screening / glitchy operation - sanity check

[dsc]

Right, ignoring the scope for a second and focusing on how the motor works. I'd say that 70% of the time it starts normally and runs normally, but every now and then (this can be a few starts in a row or every few starts) I can hear the motor glitching. It's hard to describe, but it's like the motor jumps a few steps whilst ramping up, I'd say it's a jarring / vibrating sound as if the pulses at that point come too often and the motor can't keep up. I've used both the scope and a logic analyser and the pulses are generated properly, so I can only blame noise or something on the driver side. Could this be the detent torque kicking in, similar to the problems I've had on the DM856 and low frequency pulsing (when microstepping the motor can't be kept in between microsteps and so falls into the closest full step position)?

I can only hear this jarring noise on ramp up / when changing frequency, when it's at the required speed it runs smoothly. The same jarring can be heard when using a signal generator and changing frequency. I've tidied up the wiring on the breadboard, there's only a few long wires left (for the LCD), everything else is done via flat wiring on the surface of the breadboard. I've also used a long meter cable to connect the controller to the driver and earthed the screen, but earthing (one sided) makes the noise worse! the noise only appears when the driver is connected to the driver, if disconnected it's all nice and smooth.

Any ideas on what else can be tried would be good. So far nothing I've tried has eliminated the dreaded glitches / jarring...

Regards,
dsc.

[Jonathan]

When you accelerate the motor it will pass through it's resonant frequencies, so the noise you hear may be due to this. Try recording the rpm at which you hear the 'jarring noise' and just run the motor at that speed. Also see if the noise occurs at the same speed every time. If it continuously sounds bad at that speed, or even stalls, you know you're at a resonant point. The speed at which that occurs will change if the motor is connected to a load. It shouldn't be a problem if the driver is doing what the manual claims.

Edit: Having said that, since you say it doesn't happen consistently it sounds like something else might be amiss.