Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: DennisF on October 03, 2011, 05:15:47 PM
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Hi Guy's
I have a question for the Mach Guru's if i set the velocity over 900 in the X axis the drive fault's why would it do that and if i set it to 500 the drive never fault's but it is dam slow also i f the X & Y do not have the same setting's what would happen.
Thanks
Dennis
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First question will depend on your hardware but I am presuming its servos when you say they fault. If it is then likely your tuning is out and the following error is being exceeded due tothe increased Velocity. Could also be the Velocity is too much for your motors, what does that correspond to in motor RPM and is it within the constant rated RPM of your motor?
For the second question, no doesnt matter as far as Mach is concerned but often best to have each axis as close as you can to one another.
Hood
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Hood
Yes they are servo motor's they are the bodine Big MHO they are 130 v and 2500 RPM 500 in oz's
Dennis
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So what does the 500 in Velocity equate to, ie what is the pitch of your screws and do you have any gearing between motor and screw? Also what drives do you have?
Hood
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Hood
I have the gecko servo drives I think they are the 301 or 320 the motors are connected via a belt drive and pulley set up i had everything written down as far as pitch and so forth but i can't find it now.
Dennis
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Hood
i was wrong on the motor they are baldor and they are 120 volt's i am running the transformer at 50 volts for the geckos as they can't handle more then 70 volts originally the transformer out put was 100 volts.
the thread pitch is 5 threads per inch and the ratio is 2 revs motor to one rev screw.
Dennis
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Dennis, 120v motors running at 50v will only get 50/120 = 0.4 of the rated speed of these motors, so say yours were indeed rated at 2500rpm then because you are running 50v you could only expect to get 1000rpm and it may actually be less.
With your setup you would need 10 revs of the motor to move 1 inch so for 500IPM you would be 5000rpm which is impossible. It would seem to me that you do not have the steps per unit set correctly as 500IPM is not slow and you were saying it was.
As said however the max you can expect to get is 1000rpm of the motor which would equate to 100IPM, not fast but not deadly slow like you are describing either.
Do you know what count encoders you have?
Hood
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Hood
I have just run a program and to my surprise the machine was not that slow looked to run just fine my only problem was the drive fault now that i have lowered the Velocity to 900 it seams the problem has gone away at least for the time i have run the machine.
The Encoder's are new they are HP 500 line encoder's on all drives
Dennis
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Either I am doing the calcs wrong or something is not stacking up. With the screws and reduction you have said 900Inch per min Velocity would work out as 9000rpm at the motor.
You are talking velocity of 900 inch per min and not 900mm/min I presume?
Hood
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Hood
Sorry i am in MM .
Dennis
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Ah Ok that makes more sense :)
If the rated RPM of the motor is stated as above then you should manage 1000rpm approx so at 2.5mm approx per rev that would work out at 2500mm/min so sounds like your tuning may be needing looked at.
Hood
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Hood
Do you think i should adjust the setting or leave them alone as they are, if you think i should adjust the setting's what is the formula to adjust them and thanks for the help.
Dennis
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Sorry Dennis, never used Gecko servos so dont know how to tune them. What kernel are you using and what pulse width do you have set in Motor Tuning?
Hood
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Hood
I have the geckos adjusted so don't need to do anything here for kernel speed it's set to 3500 and the step pulse is 2.
Dennis
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There must be a reason your drives are faulting, do the Geckos tell you what the fault is or does the drive just fault with no way of knowing why?
What are your steps per unit set to?
Hood
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No indicator on the geckos they just fault out don't know why. as to the steps they are calibrated for each axis but they distance is perfect no problem as i have them moving in exact amounts just the faulting issue is my only problem.
Dennis
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Could be overcurrent, maybe reducing your accel a bit will allow faster rapids. What do you have the accel set to?
Hood
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I it set to 750 MM
Dennis
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Might be worth reducing it a bit to see if you can increase the Velocity.
Hood
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So if i lower the accel then can increase the velocity is that how it works ? so what is your thought on how low it should be and then how high would i go on the velocity ?
Dennis
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You should manage to get the max velocity that your voltage/motors allow, not sure what that is as dont think you actually said what the rated voltage/rpm was but we know what voltage you are using so can work it out near enough. One thing though, is the 50v you mentioned earlier AC or DC?
What size machine is this on?
What are ALL the specs of the motors?
It could be the Geckos are just not capable enough for the current requirements of the motor but until you post the specs I cant really say.
One last thing, to me accel is more important than Velocity, Velocity is nice as well so if you can get both all the better but you may be farting against thunder to get both depending on how well the machine/motors and drives are matched.
