Re: Erratic behavior DIY CNC. Any suggestions on troubleshooting?
So, the obvious and total solution is for you to try my motor driver! LOL... sorry, but I have to try. Seriously, you might want to see if a different driver works, and the THB6064 kit I sell IS well thought of. Another option would be a geckodrive.com driver. For pete sake, do NOT buy a cheap chinese driver no matter what /they/ rate it at. Even the chinese THB6064's are junk... I have a video showing the difference.
Here are some other ideas:
1. Does it have the problem when only one axis is running, or is it more obvious when you are running 2 or 3 axis at the same time? If the latter, thin wires, or bad connections in the power supply wiring. Check the power supply at the driver, not at the power supply.
2. Does the problem happen only after it's been running for a while? Are your steppers getting hot? Everyone will tell you that "steppers are designed to run hot" and "it's no big deal" and I know beyond a shadow of a doubt that it IS a big deal, because they can lose 20% of their strength when they get hot. If it happens more when the motors are hot, put CPU coolers on them with thermal paste.
3. The Z axis is probably worse, no? And that is because it's the only axis battling gravity. It's not a "real" fix, but in marginal cases, a "quick fix" is to run a cable up over a pulley at the top and back down to a weight, offsetting the mass of the Z axis head. This means the z axis will now have twice the mass and will not move as fast, but it will move UP just as well as it moves down, which is the issue I'm seeing in your video.
4. Does the problem only happen on rapids? Higher voltage from the power supply should help that. If it happens all the time, more current might help... You could look into a battery based power supply with a charger.
5. It could easily be the optoisolators in your BOB. I hate optoisolators... try wiring a driver directly to the parallel port of the PC. If you fry it, the PC was old anyway right? I've seen bad optos cause problems just like this. Cheap crap from China again.
Hope some of that helps, and I'll make you an offer: Buy my THB6064 kit and try it, and post the results, and I'll refund the price of the kit.
James hosts the single best wiki page about steppers for CNC hobbyists on the net:
http://www.piclist.com/techref/io/steppers.htm Disagree? Tell him what's missing! ,o)