Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: eightdigits on August 19, 2006, 11:58:12 PM

Title: motors stalling
Post by: eightdigits on August 19, 2006, 11:58:12 PM
I need some help.  when I jog my motors they spin once, stall, and make a nasty noise.  They seem to work just fine with the stepperworld test program, VBStepDirXP. When I hook up my multimeter two of the terminals of the motor read .4 volts and the other two read 3 volts. Whats going on?
Title: Re: motors stalling
Post by: Hood on August 20, 2006, 03:06:12 AM
have you set up the step/unit correctly? Also have you tried increasing the acceleration time and/or reducing the velocity on the motor tuning page?
Title: Re: motors stalling
Post by: eightdigits on August 20, 2006, 07:08:53 PM
Changing the step/unit, acceleration, or velocity doesn't do anything.  well to help anyways.  I also wanted to add that when the power supply is on and the motors are in standby, the resistors and motors get super hot. I think it has to do with the motor terminals not reading the same amount of voltage.  I could really use some help.
Title: Re: motors stalling
Post by: Chip on August 20, 2006, 09:46:59 PM
Hi, eightdigits

Try setting the Step Pulse and Dir Pulse to 5 see if that helps, It's under Config - Motor Tuning, this increases the pulse width time sent out by Mach3 giving the stepper box more time to see the step signal and respond. If this helps back it off to see where the problem starts then increase it back up 1 unit as it dose affect the max speed you can run.

Your Volt meter reading's are probably just fine, your stepper control is probable set to two windings being on at a time like ab, bc, cd, da..... or 12, 23, 34, 41..... more torque than a single winding,

Hope this helps, Chip
Title: Re: motors stalling
Post by: eightdigits on August 21, 2006, 12:25:28 PM
I tried setting the step pulse and dir pulse to 5 and the same thing happened, the motor still locked up after 1/4 a rotation.  If I change the jog rate to 15% the motors run fine but the volt meter readings are still weird and the the motors still get hot when there not doing anything.

Thanks for trying chip.
Title: Re: motors stalling
Post by: chad on August 21, 2006, 02:23:24 PM
This sounds like a classic motor tuning problem (assuming you have your steppers hooked up correctly).
Your velocity and acceleration are too high for your steppers. The reason it works if you are at 15% is it is slowing the output down to the point the stepper can keep up.

Ok to find your max settings.
First you have to have your steps per unit correct ( or at least close to your machine parameters ). Second set the pulse width for step and dir to 5 (we can change this later).
Second set the velocity and acceleration to 5. I know this is slow but you have to learn to walk before you can run.
Click in the graph window and use the up and down arrow keys to try these settings. if the motors turn and behave as expected then you can go on, if not then you need to go back through the manual and make sure your ports and pins are set correct, etc.. You also have to make sure that your steppers are wired correctly. It is easy to screw up a stepper connection and get"some" some movement but not correct movement.

Assuming all that is OK now you can start to turn up the velocity. go from 5 to 10 , do not mess with the acceleration leave that at 5. Keep going up in the velocity until you start getting motor skipping again , this is your max speed stepper-skip point. Back off that about 20% and call velocity set. At this point you can start the same process with the acceleration value. Get it to the point where the steppers will skip and back this down by 20%

At this point don't forget to be hitting the axis save button alot.

If you change your step per unit number you will have to start this process over. This number has a lot to do with the tuning and if it is changed all the velocity and acceleration settings will be meaningless.

Just to pre answer a question you Will probably have, Backlash correction WILL cause your steppers to skip, don't use it, try to fix back lash in the machine.

Steppers getting hot: Yes they do. Even when they ain't doing anything. A stepper at rest will still have at least one coil energized to hold the position of the shaft. Just the nature of the beast. Even properly tuned steppers will be to hot to touch. If they are Really smoking hot then you will need to go to a different drive like gecko or rutex or some other pwm current adjustable driver. The resistors will also get cooking hot, also just the nature of the beast. The more advanced drives can limit current so you don't need any resistors. 

Good luck,


Title: Re: motors stalling
Post by: chad on August 21, 2006, 02:30:50 PM
Oh yea, A voltage meter isn't going to tell you much looking at a stepper motor output. The stepper driver is going to be putting out pluses that are too fast for a dmm to react to. The only way to properly look at that signal is to use a o-scope. And even then unless you really know what you are doing and have a duel trace sampling scope it won't tell you much. If the other program runs them fine then don't worry about the motors and just work on the mach settings.

You are getting close. We have all been here ;)


Title: Re: motors stalling
Post by: eightdigits on August 21, 2006, 11:27:31 PM
I love you man. what did it for me was what you said about the motors having one coil energized. I went back to the test program, the one that showed the same voltage on all four terminals and the shaft of the motor could be turned by hand. In the mach 3 program you can't turn it by hand, meaning voltage was applied to one coil and thats why the terminals were showing different voltages.  It all makes since now. Then I simply changed the steps/unit to a lower number and the motors spin just fine. The other day I don't think I was hitting the save axis settings, I was just clicking the "ok" button, That why it wasn't working when  hood posted that suggestion.

Thanks to everyone but I'm sure I'll be back with another stupid question.