Plugin for serial controller

[bc201081]

I currently have a homemade 3 axis router running Mach3. The stepper motor drives are being controlled by the paralell port of my laptop which works OK, however I've just acuired a nice compact industrial PC with a 15" touch screen problem is it only has 2 serial ports and 1 usb (no paralell port). I was thinking of buying a "SmoothStepper" serial controller from http://www.warp9td.com/ which comes with a Plugin for Mach3, are these any good?. I've also fond this controller for "Ocean Controls" http://www.oceancontrols.com.au/KTB-190.html which is half the price but doesn't have a plugin for Mach3. Does anyone know if a plugin for the KTB-190 exists? If not Whats involved in creating one? (I have basic knowledge of VB). Any suggestion of help is greatly appreciated

[H.O]

Hi,
The Smoothstepper works fine but it does lack backlash compensation. It has been promised since day one but have yet to be delivered, apart from that it works very well indeed.

As for the other controller you linked to - it's never going to work. First of all, the maximum step rate is only 29.5kHz and even if that is enough for you making it work properly with Mach3 will be impossible. External motion controllers for Mach3 works by having Mach3 calculate all the trajectories and then send them "in chunks" to the controller. The controller buffers them internally and "chews" them off one by one while Mach3 continues preparing and planning the next bunch of moves. The key here is that the controllers buffer can't ever "run dry", if that happens the motion stops until new motion data has arived.

This controller doesn't have an internal buffer so it would have to request an execute one move at a time, then Mach3 would have to constantly poll the controller to see if it's done with that command before sending the next - this would be painfully slow. Think of making a large circle, this would have to represented as an n-sided polygon (say 100 sides) the motion would go start-stop-start-stop-start-stop etc etc while working its way around the circle (polygon).

I'm sorry but it's simply not going to work.

/Henrik.

[bc201081]

Thanks for your reply. Could I expect to get better stepping rates with the SmoothStepper over a paralell controller? what other benifits would there be?
The reason I ask is the other option i was looking at is a PCI paralell card for the PC but I reckon that will cost about the same so im leaning towards the smoothstepper.

[H.O]

It depends.... Mach3 supports up to 100kHz step-rate thru the LPT-port but it requires a lot from the PC to do that, 60kHz is a more realistic number. The Smoothstepper supports up to 4Mhz step rate (66 times higher). So if you've maxed out the velocity-slider in Mach3 then obviosuly you'll get more speed by using an external controller able to pulse at faster rate.

However, the pulsetrain from the SS is also "cleaner" (less jitter) than what the LPT-port puts out. This means that the motor will run "smoother" at the same frequency which in turn means it's likely you be able to get a bit more speed out of it when running it with the SS compared to the LPT-port - even if you still are within the LPT-ports capabilities.

As for other benefits.... You'll get the same amount of IO that two LPT-ports gives you + a couple of additional IO, generally smoother motion and higher speeds but see above. It runs on a lower specs computer than what is necessary when "pushing" the LPT-port dirver up the speed-curve.

Drawbacks: It costs more than a LPT-port (not that it's expensive). Because of its higher speeds it's also more sensitive to noise and you need to wire your system properly (grounding and shielding) or you'll experience communication losses etc. You're dependent on a third party developer and judging by the ever lacking (but promised) backlash compensation I'm starting to have my doubts.

But again, what it does it does well.

HTH
/Henrik.