Some time ago I converted my Triac to mach3 control. Due to moving house I've only just got round to using it to run some real programs. And I've got a problem. I'm obviously losing steps somewhere, as positional accuracy is drifting. Running some basic tests it seems that several small moves seem to give a problem, but larger moves don't seem to give the same problem.
The machine has the original stepper motors, with ARC controls and a new power supply. I'm using a CNC4PC C11 breakout board, mounted in the base of the machine.
Any suggestions please, this is getting more than a little annoying now.
Kevin, I have done a few Triacs now and the problem I find is the motors. They are old style single stack type 34's and very dated. If you are using Arc's small drives you will be limited to 30 volts max which isn't really enough. Easyist way is to reduce the acceleration and velocity, to be honest we have struggled to get one running above 900 mm / min without loosing stems on the small drives and original motors.
If you change motors to triple stack type 23's they fly, even on the small drives but if you fit the larger dives and run them at 72 volt you can easily get 2500mm min
Yes, I wondered if I should have replaced the original motors (perhaps a false economy). I've tried dropping speed and accleration to the point it hardly moves and still seem to have the problem. What motor would you suggest to use with the power supply and controllers I've got (ARC 3A drives and power supply as per their web site plans). I think ARC are out of anything in this size though. Given the size of the machine I'd be happy with 1000 - 1500 mm/min, as long as it was accurate!
Have a look at the archives of the Mach3 group. Similar problems have been sorted with pulse timing changes and/or changing the timing between a direction change signal and step pulses. Just a thought
Unfortunately I've been through all the settings, even going down to realy low values on speed/acceleration, but I think it's the motor problem John suggested. Looks like some new steppers are called for. Does anyone know how powerful the originals were? I'd like to at least match that. Also I notice that ARC say the motors I wanted to fit, which are rated at 2.5A, need their bigger driver to run them. How do I make sure the motors I buy will be OK on these drives if a 3A drive won't run a 2.5A motor?
It's more the voltage than amperage you need to look to, those triple stacks, off the top of my head are 7.5 volt. That means you have a working voltage of 30 volts ? into which you divide 7.5 which comes out at 4.
Now to get a well designed and reasonably fast system you need to aim at a figure of about 20 so 7.5 volts times 20 equals 150 volts. Not obtainable with current drivers but this is why they recommend the larger driver. Now the smaller motors are on 4.5 volts and dividing that into 30 gets you nearly 7, given the smaller rotor size and inertia these will probably accelerate up to twice as fast as the larger motor.
If you are stuck on the smaller drivers I'd go for the 180Ncm model.
That makes sense, but they didn't have any in stock. I've found these
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(the MOT-125) which look ideal, as they are even lower voltage and still under 3A -and have about the same holding torque. And, for me, they are nearer to post. Having taken one of the motors off and taken it apart I should be able to use the existing front plates as they have hole centres to match the NEMA23 centres. Any idea how these compare to the original motors, in terms of power.
Kevin, I have done a few Triacs now and the problem I find is the motors. They are old style single stack type 34's and very dated. If you are using Arc's small drives you will be limited to 30 volts max which isn't really enough. Easyist way is to reduce the acceleration and velocity, to be honest we have struggled to get one running above 900 mm / min without loosing stems on the small drives and original motors.
If you change motors to triple stack type 23's they fly, even on the small drives but if you fit the larger dives and run them at 72 volt you can easily get 2500mm min
John s.
When I converted a Triac some years back I used the original stepper but driven by Gecko drivers, and didn't have any problems with missed steps.
.. he he - 4 tonnes of Beaver Partsmaster arriving on Tuesday - a bit beefier than the Triac
Yes, I've looked at the options and I think it would be best to change the drives. Which Gecko did you use, I was looking at the G201. This leaves me a lot more options for the future as well. If I do change the drives I won't be as limited to what I fit. I was looking at what stepper motors would work with the drives I have, but that's not really the right way to do it. This way I can put a bigger power supply in (I was thinking about 60v) which should drive the current motors easily -what PSU did you use? I used the smaller drives because they were a very good price -but I'll have to spend some money and do it right. I'm sure I'll find a use for the drives and PSU that come out anyway.
Yes, I've looked at the options and I think it would be best to change the drives. Which Gecko did you use, I was looking at the G201. This leaves me a lot more options for the future as well. If I do change the drives I won't be as limited to what I fit. I was looking at what stepper motors would work with the drives I have, but that's not really the right way to do it. This way I can put a bigger power supply in (I was thinking about 60v) which should drive the current motors easily -what PSU did you use? I used the smaller drives because they were a very good price -but I'll have to spend some money and do it right. I'm sure I'll find a use for the drives and PSU that come out anyway.
Regards Kevin
Yes it was the 201's with a home brew psu at the top end of the Gecko voltage spec
Kevin, If you need to change drives have a look at the MD 882 from that OZ link you posted. They will rung rings round the Gecko drives as regards reliability.
Funny you should say that, I'm waiting for a reply from the manufacturer for prices on those and some switch mode PSU's. But I think I might have to go through a dealer (which is a pain as there isn't one here).
Greetings kevin, If you are going to buy new motors and drivers why not use servos with the Gecko 320 drive? I am using these now and they are working great. Eric
Just to recap. The problem I'm experiencing is lost steps. The suspected cause is that the current stepper controller isn't quite grunty enough to drive the motors properly (mostly due to only being
35 volts -just put a meter across it). The existing stepper drivers will handle 3A, but max out at 40V. Possible solutions are:
1) Replace the stepper motors with ones that will run more happily at
35V, and less than 3A
2) Replace the PSU and stepper drives with 48V switch mode PSU and stepper drive to handle the increased voltage but keep existing motors
I'm currently looking to the second option. Although it's more expensive (cost is a big factor) if the first option doesn't work I've got nowhere to go, as I'm limited on what motors will run well at these power levels. If I go for option 2 and still have problems, I've got enough power available to put bigger new steppers in. Also it gives me the opportunity to replace the steppers with newer motors in the future as well.
So, does this sound reasonable -or have I missed something obvious? Just had a thought, I'm off to reconfigure the drives to half step or full step mode, to see if the problem is that the older drives don't like microstepping.
Thanks for all the help, I'll get this sorted in the end.
I'm currently working to produce a driver that uses the Nat Semi chips, so we can run 48V rather than the 36V limit of the Arc Euro drive. In practice, we have been running the 180Ncm motors at 15mm/sec without a problem, and 20mm/sec sees an occasional missed step. The sample 48V driver gives reliable 20mm/sec operation and may well give a little more, but we need to configure Mach3 for a higher clock rate as quarter stepping is running out of steam at 25khz before we can run some more tests ;) That and we need a set of three boards ....
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