Unipolar stepper motors

Toby Seckshund

I bet there is a whole stack of stuff on this already, but .. I tired and can't find any simple code etc. I just wanted to play with reclaimed steppers and dream of a PCB drill rig, any pointers welcomed.

Ta

JonnyMac

I wrote this a while back but it might still be helpful:
-- www.parallax.com/Portals/0/Downloads/docs/cols/nv/vol7/col/NV136.pdf

Toby Seckshund

JonnMac

Thanks for the reply its being printed now. Been drivindg all day, can't raise any imagination but don't want to slup in front of the brain destroyer. They are trying to entertain us with some bloke who thinks its normal to pass CRT EHT through himself. Whenever I did that, it was called being a cak handed tw.. , Hey ho.

Philldapill

Toby, nothing against you or your post, but this is a classic example of how the mountains of information on the forum is difficult at best, inaccessable at worst due to a not-so-great search function. I know you guys at Parallax are working on resolving the forum search issue, but here's just a small nudge to bug you guys a bit more. I think the mentioned(?) new forums software would have a better search capability?

Anyway, about your post, Toby... Unipolar steppers are some of the easiest to control because they don't require any complicated H-bridge circuitry. All you need to do is ground the center wire for each phase, and apply a positive voltage to the "legs" of the phases in sequence. Bipolar steppers are a bit more tricky to control, but offer better resolution and more torque, generally.

Rayman

You can try my stepper test code.· It's not very polished (actually, it's not polished at all), but it works!

My setup was simple:

Howard unipolar stepper P/N 1-19-4202 (12V, 3.6 degrees) (Parallax sells it? [noparse][[/noparse]don't recall])
ULN2803 darlington array to buffer and protect the Prop.
Using pins 0,1,2,3

Video of operation on this link:
http://forums.parallax.com/showthread.php?p=733644

Here's somebody elses schematic:
http://www.me.umn.edu/courses/me2011/robot/technotes/stepper/schematics.html

Here's my code:

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My Prop Info&Apps: ·http://www.rayslogic.com/propeller/propeller.htm

JonnyMac

Phil: If you use a push-pull driver like the L293 then you can drive unipolar or bipolar steppers with the same code; I've done it. The only difference is that unipolor motors have a common connection to the motor supply.

Ray: I haven't explored micro-stepping yet but I believe you will have to use a cog to handle it as you're time-modulating between two half-steps, and the modulation must be maintained to hold position -- I don't think one can pull this off in Spin (that said, I could be wrong...).

Toby Seckshund

Thanks for the info, everybody. I knew that there would be stuff available if I looked hard enough. I was just a bit tired and wasn't going to look very hard, so I thought I would ask. I suppose if too much was put on a plate, I would just keep on copying and not learning.

I have scrounged some steppers and even an old CD printer transport. I hope to get two paper printer transports soon and started to dream of making a drill assembly. I have been using FreePCB for a while now and have only just investigated the drill file format, which turns out to be glorious ascii (NC I believe)

When I was a kid I would make up all sorts of electro-mechanical things and so I thought as I am constantly being accused of being nothing but a big kid...

Rayman

JonnyMac: I pulled it off! Check it out...

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My Prop Info&Apps: ·http://www.rayslogic.com/propeller/propeller.htm