ON/OFF brushless controller.

[Thecrazzyman]

im looking to make or buy a brushless controller. i am going to be using this for a magnetic stirrer and the plan is to have the coils lined up under a plate with a magnets casted in epoxy in a cross pattern. that way when the magnets are in the dish with the liquid it should spin around and around.
it would be nice to vari the speed but that is not needed.
so im asking for any ideas on how to modify a brushless controller to just do on and off. or have a variable adjustment.
im watching this bid
http://cgi.ebay.com/I-K-A-WERKE-Lab-Disc-Magnetic-Stirrer-Mint-NIB_W0QQitemZ7574969022QQcategoryZ26235QQssPageNam eZWDVWQQrdZ1QQcmdZViewItem
and might just get that one. but it would still be fun to build my own.

thanks for any help of input.
Alex Snell

[Blue Sky]

I doubt that a brushless contoller would work. The speed is too slow and I don't think the fields from the magnets are strong enough to induce the necessary back emf.
What you want is an open loop controller like like that used with a stepper motor.
Also much simpler.
Here is a plan for a very simple electromechanical stirrer.
http://whs.fcps.org/nhisim/devices/stirrer/stirrer.html
Better yet buy the one on ebay, it looks pretty slick!

-Dave