Half complete Triac conversion needing some advice.

[Dan-27]

Hello. I was unable to post in the 'welcome to the forum' bit so before diving into the conversion question I have, a little about me. I'm a keen tinkerer, building and fixing anything that catches my interest. I primarily build combat robots, but have undertaken go karts, BBQs, RC planes and lots of other projects over the years.

The problem:

I recently took ownership of a Denford Triac milling machine and am looking to convert it to Mach 3 using the existing drivers. So far following a superb forum thread on the Denford site I've added the Step and Dir lines for the X,Y and Z axis. These all work if connected to ground. I've built a simple transistor amplifier circuit to switch these 24v lines from a 5v BOB. I've got them doing individual steps by touching onto the 5v output from the BOB but I can't for the life of me work out how to get Mach 3 to output the voltage pulses I need.

As far as I know I have configured Mach 3 correctly, as per the tutorials on their site. I am using one of the generic unbranded 5axis CNC breakout boards, and can't get any outputs to switch on. I was hoping I would be able to read around 5v on one of the Dir outputs, I thought these held either 5v or 0v to determine whether the stepper turns clockwise or counterclockwise, but I'm getting 0v from every pin regardless of how I jig the axis in Mach 3.

Any help or advice much appreciated.

Thanks, Dan.

[Kitwn]

Dan,
Welcome aboard, perhaps this will help.
The outputs of your breakout board are probably open-collector transistors working like relay contacts to ground rather than to the 5v rail. The link below is to the instructions for a common stepper driver from Stepperonline. Have a look at page 4 for a diagram of how to wire it up.

Kit

https://www.omc-stepperonline.com/download/DM320T.pdf

[Dan-27]

Hi Kit

Thanks for your input. I've been racking my brain trying to work out how to get the open-collector transistors to send 5V to the Base on the transistor required to power the Step signal on the milling machine driver. I've drawn out 2 circuits, the first it the one I have already tried and it failed, but when I connected the 2K resistor directly to the 5V source on the breakout board, rather than the X step output (Pin 2) it did cause the X axis to step once. The second circuit is my version 2, do you think this would work?

I'm open to any suggestions, all I need to do is connect the X Axis step signal input on the milling machine to ground and I need the pulses from the BOB to make and break that connection.

Thanks

Dan.


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[m_c]

You want the BOB output to switch to GND for the driving transistor, so the only way to acheive that with a single transistor is to have the driving transistor pulled up via a suitable resistor, then have the BOB output switch the driving transmitters base to GND.

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[Kitwn]

Dan,
The open-collector on the BOB (if that's what the output actually is) is a connection to earth which may be able to control the 24v line directly, though without more knowledge of the exact equipment involved I would not want to suggest you do that without checking with the manufacturer's datasheet. The fact that an open collector does not connect to the BOBs own 5v power rail gives it the flexibility to be used with different voltages from external equipment but without detailed knowledge of your specific equipment caution is advised.

The attached is a possible circuit to try. The 10K resistor pulls the open-collector output of the BOB to +5v when the BOB output is HIGH. This turns on the external transistor pulling the mill input to LOW (about +2v in practice). When the BOB output goes LOW the external transistor is turned off and the 47K resistor pulls the Mill input HIGH. It's primarily the absence of pull-up resistors which has doomed your experiments so far, though there may be one built into the mill input. Try measuring the open circuit voltage at the mill input to find out. If it's 24v then the 47k resistor can be left out. This would effectively give you an external, buffered open collector.

Note that this is an inverting buffer, you may need to adjust settings in MACH3 accordingly (I don't use it so cannot help with where to do that).

Exact resistor values are not critical, the values chosen give about half a milliamp of current in the transistors when turned on.

Kit

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[Dan-27]

Hello

Thanks for the replies. Kit unfortunately I can't open the attachment, it keeps bringing up an error message that reads 'invalid attachment specified. Would you mind trying to attach it again please?

