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Tronxy Z Axis wont move (Melzi V2)

Posted by eatumup 
Tronxy Z Axis wont move (Melzi V2)
December 03, 2017 09:38PM
A friend of mine decided to dive into 3d printing and bought a Tronxy P802 m from GearBest. He got the thing together but we could not get the Z axis to move as it should.

The motors vibrate and the motor shaft visibly sort of "hammers" back and forth. When I assembled my Folger tech I had a similar issue due to driver adjustment needed. We tries adjusting the Melzi but had no luck. Here is what we did.

mechanically, we plugged each of the two z axis motors into the Y axis driver and verified they work properly as the y axis worked at the start.
With the Y axis motor plugged into the Z axis driver the Y axis would behave as the Z axis. So that tells me that there is problem with the Z axis driver or its configure.
Searching we found lots of posts about adjusting the v-ref on the driver as I had to on my printer initially.

The label on the motor indicates a Tronxy sl 42sth40-1684a-23 as the motors model number. As I read the data sheet, that motor is a 1.68 amp motor. The resistors are R100.
So If I understand the maths right it should be as follows:
1.68 X 8 X.1 = 1.344v
90% of 1.344 = 1.209v

That looked too high and I didn't trust it. I had read that the Melzi v2 should be between .4v and.8v on the driver.
We began with the Voltage at .4v
Stepped up the voltage by roughly +.1v and tried it until we reached 1.201v.

The behavior didn't change. The axis is running two motors, but from what I could find I didn't see any mathematical adjustment for that.

At this point were stumped. Any ideas?
Re: Tronxy Z Axis wont move (Melzi V2)
December 04, 2017 03:25AM
This sounds like the usual max z feedrate being set too high in the configuration.h in marlin default firmware
ie
#define DEFAULT_MAX_FEEDRATE { 300, 300, 5, 25 }

try reduceing the 5 to a 2 and recompiling firmware
Re: Tronxy Z Axis wont move (Melzi V2)
December 04, 2017 10:06AM
Quote
obewan
This sounds like the usual max z feedrate being set too high in the configuration.h in marlin default firmware
ie
#define DEFAULT_MAX_FEEDRATE { 300, 300, 5, 25 }

try reduceing the 5 to a 2 and recompiling firmware

Ill give that a shot this weekend when I see him.

Other than that, I am still concerned that I calculated the v-ref wrong. Can anyone verify it?
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