Re: Stepper motor questions
- From: Jerry Avins <jya@xxxxxxxx>
- Date: Tue, 28 Jun 2005 10:29:14 -0400
fuentesmartinez wrote:
Hello,
I�m trying to use some stepper motors in a project but I�m concerned with the speed it is very slow.
My set up is has follows a timer 555 gives clock signal to a GAL16V8 and it feeds 4 2N3055 I don�t think there is the problem, what do you all think? Some guy told me that was a very primitive driver I don�t really understand why I would look for something more complicated if all I want is to switch between coils� Am I wrong?
Are you supplying two phases? For most steppers, the simplest usable driving waveforms look like
¯¯__¯¯__¯¯__¯¯ and
¯__¯¯__¯¯__¯¯_ . Invert one of the waveforms to reverse direction.
Both of those waveforms are bipolar; they switch between +V and -V. Some motors have center-tapped coils, often with a common center tap for both coils. With the center tap(s) grounded, current is applied to one half of a coil. Switching means applying current to the other half of the same winding, with the other side always open. 48 steps per turn usually means 24 steps of each phase. It is usually true that 4 unipolar phases are simpler to generate than two bipolar phases, so the motors are wound accordingly. There is a simple circuit that uses two flipflops. which accepts a single clock and delivers four outputs to drive 4 transistors. I'll show it if you need it.
Regarding the motor, it was salvaged from an old printer, it works
with 24 v and has 48 steps there is no more info on it. From some
sites I have found I learned they have a pull out rate and as far I
understood it won�t go faster than that, is it true?
That depends on the driver. With simple drivers it is true. The drop-out speed depends on the nature of the load. By ramping up the speed instead of trying to start at the highest speed, you can go fairly fast even with a simple driver.
What I have done is to supply 24v and increase the pulse rate until it just shakes, is there a why to cheat that max speed I have reached? If I supply 50v would I have double speed? Or would I be able to move a heavier load with tha same speed??
The motor is rated at 24 V and draws some current there. The winding has inductance and resistance, so the current builds up according to the L/R time constant whenever the current is switched. If you increase the voltage and add external resistance to limit the current to its 24V amount, the motor won't overheat, but the time constant will be shortened. For moderately high performance drives of this type, the external resistor is often double the motor's resistance, so one would use triple the voltage. I would try double the voltage with a resistor equal to the motor to start with.
I also read they have a resonance frequency but I don�t think I have hit it because once it loose steps it don�t come back to the working behavior...
I suspect you're right.
Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ .
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