Hi I have been wondering the last few days on an 'open' data format for controlling low cost, user built servo's.
The scenario of using a 'proper' closed loop servo for a small mill is very appealing over a stepper. While parallel ports are almost free and sufficient for steppers, to implement a servo it looks like you have to spend order of $100, mostly because of the encoder reading, which is a big jump. I was wondering on the viability of a PIC (or other) system driven off the parallel port. An 18F24J10 per axis(~$2) could handle the PWM and quadrature in. (At 40MHz, probably two axis) The micro would have to count encoder pulses, set the PWM out, and write/read it's designated data on the bus at it's allocated slot. Another micro would handle I/O, directly with a 40 pin chip, or multiplexed. So the idea is that EMC would clock out a semi-standard data string, and read likewise. A user could could have 1 -4 servo's and general I/O connected. They would basically sit on the parallel port bus and pick up or drop off their data as required. The four axis would be identical except for data intercepted. EMC would send out an unconditional? 11 byte packet, something like' - start byte - PWM > X (2 x 8 bit, but 10 bit used on micro) - PWM > Y (2 x 8 bit, but 10 bit used on micro) - PWM > Z (2 x 8 bit, but 10 bit used on micro) - PWM > A (2 x 8 bit, but 10 bit used on micro) - I/O (3 x 8 bit, user allocated as set up in EMC) - end byte and then do an unconditional 15 byte strobed read, something like' - Encoder X (3 x 8 bit) - Encoder Y (3 x 8 bit) - Encoder Z (3 x 8 bit) - Encoder A (3 x 8 bit) - I/O (3 x 8 bit, user allocated as set up in EMC) While this brief needs some re-hashing, - would the developers at EMC consider supporting something like this? - is it viable ? - would the system get sufficient use? I realise that the controllers is an enterprise in itself, but EMC would only support a fairly strict packet format. It would then be up to users + forums to build/buy a servo driver that complies. Regards Roland Jollivet PS; I am aware of DS-pic and a host of other step/dir systems. This a seperate topic. ** ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