Thanks

[Kitwn]

OK let's see if this works...

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[m_c]

Kit, going by Dan's second post (relevant bit quoted below to save you scrolling up!), the drives must already have internal pull-ups, so there shouldn't be any need for a pull-up resistor to the 24V.


I've drawn out 2 circuits, the first it the one I have already tried and it failed, but when I connected the 2K resistor directly to the 5V source on the breakout board, rather than the X step output (Pin 2) it did cause the X axis to step once.
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[Kitwn]

m_c,
I think you're right, I did suggest Dan check for 24v on the mill input to check. It's the lack of a pull-up on the input side that is most important here.

For those who might worry about it, two pull-ups in parallel will not cause a problem as long as the total current through the relevant transistor when on is within limits, so adding an external resistor for testing purposes will not harm anything. 2Kohms per volt (gives half a milliamp of current) is a good rule of thumb.

Kit

[Dan-27]

It's not playing ball unfortunately.

I believe I have replicated the circuit correctly, and the X axis does step once when I connect the wire from the base leg to pin 2 on the BOB, but jogging the X axis has no impact. I have also moved the wire from Pin 2 to 3 on the BOB, with no affect. Pin 2 is the X axis step and 3 the X axis direction.

The mill does have just shy of 24V on the signal input. On the picture of the breadboard touching 'X step' to 'Mill GND' causes one step.

How can I test if Mach 3 is making any impact on the BOB? I think all the results I have currently achieved could be been done with just the 5V and GND. I only have a multimeter for testing.

Also I don't think the BOB is capable of switching 24V. Aside from it being very cheap, I think the IC's in the middle handle the output switching (the 5 on the left are opto isolators) Searching 74HC245D found they are 'Octal bus transceiver's capable of handling 2 - 6v. Again way outside my electrical understanding, but I think that's correct.

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[Dan-27]

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[Dan-27]

Having a think about a suitable test to confirm whether or not the BOB is being changed by Mach 3. If I took a red LED and a 150ohm resistor and connected them between the 5V supply on the BOB and pin 3, the x axis Dir, would it light when the axis was moving on one direction and not in the other? I was under the impression the BOB would give a High output for one direction on the motor and a Low output for the other?

Many thanks

[Kitwn]

Dan,
Strictly speaking the BOB open-collector outputs are either a low impedance path to earth or a high impedance. This is why you need the pull-up resistors to get the required 0v or +5v output to your external transistors.

The LED circuit should work. The LED must be connected the correct way round, test it first. You probably already know that but just in case there's somebody reading who doesn't know about diodes.

Check that all three outputs, STEP, DIR and ENABLE are under MACH3 control. The step output will make the LED glow less bright than dir or enable when jogging since it will be pulsing when you tell an axis to move. This is a good sign!

I don't use MACH3 and obviously know nothing about your individual mill so I'm at the limit of how much help I can offer.

Kit

[Dan-27]

A quick update, after much head scratching I've worked out that the Mach 3 software will run on a 64bit windows OS, but it will not send any commands to the BOB as I am unable to install the drivers. I'm in the process of sourcing a 32bit copy of Windows then we should be in business.

Thanks again to everyone for their input.

Dan

[routercnc]

Ive just skim read this so might have missed something but I had that exact same bob several years ago and couldn’t get any pulses out at all. Given that I have made quite a few machines I should know how to wire them up and how to configure Mach and what to expect. Only cost me £8 so not much lost other than time. I tried lots of things but that was my conclusion in the end. Did a straight swap for my current (even cheaper!) board and everything worked. These boards are made to Kit’s strap line.

To answer one of your earlier questions a multimeter on the direction pin of the bob and on the ground pin of the bob (the terminal blocks that go to the driver) will read 5V or 0V depending on direction. If that is not happening no amount of downstream circuits with get it going.

