Digital control on a dividing head

[dbb-the-bruce]

This question is not "how to add a 4 axis".

What I'd like to do is attach a stepper to the dividing head I'm refurbishing and then have the capability to accurately control rotation for things like odd gears and other stuff.

I'm a software engineer in real life, and I've worked with a number of motion control systems over the course of my career. But I'm not very familiar with what is currently commercially available and affordable off the shelf.

I'm envisioning buying a stepper motor with a controller and a power supply - ie. a single axis kit. The controller would be smart enough and easy enough to configure. It would also be open enough that I can easily write my own python scripts to use with it or have existing simple utility scripts/software. Also should be OS agnostic, I'm a Linux / OSX guy.

I won't know until I've finished the dividing head refurb, but I don't think it's going to require a HUGE amount of torque to turn, and won't need a lot of holding torque either as it's driving a worm gear.

I suppose that another option would be to look for an encoder kit or even a rotary DRO - I could do the cranking by hand, but a stepper would give me enough positional accuracy and allow me to convert to full-blown CNC in the future if I so desire.

Ideally, the budget is only a few hundred bucks.

Looking for suggestions, Thanks
-Dave

 

[jwmelvin]

I don’t quite get it. Why not buy a stepper motor and driver and use a Raspberry Pi with a stepper hat or driver board? I totally understand not wanting to build one if that’s what you mean.

 

[Boswell]

I think the short answer is there is no reason that you can't do what you propose. adding a stepper to a dividing head will allow you use computer control to rotate the table. Less likely to miss a step etc. I also agree that you can probably use a very small stepper because of the likely low torque requirements. However as jwmelvin suggest, it would also not be difficult to just direct drive a small chuck (i.e. 4th axis). More versatile but possibly a little more work to fabricate. Regardless of if you attach the stepper to an existing platform or fabricate a direct chuck attachment I think, as a software engineer, that you will not have any trouble creating a simple UI to use it for simple positioning like for cutting gears. Looking forward to seeing what you come up with.

 

[MikeInOr]

There are friction brakes that are made to bolt onto a stepper motor. Energize the brake to disengage the brake. Cut the power to the brake and the spring in the brake engage the friction brake.

Look on ebay for a Parker Compumotor SX drive. SX6 is for driving big steppers, SX8 is for driving REALLY big steppers. The SX drives have the PLU/controller, stepper driver and power supply all built into a single industrial grade box. An SX8 drive was many thousands of dollars when new... a used one can be found on ebay for $100 or so. They make a really nice all in one solution and programming should not be a problem for a capable software engineer. It took me about a day to figure out the ins and outs of the stepper language to get it to do what Iwanted it to do. You program via an RS-232 serial interface. Custom software for programming them is available but I just programmed them directly via hyperterminal. There are plenty of extra IO lines incorporated into the SX box and there are even commands to automatically disengage an electric friction brake before doing any movements. All the acceleration, deceleration, hold and and configuration for specific stepper motor characteristics are all built into the PLU - stepper language... saving you weeks of time implementing such functionality yourself in a generic PLC or SBC.

 

[dbb-the-bruce]

Thanks for the info -
@jwmelvin - That's pretty much what I'm planing on, minus the pi. I don't know where to source this stuff (I know where to get really expensive stuff precision and demanding applications - avionics etc). I'd really rather not throw a pi at it unless it was out of the box plug and go-ish. For my first pass I'm perfectly happy scripting text commands to a motor controller.

As far as direct driving a chuck for a forth axis, sure that would work but I've already got (almost, just need to put it back together) a functional dividing head that I can mount my chucks and face plates on. I'd have to fabricate (a lot more work) or buy a direct drive setup. It should be a simple matter to make a stepper motor mount that can be bolted on in place of the handle and plates (handle and pin needs work and it only has one plate). The stepper resolution angular positioning will be multiplied by 40, and I can have a computer easily do the counting.

I'll look for the SX drives. Sounds about right. I was hoping that someone hear would say, "check these guys out, they sell inexpensive steppers and drives to hobby CNC folks". In all of my existing experience, someone else puts together the hardware and drive electronics and then hands me a manual for the controller and says "make it work around all these design mistakes we built into it" .

