[cnc2k]

my freind told me about this site, so far everything is good alots good informations and photos.

I'm looking for some encoder for servo motor.

[cnc2k]

also is there any good servo controller other than gecko

[ynneb]

I dont know about brands of encoders, but I made the mistake of getting single ended encoders and not differential encoders. You cant run very long lenths of control cable for single ended ones.

Another brand of driver is Rutex. These have a much higher amperage handling capacity. I guess it depends on the amperage of your servos that will determine what you need.
Have a look here for other types http://www.cnczone.com/forums/forumd...?s=&forumid=30

I plan to make up a comparisom chart in the future.

[Al_The_Man]

A fairly cheap encoder (especially if you buy 10!) is Renco, they have through-shaft type that can be fitted direct on to the motor as long as it has a rear shaft and this eliminates a coupler.
And like ynneb (benny) says, use a differential if possible for long cable lengths.
Al

[ezland00]

edit

[cnc2k]

Originally posted by Al_The_Man
A fairly cheap encoder (especially if you buy 10!) is Renco, they have through-shaft type that can be fitted direct on to the motor as long as it has a rear shaft and this eliminates a coupler.
And like ynneb (benny) says, use a differential if possible for long cable lengths.
Al

How much is it? Can you send me a link?

[Al_The_Man]

About $70 ea for qty 5 last time I bought some www.renco.com , they come in many shaft sizes.
Al

[IvanTochev]

hi, look at www.usdigital.com for encoders, the E2 is ~ $40,- and really good. (it´s TTL, not differntial)

[Sanghera]

Kind of a Newbie Question, but, what is an encoder, what does it do. Does it tell the computer where the motor is?
Thanks.

[trubleshtr]

yup, feedback, otherwise it's like driving your car with your eyes closed. Encoders are not needed but are a good feature to have if you need better positioning of your axis, most wood working cnc's don't have them because they don't need to have as much precision......

[balsaman]

They are needed if you are using servos. A servo knows nothing about where it is, the encoder sends the position back to the driver. An encoder is NOT needed on steppers. Steppers can be accuratly positioned by the drive without any feedback.

Eric

[ynneb]

Steppers can be accuratly positioned by the drive without any feedback.

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.


Encoders can have many thousands of lines. I have heard of them having up to 20,000 lines. You can imagine the accuracy they can give.

[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