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Author Topic: Missing steps! Upgraded my screw drive to R&P  (Read 9166 times)

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Offline BR549

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Re: Missing steps! Upgraded my screw drive to R&P
« Reply #10 on: December 17, 2011, 06:45:17 PM »
Well you went from 8000 to 1388 so that means the R&P is geared a lot higher (faster) and it will require a lot more torque to drive it at the same acceleration rate as you had  and to help keep it from loosing steps. You are already down very low on acceleration vs velocity

It will depend on how much reserve torque you have to work with from the original design criteria.

Changing microsteps I don't believe will help you out any.

Just a thought, (;-) TP




Re: Missing steps! Upgraded my screw drive to R&P
« Reply #11 on: December 17, 2011, 07:37:18 PM »
So let's say it has nothing to do with torque because I'm running it so slow. Should I even go lower with the acceleration? Maybe 1?  I was also told to put it in "exact stop" mode in the Constant Velocity settings, was that correct? Does this setting make a difference?

If it's not the torque (because it seems to be running fine and not stalling at all) What else can I check? I need to fix this without having to buy new components.  I have Keling KL 4030 drivers and they have always been reliable and accurate. I have 2 24v 4.5 amp power supplies, one for the Y&Z motors and one for the X&A motors. Do I need more amps? Better PSU's?
Re: Missing steps! Upgraded my screw drive to R&P
« Reply #12 on: December 17, 2011, 08:31:11 PM »
"If it's not the torque (because it seems to be running fine and not stalling at all"

Could you not be running near the torque limit of the motors, and this is causing you to loose steps and because it is not loosing alot of steps, stalling or grinding, you think it is n ot an issue with lack of torque?
Re: Missing steps! Upgraded my screw drive to R&P
« Reply #13 on: December 17, 2011, 09:16:28 PM »
How is the pinion engaged?  Spring or air?  On a heavy gantry with rapid changes of direction, a spring engaged pinion can bounce a little, which looks like lost steps.
Re: Missing steps! Upgraded my screw drive to R&P
« Reply #14 on: December 17, 2011, 09:23:05 PM »
It's spring engaged. It has a lot of tension and I've watched the gear and not even close to coming up off the rack. That's definitely not the issue here. Also, the changes in direction are not even close to being rapid or quick at 100ipm velocity and 2 acceleration.
Re: Missing steps! Upgraded my screw drive to R&P
« Reply #15 on: December 18, 2011, 11:47:00 AM »
You went from 8000 steps/inch to 1388 steps/inch, which means you will now need almost 6X the torque to get the same performance!  It is incredibly unlikely you had enough reserve torque before to be able to handle this, even at low speed.  Seems painfully obvious to me you need larger motors, which will likely also require better drivers.

Regards,
Ray L.
Regards,
Ray L.

Offline ger21

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Re: Missing steps! Upgraded my screw drive to R&P
« Reply #16 on: December 18, 2011, 12:10:56 PM »
Yes TP, I have the CNC Router Parts R&P system, which has a 3:1 belt reduction. I'm also using 495oz NEMA 23 motors which should be sufficient.

How did you determine this was sufficient? How much weight are you trying to move? How smoothly does it move. What kind of drives, and what power supply voltage?

Most people use the 381oz motors with a G540, which will usually outperform the 495's by a good margin, due to their lower inductance.

Imo, Nema 23 motors are too small for a 5x10 machine, and I also don't think the 3:1 reduction is enough for a heavier machine.
For the 4x6 router I'm building, I've calculated that I'll need 570oz motors and 4:1 reduction to get the performance I want. (150-200 accel up to 500ipm)
Gerry

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Offline ger21

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Re: Missing steps! Upgraded my screw drive to R&P
« Reply #17 on: December 18, 2011, 12:15:25 PM »
You went from 8000 steps/inch to 1388 steps/inch, which means you will now need almost 6X the torque to get the same performance!
Ray, most people with ~4x4 machines find that they actually get 2-3x better performance from the same motors when switching from acme to R&P.

You are correct about needing 6 times more power, but I believe that the increased efficiency of r&p and the lower motor rpm can actually give you more power. But you still need to have enough power to do the job
Gerry

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http://www.thecncwoodworker.com/2010.html

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Re: Missing steps! Upgraded my screw drive to R&P
« Reply #18 on: December 18, 2011, 01:03:53 PM »
Gerry, I'm using Keling KL 4030 drivers with 2 24v 4.5a power supplies. One for the X&A motors and one for the Y&Z motors. I looked and I have the drivers set to 3a each. My Y axis moves very smooth and probably weighs 15 pounds or so. Of course my gantry probably weighs 50 -75 pounds but still moves pretty smooth.  Any advice would be appreciated. Do you think my problem is with the overall power & torque?  I can get better results moving very slow, 50-75ipm and low acceleration.  It will be a few weeks before I can upgrade the motors and/or drivers & power supplies. But I do need to make this work until then so I'm thinking I'm going to have to sacrifice speed for accuracy for the time being.

Do you think I'll get my accuracy back with better power & torque?

Thanks.

Offline ger21

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Re: Missing steps! Upgraded my screw drive to R&P
« Reply #19 on: December 18, 2011, 03:44:00 PM »
Quote
Do you think I'll get my accuracy back with better power & torque?

I honestly can't answer that, but I know those motors are very weak running on 24V. Ideally, they need about 100+Volts for maximum performance.

Your problem could actually be caused by 100 different things. The first thing I would probably try, would be a different PC.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html