[thunderdork]

Hi all,

I'm new to the forums here. Just bought this kit from Automation Technologies. This is my first build from scratch that I'm documenting on my site thunderdork.com.

I have two questions:

1. The motors that came with it have 3 wires for power. Red, Black and Green. The Gecko 320x only have two channels for power. What do I do with the third wire? I'm assuming ground the green wire to the enclosure or does it matter?

2. I'm borrowing a lot of my design and buying some of the parts from cncrouterparts.com. I was thinking about buying this part for the rack and pinion drive. But theirs uses stepper motors geared down 2:1. For servos, would I want to change the gearing? I've seen people building a similar size to mine (8'x4') doing closer to 5:1.

Thanks for y'alls help!

ThunderDork

[Al_The_Man]

If this is a DC servo motor red & blk for power, the green should go to your central ground point, you should ideally set up a central star point ground where all the earth grounds and shields go to.
Also have bonding conductor from the frame of the machine.
The main reason for gearing is to use a more economically viable drive and motor, with a servo you usually have the luxury of sizing a small motor with high gearing to take advantage of the flatter rpm/torque curve of the servo.
The alternative to little or no gearing is a much larger servo and drive.
Al.

[keebler303]

Steppers have less torque the faster you go so you want to keep them running relatively slow to stay near the peak power point. Servos can keep the same torque all the way up to rated speed so the faster you run them, the more power you get. If you only need say 600 RPM for your machine, you will get 5 times the torque to run the servo at 3000 RPM through a 5:1 reduction rather than running the servo at 600 RPM with a 1:1 ratio.

In other words, pick your ratio so that the servo is near rated speed when the machine is at max cutting speed. It is difficult to get more than 5 or 6:1 ratio in a single stage so most use that and make do.

Matt

[thunderdork]

Could anybody remember a gear ratio for general use with these motors?

[Al_The_Man]

You need to know your max feed speed required and the motor to load inertia ratio to answer that question with any accuracy.
IOW, it is machine design dependent.
Al.