Adafruit Stepper any good?

I need a stepper for my project. Im thinking about using this one from Adafruit. Im really quiet new to arduino and would like to know how strong it is. Yes I know it says how strong it is in the description, but for me its just a number that doesn’t tell me anything. Could you make an example what you could drive with it?

2Kg*cm means that if there was a winding drum of 1cm radius with a string wrapped round it it could hold a weight of 2 Kg.

If the drum had a radius of 2cm it could only hold 1 Kg.

You will need to carry out some calculations or experiments to see if that is enough for your application.

If you are new to stepper motors the Thread stepper motor basics may be useful.

...R

Keep in mind that the torque figure provided is the BEST that the motor can do when it is driven under IDEAL conditions. Considering that a hobby setup is unlikely to be tuned to ideal conditions, it best to be conservative and reduce that number, perhaps in half. Also, that's the holding torque: as the motor starts turning, the torque will go down. More speed = less torque.

This motor should work for lightweight, well constructed easy moving machines. But don't expect it to move heavy weights, overcome a lot of binding or friction, or move at high speeds.

And definitely read Robin's excellent stepper motor basics thread! 8)

Im thinking about using it for something like this. Do you think it would work?

I think so, as long as you use a good stepper motor drive (not just a simple H bridge giving 5 V to the motor) and as long as you build the structure so it moves smoothly without binding up (you should be able to move it easily with one finger.) If the construction is sloppy, it won't have a lot of power to overcome a bunch of binding or friction.

If it were me, I'd try it. Worst that can happen is you need to replace it with a bigger motor and you use these in the next project. But I'm just a software guy who programmed machines using steppers, I didn't design the mechanism or electronics. I'm sure Robin will be by with a much better informed opinion. (Listen to him rather than me if he disagrees with me!)

Thanks!

first off, I HIGHLY recommend you follow Robin2's excellent advise to MEASURE your power need. easy to do with a shaft, a string and a cup that you can fill with water. (Robin, please add that to your intro on steppers) Figure out what your APPLICATION requires. as for a motor, it would be smart to select one that is between what you think and double that. there are often hidden mechanical things that consume power.

as for the motor, it's really a horrible motor. the rating of voltage is derived from the number of wraps of the coils and then the rated amps. when selecting a stepper it is better to use a motor with the lowest rated voltage.

if you were to use an H-Bridge, you would need to use 12 volts and it would work fine for the application.

I will use the word application a lot as that is the key to any engineering.

the application is a non load, no resistance application. the motor only has to get out of it's own way.

what shapshifer was alluding to without confusing you with the formulas is that in order to drive the motor as hard as possible to eak out the absolute maximum performance ( you know, like one does with a car by smashing the gas pedal all the time to get the mail or milk and such) that formula is;

32 x sqrt() inductor = max voltage.

one thing you will find on these posts is that most people (ignore applications and ) feel it is paramount to drive the motor at it's maximum rated power supply voltage to get the maximum power out of it at all times., without giving the logic or calculations for the selection. What I find ironic is that you will get that exact same advise if the motor is 1/10 the correct size or 10 times the correct size for the application. 'maximum power is required at all times' I say phooey.

but to follow the logic that you are required to use the maximum power possible, you would need to determine the correct power supply voltage. I'll go with the overwhelming consensus on "you have to use maximum voltage and applications are irrelevant"

the data sheet lists 4.3 as the inductance.

we can then re-write the formula as 32 x sqrt(4.3) or refine it to 32 x 2.7 = 66.35 volts DC

using logic, and your own intelligence, you would grasp that trying to use only 12 volts on a motor that can MUST be run at 66 volts would be using only a fifth of the power.

there is another problem here and that is that a stepper is really a coil which is an inductor. when you charge the inductor, it will consume the power. when the motor is spinning, that power you feed it turns into motion and some of that power is transferred into energy of rotation.

further, at slow speeds, the inductior is a current load. plain and simple, any driver you feed it with will only be delivering current. once the motor spins fast enough, some of the energy is transferred and the stepper motor starts to become a voltage load. the difference is called corner speed. below the motor natural corner speed, any driver you use will only be delivering current to the rated maximum of the motor. the higher the voltage you feed the motor, the higher the corner speed is. That is one of the reasons an H-Bridge will work fine in this application.

