doing is applying a sine wave to one coil and the same sine wave but 90 degrees out of phase to the other. There are many ways to generate those two sine waves - we have discussed a few here but obviously the mains plus a capacitor is, at least component wise the simplest. (If it isn't already clear the capacitor is just to get the 90 degrees phase shift).

[gary]

I think I have shown you this before Harry, but here is an example of using a stepper for a turntable drive using a PC as the sine wave generator and and amplifier to boost the current to the stepper.

http://www.altmann.haan.de/turntable/

[Harry Dalek]

Gary the transformer idea does works from a quick test .

But it seems better at half voltage 6 volts ,i found on 12 i had to kick start it .
Seems to start ok most times ...and i noticed on a kick start you can get it to go either direction .

so good

[gary]

What governs the speed Gary the line frequency?

The speed is indeed determined by the frequency according to that formula I posted earlier in this thread.

It is important to also note that the speed is also determined by the step angle of the stepper motor, for instance if you could find one with a step angle of 22.5 degrees it would run at 750 rpm from the mains (50Hz).

Alas, they don't appear to exist...

[gary]

Gary the transformer idea does works from a quick test .

But it seems better at half voltage 6 volts ,i found on 12 i had to kick start it .
Seems to start ok most times ...and i noticed on a kick start you can get it to go either direction .

so good

Good, experimentation is best. You would probably find it works even better on 12 if you include a series resistor.

Do you have the specs for that stepper?

[gary]

Harry, you'll also likely find that different types of stepper also work better than others - I found the tin can type steppers you tend to find in modern printers etc, very poor in this regard.

[Steve Anderson]

Leaping ahead...my concern at this point would be the degree of drag you're gonna get with the head-to-wire contact and whether the motor is up to it (enough torque) without losing step. This is definitely uncharted waters for me.

With a conventional wire-recorder the wire just 'kisses' the head(s) at a shallow angle inducing very little drag. This may be very different. I'm not trying to put a negative spin on this, just trying to think ahead as I do have an interest in this. Analogue magnetic media has been part of my family for three generations, particularly magnetic striping of movie films. Sadly it has all but vanished, in all its forms.

Steve A.

[Harry Dalek]

Harry, you'll also likely find that different types of stepper also work better than others - I found the tin can type steppers you tend to find in modern printers etc, very poor in this regard.

Back again had to go out ...

I am using the 5 inch floppy drive stepper...its pretty good really when you think of all the wiring it replaces its very interesting ..i ended up just using a 4.7 cap i told you about to test and it worked .
Just much better at 6 volts i have to always kick spin it to start at 12 volts and as i said either direction depending on my spin.

[gary]

Just much better at 6 volts i have to always kick spin it to start at 12 volts and as i said either direction depending on my spin.

yep, but as I said, a series resistor is likely to improve things for 12v, but if it works as required there is no need to bother. What sort of torque are you getting? It should be quite high, but these floppy steppers aren't very strong really. I would expect that you would need something of the order of at least 30-50 oz-in