Hello Guest it is September 21, 2019, 10:52:05 PM

Author Topic: Only X-axis motor is working  (Read 11489 times)

0 Members and 1 Guest are viewing this topic.

Offline rcaffin

*
  •  1,003 1,003
    • View Profile
Re: Only X-axis motor is working
« Reply #160 on: April 02, 2018, 11:28:42 PM »
When I set the velocity to 45 the motor hops around. It's back and forth all over the place.
At 100 the motor runs smooth.

At first glance, that sounds like resonance. It can be a real pain.
Simple (cheaper) drivers cannot handle this. You need a fairly sophisticated driver to do so. It can take a significant amount of processing power to suppress the resonance.
You MIGHT be able to reduce the effect by adding a 'damper'. A solid disk on the motor shaft, coupled to the shaft via something very lossy might help. Plasticene, Blu-Tack, double-sided foam tape, are all possibles. None of them last very well though.

Cheers
Roger
Re: Only X-axis motor is working
« Reply #161 on: April 02, 2018, 11:36:43 PM »
When you say resonance, are you saying electrical resonance or mechanical?

I ask because the motor does that even with a load on it.

I should shoot a small youtube video of it.

If I set the signal to low side the problem persists but is reduced.

I'm looking around for a 4 wire stepper to see if I get the same effect on a 4 wire.

Offline rcaffin

*
  •  1,003 1,003
    • View Profile
Re: Only X-axis motor is working
« Reply #162 on: April 03, 2018, 12:09:08 AM »
It's an electro-mechanical resonance (just to be difficult).

Energise the motor somehow. It will go stiff and hold its position.
But now apply some torque, and the shaft will rotate a bit. That is a spring.
When you have a mass and a spring, you can get bouncing or oscillation. If you drive the system near the right frequency, it can hit resonance and oscillate wildly. So can any other mass/spring system.

Cheers
Roger
Re: Only X-axis motor is working
« Reply #163 on: April 03, 2018, 12:41:00 AM »
A video is worth a thousand words

https://youtu.be/5s0y1Pj-8JM

Offline rcaffin

*
  •  1,003 1,003
    • View Profile
Re: Only X-axis motor is working
« Reply #164 on: April 03, 2018, 01:17:48 AM »
Resonance imho.
Try at 1/5 speed, or at 5x speed.

Cheers
Roger
Re: Only X-axis motor is working
« Reply #165 on: April 03, 2018, 01:25:35 AM »
Works fine at anything under 40 or over 55.
But it HAS to accelerate past 45 to gt to anything over 45 and it always messes up on the acceleration.

I tried to buffer the possible resonance with my finger and thumb giving various levels of stability and the motor is VERY persistent on making the steps as you see in the video.

Offline rcaffin

*
  •  1,003 1,003
    • View Profile
Re: Only X-axis motor is working
« Reply #166 on: April 03, 2018, 01:49:08 AM »
Yup.
It's a hard world: you have four choices:
Hope that the assembled system (ball screw etc) will damp it down enough
Figure out a mechanical damper (no-one else does this)
Stay below 45
Buy a new driver like a Gecko 203V

Cheers
Roger
Re: Only X-axis motor is working
« Reply #167 on: April 03, 2018, 01:55:35 AM »
Yup.
It's a hard world: you have four choices:
Hope that the assembled system (ball screw etc) will damp it down enough
Figure out a mechanical damper (no-one else does this)
Stay below 45
Buy a new driver like a Gecko 203V

Cheers
Roger


OR, I could get new stepper motors.

I just hooked up a 3A (using my driver set to 1A) 6 wire stepper motor and it worked flawlessly.

I'm thinking these are just weird motors.
I'll do more testing tomorrow but it seems like the motors just don't like to work "normal".
I have a couple other motors that aren't like the other 25 so I will check them also.

Offline rcaffin

*
  •  1,003 1,003
    • View Profile
Re: Only X-axis motor is working
« Reply #168 on: April 03, 2018, 02:38:05 AM »
If you run a 3 A stepper at 1 A, the 'spring' is much weaker. You may manage to avoid a significant response, especially once you have a toothed belt & lead screw hooked up onto the motor. If you run them at 3 A there will probably be a resonance.

I have a drawer full of old round steppers, including some quite expensive large ones. They were inherited for free. Their design relies on some ferrite magnets. Trouble is, over the years the ferrite magnets have lost their field strength, so the motors (all of them) are now gutless wonders. The pain of accepting that was high  :'(

Cheers
Roger
Re: Only X-axis motor is working
« Reply #169 on: April 03, 2018, 11:19:23 AM »
Well, if all the steppers I have are dead then they're dead. I wasn't going to use them for the final project anyhow. I can still use them as generators for a water powered light show (if I ever get around to that project).

I had intended on  using new steppers anyhow so might as well get it done.

I'm still going to do the whole oscilloscope thing and I'm going to step my driver up to 3 amps on the working motor to see if I get hinky results. After all this is all a learning process for me.

I know I have another new stepper out in my garage so I will test that one also. It's connected to a balls crew already which is why I haven't used it til now. It's pretty bulky to play with.