[Jon.N.CNC]

Hi There.

I have just noticed that the datasheet for the drivers i use have updated now with both Peak and RMS.

I use 4.1a steppers, The driver settings available are 3.8A peak 2.7A rms / 4.3A peak 3.1A rms / 4.9A peak 3.5A / 5.6A peak 4.0A rms.

Should i set to 3.8a peak or 5.6A peak.

They have been running @ 3.8a Peak for two years extensively (5 days a week constant) however recently ive had issues with them stalling which i believe to be wear in the hiwin carriages as any dust which they used to plow through now seems to be compressed and stuck onto the rails. Thinking i might be able to squeeze some more torque from the motors as a temporary fix until i replace the carriages. (Moving 250kg gantry with 3.1nm on 40:1 planetary boxes so the motors really are under powered and will swap them out for 4.1nm which will help a bit).

But i have noticed the stall is nowhere near as loud as it used to be. The drivers are dsp and say they have anti resonance technology to combat the velocities the motors dont like. Could my motors be dieing ? I have noticed that new they used to get quite warm now barely get luke warm.

Thanks

[wizard]

First off are you lubricating those linear rails? It is an imperative that they be lubricated fairly often in dusty environments. Further you should be wiping down the rails regularly. At this point you may have to disassemble the carriages to clean them if they cant be flushed out with lube.

This is a very serious issue, ive seen plugged up carriages stall out servo motors, steppers snd even result in broken leadscrew drive belts. What is worse is that the gummed up carriages will damage the bearing surfaces on the linear rails as the balls start to skip and slide instead of rolling. In other words plugged up carriages are bad voodoo!!

As for you drives documentation, frankly it sounds like garbage. The whole point of modern stepper drives is to manage current going to the windings. By definition you want no more than your setting allowed to go through the windings, so the whole concept of a peak current capability is bogus in my mind. If the drive manufacture has a good explanation for a peak rating on a stepper drive I'd love to hear it.

A peak rating is more suitable for a servo drive as it reflects the capability of the motirs better. That is current in a servo motor is a function of the torque being developed.

In any event your stepper drives should be setup with the operating current as close to the motors specs as possible but not going over. HOw well a stepper will operate at higher current levels than spec is unknown and variable from one stepper to another. However the manufactures have the current ratings for a reason and there is no real good reason to exceed the values.

It should be noted that i get a bit of flak when i tell people to set the drive to the motors current rating and leave it there. The common complaint is that the motors run "hot", but these people dont seem to realize that the steppers are designed to do so. If you dont set the drive properly, torque and performance goes out the window. This seems to be a constant issue in the RepRap world as people try to get some really crappy machines to run.

That being said it is always possible for a motor to fail. In this case though you are indicating that you know you have an issue with the carriages so I kinda doubt the motors are a problem.