Motor performance

[ToyMaker]

Lots of pcb mill folks are using 5V motors at 12V (or more). This is 2.4 times rated voltage. The rationale is that the higher voltage produces a more rapid dv/dt (voltage slew rate), which translates into more ipm at the cutting tool.

I plan on using 1.3V motors (because I have them) and driving them at 5V. This is a 3.8 multiple and so I expect to see better speed at the tool too.

Is anyone else using these low impedance motors?

What kind of performance (ipm for want of a better metric) are you seeing?

robotic regards,

Tom

[balsaman]

Hi Tom,

How much current do they draw? I would still run them at 12 volts if you can...

Sorry I can't answer your question tho...

Eric

[ger21]

You can run steppers at 20 times their rated voltage, and with such a low rating, you should run as high a voltage as you can. But, like Eric says, are they high current motors? If so, you'll probably need to use Gecko's which doesn't seem like the route you're taking.

Gerry

[ToyMaker]

The 1.3V motors are rated at 3.9A each. I have a switcher that puts out 5V @ 25A and intend to use that.

If I go to 12V I'll have to use one supply for each motor, but that's not a big deal - just get a bigger electric box to hold 'em
.

My mill is completely built (finally! ) and now I'm wrestling with the electrical/electronics.

robotic regards,

Tom

[ger21]

What are you going to use for drivers? Are they unipolar or bipolar motors?

Gerry

[ToyMaker]

The motors are universal 8 wire. I am going to drive them unipolar with a circuit from "Robot Builders Bonanza" 2nd ed.

And... while we're on that...

In all the motor drivers I've seen that use power xsistors the load (motor coil) is on the collector like this:

                       _______()_()_()_()__________ V
                      /        motor coil
                    |/
                 ---|   TIPxxx xsistor
                    |\
                      \_____
                            |
                            |
                            |
                          -----
                           ---
                            -

is there any reason not to put the load in the emitter circuit?

like:

                        ________________ V
                       /        
                     |/
                  ---|   TIPxxx xsistor
                     |\
                       \_____()_()_()_()___
                           motor coil     |
                                          |
                                        -----
                                         ---
                                          -

yes, there should be a flyback diode in there, and probably a current limiter resistor too, but I'm severely challenged in an ascii art sort of way .

robotic regards,

Tom

[Stepper3]

Tom,

You would not want to put the motor coil in the emitter leg. The basic reason is that it becomes more complicated to turn the transistor on. Since the transistor requires about 0.7 V above the emitter voltage, if you put the coil in the emitter, you require 0.7 Volts above the voltage at the top of the coil.

This is not a problem at steady state conditions, since the voltage at the top of the coil will have decayed, but, if you are switching quickly, you will have residual voltage at the top of the coil. Then you need a much higher base voltage to turn the transistor on.

Much better to keep the coil in the collector.

Steve

[bunalmis]

I use low voltage high current type step motors for high speed operations.

High voltage motor means high coil inductance. High coil inductance means slow current (soft changing current).

Therefore 5v 12v type motors can not produce high torque at high speed.

My control and drive electronics has PID curent loop and I use bipolar driver.

If you want to use low voltage motor (low inductance, high current)
your driver electronics must have good current control else motor current has big ripple and motor produce aquistic noise.)


Bulent UNALMIS

[pacosoide]

Certainly you will need a current limiting resistor if you are driving them with a unipolar driver and a single transistor as you showed.
Calculate the resistance of the coils, the voltage you are driving them and simple mathematics will tell you the value of the current limiting resistor. So 1.3 volts at 3.9 amps gives you a resistance of 0.33 ohms. At 12 volts you need a 3 ohms limiting resistor that can dissipate 12.5 watts minimum. I would make it a 15 watt resistor for safety. Joe.

[hardmill]

Glad to have you here.

PEACE

[Mr.Ed]

Interesting to see that others are struggling with this either.

I have electronics from www.nc-step.de and i couldn't understand why they sell like 3 or 4 volt steppers and allow a maximum of 44 volts to power the steppers. When i mailed them with a similar question they answered about the same.

I want to try to power mine with 24 volts and i use 3V 2A steppers. Should do the job...

Good luck Toy !

Ed.