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motor tuning
« on: May 13, 2006, 10:33:11 AM »
 Hi I posted this in the yahoo forumalso  so I thought I 'd post it here too

Hi I have some old vexta ph299 motors and I was wondering if anybody
else had the  same motors and could save me some time in setting them
up by sharing their tuning specs for their setup with me Idon't really
know what they are supposed to sound like and I don't have any tourque
speed curves to go by .
as for steps/rev : my screw is an 8tpi screw would steps/rev be 1600?
what would be the best velocity and acceleration for these motors?
can any body help me please?
Thanks Bob

Offline chad

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Re: motor tuning
« Reply #1 on: May 14, 2006, 03:06:59 AM »
Hi,

Ok,first somebody else's numbers won't do much for you. Stepper tuning is very much an individual thing. It is relayted to motor voltage, drivers, full or micro-stepping, and your individual machine characteristics
We can help you get things working but we need more info on the setup ,like:

Motor voltage (the voltage of the power supply)
--->Stepper drivers?<----
are they direct drive or is there a belt or other form of reduction?
What kind of machine is it?
what are the power transmission devices? ( ball screw, acme thread, all thread, belt,) what are the linear slide mechanisms? ( skateboard wheels, nsk slides)
are they making any noise when you try to jog?
do you have the ports and pins set correctly?
is your e- stop flashing?

Start LOW in the motor tuning. velocity 5, accel of 5,  (step pulse 5 , Dir pulse 5, these only will go down to 1 when you have all other things working.)

Unfortunally with this kind of thing there are NO short cuts. You just have to figure this stuff out and learn it. It isn't that hard you just have to devote some time to master it.
I can get pretty much any mach machine (assuming the hardware is working and wired right) in about 5 minutes moving enough to start testing and fine tuning. Besides, unless you really know how it works you will never get optimal performance out of it:)

Chad

 
Re: motor tuning
« Reply #2 on: May 14, 2006, 02:12:19 PM »
Hi Chad thanks for the reply for now I'd just like to spin my motors  they are vexta ph299-01 nema 34 motors 
 This machine is a 40x60 " router  wiit a cutting area about 36x 50 .
My machine is built from 80/40  heavy channel.
 The wheels are made of nylatron with 3/8 id skate bearings on each side. These wheels roll in the groove of the 80/40 channel, its the same for all axis.
 The x axis is a twin screw with one of these motors on each screw all screws are 5/8-8 acme trheaded rod.
 These screws will be tied together mechanicaly with a size 40 chain and 12 tooth sprockets to try to eliminate lost steps between the motors which will be slved in mach a axis to x axis
 The acme nuts are the same nylatron as the wheels this stuff is also called m6 nylon as its impregnated with moly to reduce friction
 There doesn't seem to be any binding anywhere .
   I actually had turned the y axis with a smaller motor using hobby cnc unipolar chooper board
at 24volts  full step it seemed to be slow when it turned but it didn't start well .
 This why I went to nema 34 motors the other ones seemed to be under powered .
 I was hoefull that someone else was alredy using these motoors and could at least get me in the ball park as for the settings in the motor tuning window .
 In the steps per rev is this dependent on the screw pitch if it's an 8 turn screw do you set this to 1600? or am I mistaken?
 In an ideal world and all things being perfect, how fast can I reasonably expect these motors to turn before they stall ?
 If I knew this I might have an Idea where to set my velocity and acceleration settings  you know somewhere close to optimal but probably not perfect I realize that I'll have to fine tune   everything later 
 I fooled a little with the accel and velocity with the smaller motors but they wouldn't do anything at those low settings they just set there .
 I'm not afraid of hurting my machine by going too fast as theres plenty of time to stop them since all axis are centered  on the screws .

So if anybody else is using these same motors could you please share  your accel and velocity settings with me it will save me alot of time trying to even get the motors to turn my screws at all.
Bob
 

Offline fdos

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Re: motor tuning
« Reply #3 on: May 14, 2006, 02:45:58 PM »
Chad is right...   Others settings will not help you.

