gettings started with electronics, stepper motor issue

Hello all. I am trying to build the Mendel Prusa and I just started the wiring things up. My issue is that when I press extrude in pronterface the motors buzz rather than spin. 

Here is my basic setup. I am using an Iduino Mega board with Sprinter firmware and a RAMPS shield. I have A4988 drivers and Nema 17 steppers, Minibea 17PM-K307-05VS, with 6 Pins. 

I only have one motor and driver connected. The motors are wired to the drivers as follows, stepper pins 1346 to drivers pins 1234. I tested the resistances to find the pairs with the higher resistance. I have the driver plugged into the 1st extruder socket.  I have tried setting the Voltage across the driver's potentiometer from 0.4-0.8V. My power source is rated 350W and in getting a voltage reading of 12.7V.

Does anyone have any ideas why the motors are not working correctly?

Edit 1:
Just wanted to clarify. This is not a electrostatic buzz it is like the vibrate from a massager. As if the thing is stuck stepping back and forth rapidly.

Edited 2 time(s). Last edit at 09/09/2013 05:46PM by mkaisercross.

Buzz is probably either a wrong current setting (v-ref) or incorrectly wired motors.

  /   higher  \          /  higher   \
 /                   \       /                   \
/  low \/  low  \    / low   \/  low \
|          |           |    |          |           |
UUUUUUUU    UUUUUUUU
1A     1B      1C  2A     2B      3B 

|    Coil 1       |    |     Coil 2       |
-------------------    -------------------

OK, I've not done six wire motors, but here is how I understand it. 1A to 1B should read a low resistance, 1B to 1C should read the same resistance (in an ideal world), and 1A to 1C should read higher than the other two measurements. Same for 2A, 2B, and 2C. Once you have identified these pairs, check all resistances between coil 1 and coil two wires, they should read infinite. Connect 1A + 1C of the stepper wires to 1A and 1B on your driver. Connect 2A + 2C of the stepper to 2A and 2B on the same driver.

If that is all good, find out what amperage (current) your motors are rated for. The 0.4 volt v-ref will ideally produce some where around 1 amp. I have 1.6 amp motors, but I run them at 0.4 and they do fine. However, if you have 0.5 amp motors, you will have to turn the v-ref down below 0.2 to keep from over feeding your motors. Too low and they won't work correctly either. Over and under current can produce all kinds of strange noised. Over current can even produce smoke and a busted motor. Both can also produce missed steps.

I just tested the resistances again and they I am getting the proper readings as you say. 1A to 1C is 10 ohms and 1A to 1B is 5 ohms and 1B to 1C is 5 ohms. Here is how I have it wired.

Stepper Motor
================
1A 1B 1C 2A 2B 2C
| . . .| . .| . . .| . . | . . |
| . .___| . . .| . . . . . |
| . | . . ____| . . . . . |
| . | . . | . ._______|
| . | . . | . .|
| . | . . | . .|
1 .2 . 3 . 4
================
Driver

I tried also just tried using only a half coil wiring. Instead of pairing 1A to 1C I paired 1A to 1B and the same for the second half. No luck still getting the buzz rather than spin.

I am having trouble finding the datasheet for my motors. It looks like the exact model I have is either custom made or discontinued. Here is the link to the "family" of motors mine belong to link. I emailed the company yesterday asking for the specsheet but no reply yet. But I tested the motors at several different voltages between 0.2 and 0.8 volts now at around 0.05 steps. It shouldn't be that sensitive right? Could it be incompatible drivers or a faulty ramps board?

Edited 4 time(s). Last edit at 09/09/2013 05:49PM by mkaisercross.

I was not able to get the stepper motors turning with Pronterface. I am still not sure if it was the steppers, or the electronics. I just went ahead and ordered a brand new Arduino mega, RAMPS board, and drivers from Sainsmart.com. This company looks legit and hopefully everything should be good quality and compatible. So I just recieved the new electronics today and tested it. So far I have only tried operating one stepper at 0.2V and again at 0.3V. The motor doesn't move at all. I have no idea what current my motors should be using because they are custom made. I emailed the company, which is Minibea, and they replied that the model number indicated that it was custom made and they did not have the specs for me. However these motors are in the same product family as mine and they are rated between 0.9 and 1.4 amps, so I have a ballpark. According to the datasheet "Current Limit = VREF × 2.5" so to get 1 amp I need to set Vref to 0.4 and to get 1.4 amps I set Vref to 0.56.

So my new questions are 1) Can I try setting Vref=0.56V, I=1.4A without risking the electronics (RAMPS, Arduino, drivers) 2) Could it be possible my motors require more current 1.4A and as a last resort could I test higher than 1.4A without risking the electronics, but possibly killing the motors.

I'd appreciate any ideas. Thanks! Here's my awesome reprap so far!
Photo of my Reprap

while building my printer, I tested all the driver boards using a bread board and the arduino each driver at a time. much easier to troubleshoot the wiring that way.

here are some tutorials to play with your electronics....

[www.lucadentella.it]

I believe the problem was that I did not have the pin jumpers plugged in below the stepper drivers. The wiki made it sound like it was optional that you could use for setting the micro stepping. Not sure if you have to change something in the firmware or maybe it is supposed to be controlled by changing the jumpers only and my driver is not functioning correctly. But changing from zero jumpers to three jumpers was what fixed the vibration problem for me.

If you dig into the data sheet on the chip used in the stepper modules, you set the current limit to 1/0.7 of the current you want. For a 1A motor you set the limit to 1.4A. It splits current between the two windings.

I'd check your power supply if that's what's in common between the two setups.