if you were to listen to shapeshifter, the H-bridge would be a bad choice. however, any driver you use with 12 volts, (the motor nameplate voltage) will be doing pretty much the same thing. delivering current. in fact, the H-bridge, at 12 volts would be an excellent choice for this application.

reading Robins's fine article, he skips over the voltage as detailed above as it can be confusing to a newbie, and then offers that a microstepper is a proper driver. in your case, you have not worked out the speed, nor the power. what is also skipped over is that to use a microstepper for your application with that motor, at 12 volts is just bad engineering. to use a fancy chip on a bad motor and then feed it minimal power, is bad engineering.

suffice it to say that your project would work fine with an H-bridge at 12 volts. and it would work fine with a microstepper at 12 volts because you do not need much power.

Also the microstepper would be easier to buy pre-made, and once you are done with the project, you can use it for other things. I am VERY fond of microsteppers and agree with Robin2 that if you can use one, you should.

if you want to battery power the project, then you must get a much more efficient motor, this one is very inefficient. pololu offers better motors.

the motor you are looking at is designed for an H-bridge driver. I say this because clearly the proper voltage for a chopper driver would be 66 volts, and over 90% of the hobby chopper drivers have a maximum voltage of around 35 volts, putting this motor out of range of a chopper driver. further, since power is proportional to voltage, you can only use half the power of this motor with a hobby chopper, so, for the same money, you can get a lower voltage motor and get twice the performance if you follow engineering principals and common products.

also, 12 volts is a hobby voltage. an H-bridge would be used at the motor nameplate voltage, putting this motor out of the reach of a chopper driver and squarely into the realm of an H-bridge.

the amp/volts of a stepper nameplate are what you can feed it in a steady state. in other words, using a chopper driver to drive it at the nameplate voltage is almost silly. Almost silly because it takes time to charge the coils. at nameplate voltage, you can calculate the time, then multiply that by 200 steps to determine the maximum RPM you can get at full power in your application, you probably do not need full motor power so you are not required to charge the coils to maximum in order to get it to spin. so, your project is blessed with two safety valves. slow speed and low mechanical resistance. (again application trumps group consensus)

What saves you is that your application can suffer mismatched drivers, poor motor selection and haphazardly selected power supply voltages and since it is a non-contact application, it will still work.

just to toss in a bit more, if you do want to use a battery to power the project. find the lowest power robbing driver you can. each will offer what voltage drop it will consume. then get a motor and driver that will fit the power from your batteries, and shut the thing off when not moving. not just put it in idle where it will consume power, but shut the power off to the driver. the only power you should be using is power needed to move the motor. if you find that an h-bridge will work, then do not put in diodes to short the back EMF to ground. put in a cap on the power supply to absorb the voltage. get one rated for 4 times the voltage to allow for the spike. the formula for the cap is :

(80,000 * I) / V = C

if you chose a Polulu 2267 (Stepper Motor: Bipolar, 200 Steps/Rev, 42×38mm, 2.8V, 1.7 A/Phase)

and you make an H-bridge using FET's and you want to feed it with 5 battery power volts, then the capacitor would be (80,000*1.7) / 20 = 8,600uF, which is a HUGE cap. you can use multiple smaller ones. the cap will store the spike and then deliver it on the next step. this will save some of the battery life.

the knee-jerk reaction is to always put in a diode to protect the circuit from back EMF, however, application trumps again. the motor will be running at slow speed and will not coast with the loss of power. the back voltage spike will not be more than 4 times the power supply voltage, so you can engineer the application to take advantage of the tiny bit of back emf without damaging your power supply.

I would offer that Poloulu has notes on the A4988 chip recommending a 47uF cap on a motor to help reduce the spike. this is a good idea for any stepper driver. they allude to back emf "under the right conditions" those being high speed (which you do not have) and a heavy load (which you do not have) that forces the motor to become a generator under a fast deceleration (which is not your application)

much of what I have mentioned above can be found in a white paper from Geckodrives.com they are probably the foremost stepper supplier for machine tool stepper drivers. the owner/chief engineer has been designing stepper drivers for over 20 years. http://www.geckodrive.com/gecko/images/cms_files/Step%20Motor%20Basics%20Guide.pdf

I am VERY fond of microsteppers and agree with Robin2 that if you can use one, you should.

