Hacking up a bad controller

[originator]

I have a MAXNC10CL that has not run right since day one, and it has died altogether once. Now it is basiclly useless again. The wll not run hardly at all. I swapped out the X micro from the unused A driver, I also swapped out the TIP120's.

The motors are 8 wire uni. 210 oz, 2 amp. Their system runs in quadrature and requires special drivers for MACH3, for which I have never had it really work well, but is prefernce of machine software There are encoders attached which I can lose.

Please tell me if this is semi workable as a cheap and dirty temporary solution:

I keep their controllerbox, with limit switches and parallel port in tact on their box so less to reinvent. I cut traces on their board to access the input pins 4,5,6,7,8,9 pins. for step and dir. I keep their 4 TIP120's per motor in tact, cut the traces to them.

Either A. write some simple code for an SX to receive the Step an Dir, and output the appropriate sequence to the already existing mosfets, or B. Get a simple driver like an EDE1200 6 wire driver. The 1200's are a shiort drive, the SX are on hand as well. I also have th SX28's on hand and could perf board the whole thing.

Hopefully someone can say this is workable or not. MAX wants 450 for just the stuffed board, but why try that again when it never worked, and I am still locked into that company like a prisoner. Gecko is 3 drives at 120 ea plus a PS, but would work, but would require some other extrenal box plus rewiring everthing.

Thanks for any suggestions.

[pminmo]

Can you post some pictures of the board? Probably some clues there.

[originator]

Ok here is the poard. It has X, Y, Z, A. Quadrature, 6 wire unipolar.

I picked up some EDE1200 unipolar drivers today to breadboard. I see no reason I can't just cut traces and use the existing box, PS, TIP120's. I guess we'll find out soon.

http://www.elabinc.com/ede1200.pdf#search=%22ede1200%22

[pminmo]

Just looking over the data, looks to me like a normal unipolar stepper driver, 2 phase full ste, half step. Using the TIP120's to sink the appropriate amount of current. Since the LPT port has defined inputs and outputs, I can't say I see what the problem would be running it from the standard software controllers. Mach3 for winxp, and many others for older win9X systems or dos. How are you powering the board? Do the motors have lables giving resistance, voltage or current? You say 8 wire unipolar, I assume you mean they are eight wire motors, wired for 6 wire unipolar?

[originator]

I am sorry if I said 8, I was in a rush. They are 6 wire motors. Lin engineering 5718M-05 2 amp. I picked up the EDE1200's and breadboarded one for a test using the Step and Dir from the parallel port. I cut the traces from the existing board to the parallel port, ran the Step/Dir pins to the EDE1200 uni driver IC. Set it to full step for testing. I cut the traces to the 4 TIP120's, and left the outs in tact to the motor. The center tap to the motor is at 18v from the old xontrllers PS until I plug the motor in, then it drops to 8 volts for some unkown reason. Prior to tonight the rail was usually around 18 to the center tap with all motors plugged in, but now cutting traces or something else has caused the rail to drop in half when just one motor is plugged in, also the controller's breaker is popping often now as a result. The motor is getting quite hot, and I don't recall it getting hot before todays changes.

The inputs to the TIP120's are now from the breadboarded EDE1200 driver IC. The driver is basically a PIC packaged for driving unipolar motors. In testing the driver with LED's first, everything looks right, but when trying to run the motor, it will attempt to rotate in the correct direction, but is not quite right, it stutters, shakes, sometimes goes around partially, it will reverse according to the reverse jog key, but the same thing, very rough. These tests are at very low jog speeds. At high speeds, it will not turn at all, just sits still buzzing. I have tried other combinations thinking I had the phases wrong, but haven't had any luck, I think it is plugged in right though. The problems must be related to the motor getting hot and sinking the rail, which may very well be causing it not to turn properly. Why it is sinking the 18v rail now is a mystery. Once that is solved, I think Mach3 will drive it just fine once this rail issue is solved.

Just to clarify the problem: Whe I plug the motor into one of the unchanged outputs where there were no traces cut for the axis, the rail stays at 18v, but when I plug it in on the output of the TIP120's that are now routed to the EDE1200 outs, the rail goes to around 9 volts. I even floated the 4 inputs to the TIP's and still the rail is dropping.

