Stepping Signal Problem

Hiya everyone,

I've just built a Prusa (Dunedin Makerspace). On the initial test run, X, Z, and extruder steppers behave as expected. The Y stepper doesn't move (even when free from the frame). The problem is not the motor, nor the driver (logically excluded). I thought it would have been my RAMPS v1.3 build, but when I remove the shield from the Arduino mega and snoop on pin A0 (X_step) I see a nice clean square wave, on pin A6 (Y_step) I see a messy signal which rises high appropriately, but slopes back down to ground, the Z_step signal is clean and square. Anyone have any ideas? Do I have a faulty Mega or a faulty shield that damaged the Mega? What would cause this problem (bad cap?). I will test a virgin Mega, but it'll take a few days to get the Mega and oscilloscope at the same place again. The other problem I see is that the LEDs on the drivers don't light, but I do NOT suspect a major polarity problem as the shield's transmission LED works as expected and the opto-endstops also operate as expected. All the polarised caps, diodes, and transistors are placed properly, and I can't find any solder bridges. Going through the teacup firmware I couldn't find any inconsistencies between the definitions and actions on pinA0 and its symbols from those for pinA6 (except a single statement in an analogue-mask routine present for X, not present for Y) and a commented-out statement in X active in Y (which just inverses the direction). Thanks in advance for any suggestions you share.

Cheers,

The Y issue does sound like a mega issue.

LEDs on the drivers?

What drivers are you using? Standard pololu drivers have no LEDs

Thanks Dust! I am using typical Pololu (http://www.pololu.com/catalog/product/1182) I didn't look closely. I assumed the two green SMDs were LEDs!

Problem solved! After solving this problem we found discussion of the solution online, but we couldn't find it before stepping through the teacup code so I hope the search engine crawlers pick this up!

System: Arduino ATMega2560 using the Teacup firmware (http://reprap.org/wiki/Teacup_Firmware) with a RAMPS v1.3 shield and standard Pololu stepping motor drivers for my Prusa Mendel with a heated bed, operated with the RepRap GUI

Diagnosis of the problem: X, Z, and extruder motors work as expected. Bed temperatures are wacky (mine were reading around 750-851 degrees C), Y-axis motor is working hard without moving, and using an oscilloscope to peek on analog pin 6 (driver step signal) while using the interface to command a Y-axis move I see a rapid signal rise, but an ugly sloping fall instead of a clean square wave like you see on analog pin 0 when commanding an X-axis move.

The analog_mask routine in the code shifts incoming values to something wonky, so a work-around is to explicitly state the pin usage in the config.h file. Line 289-291 are by default:

// name type pin additional
DEFINE_TEMP_SENSOR( extruder, TT_THERMISTOR, AIO13_PIN, THERMISTOR_EXTRUDER)
//DEFINE_TEMP_SENSOR( bed, TT_THERMISTOR, AIO14_PIN, THERMISTOR_EXTRUDER)

I uncommented the bed sensor line because I have a heated bed so I properly changed it to:

// name type pin additional
DEFINE_TEMP_SENSOR( extruder, TT_THERMISTOR, AIO13_PIN, THERMISTOR_EXTRUDER)
DEFINE_TEMP_SENSOR( bed, TT_THERMISTOR, AIO14_PIN, THERMISTOR_EXTRUDER)

But explicitly stating the relationship makes all of the problems go away:

// name type pin additional
DEFINE_TEMP_SENSOR( extruder, TT_THERMISTOR, 13, THERMISTOR_EXTRUDER)
DEFINE_TEMP_SENSOR( bed, TT_THERMISTOR, 14, THERMISTOR_EXTRUDER)

I couldn't have solved this problem without the super folks at the Dunedin Makerspace !