Denstep control stepper board w/ Mach3

[eabrust]

I recently acquired a Starturn8 lathe which was upgraded w/ Denstep controls (red LCD). Prior owner started this thread viewtopic.php?f=46&t=2087 The prior owner was demoing the Lathe w/ VR Turn, his only issue was fluctuating spindle speed. I believe I found the issue for that to be a broken wire for the spindle encoder.... but onto what I'm doing with it

I'm beginning to work at retrofitting to Mach3/EMC due to the cost of VR turn and risk of it not being supported for my lathes odd configuration, and have a few questions about minor issues I'm having.

Issue 1:
When I power up the baldor/Denstep control w/ the Denstep control board in place, everything comes up good, and it winds up with '8' on the LCD. It takes a few seconds before the steppers lockup also. The board also has power on the +12 and -12 VDC outputs, which is also used for operating the spindle relay on this lathe the way it is setup.

When I remove the Denstep card so that I can connect step/direction signals from the parallel port of computer to the 96pin connector area, it powers up and the steppers lock, but I lose the +12 VDC output. Does anyone know how to enable it without the control card on? I notice when I power up without the Denstep card, the steppers lock instantly, so it appears there is some initialization going on of some sorts. I'd hope to not have to add another power supply for the spindle relay if I can re-enable the +12volt onboard supply.

Issue 2:
I got the x & z axis moving under control of Mach3 by direct connection to the board. Axes move great below 20 inch per minute, and above ~25-40 inch per minute. However in the range of 20-25 inch per minute feed rate ( I figure to be about 2000 Hz step rate), the motors go into a resonance and the axes stall out. I've tested with both EMC and Mach3, and pulled the steppers out to be unloaded, and still have the issues at the specific speed range. I have no way of knowing if there is something different about driving the motors with the Denstep vs the direct Mach3 connections with regards to half/full stepping, etc . Has anyone done this conversion and had issues with motor resonance? The starturn8 has it's original Nema34 steppers. I've also tried grounding and putting 5 volts to the 'BOOST' pins, and it seemingly does nothing that I can tell.

Any input on these would be greatly appreciated.

Thanks
Eric

[Denford Admin]

When I power up the baldor/Denstep control w/ the Denstep control board in place, everything comes up good, and it winds up with '8' on the LCD. It takes a few seconds before the steppers lockup also. The board also has power on the +12 and -12 VDC outputs, which is also used for operating the spindle relay on this lathe the way it is setup.

As far as I can tell the +/- 12v is supplied on the 96-way header and doesn't need anything from the top board to enable it.
It is only a 100mA supply so maybe it's being shutdown (overcurrent) ?

I've no experience of the resonance issue but I'd certainly try a new stepper motor for what they cost.
Can you tell whether the step pulse is clean ? maybe there is noise or it's not switching cleanly.

[angel-tech]

Hi Eric.

Issue 1. I take it the 24v dc supply is present, if so either put a 12v reg in there to run the relay or replace the relay for a 24v one.

Issue 2. Try changing the pulse width to 5 or more

[eabrust]

Hi and thank you both for your input.

AngelTech
This lathe does not have any 24Vdc supply in it, it has a AC transformer which spits out 12VAC (used on a few relays) and 24VAC which was fed to the Denstep, which was where the 12Vdc was generated . Perhaps it was poor quality of AC power feed to the Denstep causing issue?

I also run a milling machine with the same computer, and have no issues with step generation for that machine. I had extended pulse durations for the step inputs, and also tried 'sherline mode' which provides extended duration step pulses. None of this made any effect on the stepper drive stalling issue. Being it operated fine at slow step rates, and at very high step rates, and there was a narrow band where it kept stalling, it appeared to be a mid-band resonance issue that explained the problem.

Unfortunately while I was probing about with my oscilloscope checking things out, I slipped and grounded one of the stepper motor outputs while it was energized, and it blew out one of the L298 drivers. The Baldor board now just blows fuses. I assume it could be repaired by replacement of the one driver? One of the L297 chips also appeared to have gotten warm.

