Create/design a controller for me

[Demon]

This is where I learned a lot about stepper motors and drivers:
http://groups.yahoo.com/neo/groups/mach1mach2cnc/info

I can think of 2 ways to be certain where the "head" attached to the main shaft is located.

1. There are optical readers that attach to the back end of stepper motors (that's why the shaft comes out both ends on some steppers). Signals from these encoders tell you exactly how much the motor has moved.

2. For short main shafts, there are optical strips that can be run along the main shaft. An optical sensor riding along this strip tells you exactly how far the head has moved (I saw this in a inkjet printer).

For both systems, take a reading at far left and far right, center is mid-way. There are probably dozens of ways to do what you want.

It's all a matter of knowing your needs. I wanted to do a DIY CNC with 0.001" accuracy for work on PCBs, accuracy is everything. It you're moving Coke cans, a center switch is good enough.



Note: measuring motor movement is less precise, there can be some play in the attachment under the head. Measuring actual head movement is the ideal method, but the mechanism may be unreliable in extremely dusty environments.


Also, if you want to return to exact center every time, a center switch will not give a true reading. If the head is moving left, it will stop a fraction of an inch to the left of the switch, and vice versa moving right.

Robert

(don't you hate typing a long post at the same time as someone else)

[Demon]

I suggest you download this before it is no longer available:
ftp://machsupport.com/Mach/Mach2R6.11N.exe

It is demo CNC software (1000 lines of code max), current versions are now Mach 3 and 4:
http://www.machsupport.com/software/mach3/

Without a license, Mach3 will operate in Demo mode. While in Demo mode, the software has the following limitations:
•Mill & Plasma: 500 line gcode limit (10,000,000 limit after licensing)
•Turn: 50 line gcode limit (10,000,000 limit after licensing)
•Kernel Frequency locked at 25kHz (only applicable if using the parallel port driver)
•Set Next Line function disabled
•Run From Here function disabled
•Turn: Threading disabled
•Plasma: THC functions disabled

Mach software can support multiple axis, you only have to use one and ignore the others.

You will be able to move the head along your axis as you want it. You can make your own G-code scripts that will control the head.
http://en.wikipedia.org/wiki/G-code

Your requirements will be relatively simple for what the software and hardware can do. You will move along a single axis, ie: G1 500,0 moves 500 units left, G1 -500,0 moves right. Read Mach 2 help files for exact syntax.

Simply put:
- edit your G-code file.
- run Mach 2 software on PC using G-code.
- Gecko drives connect to PC using parallel cables.
- Mach 2 uses G-code file to tell the Geck drives what to do.
- the Gecko drives moves the head along the main shaft using limit switches.
- Mach 2 has manual override to move drives.

If the head has complicated movement, you can replace the Mach 2 software with your own PC interface.

Robert

[wheelie34]

Thanks for the input Robert

As you put it, I am moving coke cans, indoors at normal temperatures.

No need for accuracy, I understand about the optical sensor, all I need to know is the pinion will not try to run off the end of the track, either end, after a hiccup, if that happens it just needs to get the signal from the switch, exit the current loop, "find centre" then revert back to whatever the pots are telling it, it will never be left alone, the user/operator will always be present as the items its pushing/pulling will vary.

[HenrikOlsson]

Hi,

Which PICKit3 version do I need? PG164130 or DV164131

What you NEED is the PG164130, that is the actual programmer/debugger itself. The DV164131 also includes a little development board which may or may not be useful.

100 iterations per minute, each 2*4 inches long (max) is 800 inches per minute average velocity, the peak velocity will need to be much higher since you need account for acceleration/decceleration - This might not be THAT easy.... Using a pinion with a 2" effective circumference means the motor must turn 400rpm to reach 800ipm (again faster than that in reallity) but there's only two revolutions of travel so the acceleration must be sort of insane.... Using a smaller pinion means the motor needs to trun even faster (bad), reduces torque requirement (good), have less load carrying capabillity (bad, but can be adressed by using a wider pinion) but at one point you still need to fit to a shaft so it can't be made THAT small.
.
I have a feeling this requires some pretty serious motor/drive combination, a stepmotor may not be the best. I'd probably look at a ballscrew driven linear stage with a high pitch screw, something like 10-20mm (or 1/2" - 1") driven by a servomotor. Plenty available on EBAY.

/Henrik.

BTW, using encoders on stepmotors is very uncommon as it kind of defeats the simplicity of an open loop stepmotor. There ARE closed loop systems available but then the motor/drive behaves more like a servosystem than a stepmotor system. You read on DIY CNC lists and forums that step motors are notorious for loosing steps but that only happends when you're operating them outside of their limits - ie you're asking more from the motor than it can deliver. Properly dimensioned and used it is as reliable and rugged as a servo system but each have their benefits and drawbacks.

Geckodrive used to be great, my G210's are 14 years old and still going. However, if I'm not misinformed the founder has cashed in and left the building and it's not what it used to be - or so I hear. Still great step motor drives though!