I am going to build a 3 axis servo control

[markey1979]

Oh, but steppers are not that bad, I just really like a challenge. Seriously though, I really decided to take the servo challenge because:

1) I would like to be able to contribute something instead of just taking all the time.

2) Because I can come up with dc motors and encoders for relatively free.


The setup I will use the servo control for will probably use mostly junk car and printer parts. I did not design the table yet, but I feel that it will be slightly easier than the control. I am envisioning using automotive power window motors for the servo motors, with serial mouse encoders, or possibly inkjet printer encoders, but the chop wheels look much more professional on the mouse parts. I did however already buy sealed bearings for the slides. Precision round rods are found in shock absorbers, and most spare tire jacks have a really nice acme thread forcing screw, with nut. I am not looking to build a huge setup, this time, but I would like to leave room for expansion in my control design.

I was not even thinking about a mouse for the quadrature encoders but it makes perfect sense. I read this guy's blog about it:

http://www.boondog.com/tutorials/mou...kBeforeWeb.htm

...back to the servo control.

National semiconductor makes a deticated chip for precision motion control called the lm628/lm629. The problem with it is price. The lm629 is about $52 us. for each axis, making it very cost prohibitive for the hobbyist, but the lm629 would be the easiest way to go because it can output directly to a motor driver. I actually would make a go with it anyway, but it was not on the free samples program. Jkerr makes a chip for about $20 us. for each axis, but I think that I can do it cheaper. Right now, I am reading the 392pp datasheet for the Microchip PIC18f4431. Its a pretty stout programmable microcontroller that has a quadrature encoder interface already built in. This makes it a perfect candidate for the servo control, and at just under $7 us., it is getting very close to my tight budget. I don't know if it can be sampled, but I have already sampled its little brother the PIC18f2431.

Microchip also has sample code to perform servo control for certain processors in its application notes this one is for the PIC17c42:

http://www.microchip.com/stellent/id...pnote=en010998

I know that my idea CAN work, but with my busy schedule, which consists of a full time job, a part time job, and school, this may take at least six months til I have something real to display.