[The_NESt]

Hello.

I have build a step controller based on a PIC16F631 running 20 MHz maybe i will upgrade at a later time to a faster PIC it's on the edge of handling micro stepping with the PMW way or i need some optimizations

OK I found it's max speed at 1200 RPM on a 200 step motor but it's not the controller's fault it's lag of toque.

Then to my question sometimes my step motors stall even at low RPM (600) and it seems to get worse if i turn up the amps.
This happens more if it cut's long straight lines. Example if i cut out a 10Cm*10Cm * 1Cm square in 1 mm layers at mm/min it's not likely to do it with out stalling. But if i cut a flower at the same size and speed no problem.

I have some ideas to why.

It's based on the 2 Comparators in the PIC controller and TIP120's to create a PMW to set the amount of amps used in the windings. The TIP120's is protected by a zener diode on 96v. Maybe this creates some kind of magnetic field that stops the engine just a bit when it hits the 96v limit?

Or is it harmonic noise en the windings?

Or can there be another explanation on the phenomenon?

[Andre' B]

My guess.
Geckodrive Technical Support Library

[vanjast]

Do you have a rough/basic circuit diagram to show ?

[The_NESt]

I think Andre' B is right.
I have put on a special fly wheel, this gave me 20% extra speed:


Her is the schematics:

I'm not sure that the 100pf on step line and on measure line is OK I have left them out so they did not filter out the fast signals on these lines.
If I'm right then the vreg will cut out if the TIP120's over heat when they are on the same sink.
I have not tested if the PIC16F631 20Mhz is fast enuf to do micro step.
It runs the engine in 10Khz PWM based on it's 2 comparators.

And the layout:

[Horsedorf]

Tip 120's are only rated to 60volts.
tip 121's are rated to 80v and tip 122's are rated to 100v. you likely want to use tip 122's in there in stead of tip 120.
Also, make sure you are running them at saturation and not in the linear range. ie, use the hfe and calculate out what your maximum current draw through those motors will be and make certain that the base current limiting resistor is properly chosen to ensure that those tips run at saturation and not in the linear range.

[Larken]

On your circuit, you may have the RC filter between the sense resistor and the pic wrong. The capacitor should be closer to the pic. (resistor then capacitor)

I would change the Tip120's to a 5 volt Mosfet for much faster switching.

Also the higher the PS voltage the more RPM you will get. Be sure to use a High currrent motor (at least rated 3 amps) if you want speed. You can't get a 1-2 amp motor to spin fast unless the voltage is very high.

How is the microstep precision with your circuit ?

Larry K

[James Newton]

This is almost certainly mid band resonance. The gecko web page Andre referenced explains it. Look for a hock puck or other damper design to provide a mechanical solution or move to microstepping modes to reduce the ringing. You may want to look at the open source Linistepper PIC design for inspiration:
PIC Linear Stepper Motor Controller

[Larken]

At 1200 Rpm, thats 20 turns/second. Thats faster than you can reliably run a stepper anyway.
Most people don't run a stepper faster than 10 turns/second, after that they have lost 80% of their rated torque and jam very easy.
The reason it probably jams more on the straight line, is because it gives it time for a resonance to build. A curve is constantly changing the incoming step frequency and is less prone to resonate.

Larry K