Y access Jumping belt, skipping steps

Machine: _K40 M2 Nano

Board: _Cohesion3D LaserBoard

Firmware: _Smoothie

Problem/ Question: _Shortly after changing out the board to the new Laser Board and Display the machine started skipping steps and making loud noises when trying to burn more complex vector graphics. Simple shapes were a none issue. While trouble shooting I found a number of problems. The left belt tension screw was striped. The bearing in the left tension pulley feels rough. The bearing 625zz bearing behind the drive gear is also not running smooth. And on top of that the wrong belt is installed on both sides its a 5mm vs the 10mm the gears and idler are made for. I have repaired the tension adjustment and forced some grease in the bearing while I wait for the new ones arrive. The M2 Nano board had no issues with thee current mechanical problems, my assumption is the acceleration is lower with the old board. Should I be able to go into the config file and reduce the acceleration while I wait for parts to arrive?

One more thing to add, there seems to be some kind of balancing act going on if I add belt tension it seems to bind up and jump the belt, if i reduce belt tension it jumps the belt

It could be a combination of stepper current and acceleration. Look up the current values for your particular motors and set the config file accordingly. The entries in question will be alpha_current, etc.

Acceleration is per-axis - search for terms like alpha_acceleration and you’ll see the default setting of 1500. If, after adjusting the motor currents to match the spec sheet, you still encounter skipping, I’d adjust it down in 500mm/sec^2 increments until it stops skipping, then adjust up in smaller increments until it starts to skip again, then back off until you can find a reliable stopping point.

First the stupid question what is the relation of alpha to x or y

the Y stepper is a 17HM4410N03AD-Z 1Amp
the X stepper is a 17HM3448N-15AD .48 Amp

Stepper module pins ( ports, and pin numbers, appending “!” to the number will invert a pin )

alpha_step_pin 2.0 # Pin for alpha stepper step signal
alpha_dir_pin 0.5 # Pin for alpha stepper direction
alpha_en_pin 0.4 # Pin for alpha enable pin
alpha_current 0.4 # X stepper motor current
alpha_max_rate 24000.0 # mm/min
alpha_acceleration 2500 # mm/sec²

beta_step_pin 2.1 # Pin for beta stepper step signal
beta_dir_pin 0.11 # Pin for beta stepper direction
beta_en_pin 0.10 # Pin for beta enable
beta_current 0.6 # Y stepper motor current
beta_max_rate 24000.0 # mm/min
beta_acceleration 2500 # mm/sec²

gamma_step_pin 2.2 # Pin for gamma stepper step signal
gamma_dir_pin 0.20! # Pin for gamma stepper direction
gamma_en_pin 0.19 # Pin for gamma enable
gamma_current 0.6 # Z stepper motor current
gamma_max_rate 24000.0 # mm/min
gamma_acceleration 2500 # mm/sec²

Alpha is X, beta is Y, gamma is Z.

What would low current do?

Low current could potentially cause the motor to not produce the torque it needs to overcome mechanical inertia, which will lead to motor stall and skipping.

Alternatively, high current will result in excess heat (motors should be warm, but not hot), could result in grinding noises and missed steps (this time due to a different physical phenomenon), and may, in extreme cases, result in smoke (at which point it’s time for a new motor).

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