Messages

711

General Mach Discussion / Re: How to wire steppers???

« on: April 12, 2008, 02:48:38 PM »

Ian and Ian - Yes I know I was missing out a great deal about inductance, and current lag and all the other things I've read about. I would understand it if I spent enough time reading and studying it - but I haven't the time.

We are, though, near the end. The Gecko works a treat and I have it up to 30ins per minutes, which from a start of 4" in quite remarkable.
Ian or Ian - sorry are you saying from coils in parrallel I should settle at 3.5amp - not 5amp. I will keep checking the motor - it was not getting warm (although it was only on test - and not working). I can drop the rating on the Gecko.

Certainly where I went wrong was - when the motors said they were rated at 2.5amp at 7.5 volts - per coil - I then opted for 2.5amp drives. There are four coils of course - two pairs - and it follows that you need more current capability.

I have done all this by merely altering the motor wiring and upping the current capability of the system - I have the voltage side to go at yet - although that would mean Gecko's right through, rather than just the one I have at the moment.

I better stay as I am for the moment (otherwise the financial director will complain) - I have the two motors using only 2 coils on the y and z - using their original drives upped to the Max at 2.5amps. The X (or Z on the lathe) with the four motor coils in two pairs, powered by the Gecko.

Either way we have a big improvement in performance !!! Y and Z at 16 ins per min and X at 30. I am settling for 14,12 and 28 for accuracy and see how it will go.

712

General Mach Discussion / Re: PWM spindle control setup

« on: April 12, 2008, 02:09:51 PM »

Your CW (M3) and CCW (M4) are configured on Config/Ports and Pins/Spindle Set-up.

You allocate M3 and M4 to different outputs ( nominally Output #1 and #2
Whilst on this page under Motor Control tick use Spindle Motor Output, which will also then let you tick PWM Control.

If you then go to Ports and Pins/Output Signals and allocate Output ~1 and #2 to output pins (perhaps 16 and 17)

Then go to Ports and Pins/Motor Outputs and tick the Spindle as enabled and show a pin against the step column. PWM information is output on this pin when in PWM mode - perhaps pin 14.

I do not understand why you want an enable signal - although you have not said what you are going to use to control your spindle.

On my system the three pins above are used. M3 and M4 drive relays which are used to control an Omron Inverter driving my spindle motor. They are constant signals, therefore do not need an enable - M3 is on clockwise,  M4 is on anticlockwise and M5 turns both off. Both cannot be on together or the Omron shows a fault.

The PWM signal feeds a digispeed converter - which changes to PWM output to a voltage signal (between 0v and 12v) which is fed into the Omron and regulates the speed.

That is the basics of the system - but unless we can understand what you are driving, then I cannot help you further.

713

General Mach Discussion / Re: How to wire steppers???

« on: April 11, 2008, 02:52:15 PM »

I cant nsupply the answer yet, becasue I've been away and only got back tonight, Went straight down to the post office and picked up my Gecko drive - looks good. Will try and fit it tonight.

As far as power in a motor is concerned Watts is the measurement. Watts = Amps x Volts. The only trouble is you need to increase voltage to increase the amperage becasue Voltage = Resistance x Amps - and for the sake of the argument resistance of the winding is constant ( in this case at 3 ohms - given in the rating of 2.5amps at 7.5volts).

There are, we have found, several different ways to connect steppers ( the four coil variety).

1.) In my first effort - with two windings in series - I was effectively putting 6 ohms of resistance across my voltage. Using the 7.5 volt rating as a rough guide, then this would mean that the two coils would draw 1.25 amps. Again using 7.5 volts this would give 9.375 watts x 2 = 18.75watts absolute maximum.

I am not aware what effect the chopping of the applied voltage (24v) has on the final voltage at the motor. It must be similar to the PWM output and vary with the number of pulses per sec opposed to the carrier frequency. Since the carrier frequency is usuall well above the maximum chopping frequency, then there must be quite a cut in apparent voltage at the motor - hence I will use 7.5 volts in all the examples. (It does - however - increase with speed)

2.) In the ONLY WIRING TWO COILS ON THE MOTOR scenario - each coil is 3 ohms resistance - and draws 2.5 amps (the rating for the drive) but bear in mind there is only one coil operating - this give 18.75 watts - BUT THE EFFECTIVE VOLTAGE INCREASES AS THE SPEED INCREASES - THEREFORE THE APPARENT POWER OUT INCREASES. To me it seems that twice the speed (of pulses) would give twice the apparent voltage right up to the point where current limting came into play. It seems to me also, that the current in the coil would rise much more quickly than in No.1 and therefore be higher longer and give more power earlier - perhaps helping it get over the limits of the series wound option.

