OpenServo.com

[Gyrometer]

Hello Open servo,

I'm Steve (Gyrometer) and I live in Melbourne Australia. My interests are DSP and related stuff. I'm really interested in developing a servo control system for CNC machines (and the metal hardware as well).

Why? It's already been done I know - but it is very interesting and I just want to. Plus it turns "number-shuffling" into real world artefacts that you can touch. A nice change from databases and networks.

I'm currently playing with a PIC32, which is amazingly fast and 32 bits (in a $5 chip!) that runs at 80MHz. I'd like to make sure that my H-Bridge design is reasonable and that my PID control is also not too outlandish and find other like minded people with whom to shoot the breeze about servos and other esoteria. Thanks for having me here!

(I found your forum after typing something about H-bridge design and locked antiphase PWM commutation into Google.)

Regards,
Steve

[jharvey]

Hello and welcome along.

In terms of $/performance, ARM processors are typically king. In terms of low power draw, AVR's are typically king. PIC's often hit the low up front $ investment category. All of these have some good features.

About the CNC thing, have you seen the OpenEncoder option? It allows full rotation of this type of servo motor. When combined with the MG995/996 they would likely make a nice CNC drive motor. Perhaps not the fasted, but powerful and similar cost to a stepper setup.

Hope your CNC project goes well.

[Gyrometer]

Hi Jarrod,

Thanks for your welcome. The open encoder sounds interesting. I checked it out.

The CNC servos I'm playing with are Fulhaber ironless rotor Samarium Cobalt motors, at about 200 watts. While not the most powerful they are very compact (about the size of a D cell torch battery). The encoders are 1024 line (4096 edges) HP (or Avago) encoder wheels and sensors that we have mounted in our own housings. The ball screws are 25mm zero backlash 5mm pitch items. The servo amplifiers I'm building are based on the Intersil HIP4081A and IRFP1405 MosFets. Eventually I want to do a three-phase brushless commutation drive, with sensors, based on the same kind of stuff. When everything works as expected, then I want to scale up the drives and machine sizes to soemthing less 'hobby' and more industrial.

The PIC32 is a major departure from the standard PIC offerings and has a MIPS-4K RISC core, so it competes happily with the ARM stuff. A 32 bit core running at 80Mhz is pretty cool!

I have run the gamut of DSP (DSP56002 etc) cores, to embedded x86 and now the PIC32 for servo control. The 24bit 56K is well obsolete now. The Freescale DSP-Micro-controller offerings are 16 bit by and large and if you want more, the price becomes astronomical for my taste.

Anyway, I've settled on the PIC32. The PIC hardware and compiler work very well. The only complaint I might have is the Microchip documentation is still a bit ragged in parts, but I imagine this will improve! Though the PIC32 is not a dedicated DSP machine, it still has a hardware multiply and an instruction cache, so it pretty much does 80MIPS for all intents.

I guess too I'm interested in finding access to people who are control theory nuts!! And who have real world electronics exposure to swap ideas with.

Nice to hear from you Jarrod,

Best Regards,
Steve