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Author Topic: Steppers are too slow  (Read 32741 times)

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Offline stirling

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Re: Steppers are too slow
« Reply #10 on: November 30, 2011, 08:09:24 AM »
Stuart - from the info you've given and what I've been able to find...

With inductance of 9mH your "ideal" power supply voltage for your motors to achieve max torque/speed is 96Vdc. Your drivers can only handle a max of 50Vdc and your power supply is only 24Vdc. I'm afraid this is NOT a well matched system if high speed is what you want.

Ian

Offline Tweakie.CNC

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Re: Steppers are too slow
« Reply #11 on: November 30, 2011, 08:28:59 AM »
Ian,

Even if his system is not that well matched don't you think he should still be able to achieve better than 50 rpm ??

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline stirling

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Re: Steppers are too slow
« Reply #12 on: November 30, 2011, 09:14:45 AM »
Tweakie - well I suppose, but ultimately we'd be guessing wouldn't we?

We know that typically a doubling of voltage will double the stall speed so with the 24V as opposed to 96V we can generally expect a quarter of potential. Is 200RPM still slower than we'd expect then I suppose maybe yes but it's a hard call at this distance. Stuart has stated that they run smooth so I'm thinking the drives and Mach are OK. I'd stick the microstepping as close to 10 as possible for starters but after that - like I say from this distance it's hard to tell what other issues (if any) may be at play.

Ian

Offline RICH

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Re: Steppers are too slow
« Reply #13 on: November 30, 2011, 07:48:30 PM »
Quote
bought ex China ...............the supporting documentation was minimal (read Nil)


Not able to assist without posted info on your drives and bob.
Till then,
RICH
Re: Steppers are too slow
« Reply #14 on: December 01, 2011, 04:39:44 AM »
Hi Ian & Tweakie.
Thanks for your help so far with this problem.

Today I disconnected all drivers from the BOB and connected each one individually one at a time. As I reconnected them, each one still ran slow and the microstep switches still have no effect on speed or torque levels. The motors don't even make a different sound with each selection. Also I went into Mach 3 and changed the kernel speed through the range of 100 hz to 75000 hz with absolutely no effect.

The computer is about 8 years old and is a Pentium 4, 3.2 Ghz processor wit a 2.75 Gb of Ram. I had a fairly new hard drive completely formatted and windows reloaded to be used for this purpose when I first started to set up for this project. the steppers are running off the parallel port on the motherboard but it does have another parallel port PCI card installed. Do you think it is worthwhile trying to use this other parallel port, or maybe removing the card in case it is having any effect on the output pulse rate?

I do have some doubt about the BOB as I still can't get 2 of the output pins to work on any of the stepper drivers but they will work if connected to the other available pins. My next thought is to replace the breakout board with a different type. Do you have any suggestions?

I appreciate this might not be the best matched system, but the attached You tube URL has the identical components on a friends machine and it can be seen how fast it operates. There is no way these steppers are running this fast.

http://www.youtube.com/user/vanhaydn#p/u/121/2zhwnxttPbE

Stuart

Offline Tweakie.CNC

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Re: Steppers are too slow
« Reply #15 on: December 01, 2011, 05:15:46 AM »
Hi Stuart,

Can I suggest you carry out a couple of very basic tests.

Initially just one controller set microsteps (SW 5-8) at 1600 steps per rev and the motor current (SW1-3) at 3 Amps.

Go into Mach, Motor tuning and set "steps per" to suit your machine screw pitch (theoretical) then adjust motor velocity.

What speed does the motor stall at ??

Connect a voltmeter to your power supply output.

Does it maintain the 24 Volts during the above test ??

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline stirling

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Re: Steppers are too slow
« Reply #16 on: December 01, 2011, 05:23:22 AM »
Today I disconnected all drivers from the BOB and connected each one individually one at a time. As I reconnected them, each one still ran slow and the microstep switches still have no effect on speed or torque levels. The motors don't even make a different sound with each selection.
IMHO your not going to be able to detect visible or audio changes with different microstep settings. Though technically microstepping does have subtle effects on torque I really doubt you'll be able to see or hear any difference. Maybe between NO microstepping and (say) 10 but other than that I doubt it very much so I'd not get too bogged down in that. As I said - set them as near 10 as you can and leave them there.


