Practical power of stepper motors?

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Yafimski
 
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Practical power of stepper motors?

Post by Yafimski »

From my ignorance in basic physics and electronics, I was able to gather that to move something small with a stepper motor, let's say drag a 200g object across a table, I would need no more than 1 Newton force.

How can I understand which size/strength stepper motor gives me that capability? I'm a bit lost.
The solution i'm looking for is the SMALLEST motor, for reasons of both space and especially price.

What I also need is to find a stepper motor that can do this, but be switchable between directions, meaning I can make it turn clockwise or counterclockwise through a code programmed into its behavior.
I think this is a "bi-polar" stepper motor, but maybe a uni-polar motor can do this as well?


Thanks again and sorry for the lack of understanding in these matters, often without previous knowledge it's difficult to understand all the electronics and physics.

Cheers!

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adafruit_support_bill
 
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Re: Practical power of stepper motors?

Post by adafruit_support_bill »

This is a good guide to start with: https://learn.adafruit.com/all-about-stepper-motors

Unipolar and biolar refers to how the coils are wired. Either type can step in both directions.
Most stepper motors have a torque rating. For smaller motors, this is usually expressed in Newton Centimeters (N-cm) That is the amount of force produced at 1 centimeter from the axis of the shaft. For example, a motor capable of 1 N-cm and equipped with a pulley with a radius of 1 cm can pull with a force of 1 Newton.

The other question you need to ask yourself is, how fast do you need to move that object? A very tiny motor can exert a lot of force if suitably geared down for mechanical advantage. The tradeoff is speed.

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Re: Practical power of stepper motors?

Post by Yafimski »

Hi,
Thanks for the reply!
I read that link you posted already before posting this issue, but now that you say that every motor is capable of turning both ways, then what exactly is bi-polar or unipolar better for? what is the practical difference when to use each one? do you have an example?

Also, there is a 4-wire, 6-wire, 8-wire... what advantage does 8 wires give me over 4? is it about speed? it's quite hard to understand from the limited paragraphs in that introduction...

About the force - basically I understand that the lower the step count, the more force I get, so what I should be aiming at is a low-step-count motor with enough initial power to move a 200g object across a table... is this right? Do you have an actual motor to recommend in this case?

For example I found a NIMA 17 motor on ebay, that has "Holding torque : 2.8 kg.cm", so how much weight can this motor support theoretically if I put that weight at a 1cm distance? 2.8kg? or is it some other conversion from kg-force to newtons and then back to kg... Point is i'm trying to find the cheapest motor for my project, I don't want to pay 15$ for a motor when a 5$ one could do the same job...

Thanks again very much.

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Re: Practical power of stepper motors?

Post by adafruit_support_bill »

what exactly is bi-polar or unipolar better for?
Unipolar can be powered with a simpler drive system. Bipolar can have more torque for the same size motor.
Also, there is a 4-wire, 6-wire, 8-wire... what advantage does 8 wires give me over 4?
6 or 8 wire motors can be configured for either unipolar or bipolar operation.
If you follow the links on the resources page, there are countless types of stepper motors and tons of information about them on the web.
About the force - basically I understand that the lower the step count, the more force I get
Step count alone has little to do with torque. Although torque decreases with increased step rate, high step count motors can have very good torque at low speeds. Holding torque simply means how much resistance it can provide when standing still. Torque will decrease as speed increases due to the inductance of the windings. You also need torque for acceleration and to overcome the friction and inertia in the system. There are many online resources for calculating such things.

As noted in my previous response. In order to select an appropriate motor, you need to specify how fast you expect to be able to drag this object. You don't necessarily need to go through all the math to calculate the optimal motor for the job. But you at least need to know if a motor is at least adequate to the task.

These motors are low-cost and compact. They have 15 N-mm of holding torque at 5v. I suspect they are capable of moving your 200G object. But they are pretty slow.

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zener
 
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Re: Practical power of stepper motors?

Post by zener »

Do you have to use a stepper motor? For the application stated a DC gear motor might be suitable. Depends on whether the system needs to know the exact location or not.

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Re: Practical power of stepper motors?

Post by Yafimski »

Thanks a lot bill! Much appreciated.

zener, i want also to involve sensors for position and to move the object back and forth, but im going to move it a certain fixed amount, so i dont know but i think a stepper motor is right for the job… ? Can a dc motor like you mentioned turn both ways and be programmable?