Hood
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Hood
The motors run on DC 50 V the machine is a full size floor model 3 phase 5 hp , the servos are the Big MHO by baldor motion specs are 120 V/ DC, 500 in ozs torque, 39 amps, no load speed 31902 this is everything on the motor spec label other then the part #.
Dennis
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31902 rpm ?
Hood
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Free rpm no load thats what it says on the label anyway, In no way dose the motor spin this rpm while the machine is running.
Dennis
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Well never seen that before on a motor, usually it has a rated RPM for the rated voltage or sometimes a voltage constant. 31thousand RPM is fast ::) Could see if it was 3190 at 120v.
Do you have a link to info on the motors?
The problem may well be over current fault on the drive, if you are trying to push things too fast at too great an accel its possible the Gecko is tripping on over current as I think they are only 20Amp or so, not sure if they will just limit the current to that or if the motor asks for more it may trip out. If it just limits then its possible its a following error fault as the motor requires more amps than the geckos will give so it doesnt get to where its meant to be in the time frame required and thus you get a following error.
Hood
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Hood
The motors are 120 V DC this must be the why they have that spec, it may very well be that the drives are not capable of anything more then i am getting as they are rated for a max of 70 V the new ones are now rated for 80 volts originally the motor's were running at 100 V DC.
I did check with a transformer company and they advised me that there would not be much difference between the 50 V DC i was using and a new transformer with 70 V DC so i didn't change anything i really don't want to rewire the machine to use larger drives plus the money thing's being the way they are right now tight on cash.
Dennis
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Voltage will give you RPM so the more volts the faster RPM you will get on a DC Servo.
I think it may be the current that is your problem.
Hood
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I think Hood hit the nail on the head.
The motors are rated at 120v X39a = 4680 watts of power
You are running them at 50v X20a = 1000 watts of power.
IF the machine design NEEDS that 4680watts to work correctly
then 1000 watt may be causing the problem. Following errors the motor can no longer keep up to the demand.
YOU COULD gear down the feedsTo get more torque BUT you then loose speed.
BUT at least you can run the machine and do work. It just may take longer.
Just a thought,(;-) TP
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Thanks guys for the help looks like i will have to either slow the machine down or upgrade the drives well since money is the issue and i don't have a lot of work for the machine right now slow and steady it is thanks again.
Dennis
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Yes Dugong drives with a 120V PSU would be what your machine needs but obviously if money is tight at least you can use the way it is.
Hood
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Hood
They look like very nice drives but wow about $200 USD +S&H to the USA a bit steep is there anything made here in the USA that would do the same?
Dennis
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(;-) Now you have entered the CATCH22 zone. Big motors ,Big Hurry , BIG drives BIGGER price tag.
yOu can LOOK aroound BUT you have to be REAL carefully of what you buy for the older DC motors. You may require step/dir control and most older drives for the BIG motors were analog. AND you never know how old or used the used ones can be.
The ac drives (step/Direction)I use here NEW are about $800 each. The Mazaks here are $1800 ea refurbished.
AN option may be to replace the "motors" with something MORE compatible to the lower end drives you have. That and a little gearing MAY solve your problem and allow you a lower cost replacement IF you loose a drive along the way.
Just a thought, (;-) TP
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You can get the Dugongs in the USA from CNC4PC I believe. There will be USA drives of similar specs I am sure but they will be Industrial marketed drives and will be more expensive. There are the Vipers and Rutex drives but lots of bad in amongst the good reports on them.
Hood
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Hood
all good info to know i have a CNC4PC break out board in the machine now i will take a look at themwhat about larken drives ?
Dennis
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The Larken drives were the Vipers I mentioned above. I have never used them so cant give you first hand experience but there are good and bad stories about. Suppose that can be said of most drives in this sector of the market but not heard any issues with the Dugongs yet.
Hood
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Thanks Hood for all your help I have the machine running with out so far a drive fault out at 760 velocity and 950 on accel running the program at 350 MM per min i think that's not to bad.
Dennis
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Hood
Would you think that the code could have anything to do with the drives faulting out i was running the machine everything was going well no problem then about @ line 7652 the drives faulted out coming out of an arc man what a pain.
Dennis
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Unlikely to be the code.
Hood
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well back to the money pit how much wiring change would you think i would have to do to change the drives from gecko to Dugongs
Dennis
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Wouldnt think there would be much rewiring needed.
Hood
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I already have a CNC4PC break out board in the machine now i am going to check into going with new drives at the least
Dennis