geckos servo or stepper

[mjs79]

hello cnczone
i have read the threads on servos v.s steppers , i know they both have positives and negitives .
now my question is what would you use stepper motors or servo motors , and why would you use it .
also what geckos would i need to run the servos ? any info would be very helpful !

the drives and motors are the last of the parts i need for my cnc mill .im looking for the set up that will run the best within my budget of around $700 for motors and drives . gecko drives are what i want to use due to the high level of customer support i have seen .
Thanks for any help you can provide it will help me alot .
cheers
mike

[Richards]

I have both steppers and servos. The steppers are being driven with Gecko G202 and G203v stepper drivers. All new applications will be using the G203v (until Mariss releases something that outperforms the G203v). The servo is running from a G340 that was backwards modified to be a G320. Future servos will be run using the G320.

Using steppers is simplicity itself. My first rule of thumb is to grab the closest size 34 motor that has a torque rating of 600 oz*in to 800 oz*in and hook it up. So far, that has worked in every case. With proper gearing, the steppers have worked perfectly.

The servo is a little different. It took a few minutes to tune it properly; however, the instructions that came with the servo driver were perfectly clear. The main issue that I have with servo motors is that they have to be geared in order to develope enough torque to do the job. The monster that I have runs at 2,200 RPM at 70VDC. My application only needs about 200 RPM, so I have to gear the motor down 10:1. That means using a 5:1 ball screw and a 2:1 belt drive. With that combination, I get about 1,700 oz*in of continuous torque.

So, bottom line - either will work. Steppers are easier to use - in my opinion. Both cost about the same - excluding mechanical gearing for the servos.

[mjs79]

thanks alot for the info . i think im leaning towards servos . now is gearing 100% needed . im just using actuators that the motor mounts in line with the ball screw shaft so gearing may be tricky to do . heres a pic to better show what i mean .

any guesses as what i should do ?
thanks for the info cnczone
cheers
mike

[Richards]

It's hard to know what to suggest. I always start with the easiest approach. Start with what you have that is available and see what happens. The torque charts for the size 23 motors (ID2300x) show too little torque, even at 5:1 for my use. The ID23005 motor comes in at about 280 oz*in. That may be sufficient, but I would feel a lot better having 2X that torque. The torque charts for the size 34 motors (ID3300x) show higher torque, with constant torque figures of about 75 oz*in to 225 oz*in. When those figures are multiplied by 5 (5:1 ball screw), some of the motors would be usable - direct drive - in my mill.

The other consideration is speed. At 5:1, Mach 3 would have to send 10,000 pulses per inch of travel. Using the 45,000 step rate, that would be about 4.5 inches per second or 270 inches per minute. That's too fast for the mill and way too slow for a CNC router. My Shopbot can jog at 1,800 inches per minute.

So, if I were in your shoes, I would try whatever is available and see how it works. The Gecko servo drives can be used will a lot of different motors, so, if one motor doesn't do the job, try another.