*Update: I have narrowed down the issue with the rail getting dropped. The way that MAX had it set up, a PIC had 4 outs that drove a NAND, using the NAND as an inverter. The 7400 NAND went to the 4 TIP120's, straight to the motor connector. What I have done is cut the traces from the 7400 to the TIPS on one axis and insert both the EDE1200 and an SX processor, one at a time to test driving the TIPs directly. If I plug the motor into an output as it was from the factory 7400NAND>TIP>connector The highside rail stats at 18. BUT, when I insert either the EDE or SC, the rail drops to 7 volts, the PS breaker pops not to long after that.

I have spent hours trying to see what is different between their NAND gate and my IC's, and have found no answer. I have even tried taking had wire and running the TIP inputs to GND and VDD, still the rail is dropped. I have tried cutting the traces from the NAND to the TIPS, no change. The TIP's have a 5V 1k pullup, I have tried leaving them in and taking them out. Once I get past this mystery life will be good. I have been able to drive the motor more smoothly, a few .01's here and there have helped.

BTW the NANDS outs are all sitting at 0. I can't understand why me cutting traces and taking 4 wires from the TIP ins to GND is producing a different result.

[HillBilly]

I am not familiar with the EDE1200 chip. But it sounds like it has no current control. The Max controller used a chopper output to the tips for current regulation (that is the ringing you hear at stand still). If this is the case you will need a balast resistor or a chopper circuit between the rail voltage and the motor to limit current.

Darek

[pminmo]

I am not familiar with the EDE1200 chip. But it sounds like it has no current control. The Max controller used a chopper output to the tips for current regulation (that is the ringing you hear at stand still). If this is the case you will need a balast resistor or a chopper circuit between the rail voltage and the motor to limit current.

Darek

While I can't make out all the ics on the pcb, I didn't see anything that would make me think there is chopper components? No power resistors for current sensing..... Doen't mean there might not be, but.....

[pminmo]

Darek is correct that you will need some current limiting, i.e. power resistors or a chopper circuit. Probably why you are seeing a rail voltage drop and breaker pop. Your breadboard wiring will also pick up noise. If you want a unipolar chopper, look at my L297uni on my website. http://PMinMO.com

[HillBilly]

The MaxNC micro chip outputs PWM to the TIP's, not just on and off.

Darek

[pminmo]

The MaxNC micro chip outputs PWM to the TIP's, not just on and off.

Darek

You still need some method to sample current. PWM alone isn't enough.

[pastera]

If you can control the power supply voltage and the motor specs, you can get some control in open loop. The issue is you'll fry the motors if they stall.

IMHO, scrap the board, salvage the connectors and build your own.
a few LM324's, IRCZ44's and an SX will get you where you want to go.

Aaron

[originator]

Thanks for the notes.

The first step was to get an understanding of how the board was working and I have done a pretty good job of getting that part down. Unless they were chopping the PIC outputs, there is no obvious current limiting going on. There is clearly no sense R or circuit, or other PWM signal anywhere that I can find. The only resistsors to the NAND or TIPS are pullup 1k's on the outs of the NAND gates. Why pullup and logic gate? Who knows.

OK the mystery still remains about why it is that I can leave their 7400 NAND in place: so the path is NAND>TIPS>Motor and the common 18 volts to the stepper stays at around 18. BUt, when I do this

SX>NAND>TIPS>Motor or

EDE1200>NAND>TIPS>Motor

...the rail drops, even if I have all inputs to the NAND at 0 or all at 1 or using any coil sequence applied. Theoretically, with no signal present at the TIPs, they should be open and not shunting one side of the coil(s) to GND. OK so if using the NAND the reverse is true, a signal present at the NAND means no singal to the TIPs, and no shunt to the coils = rail is unaffected.

I'll dig on and maybe have an AHA! moment.

Next, once that will work, I'll simply make an SX board that mounts on to the existing board, use the same connectors, but replacing the PIC processors. I can even use the existing encoders and count/monitor pulses/movement, and E-stop or pause in the event of stall. Honestly, I have burnt up 1 spindle motor, 3 backlash nuts, a dozen end mills prior, so what I had before didn't have any safety feature while using MACH3 at least. I do believe that using their software it would stop in a stall, but I am not sure. I can address that directly myself though with my own code and Estop. Once this thing will get me by for the immediate needs, I'll just put it is Eagle send out for a fresh board, same size to fit the box, make life simpler.