pic and maximum step frequency

[niclatrique]

Hi everybody.

I'm new to that kind of stuff but I plan to make my first router. I'm in the development of my own stepper driver board. I use a PIC16F685. I want to implement FULL step, HALF step and MicroStepping mode in my driver board. I'll use discrete N channels mosfets with FET drivers to raise Vsup up to 60-80 volts. I'm inspired by the geckodrives.

1- Now, as I'm totally new to cnc, what would be a great target as maximum step frequency ??

I've read the Gocko's manual and they stipulate a max step frequency of 200kHz. Even with a crystal at 20MHz, I can't get more than 75kHz of step speed with my pic's program. For a 1/8th microstep mode it gives me a max speed of 2812RPM which is 2.34 inch/sec with a 0.050" pitch ballscrew.

2- Is that fast enough ??

Thanks for the replies and all suggestions are welcomed.

niclatrique

[pastera]

If you are going to use a parallel port control, you won't get over about 45kHz step frequecy.
As far as if thats fast enough, you won't have a whole lot of torque at that speed. Also you'll need to impliment some form of damping to get through the midband resonance issues.

0.050 pitch ballscrew? do you mean leadscrew? I haven't seen a ballscrew with that small of a lead.

Aaron

[niclatrique]

Thanks for the reply on this. You make me confident on the work I already did. I need to read about the midband reasonnance now...

About the ballscrew, by ballscrew, I mean an endless screw with rounded thread which carry a nut with bearings inside its body.

Anyway, thanks a lot for the advice on the step frequency.

Best regards,

nic

[pastera]

0.050 pitch is 20 turns to move 1 inch - I didn't think they made ballscrews that fine.

As far as stepping at 200KHz, you won't be microstepping at that speed - you'll need to switch to full steps long before, so you only need to be able to support 25000 full steps per second.

A 200 step.rev motor would turn at 7500RPM at 25000step/sec - without very special motors you'll never get to this speed with any torque left.

Aaron

[niclatrique]

Thanks Aaron,

I won't worry about it anymore

thanks again

nic