Another thought is to get the pin out diagram for the parallel port connector, unplug from Bob (but still in at PC end) and check direction pin vs ground in the cable end. Then toggle direction of that axis in Mach3 using the cursor keys (should see DRO move accordingly) and read 5V or 0V on the cable pin according to the direction. If this works then Mach3 is working and bob is under suspicion.

Also the parallel cable needs to be the right type, one is crossed over and one is straight through. Can’t remember which you need but a quick search should find it.

[Dan-27]

Hello

After a few months of tinkering I'm slowly making progress. I manged to install a 32bit version of windows that is running Mach 3 and outputting the required pulses down the parallel port cable. Using the circuit suggested by Kit, and others, on the previous page I was able to get all axis running with reasonable success. I've also reconnected the micro switches that cut the power to the axis if they hit their maximum travel. Jobs left before I can start making chips; 1. Either revive the optical sensors on the mill or install more micro switches for homing. 2. Work out a means of powering the Spindle, this is where I could use some help.

The motor that powers the Spindle is a SEM DC Servo motor, model number MT30U4-36. There are a few DC servomotor drivers on eBay but they seem to top out at around 80V and this one runs up to 140v, any suggestions would be much appreciated.

Here's the info from the motor label
Model MT30U4-36 No.00262-004
Stall torque 4.5NM Amps 13.2
Max 4000 rpm 140V 75A
Tacho 9.5 V/KRPM IP44/65 IC 400
C2000
Ferrite Brushed DC Servomotor


I do have one other problem. The Y & Z axis move fine, but the X axis behaves in an odd way at full speed, bit hard to describe so I've uploaded a video with the link below. I have removed the motor from the machine and it runs fine with without any load, but connected to the machine it sort of cuts out at max speed. I can turn the lead screw without too much resistance so I'm not sure what's causing it? Any thoughts?

https://photos.app.goo.gl/6StZyicUyWeMPB5XA In the video the problems start after I run it at full speed, the first few small jogs are intentional. You'll hear a high pitched unhappy motor sound when it cuts out.

Thanks in advance for any help.

Dan

[m_c]

For the spindle motor, you need at least a basic SCR drive. Most common are KBIC drives, but you have to be aware the control circuitry is non-isolated, and floats near mains voltage. You can get isolated versions.
IIRC Sprint also do fully isolated SCR drives. If you do a search on RS for "Sprint drive" they have various options.


I've not watched the video, but I'd guess the X-axis motor is simply stalling. It's what happens if you try pushing a stepper motor too hard. Either drop max speed, or drop acceleration.

[Dan-27]

Hello.

I’m creeping towards the finish line on the milling machine conversion and have hit another snag, while trying to find the stall point of the x-axis I managed to cook the ‘single phase RFI filter’. I’m looking for a replacement, but can’t find an exact match. I don’t know much about these, would someone mind advising how to find a suitable replacement please?

Here’s the info on the one I smoked.

Single phase RFI Filter
Type: RS 1010-IDF
10A@40C, 250VAC, 50 - 60Hz
HPF -25C to + 85C

I’ve found this one on eBay, but it’s rated at 14A, will that be an issue?

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F 112625692608

Many thanks. Dan

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[Sterob]

A higher current rating won't be a problem.Its only when you go lower that you have to be careful.

[Dan-27]

Thanks for the help Sterob. Just to confirm, because I really don’t want to buy the wrong thing and trash over a years work. The one on eBay is labelled ‘Mains input’ and ‘inverter’ where the one I have removed from my machine is labelled ‘load’ and ‘line’.

Am I right to assume ‘line’ and ‘mains input’ are the same and ‘inverter’ and ‘line’ are the same? I’ve attached an image of the eBay item I’m referring to.

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Dan

[Clive S]

Am I right to assume ‘line’ and ‘mains input’ are the same and ‘inverter’ and ‘line’ are the same? I’ve attached an image of the eBay item I’m referring to.


You are correct