RF noise causing stepper chatter

[PsyKotyk]

I've been testing my machine, and discovered that when I turn the spindle up to just over half way, the Z axis stepper starts twitching. I'm using a mini-mill spindle assembly with speed controller and a simple TIP120 Unipolar driver for the steppers (until I build a PICStep).

Any ideas why the RF noise is affecting the drivers? It only happens when the interface is powered up (computer can be on or off), and the spindle speed is above half.

This weekend, I went through all the trouble of replacing the spindle power wire with a sheilded one, and ensuring all the stepper wiring is shielded and grounded as well. The drivers are inside a SCSI box, so they should be well sheilded. I tried wrapping various things in tinfoil to try and isolate the source; to no avail.

I'm going to try swapping out the Z driver next in case it's particularly sensitive to RF noise.

Does anyone have these kinds of issues with their PICStep drivers? Maybe my solution is to hurry up and get new drivers made.

BTW. If anyone is using a mini-mill spindle for your machine (ie from Little Machine Shop), be sure to open up the electronics box and connect the ground wires together. They usually are bolted together when mounted to the mini-mill, but in this case they are just floating around the box.

[Torchhead]

Most likely it's not "RF" (Radiated noise). It's probably coming in through a common ground (conducted noise). Properly bypassing the low level inputs to your home built driver will help. There is some magic involved in motor drive design and dealing with noise is one of them. Motor speed controls are historically noisy and put nasty stuff out on the AC line. Line filters can help. If the internal logic runs from it's own power supply you might consider not making the chassis the common ground. A lot of drives use opto isolated inputs so the motor DC and drive electronics can run on a separate floating power source from the PC and port outputs.

Tinfoil and even sheilded wire does nothing to eliminate conducted noise. The tinfoil may help prevent aliens from reading your brain waves but nothing to block signals below the microwave frequencies (:-)

[pminmo]

Do you have a picture of your electronics assembly and your z axis wiring? Wire routing can be an issue. Since it's your Zaxis I wonder if you have your Z stepper wiring running near the motor itself.
Also putting in a line filter on your electonics assembly maybe a help. Common/ground wiring is always a potential issue, including where you have your mill plugged into ac vs where you have your electronics plugged into.
Bottom line, these are electrically noisey enviornments, one of the reasons I put filters on my driver designs.

[PsyKotyk]

Here's a follow up in case others have this problem. I finally got around to replacing the wire between the interface box and the computer with a shielded one (both ends of the shield tied to shell ground/chassis ground), and the chatter seems to have been resolved.

Mental note: Tinfoil is for baked potatoes.