Also I went into Mach 3 and changed the kernel speed through the range of 100 hz to 75000 hz with absolutely no effect.
To calculate the CORRECT kernel speed multiply your steps per unit by your max velocity (in motor tuning) and divide by 60. Do this for each axis and choose the LARGEST figure. That gives you the max steps per sec you'll ever use. Then pick the LOWEST kernel speed above that figure. Any kernel speed above that is not only pointless but may cause other problems. Post your figures so we can check.

The computer is about 8 years old and is a Pentium 4, 3.2 Ghz processor wit a 2.75 Gb of Ram. I had a fairly new hard drive completely formatted and windows reloaded to be used for this purpose when I first started to set up for this project. the steppers are running off the parallel port on the motherboard but it does have another parallel port PCI card installed. Do you think it is worthwhile trying to use this other parallel port, or maybe removing the card in case it is having any effect on the output pulse rate?
I very much doubt this will make any difference.

I do have some doubt about the BOB as I still can't get 2 of the output pins to work on any of the stepper drivers but they will work if connected to the other available pins. My next thought is to replace the breakout board with a different type. Do you have any suggestions?
You may or may not have a couple of pins out on either your parallel card or your BOB but if all four of your axis are working on other pins I very much doubt this is the cause of your speed problem.

I appreciate this might not be the best matched system, but the attached You tube URL has the identical components on a friends machine and it can be seen how fast it operates. There is no way these steppers are running this fast.
Well if you say it's identical fair enough - but are you absolutely sure?

Exactly the same power supply, drivers, motors, AND GEARING? EXACTLY? The reason I'm checking is if you look at this link (http://www.wantmotor.com/ProductsListB.asp?id=88&Pid=75) the systems APPEAR to be similar to yours but if so, they seem to "randomly" include different power supplies. For example the THREE axis kit has a 24V 350W ps but the FOUR axis system has TWO 36V supplies. It's not clear to me if that's TWO 350W or TWO in parallel give 350W.

IF for example you had TWO 24V 350W supplies you could series them and get 48V at 14.5A which would double the stall speed of your system. (incidentally this is why I say random supplies - 14.5A is waaaaaaaay more than those 4 motors need, so with that supply, the voltage is way too low and the amperage capabilites way higher than neccessary)

Ian

EDIT: didn't see Tweakies post when I posted but FWIW with a supply of 14.5A (if that is indeed what you have)  I doubt very much you'll get a voltage drop. Just a thought.
« Last Edit: December 01, 2011, 05:39:48 AM by stirling »
Re: Steppers are too slow
« Reply #17 on: December 02, 2011, 05:48:47 AM »
Thanks guys,
I am tied up with work at the moment. Shall do these tests within 24 hours and report.

Stuart
Re: Steppers are too slow
« Reply #18 on: December 03, 2011, 06:52:40 AM »
Hi Tweakie and Ian,

Well finally some good news.

Tweakie, before actually reading your previous post, I decided to strip the whole thing down to do a rewire from the start and run it in a new profile of Mach 3 with all new configuration settings. So, after reading your post I did the rewire and ran the profile config as you suggested, and whoa, some success. Speed was up to a very respectable speed, however the "X" axis did not work when connected to the suspect P2 and P3 on the BOB. I changed this to P1 and P17 and found it worked fine. I am pretty confident this is a BOB fault. I have a multimeter with a frequency counter built in and I was getting a pulse rate of 6.39 khz at the pulse terminal on the BOB for each axis except the P2 & P3 pins.

I calculated a "steps per mm" figure of 320 (5mm ball screw at 1600 steps) and found the motor would stall at 1600 mm/min. Prior to the stall, the power supply was stable at 24.008 Volts. When stalled there was a minimal increase in voltage to 24.012 volts. The highest current draw with all 4 motors running (no load) was about 3.5 amps which is well below the rated value for the power supply. I dropped the speed down by 25% to 1200 mm/min and they all ran very smoothly.

The frustrating point now is, what was wrong and what fixed it. Hopefully time will tell.

Anyway, thank you both for your help here. We are a little isolated down here to seek advice. I appreciate your time.

I have attached a couple of pics of the configuration I have put together with the power supply, Drivers and cooling duct. Please share any opinion or advice if you think I should be doing anything different.

Cheers

Stuart

Offline Tweakie.CNC

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Re: Steppers are too slow
« Reply #19 on: December 03, 2011, 07:09:44 AM »
Hi Stuart,

I am pleased it is all starting to work out for you.  ;)

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.