Messages

21

General Mach Discussion / Re: Steppers are too slow

« on: December 05, 2011, 04:50:46 AM »

Hi Ian and Rich,
I understand your reasons for the capacitor across the supply terminals without much problem. I will give that one a bit of thought before fitting one though. The fact that the PS will hold a very stable output voltage leaves me to think that it already does contain capacitors internally as part of the regulation process. Shall try to get some sense from the manufacturer and seek their advice.

Tests today result in the following:

Rich, you are quite correct. There is no way that PS is going to deliver much more than 24 volts. All negative terminals are common as are the positive terminals. The extra terminals just allow for extra terminal space to connect to.

The current draw was quite a surprise. All readings were taken by placing a digital multimeter in line with the 4 drivers and the power supply. ie. disconnected the +ve supply to the drivers and inserted the meter between the PS +ve terminal and the +ve leads to the drivers. The results were: all four stationary  3.615 amps. 1 motor running  2.911 amps, 2 motors running  2.343 amps, 3 motors running  1.726 amps and with all 4 running it was 1.177 amps. I guess this makes good sense as I would expect the current draw to be highest whilst the motor is not able to rotate. I have the ability to hold the peak reading on my meter during the start up, but didn't take it on this occasion. I can do if you are interested in the result.

Ian, I understand your supply star connection. I will run 4 separate figure 8 cables from the PS terminals, with each one dedicated to each individual driver.

Today, I have tried a few other "step per mm" settings and found it to operate quite successfully throughout the range, so hopefully all should be OK now.

Stuart

22

General Mach Discussion / Re: Steppers are too slow

« on: December 04, 2011, 05:09:15 AM »

Hi Ian,
I am fairly confident that my port outage is related to the BOB as I use the same parallel lead from the computer to another combined BOB/ Driver for 3 axis and I am pretty sure this board uses those pins from the computer and it works fine. I am away again with work this weekend but shall be home in the morning and shall confirm then.

I have to admit, the 3.5 amp current rating was taken from a fairly crude analog ammeter fitted internally to another bench top power supply I was trying at the time whilst somebody else manually jogged the 4 motors. I have never really considered how accurate this meter is. I can easily connect my digital multimeter in line with the 4 drivers tomorrow and post an accurate reading. The drivers are set to 3.32 amps from memory.

I have not been made aware of needing a cap fitted across the terminals of the PS. I would be interested to know the theory why. Was the intent to further smooth the output of the DC supply or for some form of protection of the PS from damage.

I have been trying to work out what may have been the cause of my problems as well, and you have just had me thinking about a change I made during the rewire with one of your comments. You will notice the power supply has 3 sets of 24 Volt connections. The way I had it connected before was like this; one set of terminals to 2 drivers, another set to the other 2 drivers and the 3rd set connected to a small printed circuit board with 3 voltage regulators and a couple of filter caps on it. Two of these regulators provide a very stable dual supply of 5 volts to the BOB (The BOB has a couple of jumpers to remove from the board if running dual 5V supply) and the other is a 12 volt regulator to run the cooling fan located in the end of the duct. When I did the rewire I isolated the circuit board with the regulators and provided the 5V to the BOB with a separate single plug pack totally isolated from the PS, and replaced the jumpers. The other change I made was to connect all four drivers to the same PS terminals. (and you are correct, this is done by having 2 sets in series connection joined in parallel at the PS. I can change that to parallel for all 4 without any problem). The other test I will make tomorrow is to see if the three 24 V positive and negative terminals are actually connected internally in the PS. (testing for continuity between terminals with an ohm meter) If they are not, it may be possible to series connect 2 of these to get the preferred 48 volts. Will let you know what I find.

Thanks for your feedback Ian, much appreciated.

Stuart

23

General Mach Discussion / Re: Steppers are too slow

« 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

24

General Mach Discussion / Re: Steppers are too slow

« 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

25

General Mach Discussion / Re: Steppers are too slow

« 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

26

General Mach Discussion / Re: Steppers are too slow

« on: November 30, 2011, 06:27:55 AM »

Sorry,
These motors are actually 425oz as per the details below. The power supply is 24 volt 400 watt

Technical Specifications
Part No.:                           WT57STH115-3004B
Frame Size:                      NEMA23
Step Angle:                      1.8 degree
Voltage:                            6.3VDC
Current:                            3 A/phase
Resistance:                      2.1Ohm/phase
Inductance:                      9mH/phase
Holding torque:                30Kg-cm       425oz-in
Rotor inertia:                    810 g-cm2
Detent torque:                  0.89 kg-cm
Number of wire leads:      4
Weight:                             1.55KG
Length:                             115mm
Shaft Diameter:                8mm
Front Shaft Length:         21mm
 
Stuart

27

General Mach Discussion / Re: Steppers are too slow

« on: November 30, 2011, 06:19:04 AM »

Thanks for the prompt replies guys,

This is my first attempt at anything CNC, so I apologize in advance if this turns out to be anything basic.

.xml file attached of current setup.

Stuart

28

General Mach Discussion / Re: Steppers are too slow

« on: November 30, 2011, 06:09:15 AM »

Hi Sargon,
I will see what I can find out re the inductance and let you know. As mentioned above, the supporting information is pretty minimal. However, this combination is working fine on a friends machine.

Stuart

29

General Mach Discussion / Re: Steppers are too slow

« on: November 30, 2011, 06:03:41 AM »

Ian,
The steppers, drivers and power supply were bought ex China at the recommendation of a friend who has the same setup. As you could probably imagine the supporting documentation was minimal (read Nil), but I will source what I can and reply

Stuart

30

General Mach Discussion / Re: Steppers are too slow

« on: November 30, 2011, 06:01:32 AM »

Hi Tweakie,
Yes I was setup almost identical to your screenshot. I had 500 steps per mm but otherwise the same. I changed to reflect what you have here but still no change.

Something I omitted to say in my earlier post is that I am not able to get a driver to work when connected to P2 and P3 on the breakout board. It is now connected to P17 & P16 and operates, but slow like the others. For this reason I am a little suspect of the breakout board. Also the motors are only sitting on the bench top, ie. they don't have any load on them. Is this likely to have any effect?

Stuart