Single Axis Controller to run two motors

[edo]

I just finished building a JGRO router with the HobbyCNC 3-Axis controller. To help justify all the time (and money) I'm investing in my new hobby, I promised my better half that I'd automate her quilting frame for her. I won't need nearly the power of the JGRO to move the sewing machine carriage around the frame and will probably buy another HobbyCNC board for that. But before I do that, I need to automate the take up roll. I designed a gear and chain setup to do this and I need to control motors to turn the roller.

I plan on putting one stepper motor on each side of the roller and turn them in synch (in opposite directions.) With the size gears I want to use, the motors will have to run somewhere around 300 RPM to move the material on the roller 2", and ideally this would happen in 1 second. I considered using DC motors, but would like the holding torque of steppers.

I'm looking for is a simple 1-Axis controller to run the two motors (Vexta PH266M-E1.2, 2-Phase, 0.9°/Step, DC: 6V, 1.2A). This won't be computer controlled, so I'm using mechanical switches to tell the motors when to run and which direction. The idea is that each time her sewing machine carriage hits a switch, the roller would either roll up or unroll 2" of material.

Any ideas on a cheap controller for this? I don't mind, and may even prefer, building my own. I'd also like some input on what size power supply I would need - I was hoping to keep it small enough to use a surplus laptop supply. Thanks.

[Hacksaw]

There once was an Arcsyn 2 motor/single axis board but alas they are sold out and according to the creator he has no plans of ordering more boards or selling the plans for them.

[rstringer]

In light of Hadksaw's information, your best and easiest bet will be to go ahead and do a two-axis, ala pminmo.com using either the 5804 or the 3977 plans. The 5804 chip can be found at cncresource.com for about $6.00 each or the 3977 can be requested from allegro as a free sample--I got 5 that way--but it is a bit more complicated to build as it is SMT. It comes in two flavors, square smt or low-profile SOIP (very low DIP profile). I have not been able to find a schematic using the SOIP chip. The 5804 is really easy to build if you know how to transfer the layout and etch a PCB. If you don't, there are several good tutorials on toner transfer--or use your cnc router to cut one.

RWS

[rstringer]

DARN those fat fingers!!!! I meant HACKSAW!!! Obviously, you will have to make two boards, the sticking point is the requirement that the motors run in opposite directions and, barring an extra gear on one side, a controller for each motor will be required.

RWS

[Walt Taylor]

All that is needed to reverse the direction of a stepper motor is to reverse the wiring to one of the phases.

Just a note!

[edo]

Thanks for the info, I'll relook at the PMINMO stuff.

Couldn't I run two motors in different directions from the same controller just by reversing the wires on one of them?

Also, since I don't want to use a computer for control, I need some sort of circuit that generates the pulses needed to move the motors. I think there was a mistake in my math and I don't need 300 RPM. A .9 deg stepper needs 450 pulses per rev and I'll need about one revolution per instance of movement - so I'll need something that can generate 450pps. That shouldn't be too hard, eh?

[Walt Taylor]

You can run two motors from the same driver by connecting the phases in parallel (requires twice the current from the driver), or connecting the phases in series (single motor current value, but will limit the speed). I would suggest a PWM based driver, and series the phases.

Allegro has several PWM based drivers (A3986) with a built in stepper table that would be the best option. Just supply a direction bit and a square wave clock (an old NE555 will do). www.allegromicro.com

Regards,
Walt