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Re: Practical power of stepper motors?

Post by Yafimski »

Okay I'm changing this reply after some search :)

I understand that the Arduino Uno R3 is the cheapest board for programming motors, is this correct? It costs here about 25$, question is - are there any cheaper ways to get the same result?

About DC motors vs. Stepper motors - I understand from an Arduino, I can control either 2 steppers or 4 DCs.. is this right?
Is there any way to control more motors than 4 from a single Arduino board? maybe not Arduino but something else?

About actually moving objects - a while back I looked into DIY 3D printers such as the Prusa Mendel etc. They were using a "T5 pitch timing belt" for the NIMA 17 motors. Do you know of any belts that work with smaller stepper motors or with DC motors? What are they called because it's hard to find online the correct names...
Also, to "put on" this belt on the motor, I guess if it's a T5 pitch timing belt, I also need a "gear wheel" of some sort to be placed on the turning shaft of the stepper motor... what is this wheel called? I haven't seen it being included in the motors when they sell them...


Thanks a lot and I hope you guys can clarify some of these points.
Much appreciated so far.

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Re: Practical power of stepper motors?

Post by adafruit_support_bill »

I understand that the Arduino Uno R3 is the cheapest board for programming motors, is this correct? It costs here about 25$, question is - are there any cheaper ways to get the same result?
The Uno or Leonardo are your best options.
About DC motors vs. Stepper motors - I understand from an Arduino, I can control either 2 steppers or 4 DCs.. is this right?
One V2 motor shield can control 2 stepper or 4 DC motors. However, you can stack up to 32 V2 motor shields for control of up to 128 DC motors or 64 steppers. (Note that with 64 steppers, the I2c bus will be a significant bottleneck limiting the aggregate step rate)
They were using a "T5 pitch timing belt" for the NIMA 17 motors. Do you know of any belts that work with smaller stepper motors or with DC motors? What are they called because it's hard to find online the correct names...
NEMA classifications only tell you the size and location of the mounting bolts on the faceplate. For power transmission components, you are more concerned with the shaft size. Timing belt pulleys are available for a variety of shaft sizes. We carry a small selection that fit all of our 5mm shaft motors. You can find a wider selection at suppliers such as McMaster-Carr.
https://www.adafruit.com/search?q=timing%20belt

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Yafimski
 
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Re: Practical power of stepper motors?

Post by Yafimski »

Hi Bill,

Thanks for the reply. I will search for the correct belts.

About the amount of motors, due to my lack of knowledge of the interface between the driver and the arduino board - I understand that I can stack drivers (motor shields), but can all those 32 V2s be connected to a single Leonardo or Uno? That was a bit unclear to me...


Thanks.

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Yafimski
 
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Re: Practical power of stepper motors?

Post by Yafimski »

I would also like to add:

On this site, as well as on ebay, the bores for the shafts come only in 5mm and 8mm diameters.
Looking at the small DC motor on this site, it has a 2mm diameter.

https://www.adafruit.com/products/711

So this means that a timing belt on that particular motor isn't available, and I have to get a bigger motor just to have a transmission component?
Have you come across smaller than 5mm shafts?

Thanks again.

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Re: Practical power of stepper motors?

Post by adafruit_support_bill »

You can find 2mmx5mm shaft couplers. But that motor is not a good candidate for driving a timing belt directly. It has a very high RPM and a vary low torque. If you want to use a DC motor you should be looking at DC gear-motors. http://www.pololu.com/category/22/motors-and-gearboxes

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Yafimski
 
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Re: Practical power of stepper motors?

Post by Yafimski »

Hi Bill,

Thanks.
I looked around that site quite a bit now, it seems they have good products.
I am trying to figure out of those "mini plastic gearmotors" are able to be programmable and turn bi-directional, although i'm pretty sure it's the same process as with stepper motors (doing an H-bridge).

I guess i'll just trial these things to see how it actually performs.


Thanks for all the help so far, i'll write more here if I have questions in the future.

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Re: Practical power of stepper motors?

Post by adafruit_support_bill »

Those motors are capable of speed control and reversal via an H-bridge. Although, speed control with the plastic motors tends to be a little erratic a slower speeds.

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Re: Practical power of stepper motors?

Post by Yafimski »

I basically need the object to get from point A to B so at least at this stage the smoothness of the speed won't matter much.

Thanks again :)

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