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losing steps - hot motors
« on: March 04, 2011, 08:24:10 AM »
FWIW - I was having serious problems with losing steps.  I tried everything including adding mechanical advantage to stepper motors, increasing microsteps, increasing pulse frequency, increasing pulse duration, bonding signal cables to floating ground, bonding motor cables to equipment ground at power supply.  Nothing seemed to work until I decreased acceleration of stepper motors.  Apparently the mass of my gantry was overpowering the steppers.  I have my steppers accelerating at 10 in/s/s with top speed of 150 in/min.  Question - My stepper motors whistle while idle and get hotter than a 2 dollar pistol when running.  Is this normal or is there something that I need to do to correct this situation?

Offline Hood

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Re: losing steps - hot motors
« Reply #1 on: March 04, 2011, 09:03:48 AM »
Yes, steppers get hot and depending on the drive used may or may not whistle. How hot yours are I dont know as I dont know how hot a $2 pistol gets ;D
Reducing the max current a stepper can get from a drive will reduce the heat but  it will also reduce the available torque, it is a bad idea to feed a stepper more than its rated current so if you are doing that it will be where the heat is coming from.
You have also found the bad thing about steppers, the faster you go the less torque you get and it can drop off very rapidly. Steppers can and do work very well as long as they are sized to the load and you dont want fast acceleration and blazing rapids, if you want these then get servos but again you need to size the servos correctly for your load or you will constantly get the drives tripping with overcurrent or following errors.


Hood
Re: losing steps - hot motors
« Reply #2 on: March 17, 2011, 10:31:09 AM »
I'm still futzing with the setup.  By increasing micro steps and increasing baud rate I have eliminated the hot motor problem but I am still losing steps.  The motors are not now overpowered but with the better mechanical advantage the run very rapidly.  I am futzing with the acceleration rate to see if that fixes the lost step problem.  I may have to insert g28.1 lines into my code periodically to get things back on track.

Offline Tweakie.CNC

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Re: losing steps - hot motors
« Reply #3 on: March 17, 2011, 11:48:49 AM »
You need to track down the problem of lost steps, G28.1 is no solution.
Is your stepper motor and switch wiring shielded and is the shield connected to ground at the controller end only ?

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: losing steps - hot motors
« Reply #4 on: March 17, 2011, 11:57:06 AM »
My stepper motor output from the drivers to the motors is shielded and bonded to the equipment ground.  My control wires from the interface card and stepper drivers are bonded to each other.
Re: losing steps - hot motors
« Reply #5 on: March 17, 2011, 11:58:55 AM »
You might set your accel and speed very slow to start with.
Like 3 for the accel and 30 for the speed, then check all moves for lost steps. If none, increase gradually until it starts loosing again, then decrease a bit.
If it's loosing at the low settings then there is other problems.
I'd just eliminate the speed and accel first.
Russ
Re: losing steps - hot motors
« Reply #6 on: March 17, 2011, 12:05:32 PM »
I tried speed/acceleration adjustments to no avail.  What next?
Re: losing steps - hot motors
« Reply #7 on: March 17, 2011, 12:09:51 PM »
What is you Kernel speed set at?
It can cause skips if it is set unnecessarily high.
Mine did until I reduced it.
Just grasping at straws,
Russ

Offline Tweakie.CNC

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Re: losing steps - hot motors
« Reply #8 on: March 17, 2011, 12:11:21 PM »
My stepper motor output from the drivers to the motors is shielded and bonded to the equipment ground.  My control wires from the interface card and stepper drivers are bonded to each other.

Are your limit switches wired with shielded cable ?
Are those shields bonded at the controller end only ?
Are your stepper motor cables bonded at the controller end only ?

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: losing steps - hot motors
« Reply #9 on: March 17, 2011, 12:14:55 PM »
I had already grasped that straw.  Tried all settings (restarted program between changes as advised).  It seems to make no difference.  Limits not shielded except for the z-axis.  all others are well away from anything else.