3.) When I connected the motors with two coils in parrallel, the effective resistance Rt = R1 x R2 / R1 + R2 = 9/6 = 1.5ohms. This has the potential to draw 5 amps - and the current limiting would be working over time to keep it down to 2.5 amps - BUT there are TWO windings working on each pulse therefore twice the power - so although there was only 2.5 amps to share between the coils, I think it was sucking a bit more out and then with twice the number of coils, giving a little over that at No.2. Again because resistance was less, current would rise more quickly giving more power per pulse.

It certainly had a bit more Omph.

I will wire the Gecko up and try it wired to give the full five amps to a motor connected in parrallel and let you know the result.

 

714

General Mach Discussion / Re: How to wire steppers???

« on: April 10, 2008, 02:40:14 AM »

Yes- thanks -

I have the instructions, the set up is much the same as for the 10 amp, you turn a pot til the voltage on two pins in 1.4v multiplied by the amperage you need. It is working well - as must be by definition, current limiting. I feel I could go back to the motors in parrallel and run them - as long as I set the outputs right.

Someone is lending me a Gecko drive - rated I think, at 7 amps and voltage way up.
I am going to try this on my leadscrew so I can put the full current through the motor. If I add another battery to my system, I can put the voltage up to 36 volts on the Gecko - that sould make the sparks fly.

I am thinking of adding a forth axis to the system - so that will be a chance to get a more powerful driver card.

715

General Mach Discussion / Re: Check out this thread....

« on: April 10, 2008, 02:23:27 AM »

Yes Benny - I like that very much.

Is the siftware already incorporated in the Blue Screen set that was talked about?

716

General Mach Discussion / Re: Toolpath Crosshairs Display incorrectly when using Work(fixture) Offsets

« on: April 09, 2008, 12:07:44 PM »

I've had a lazy day and put my mind to this, It is much as I said. The toolpath display does not follow the offsets, but displays what it sees taking place in the program co-ordinates.

I wrote a lttle program which is a 4"square (put in to define the limits of the display), then in each quarter of the square is a 1 inch circle, the starting position is determined by g54 (0,0) g55(2,0)g56(0,2) and g57(2,2).

I gradually added bits in to try and make it give a full display, but without success.

It draws the square (g53 co-ords), it draws the first circle(g54 - 0,0) (essentially no offset) - but, then, for the other offsets,  instead of moving to a new start point - IT MOVES THE START POINT - then comes back to the first 0,0 position and carries on from there, drawing a circle on top of the first one. It does exactly the same with the other start points.

I even put a g53 move in before the offset to see if that would do anything - but NO,

I have had it show all four circles on the schematic before it is run ( and then sometimes it only shows 3) - all it does then, when it starts running, is follow the program co-ordinates.

The only thing I haven't done with it is actually try it on the mill - becasue I am set up in lathe mode at the moment. If anyone would like to try it it is posted below.

717

General Mach Discussion / Re: Toolpath Crosshairs Display incorrectly when using Work(fixture) Offsets

« on: April 08, 2008, 03:20:33 PM »

I think I am missing something - the BubbaG.txt file doesn't have G58 or G59 in - do I have to put them in myself

718

General Mach Discussion / Re: Z and A axis problems

« on: April 08, 2008, 03:02:32 PM »

It is possibly something to dowith CV - constant velocity. This is where, towards the end of a move, as one axis decelerates, the axis for the next move accelerates.

Try knocking off CV and use Absolute Stop instead, where one axis must stop before the next moves.

See Config/General Config/column two - Constabt Velocity/Absolute stop.

719

General Mach Discussion / Re: First post, LPT and limit questions

« on: April 08, 2008, 04:14:02 AM »

If this is just out on the workbench then you can do a lot with it.

First - check that you have five volts coming out of the port. Pins 2 to 9 carry the axis signals and you can check the voltage on any of the "dir" pins as you change direction. Should be 0v one way, and +5 in reverse

To put a signal into the computer fasten a NO switch between pins 10,11,12,13 or 15  and one of the ground pins (18 - 15)
You must configure your Ports and Pins/Inputs correctly and show X and Y limits on say pins 10,11,12 and 13 and a Z limit on 15.
You want to tick "active low" - in other words the switch is active when the input is grounded. If you switch to active high, they will show as on all the time until you switch the switch.

If you then go to the diagnostics page - all the inputs are listed there and if you switch your switch you should see the leds light up - depending on which wire you have connected.

720

General Mach Discussion / Re: Toolpath Displays incorrectly when using Work(fixture) Offsets-is it me?

« on: April 08, 2008, 03:59:42 AM »

Can you post your code with the two offsets. I.ve run Bubba etc that was on the bottom of the screens display - but tat doesn't seem to be the right on.

I'd like to have a look and a ponder.