Stepper Motor Size Rule of Thumb

[jallenmorris]

I've found this package of controller / motors / power supply.

http://www.stepperworld.com/FET3dynamo.htm

The larger motors are 190 oz in and I was wondering how do you gauge the size of motor you need for your application?

[ger21]

http://www.geckodrive.com/support.aspx?n=541652

[wannabeee70]

Originally Posted by ger21 http://www.geckodrive.com/support.aspx?n=541652

That's a problem, it doesn't take into account mechanical efficiency of a machine.

[LeeWay]

I would hate to try and read something that would have all the answers for every type machine a fella could dream up.
There shouldn't be a problem with that. It is what it is. It will give you a starting point to see what type system you would want.
THEN, you gotta take into consideration the efficiency of your ways and power train. Axis length, turns per inch, loaded weight of machine with parts and extra fixtures, rigidity, material being cut, etc......and the list can go on and on.

I don't think all the answers are in any one place. Sometimes there are many many right answers. Building your own machine is more of a path that you take and not necessarily a recipe that you follow, though you can certainly do that. Then in those cases, most questions have been answered.

[jallenmorris]

So it looks like the package I found would work for a mid-sized CNC router. Say a 48" x 48" made with MDF. I suppose the best thing would be to get them, get a small application built, maybe 24" x 24" and see if it works. THen make a larger one and try the motors. If the motors don't work, I have my answer: Get bigger motors.

[pminmo]

You do realize that isn't a current controlled driver board?

[ger21]

Originally Posted by jallenmorris So it looks like the package I found would work for a mid-sized CNC router.

It'll work, but not very well. The Stepperworld is an inefficient drive, and is outperformed by most drives on the market today. You won't see many people using them here.

Originally Posted by jallenmorris I suppose the best thing would be to get them, get a small application built, maybe 24" x 24" and see if it works. THen make a larger one and try the motors. If the motors don't work, I have my answer: Get bigger motors.

Wrong answer. Bigger motors would probably be less likely to work. The motors and drive need to be matched together for best performance. Not all motors work well with all drives, although the better the drives, typically, the wider range of motors they're capable of running well.

[jallenmorris]

I'm new to this and honestly have no idea what you mean.

Originally Posted by pminmo You do realize that isn't a current controlled driver board?

[ahren]

Most drives (like the Gecko G540) use PWM, or Pulse Width Modulation, to effectively control current. This is basically pulsing the coil voltage on and off at a very high rate. Since the motor coils are inductive, they can't change voltage at this rate, so this effectively looks like a reduced current. Pretty slick.

In contrast, the stepperworld controllers appear to use power resistors to control current at higher voltages. This is remarkably wasteful, and sends a lot of the power into heat, rather than into your motors. Agreed with Ger -- I would keep looking, Gecko makes a great product, although it may be out of your budget. Probotix isn't bad either, and is a lower current but also a lower priced solution than Gecko.

Ahren
www.cncrouterparts.com

[jallenmorris]

Thanks for the insight. I understood it the way you explain it. Energy has to go somewhere, and if you're sending more than necessary, it usually isn't good. That heat can build up over time and cause problems.

My budget (provided a few clients pay me on time this week) will actually be about $1,000 to $1,500. I don't have a huge shop, (2 car garage turned into a wood shop), but should have room for a 48" x 48", maybe larger, but I don't think I need it for any of my projects.

My only concern is finding good plans and being able to follow them.

Originally Posted by ahren Most drives (like the Gecko G540) use PWM, or Pulse Width Modulation, to effectively control current. This is basically pulsing the coil voltage on and off at a very high rate. Since the motor coils are inductive, they can't change voltage at this rate, so this effectively looks like a reduced current. Pretty slick. In contrast, the stepperworld controllers appear to use power resistors to control current at higher voltages. This is remarkably wasteful, and sends a lot of the power into heat, rather than into your motors. Agreed with Ger -- I would keep looking, Gecko makes a great product, although it may be out of your budget. Probotix isn't bad either, and is a lower current but also a lower priced solution than Gecko. Ahren www.cncrouterparts.com

[ahren]

You might check out the plans offered from myself and Nate at Fine Line Automation (www.finelineautomation.com) -- they're free, and can be downloaded from either website. If you want a larger machine than the current 2' x 3', Nate has modified the plans and kit he sells for people in the past -- you can see various permutations in the build logs on my site.

Ahren
www.cncrouterparts.com

[ger21]

Also look at Joe's 4x4 hybrid plans. They're very popular, and apparent;y quite easy to build.
www.joescnc.com