Stepper Driver Query

Hi Gents,

I'd appreciate some advice regarding a Chinese-sourced stepper driver I've recently acquired. Here's a picture of the of the driver PCB:

(Click to enlarge)

— and this is the relevant Ebay listing showing such 'documentation' as is available for the board:

Ebay Listing

The simple stepper driver boards I've used in the past have only required me to set the Current Limit and the Stepping Fraction (this board refers to these as 'Current Settings' and 'Excitation Mode'. However, this board also includes 2 further settings designated:

(a) Torque Settings — 20%, 50%, 75%, 100% (DIP default set at 100%)

(b) Decay Mode — 0%, 25%, 50%, 100% (DIP default set at 100%)

I've done some Googling but really, I'm none the wiser regarding what these 2 settings mean in the context of this board and the purpose I have in mind. I plan to use this driver in a Steve Ward ('Kwackers' Electronic Division Control Box (Division Master clone). It will drive a motor hooked up to a small homebrew dividing head used purely for circular positioning. I don't intend to use it for rotational machining i.e circular routing or edging.

My instinct is to leave these 2 settings at their defaults and get on with the project! Can someone who knows what's what confirm that that's OK, please? Or is there some reason why is might be desirable to change these settings?

Thanks

Joe

Edited By joegib on 19/12/2012 10:05:19

Edited By joegib on 19/12/2012 10:07:26

Edited By joegib on 19/12/2012 10:08:49

tosh's app note might help pdf..I see reference to decay wave forms

Hi Joe,
You may find the data sheet on the IC used on the board explains the setting so that you can set them to match your use of the board. I found the data sheet HERE.

Les

Joe -

The torque setting determines the current when the motor is not being stepped. The default (100%) says that the motor current will be 100% of the current that you have selected on the current limit setting. If you select (say) the 50% setting, then the drivers drop to half of the selected current setting when the motors are not being stepped. This helps with keeping the motors cool when they aren't moving an axis.

Regards,

Tony

Les and Jason,

Thanks for linking those data sheets. They've helped to clear the mists a bit.

Tony

Thanks for that clear explanation of the Torque Settings adjustments. The crucial factor for the way I want to operate the dividing head is Holding Torque rather than Dynamic Torque — the motor needs to maintain the indexed position and resist side thrusts arising from cutting operations. So, if I were to reduce current delivery below 100% while the motor's stationary, presumably I would be reducing the Holding Torque proportionately. Since that's not desirable it seems sensible to maintain current at 100% while keeping an eye on heat generation/dissipation in the early days of operation.

Is that a reasonable approach, please?

Joe

PS — I must say, it's very generous of you to help someone who's building an alternative to your own design.

Joe -

Your assumptions are correct - the holding torque is directly proportional to the motor current. So if holding position is important to you, then leave it at 100%. However, if you are using a worm drive for the dividing head, there is very little possibility of back-driving it, so the holding torque requirement is minimal. If you aren't using a worm drive, seriously consider changing your design

I have no problem whatever with people building alternatives to my design - after all, it isn't as if Divisionmaster was the first stand-alone rotary controller in the world. Mine is better of course...

Regards,

Tony

Yes, I'll be using worm drive for the unit. Anyway, your comments suggest I've got more room for manoeuvre than I thought.

Thanks again

Joe