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Author Topic: Missing steps! Upgraded my screw drive to R&P  (Read 9176 times)

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Re: Missing steps! Upgraded my screw drive to R&P
« Reply #20 on: December 18, 2011, 04:50:49 PM »
It's the same PC that I was using when I had my 3' x 4' screw drive system and never had any problems, Accuracy was perfect.  Basically, I'm using the same PC, motors, drivers, power supplies as I was on my smaller system so the problem should be mechanical I would think. I'm thinking it must be the motors, drivers, or psu's. I've already checked for slippage, backlash and freedom of movement and all those check out ok.

Again, even though I may be under powered, I have not seen or heard any stalling, even running at 400ipm - something is happening on a much smaller scale. I'm still getting measurements that are .01 to .02 off when cutting parallel lines but the errors are smaller at much slower speeds.

Any other thoughts?  Thanks,
Jon

Offline BR549

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Re: Missing steps! Upgraded my screw drive to R&P
« Reply #21 on: December 18, 2011, 05:05:08 PM »
BUt yourare geared much different(requiring more torque) AND I bet the gantry is much heavier leaving more inertial weight to deal with(requiring more torque) also with the higher gearing your resolution per step has changed to the worse.

If you can change the gearing to about 5-6:1 instead of 3. That will give more torque BUT it also slows down max velocity. 

My guess is you are loosing mini steps at each change of direction. Try setting the Accel to 1 but then you face the delima of slow accelleration and CV rounding. So you may have to run exact stop mode.

Just some thoughts, (;-) TP

Re: Missing steps! Upgraded my screw drive to R&P
« Reply #22 on: December 18, 2011, 05:09:21 PM »
Yes, I have already switched to exact stop mode and acceleration to 1, I have my velocity set at 75 and in Sherline mode. Accuracy is noticeably better at these slower speeds but not perfect yet.

Offline ger21

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Re: Missing steps! Upgraded my screw drive to R&P
« Reply #23 on: December 18, 2011, 07:53:44 PM »
With accel at 1, I doubt it's the motors. Most CNC Router parts r&p users are using 30-40 accel with 380oz motors.
Try lowering the velocity to 40-50 as a last test, as the voltage could still be the issue.
Gerry

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Re: Missing steps! Upgraded my screw drive to R&P
« Reply #24 on: December 18, 2011, 09:06:06 PM »
I will try an even lower velocity and raise the accel. If it is the voltage, would getting a new power supply help? Maybe 48v?  My drivers only allow 3amps max, is that enough? Thanks.

Offline BR549

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Re: Missing steps! Upgraded my screw drive to R&P
« Reply #25 on: December 18, 2011, 09:56:42 PM »
Make sure you check the max rating of the drives.

(;-) TP

Offline RICH

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Re: Missing steps! Upgraded my screw drive to R&P
« Reply #26 on: December 18, 2011, 10:53:11 PM »
Your driving 2 motors at 3 amps each using a  power supply which is 24V @4.5a. I would recommend that the power supply have the current capability for  both motors which would be 6 + and an increase in voltage also. That will increase the motors preformance. Without a motor
curve  it is only a guess on available torque and rpm unless someone has experience with that particular motor. You have not noted how the motors are wired and that can also make a difference. 

FWIW,
RICH
Re: Missing steps! Upgraded my screw drive to R&P
« Reply #27 on: December 20, 2011, 08:54:43 AM »
Dont know if its relavant, but I have had issues with the 4030`s on highly detailed small parts. (Jewlery waxes)

They would just act stupid as in what you are describing.  On simple profile shapes they would work fine, it was the small very small 3d movements that would give me grief.  I replaced them with the 5056`s and all was fine.
Re: Missing steps! Upgraded my screw drive to R&P
« Reply #28 on: December 20, 2011, 02:14:48 PM »
Well I'm going to try out some Nema 23 380's and Gecko 540 with a 48v 12.5a power supply. We'll see if my problem goes away. We can't find anything mechanically wrong at this point....

Offline BR549

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Re: Missing steps! Upgraded my screw drive to R&P
« Reply #29 on: December 20, 2011, 07:11:51 PM »
For a 5x10 table I would consider Nema 34s as a better solution.

Just a thought, (;-) TP