I am going to build a 3 axis servo control

[markey1979]

Do not worry, you are not late.....

I am still working on my design. I totally understand your 9600 baud problem. That is why I would like to incorporate usb into my design. It is infinitely faster than a normal serial connection. USB has been slow to in its implementation for industrial applications. I have been using an Analog Devices usb isolation ic in my design phase, but I may switch up to an Atmel uC because the open source community is more inclined to them. Microchip is still at the front of my design because they give out a light version of their IDE for free, but in linux, which I use, Atmel is much easier to work with.

My table is almost complete. I have the x axis, and most of the y axis done. I just have to mount the lead screws and the limit switches. I am going to use a modified computer switch mode power supply. I can use it to power my drive controller, and use the drive controller to turn on the power supply. All I have to add is an scr to turn the cutting head on and off. I have a dedicated computer with EMC 2.4 loaded, all ready to go, and I have been reading up on creating the drivers.

I would say the whole project is about 50% complete, since my last post. I would have liked to have been making chips by now, but I feel satisfied that I at least have some progress.


Thanks for showing interest..

[black5f]

I have a very capable but old card, I use an eprom that is designed to respond to drip fed commands form a pc, but limited buffer. Commands can be 10 - 15 asci chars plus checksum and the card can take up to 50ms to respond or though its often less when I measured it. For smooth servo move it needs continuous commands and the RS232 just don't do that. The card will interpolate 3d straight moves and circles / arcs in any two axis but not complex moves, spirals etc. So, to sum up, complex moves must be short 3D interpolated. At the moment in my optimisation home brew, the host pc software works out the time the machine needs to complete a move ahead of the move. If it's less than 50ms it does a suitable ramp up and ramp down as the card will do a controled stop (out of my hands!) if it cant maintain constant velocity. This makes it very slow on complex multiple short fast xyz moves.

I am probably making a very naive statement but presumably this chipset is a simple swap from pwm to a voltage signal which my free but massivley good MAX250 amplifiers need? Very interested in your developments especially if it could do arcs, spirals on board, even if that just means a decent move buffer like next 40 or 50 moves or high speed comms. Don't like the pulse and direction type controllers for servos, sort of defeats the object and demands Mach3, might as well have steppers..

Basically, very very interested!

Tom

[Sikspens]

Hi Mark,

I'm new to this forum myself, and stumbled on MyCNCUK while Googling for bits to complete my tabletop mill. I was going to go with servos, but the daunting complexity of feedback loops and tuning has put me off for now.

I totally understand what you are setting out to do, and commend you for taking it on with the limited means of a student. I'm forever canibalizing old photocopiers, printers and scanners, which will yield nice precision rods and bearings, drive pullies, ballraces, power supplies and stepper or even servo motors with encoders. For readers wanting to go the servo controller route with Gecko-style modular purchases, I've stumbled across this guy on my doorstep here in Pacific Coast Canada: DMM-Tech.com who supplies servo drivers and controllers and motors at prices comparable to the popular Gecko stepper stuff. No connection, or recommendation, I just happen to know of them.

Off-topic, my own project is conversion of a wood mortising machine into a table top mill, using steppers and ball screw actuators. The objective is a compact, very accurate steel and aluminium-capable 3-axis (expandable to 4) bench-top sized machine, with a work space of about 6 X 8 X 8 in, or 1500 X 2000 X 2000 mm.