I'm looking for a single axis, wire up a stepper to a controller and talk serial to it that's on the cheap side.

A simple encoder readout could also work, but it would be nice to not have to do the cranking by hand.

-Dave

 

[Boswell]

I know a lot of people find steppers on ebay. You might also check the hobby robotics sites.

 

[gzoerner]

Dave,
Check out stepperonline.com. They have a great selection and good prices. I got my NEMA 23 stepper motor, controller and power supply from them. Super fast shipping.
Glen

 

[ThinWoodsman]

Thanks for the info -
@jwmelvin - That's pretty much what I'm planing on, minus the pi. I don't know where to source this stuff (I know where to get really expensive stuff precision and demanding applications - avionics etc). I'd really rather not throw a pi at it unless it was out of the box plug and go-ish. For my first pass I'm perfectly happy scripting text commands to a motor controller.

The thing with using a Pi or Arduino or Beagle or whathaveyou is that it's likely to be far cheaper than a dedicated servo+controller. If you haven't had much exposure to the hobbyist end of this sort of thing, check out SparkFun - for example the Motors and Drivers section, or the Kits (mostly for playing around/learning).

You could probably bang together a servo with a driver board that listens on a serial interface for text commands. Back about ten years ago when I was working with this stuff, it was all C, but that has likely changed by now given the huge community of Python users.

 

[JimDawson]

I'm looking for a single axis, wire up a stepper to a controller and talk serial to it that's on the cheap side.

While it's not on the cheap side as far as steppers and drives go, it does talk serial and is well documented in English, these are the drives I use for most applications.
https://www.automationdirect.com/ad.../stepper_systems/stepper_drives/stp-drv-80100

On the cheap side is EBay, hundreds of steppers & drives to choose from. Also do a search for stepper controller.

 

[MikeInOr]

I'll look for the SX drives. Sounds about right. I was hoping that someone hear would say, "check these guys out, they sell inexpensive steppers and drives to hobby CNC folks". In all of my existing experience, someone else puts together the hardware and drive electronics and then hands me a manual for the controller and says "make it work around all these design mistakes we built into it" .

Yeah... no, you misunderstood. Parker Hannifin IS the HEAVY WEIGHT in the industrial controls world. As in their 20 year old discontinued SX drives are FAR superior to anything you are going to find in the hobby market today! Want to know if your stepper motor skipped a step... then do something about it... the SX drive has you covered. Want to detect when the force the stepper is putting out exceeds a threshold... then do something about it... the SX drive has you covered. Want to vary the wave forms sent to the stepper based on the current speed, acceleration and torque of the stepper... the SX drives not only allows you to do this they will do this automatically by just enabling that functionality. Pretty much any stepper parameter you can think of is built into the SX drive.

Parker takes everything you could ever want to know about steppers and every thing you would ever want to do in driving a stepper and wraps it up in to a single package with the intelligence built in... then sells it on the INDUSTRIAL market for $10K for a single axis of control. You pay $10K for a single axis drive because it will do everything you need it to do... everything that you don't know you need it to do... and do it for the next 50 years without maintenance. My father worked for Stanley tools, he was the head of product engineering. His team designed plants, production lines, processes, tools and insured the produced product exceeded the standards (Proto and Mac industrial tool level standards... not Stanley home mechanic standards). They used the SX drives extensively in the machinery they designed for producing quality tools day after day for decades.

So why can you pick up an SX drive on ebay for $100... because the stupid SX drives have outlasted the industrial equipment they have been controlling for the past 20 years. There are no corners cut on a Parker Hannifin control. The SX drives have minuscule amounts of flash and RAM compared to Parker Hannifin's modern Zeta drives... but they are a great match to what you described you want to do.

The lift on my fathers router table (woodworking) is probably the strongest, most accurate automated router lift you will ever find. I helped him build the table and programmed the SX drive for him. We used a Parker Hannifin Compumotor industrial grade linear actuator that could have lifted my entire shaper (woodworking) to .001" (maybe even more precise) of where I wanted it. At one time I had a table saw fence in which I could dial in a cutting width I wanted and the fence would move to that width automatically. When I changed the blade on the saw I would hit a button and the fence would creep over to the blade until the blade just touched a copper plate on the fence then used that for its new zero reference.