Hi all

Trying to make some sense of this

Objective : maximize torque and rpm and validate my (mis)conceptions

Application is non reprap

Motor :wantai nema 23, type 57byg621 torque curve attached

[www.wantmotor.com]

Max torque, 12.5 kg cm at 24 V, half step

Halfstep gives 40% more torque than full step, but some say 4988 enegizes both coils at full step too, but can't find it in the spec sheets-confirmation would be great

Typical power supply is 12V so torque=50%?

If a gearbox is used, for torque multplication, this often needs an increase in rps, to keep speed, this increases pps, torque is reduced -high pps drops torque ?-see attached torque curve(also efficiency of gearbox costs up to 50%)

Possible solution:increase volts to max 25 times (according to Gecko) the rated voltage, say max 45/48 volt? (using DRV driver instead of pololu) Driver amps set to motor amps in spec sheet . Motor will run hot. This doubles torque?? (Almost) but assume that BEMF becomes an issue-considering to use L6470 driver for compensation

If microstepping is used, torque as total remains the same, just divided per microstep?

But microstepping increases pps, so lower torque again-as per curve?

Appreciate your help in this

Coolerooney

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so if say my sanyo denkis ...

9VDC, 0.85A, 59oz/in ...

theoretically energized @ 2coils x0.7 factor of the rated power in a A4988, it should get the 59oz/in holding power? is that the way to put it?]]>

An allegro puts both coils on at 70%, even in full step mode, so to to get the rated torque you set VREF so that the current is 1A when two coils are on, i.e. 1.4A when a single coil is on. Power dissipation is constant all the way round as well, so the motor have the temperature rise stated on the data sheet for two coils on.

When people say microstepping reduces the torque they are just not comparing like with like.]]>

> With these drivers you get exactly the same torque

> with full step or micro step, and in any position.

Perhaps I'm not being clear. The majority of stepper motors are spec'd with torque measured when both coils have Imax flowing through them (a vector sum of Imax * 1.414). Meanwhile, microstepping drivers use a vector sum Imax in all positions. This should mean that microstep torque is 0.707 * rated torque. Does that sound right?]]>

> Thanks for sharing, Annirak. What does that

> frequency relate to? Step rate of full steps? Half

> steps? Microsteps?

It refers to the full-step rate, regardless of micro stepping level. E.g. if you're using 1/16 drivers then multiply that frequency by 16 for the micro step rate.

@Nophead, that's what I meant. Is my K value correct? Or do you get .707 times the full-step torque when micro stepping?]]>

Quote

Microstepping drivers have a maximum torque with one winding energized at maximum current, while stepper motors are rated with both coils energized at maximum current.

Microstepping drivers have a maximum torque with one winding energized at maximum current, while stepper motors are rated with both coils energized at maximum current.

Microstepping drives have constant torque in each position because the vector sum of the currents lies on a circle.]]>

The adjusted value for K is:

K = (Holding torque in N-m / (2 * max coil current)) * (2 * pi radians/ 200 steps) = 0.0329867 volt seconds/step

With that change, the picture is not so bleak.

+---------------+------------------+------------------+------------+ | Drive Voltage | Full Torque Freq | Half-Torque Freq | Stall Freq | +---------------+------------------+------------------+------------+ | 12V | 370Hz | 546Hz | 727Hz | +---------------+------------------+------------------+------------+ | 19V | 776Hz | 956Hz | 1151Hz | +---------------+------------------+------------------+------------+ | 24V | 1055Hz | 1245Hz | 1455Hz | +---------------+------------------+------------------+------------+ | 30V | 1381Hz | 1587Hz | 1818Hz | +---------------+------------------+------------------+------------+]]>

On a 2cm pulley, 152Hz is 47mm/s, 384Hz is 120mm/s and 497Hz is 156mm/s.

To find the step rate, I solved the following equation for t, which is the full-step time:

I = (V-K/t)/R * (1-exp(-t*R/L))

where I is the maximum coil current

V is the driver voltage

R is the winding resistance

L is the winding inductance

K is the step-wise torque constant

K is derived from the holding torque and coil current:

K = (Holding torque in N-m / coil current) * (2 * pi radians/ 200 steps) = 0.0329867 volt seconds/step]]>

The other values are OK ...]]>

which says it supports up to 2 amps and up to 35 volts max (with additional cooling). Its typical to use NEMA 17 motors with these drivers but I would like to run one axis of a 3d printer using a NEMA 23 motor so I can get higher torque. The problem is that I don't know enough about steppers to know what is good and what is bad. I need it to run fairly cool as they are mounted using ABS brackets.

Here are the stepper options I'm looking at [store.kysanelectronics.com]

What factors are important to consider? I'm really interested in the 57BYGH301

2 phase

5.88 volts

1.4 amps

4.2(O) resistance

15mH Inductance Phase

15 Kg./cm Holding Torque

That seems like a good option, but all of this almost seems to simple, that is nearly 3 times the torque of my current NEMA 17 steppers. Am I overlooking something?

Please let me know

Thanks,

Clay]]>