It really is down to your own machines loads/friction etc, your drives, whether you are microstepping or not, and the voltage applied to your drives.

I would not have the two motors linked as you suggest, it may even make matters worse.  Mach can slave axis's as yo may already know.  I assume you are planning on using two drives also for that axis?

It also helps with steppers to drive the machine 1:1. I'm still amazed how many people assume they will get more torque by using reduction.   This can be self defeating as the motors torque drops off rapidly with speed.

You jus got to try it out.   What drives are you using?
Re: motor tuning
« Reply #4 on: May 14, 2006, 03:19:04 PM »
Everything is direct drive (screw coupled directly  to stepper) the reason that Iused a chain to link the screws on the x axis  is that someone said that this would help eliminate lost steps from one screw to the other so that the two screws on the x axis wouldn't get out of alignment and yes Iwas planning on seperate drives for each motor this is why I had bought and built a hobbycnc 4axis unipolar chopper board from Dave and as i had said it was turning my smaller motors with some succes thats when I bought the bigger motors and was told that I could run the bigger motors off this board if I set the max amps at 3 amps as per Daves  specs. I was told that the motors just wouldn't have the rated torque  but when I did this the board smoked so I'm probably going to quit fooling around with unipolar steppers and boards and go buy some gecko's
Bob
Re: motor tuning
« Reply #5 on: May 14, 2006, 03:29:50 PM »
 maybe I should ask the question this way if I've just got the motors sitting there in front of me and I want to spin them to their top speed without a load using full step  and 48volts how fast can I expect these motors to turn? rps or rpm it doesn't matter Iguess I can see your point the ipm/ips  is base on how fast I want and can actually travel  and not  motor speed . as for accel rate with no load can i expect to be able to use a fast accel rate as it shouldn't take any effort to get them going?
Bob

Offline fdos

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Re: motor tuning
« Reply #6 on: May 14, 2006, 03:41:21 PM »
testing on the bench, the motors normally will stall at a lower speed than they would under normal machine load.  SERIOUSLY.

Steppers need some load to work correctly.   You can test them on the bench, but in my experience you can normally up the max velocity a fair bit after fitting to the machine.

Do yuo have some form of flexible coupling between your motor shafts and the screws?   They also work better that way rather than rigid coupling.
Re: motor tuning
« Reply #7 on: May 14, 2006, 06:40:57 PM »
Thats weird  to think that a stepper would turn faster under load but I guess anything is possible. I don't have flexible couplings because there again I wanted to avoid lost steps which I asume could happen if there was any flexing in the couplings I mean wouldn't that almost be the same as backlash ?

Offline fdos

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Re: motor tuning
« Reply #8 on: May 14, 2006, 07:05:58 PM »
Yes It does seem strange but Steppers do not like being unloaded.  Try it on the bench...  They will stall at high speed and will actually stop turning and scream at you!

Note the speed at which this happened, Load them up, and you will get a higher speed before they stall.

Re the couplings, Not it's not like backlash, unless they are sloppy!   The type I use are fenner type, with a nitrile rubber insert between two hubs.   This nitrile has quite a high Shore rating and you can hardly deflect it by hand when it's assembled.   Probably as stiff as a toothed belt on a servo system.

In fact sometime ago it used to be recommened steppers were driven through a viscous coupling, this is not really required with microstepping drives, but something in between that and a rigid coupling does help a lot.   

Rigid couplings add more problems as it's very difficult to get both angular and radial allignment perfect.

I've done a lot of retrofitting, and ony passing on what I've learnt the "hard way"!
Re: motor tuning
« Reply #9 on: May 14, 2006, 08:46:10 PM »
can you provide me with a link to the fenner type coupling are they simmular to a lovejoy coupling like these
http://www.lovejoy-inc.com/jawtypecouplings.htm
« Last Edit: May 14, 2006, 08:51:01 PM by boblee »