[AndiKid]

I run a rack & pinion setup and use CandCNC Electronics. My Y Axis uses two motors which are slaved. Motor tuning and steps have been set up equally on both motors.

I use it as a plasma cutter and do routing work as well with it. I am really happy with it but encountered a problem.

When I do a pattern with a lot of holes and a lot of different movements the machine starts running wrong and losing it's correct positioning.

Meaning for example, that the cuts for the outlines (cut after the holes) are 1 or 2 inches from where it should be.

When I then "Home" the two axis - the one side "arrives" a little later than the other.


Has somebody experienced something like this and could lead me in the right direction how to fix it?

[AndiKid]

Isn't there anyone how could help?

I have been thinking what I think it could be..

I soldered new wire on the Y Motors because the original ones from CandCNC were too short. Coulod that cause that maybe the resistance sometimes is too high and cause problems?

[Black Forest]

Is this a new build and done this from the beginning or did it work correctly and now starts to exhibit this problem?

[AndiKid]

Moin Schwarzwald

I built the machine myself and the strange thing is that contour cuts run perfectly. It seems that only doing a lot of holes (or having a lot of quick back and forth movements) it seems to cause this problem..

[Cheeta]

You might want to check the motor configurations. steppers will stall if the acceleration or speed is set too high. If the stepper cannot supply enough torque, it will manifest itself in this behavior.
Another thing to consider is backlash. You mentioned the back and forth movement which could indicate an accumulation of translational error introduce by excessive backlash.

[Black Forest]

The thing I would check would be the pinion gears on the shaft to make sure they are really fixed and not slipping back and forth on one motor. Just a small rotation on the shaft will give you something like this maybe.

[ajclay]

I'd follow Cheeta's lead on the problem. Sounds like you are loosing steps for one reason or another. You mentioned that the steps per in/mm are the same for both motors, make sure that the acceleration and rapids are the same in the motor set up... I'd make a change even if they are. Slow things down 25%.

If you are loosing steps because the motors are over taxed, slowing the movement down will help the problem.

Backlash may come into play if one side has a larger amount of backlash than the other causing the gantry to get out of square... I wouldn't think it would stack up and cause the gear rack to jump a tooth... The gantry would only be out the amount of the backlash and not progressively get worse.


stay in touch.

aj

[BTA PLASMA]

Thats the one problem with steppers is that you can send them instructions and if the resistance to movment is too great they loose a step. A well engineered system will not loose steps. If he is getting good holes he doesnt have mecanical backlash. But he isnt giving all the info needed to make a consideration. What is the weight of the gantry and what are your tuning numbers?

[AndiKid]

Hey thank all of you guys so much for your input. I got engaged and have been out of the Country for many weeks.

I now had time to take care of some things. Here are my specs for the machine. I am running the 620oz Dragoncut Motors. My Gantry weight is precisely 150 Pounds.

The Speed I set in the Motor Tuning is: Speed 6000mm/min (236 In/min) and Acceleration 1200 mm/s2 (47 in/s2)

Is that an ok set up?

[ajclay]

I'd like to look at the graph in mach but need all the info. What is the steps per....?? It takes all three variables to take a look at where you're at...

Aj

[Kerryfisher]

If it helps this is what I have mine set at, same motors, 3.75:1 reduction, gantry weight maybe a little less than that.

Touchwood it's going very well so far, thanks to AJ keeping me on the right track

Attachment 188418

[Torchhead]

Hey thank all of you guys so much for your input. I got engaged and have been out of the Country for many weeks.

I now had time to take care of some things. Here are my specs for the machine. I am running the 620oz Dragoncut Motors. My Gantry weight is precisely 150 Pounds.

The Speed I set in the Motor Tuning is: Speed 6000mm/min (236 In/min) and Acceleration 1200 mm/s2 (47 in/s2)

Is that an ok set up?

Well everything is a little on the high side. The gantry weight is about 50 lbs over what we suggest for those motors with a 3:1 belt reduction to a 1" pinion.

The acceleration is a function of the linear force (derived through pinion from rotary torque) divided by the MASS (weight /32) of the load. There are also frictional forces but are not as big in the equation. If the steeppers have to supply more torque than they can (steppers are torque limited) they simply stall.

Back all of your acceleration off by 50%. Than see if there is anything you can do to lighten the weight of the gantry. If the table cuts okay on slower cuts or longer contours it is not an electronics or mechanical issue.

You can get quicker support on CandCNC products on the CandCNC Support forum on Yahoo

TOMcaudle
www.CandCNC.com

[Kerryfisher]

Having just had a gearing tutorial today from AJ you got me thinking as well

In one of your earlier posts you mentioned this as the spec of your gearing, maybe I have it wrong (quite possible) but should your 'sprocket' and 'pinion 1' not be the same diameter to get the 3.6:1 ratio 72/18???

Sprocket: Modul 2 - 20 Teeth - Diameter: 44mm (1.73 Inches)

Pinion 1: HTD 15mm - 18 Teeth - Diameter: 28,65mm (1.13 Inches)

Pinion 2: HTD 15mm - 72 Teeth - Diameter: 114,59mm (4,51 Inches)