Recommended encoder?

[ESjaavik]

Actually there are 2 LED's and sensors slighthly skewed. They give a 2-phase output Ch.A and Ch.B. This makes it possible for the electronics to determine if it's turning CW or CCW by looking whether B leads or lags A.

Running CW>>>><<< Running CCW
__--__--__--__--__--__--__--__--__ A signal
_--__--__--__--____--__--__--__--_ B signal

BTW glass scale DRO's work exactly the same way, just not with a disk, but a strip of glass with lines.

One of my servos have 131072 pulses/rev! :-O Don't ask me how they can cram that many lines onto the disk and still "see the lines".

[Sanghera]

Thanks, but, why would you need feedback? If your motors are moving at whatever settings and for hatever drawing, why does it matter? Why does your software need to know where the motors are, can't it just tell it where to go?
Thanks.

[ESjaavik]

No. The motors don't know where they are. They can be "told to" move faster/slower by applying more/less current but have no idea when they get there. It's just like if you were using your lathe/mill blindfolded. You can't move 34mm up and 56mm right because you don't know when you get there. The feedback is the measuring instrument that tells the software when it's getting closer, and finally when it'son the spot. It also makes it possible for the software to know at any time where it is exactly, and thus whether it should accelerate, brake or go steady.

[balsaman]

Originally posted by ynneb Unless the stepper loses a few steps due to too much load on it. Then the stepper is blind and the computer does not know that it missed a step. A servo encoder will always report back to the computer where the servo is, regardless of the load.

Yes and no. The stepper will loose position if there is too much load on it, but so will a servo, because once you go over 100% of what a stepper can do, it looses steps. Once you go over 100% of what a servo can do, the drive faults. The result is the part is scrap.

A servo encoder (at least the ones we use on out hobby machines) do not report back to the computer, they report back to the drive. The computer knows nothing about the position of the motor. It assumes the drive is looking after it. Actually it assumes there is a stepper out there. If the motor can't keep up to the computer commanded position, the drive gives up and faults.

It IS posible to have the drive let the computer know something bad is happening, but the computer can't compensate for it. All it can so it stop trying to move the motor, by stopping the pulse stream to the drive. Again the result is a scrap part.

The biggest benefit you get from servos is:

1, you KNOW when you have a scrap part without having to wait for it to complete then measuring.
2, it's cheaper than steppers for applications that require higher power levels and higher speeds.
3, thier power curve is almost a straight line relative to speed
4, you can tell your friends it's got servo's

Eric

Eric

[ynneb]

LOL @ 4, you can tell your friends it's got servo's

A touch of S.P.S. hey? ( Small Penis Syndrome) The smaller the penis, the faster the car, the bigger the TV and you have servos instead of steppers.

I am glad my servos are not overly big.

[ger21]

Hey everybody, I've got steppers

[ezland00]

I used the information from this site and built my self the driver. http://www.luberth.com/plotter/tip120pcb.htm For some reason it start smoking on the tip120 chip, after i connect the printer port. does anyone know what's wrong? i'm using power maxII Model: p21nsxc-lss-ns-03.

[ynneb]

I dont know circuitry, but maybe its just a case of fitting heat sinks.
Just a thought

[ESjaavik]

I guess the resistors we see are the base resistors based on being 1/8 or 1/4 Watt. So where are the current limiting resistors? If you have none, then let's hope the transistors are better smokers than the motor! With 24V input and no current limiting, that's a motor cooker we see there. If the power supply is delivering enough amps it may even demagnetize the motor, which is done in fractions of a second. You need to drop the steady state current to what the motor allows. And if your PC have the parport on motherboard don't use that circuit as the potential for killing your parport is fairly high. Use one on an expansion board that is cheap to replace.

[ezland00]

will the motor at least spind? i'll order some resistors of mouser. thanks for the info.