Dear All,
I'm building a brand new Prusa Mendel based on Gen7 electronics, and I've installed A4984-based stepper motor drivers I'd bought on eBay from a member of the community. Once I started testing, I've got strange issue with my motors. Seemingly there isn't enough torque being produced. The holding torque feels okay, but movements is rather jerky, if any at all. Worst is that Z-axis is unable to move, there are only a single jerk followed by a humming sound even on maximum current settings. This doesn't seem to be affected by microstepping settings, I've tried various combinations of MS2+MS3 (MS1 is hard-wired on Gen7).
Additionally, the chips tend to become very hot. I've tried various current settings. Some drivers remain luke-warm on most pot settings, while some tend to get very hot even with 1/5 juice, but, nevertheless, none of them can handle Z-axis.
I spent few weeks trying to investigate issues with my hardware and electronics, until I gave up and decided to give a try to a newer A4988-based driver, so ordered one. When I got the driver installed, all problems disappeared. Even Z-axis is moving okay while the chip itself remains merely warm, around 45C, on 50% current limit.
Strangely enough, when I measure current in windings, it seems that for both drivers everything is perfectly the same, i.e. current is about 500 mA in one of the windings, and 200 mA in the other (depends on the position). This confirms my initial observation that the holding torque is okay for both drivers, but doesn't offer any insight in the nature of the problem.
So now I'm completely puzzled. It does look like the drivers are faulty, but may be my fault. Next week I'll probably try finding an oscilloscope to see if there would be any noticeable difference between two versions of the driver in stepping signals.
Having spent quite a while on this, and I'm absolutely desperate, so I'm actively looking for an advice from you guys. What would you recommend checking out next?
