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Thread: Lost steps on A/X axis
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31st August 2011, 02:37 PM #1
Lost steps on A/X axis
I recently added an extra motor to my CNC machine in order to cure an unfortunate propensity of the gantry to crab and lose steps.
It was previously driven by a single 1200 oz motor that pulled from the middle on a table that is two metres long. I have added another 1200 oz motor and moved the original drive from the centre of the table to the edge and paralleled it with the new thread and motor so that I now have both an A axis and an X axis.. The drivers I am using are Gecko 203Vs and an 80 volt unregulated power supply.
The steps are set at 400with an acceleration of 600 but when the velocity is set over about 2500 it starts to lose steps on one axis and so it immediately all goes out of square.
OK, this combination is enough to pull a car apart but not enough, apparently, to get a nice smooth drive from end of the table to the other.
Does anyone have any thoughts or suggestions to improve the speed?
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31st August 2011, 03:18 PM #2SENIOR MEMBER
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Hi, bob is it the motor which took a swim or the new motor you added that is causing a problem? or does it alternate between the 2?
Has the PSU got enough grunt to drive all the motors?
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31st August 2011, 04:23 PM #3
Hi Chris
It seems to be mainly the newer motor that is stalling.
I must have wired it up correctly because it is actually moving along OK.
The power supply I use is an AnTek torroidal PSU that puts out 70Volts DC at 11 amps
This should be able to handle the ...hmmmmmmm just checked on your site, and the 1200 oz motors draw a maximum of 6 amps each, so that is 12 amps even without the other two smaller motors which also draw about 3 amps each.
Damn
What to do now?
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31st August 2011, 04:55 PM #4
Well. I could buy another one of these to go with the one I already have.
Or
I could go for a larger one that handles up to 19 amps. If I go this way then it would cost another $225 plus postage,, but I would then be able to sell the old power supply for about $120 or so.
Bob Willson
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31st August 2011, 04:57 PM #5SENIOR MEMBER
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31st August 2011, 06:07 PM #6
Good suggestion Chris
I did that and I can get the speed back up to 4000 again.
I ran it through about 20 iterations of
G0
X0
X1550
and it ran fine. Even got a bit too much whip on the screws due to the speed.
I'm just going downstairs again to try it at 5000.
Nope, that didn't work, but then again I didn't expect it to.
Bad thing is that definitely means that I need to spend more money on this pale elephant.
Bob Willson
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31st August 2011, 07:45 PM #7SENIOR MEMBER
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It might be worthwhile looking into a 2:1 increase with those massive motors and 5mm ballscrews, it should give you better performance.
About the PSU if you dont want to spend too much money a seperate switchmode PSU would probably be the cheapest option.
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31st August 2011, 08:58 PM #8
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2nd September 2011, 09:02 PM #9
I ordered a PS-10N70R5R12 power supply from AnTek. which supplies 14.3 amps at 70 V at a cost of (US$180) plus (US$44)
I had originally intended to order their PS-15N73R5R12 power supply. This would have given me 19.5 amps at 73V, but not only was the price for the supply a fair bit higher (US$ 240)but the delivery was almost 5 times as much as well at US$200
Bob Willson
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1st October 2011, 01:03 PM #10
Ok, I got the new power supply and the wired it all up to the motor drivers and then sat back to wonder why the motors weren't holding or turning at all.
Can you spell dlckhead? I had wired it all up back to front and blown the fuses in the Geckos. Two days later when the new fuses arrived and I had wired it all up properly using colour coded wires this time, and the motors turn on and hold.
Start testing and F@#$. It didn't make any difference at all to the way the machine behaved. Still lost steps in one motor or the other.
I re-ran the driver test and it said that all was OK.
Is it likely to be the BOB? I have had trouble in past with same board.
Bob Willson
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1st October 2011, 05:57 PM #11GOLD MEMBER
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1st October 2011, 06:22 PM #12
Bob
What sort of B.O.B. are you running?
I have had some issues with CNC C10's in the past.
Presently running dual motor machine '(i.e. Y and A axis) and initially had somewhat similar issues with racking when reffing but cured the problem by chaning out the B.O.B.
Cheers
Noel
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1st October 2011, 06:31 PM #13
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1st October 2011, 06:35 PM #14
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5th October 2011, 12:47 AM #15
Solved the problem. It was all because I had set the steps too high at 400. Apparently this should have been 138.68285.
Using this number I can now set the acceleration to 1000 and velocity to 4000. this was of course brought about by my having put a 44 tooth pulley on the motor and a 15 tooth pulley on the shaft. No doubt I could make it a lot faster, but that is fast enough for now. At least it is all going again.
Now, ????? what to make? Hmmm.
Bob Willson
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