I think based on that accident, my direction is now to remove the Baldor/Denstep control completely and use some current technology drivers which offer microstepping and mid-band resonance damping and a new power supply.... Not all quite per plan of being on the cheap, but perhaps it will be a better machine in the end!

Regards,
Eric

[angel-tech]

That's a shame on the ic failing, it's not that hard to replace.
I've not experienced mid band resonance on these controllers throughout the product range, and although microstepping may be nice you'll probably not need it.

A wanted ad may provide a source of a replacement board.

As the tx provides 12v ac, it would be simple to get 12v dc from that supply.

[Denford Admin]

There may be some useful info about the L297 repair here:
viewtopic.php?t=2615

The chips are cheap (as chips) and if I were to be spending more money, I'd rather fit new motors than scrap the Baldor drives at the moment.

[eabrust]

Thanks again for the continued input, It probably is worth saving the Baldor board from the trash for the ~$10 in ICs to replace, but I'm still not sure I want to reuse it based purely on hopes for better performance.

I did forget to mention one other thing I tried before I blew the drive. I had a new NEMA23 sized stepper sitting around that I hooked up in place of an axis motor and jogged it around unloaded. It also had a band where it stalled, but would jog fine when at low and higher step rates.

I guess I mention this looking for more input from Admin. I'm not to familiar w/ stepper driven setups, my prior work has been with servo driven systems. Admin, you seem to be biased towards thnking stepper motors will bring more improvement than an updated driver, or perhaps you are looking at it from purely a cost point. Could you clarify if you recommend this direction as improvement per cost, or as most likely to improve the situation?

In my thoughts (mind you I'm no expert), I would think that a stepper motor is pretty much a stepper motor, and not much has changed in recent years with design/performance. About all I could do is select other size/voltage/current steppers to try and better match the Smartstep board. On the other hand, the control side seems to be where the biggest bang for the buck is in my opinion. The Baldor control card seems pretty 'plain', with no current limit adjustements or other smarts that I can tell.

Since my lathe seems to be a 'retrofit', do you know what all the original factory Smartstep setups ran for motors, was NEMA 23 sized motors the limit on factory setups? And what voltage? Does anyone have data on the original NEMA 34 motors on the Starturn8? (inductance, current, etc)?

Thanks again for any help, I am still trying to make the best decision going forward.
Eric

[angel-tech]

Steppers normally have a fixed current rating and allow a wide variation of voltage to drive them.

e.g. A normal level of drive current for a single stack 23 is 1-2 amp at around 24 - 36v. You can't alter the current much, but you can go wild with the voltage. I've had 23s running at 80v and they really whizz along at that voltage, and getting 3m/min rapids on 16 x 5mm screws.

The thing is, there's not much point in having 3m/min rapids on a machine with 200mm max movement like the starturn, so how far do you go with the mods.?

[Denford Admin]

I would think that a stepper motor is pretty much a stepper motor,

That may be true for the last few years but I'd guess Starturn 8 motors will be from the 90's or even 80's ?
Improvements in manufacturing and the use of rare-earth materials have improved torque and efficiency since then. Having new bearings might also help
One thing to look out for though is the possible need to make an adaptor plate and/or a new pulley...maybe the cost difference between replacing motor or drive may not be that great in the end.

As for microstepping, I'm sure the Baldor steppers are half-stepping so you get 400 steps/rev - if you look at the balscrew and pulley ratio and use this to work out steps/mm, then work out how many pulses are required at a certain feed (eg 3000mm/min) then you might find that going to microstepping may tip you over the max step frequency of Mach.
If you're looking for a stepper motor, I'd calculate what max speed you'd like to go at and work that back to the motor RPM, then examine the stepper datasheets...they all have different torques curves which drop off pretty suddenly when at speed (that's when the motor will normally stall)
It's a case of deciding what speed and resolution you want to acheive, then picking the best motors or drives within those limits.

Worth bearing these things in mind when you decide what to do !

angel-tech is right about the voltage - it's just OHMS law, the stepper will draw the same current regardless of voltage - the voltage you want to use is another factor when choosing the drives and motors.