Stepper Motor question

[biplanefan]

I'm in the planning stages of building a CNC hotwire machine to cut out Radio Controlled aircraft parts and I have a stepper motor question. I found some stepper motors for a good price and was wondering if they would work. Here's the info off the sticker on the back of the motors...

Astrosyn Miniangle Stepper
p/n HM000310000
AST TYPE 23LM-k055-01
NO. H1524
3.4 V/Phase
2.1 A/Phase
1.8 Deg/Step
Minebea Co., LTD

If these are not what I need, what should I be looking for?

Thank you

[Robin Hewitt]

I usually look for the diameter rather than the coil rating.

More diameter = more leverage on the rotor

[biplanefan]

What should I be looking for when shopping for stepper motors? I trying to buy the pieces as I go, I can't afford a complete setup like hobbyCNC sells at this time.

What is the difference between Bipolar and uniploar? What is the difference in the number of wires.

[Robin Hewitt]

The web is full of stuff on steppers, but if I had to pick out one thing to look for it would be a graph of torque against speed.

Max pull in rate is fairly imaterial once you hang heavy lead screws on it.

Detente/holding torque tells you little about dynamic performance.

Inductance/resistance and volts want to be low, but you will end up driving it way over the stated voltage anyway.

OTOH, a diagram showing which wire goes to which coil is very desireable

[cnccutter]

Steppers are easy, everthing else is hard. check out www.probotix.com they have a 4 axis system. Software is your next problem http://gm.cnc.free.fr/index_en.html ....seems to work the best....I just finish a cutter...trying to work out all the bugs.
Mark

[flyingwingnut]

I'll add to the question.

I'm also planning a CNC foam cutter for wings, mainly. What is the minimum holding torque I should be looking for, for a simple machine like the 8linx setup.

Is a nema 17 equivalent too small? Should I be shooting for a nema 23? Like most guys I'm all about a good deal. But I won't buy cheap or underpowered gear like the motors and controllers.

Also, it's hard to find a deal (i.e. ebay) on 4 steppers together. Usually they sell in 3's. So I'd like to know that the motor will work when I see it.

BTW, just bought 5 Vexta PX245 6v .8a 1.8deg steppers (nema17) for $18 shipped, so I won't complain if they're too small.

[Robin Hewitt]

Originally Posted by flyingwingnut Is a nema 17 equivalent too small?

Nothing is too small, but 1.7" is about as small as they get.

Your design may need to compensate for the lack of torque if you want any kind of speed, but is that a problem?

[flyingwingnut]

Originally Posted by Robin Hewitt Nothing is too small, but 1.7" is about as small as they get. Your design may need to compensate for the lack of torque if you want any kind of speed, but is that a problem?

No, not a problem. I'm not really worried about speed at this point. I'm cutting for myself. I'll build in the ability to swap out motors at a later time if necessary.

[BrianT]

Foam cutting works by the hot wire providing enough heat to melt away the foam. There is zero contact between the wire and the foam. Equally there is zero force to be overcome by the stepper motor if the feed is slow enough to 'premelt' the foam before the wire.

NEMA 17 should be plenty for a well controlled hot wire rig.

HTH
BrianT

[flyingwingnut]

Originally Posted by BrianT Foam cutting works by the hot wire providing enough heat to melt away the foam. There is zero contact between the wire and the foam. Equally there is zero force to be overcome by the stepper motor if the feed is slow enough to 'premelt' the foam before the wire. NEMA 17 should be plenty for a well controlled hot wire rig. HTH BrianT

It's interesting that HobbyCNC offers 84oz/in and 127oz/in packages. Are the high torque motors faster? Does more torque equal more speed in this case?

[Warpspeed]

If you want to get a good finish on your foam, run the wire only just hot enough to do the job, and go very slowly. As Brian T says, there is really no mechanical load on the motor at all if the wire is melting through the foam properly.

The motors you have should work fine for small model work, such as you are doing. There is simply no real need for vast speeds or very high power.

[kreutz]

Originally Posted by flyingwingnut It's interesting that HobbyCNC offers 84oz/in and 127oz/in packages. Are the high torque motors faster? Does more torque equal more speed in this case?

The torque vs rpm decay does not depend on motor initial torque, generally, higher torque motors have a curve that decays faster vs speed, the effect is more noticeable when you go up in size from Nema23 to Nema 34 (and so it is associated with torque because higher size generally correspond with higher torque for the same technology).

Factors that influence the curve are: Motor Voltage, wiring (unipolar, series, parallel), and mechanical /electrical constants (L/R) of the motor.