Robin2,

I hope I am not putting words in your mouth, it was not my intention. Just wanted to say that microstepper drivers that are available today in the hobby arena are a blessing to those who want to just buy a board and use it. there are huge benefits beyond the microstepping.

for this project, I think half step would be all that is needed and much more would be a waste of time to make the steps.

what I did not mention was that on an h-bridge, the control requires 4 pins. 2 pins for each h-bridge.

the A4988 which is a great microstepper, only requires 2 pins. a step and a direction. this makes it easier to program and easier to implement.

separating the logic side from the power needed to move the motor, and looking at using the available parts, the microstepper is much easier to implement.

I feel that this application can be powered with any driver. to use a microstepper, one would need to increase the voltage and pick a motor that was in-line with the driver and power supply.

I knew someone would be by with a better response! 8) Listen to him.

dave-in-nj: what shapshifer was alluding to without confusing you with the formulas

Precisely, I was trying to keep it simple. No need to overwhelm a person for a relatively simple application. ;)

That's the main reason I suggested the driver rather than the H bridge: simpler control. With the H bridge you have to be careful how you control the enables, so that you have enough dead time to prevent shoot-through, but not so much that it affects performance. With a simple driver, you just have step and direction: much easier and safer, even if it's not an optimal solution. (Many hobbyists are not able to make a highly optimized system, and aren't really interested in an optimum solution: they just want to get things to work. They are hobbyists, not engineers.)

Engineers strive to find the elegant, simple, and optimum solution. Not so much with hobbies to. Dave, you sir, are obviously thinking like an engineer, and there's nothing wrong with that! But in the end, for this application, maybe it's not necessary to analyze it that much? (But it's still a great post, I enjoyed reading it, and learned a thing or two in the past.

My last stepper project had some home-brew drivers where I would output a set of enables and a DAC reference voltage for each coil. These went to an FPGA and comparators to control the coil currents. I didn't design the hardware, just wrote the code. I needed to output the right voltages to do 256 microsteps plus handle acceleration and deceleration profiles. It was a real PITA, I dreamt of having a higher level controller to talk to. That was more than a couple years ago, and I guess I still have that memory in the back of mind. I'm just trying to keep it simple for this project.

32 x sqrt() inductor = max voltage.

I only came across this for the first time quite recently. My understanding is that it represents the maximum voltage for the motor rather than the desired voltage. From what I recall of datasheets that have graphs of torque and speed they do not use really high voltages like that.

I have these motors with an inductance of 48mH and that formula gives a voltage of 221v - which may exceed the winding insulation limit. They seem to work well at 20v with an A4988 driver.

I will think about your idea of adding a piece about the string and cup - though I used dry pennies as weights rather than wet water.

...R

Robin2: I will think about your idea of adding a piece about the string and cup - though I used dry pennies as weights rather than wet water.

...R

I think pennies are much better. you can get an approximate weigh by counting them. with water, you have to have a way to measure the weight. not everyone has a suitable scale. either way is valid, depending on what the person has to hand. admittedly, this part is not rocket science ! and even worn pennies are better than a blind guess.

ShapeShifter: I knew someone would be by with a better response! 8) Listen to him. Precisely, I was trying to keep it simple. No need to overwhelm a person for a relatively simple application. ;)

That's the main reason I suggested the driver rather than the H bridge: simpler control. With the H bridge you have to be careful how you control the enables, so that you have enough dead time to prevent shoot-through, but not so much that it affects performance. With a simple driver, you just have step and direction: much easier and safer, even if it's not an optimal solution. (Many hobbyists are not able to make a highly optimized system, and aren't really interested in an optimum solution: they just want to get things to work. They are hobbyists, not engineers.)

Engineers strive to find the elegant, simple, and optimum solution. Not so much with hobbies to. Dave, you sir, are obviously thinking like an engineer, and there's nothing wrong with that! But in the end, for this application, maybe it's not necessary to analyze it that much? (But it's still a great post, I enjoyed reading it, and learned a thing or two in the past.

My last stepper project had some home-brew drivers where I would output a set of enables and a DAC reference voltage for each coil. These went to an FPGA and comparators to control the coil currents. I didn't design the hardware, just wrote the code. I needed to output the right voltages to do 256 microsteps plus handle acceleration and deceleration profiles. It was a real PITA, I dreamt of having a higher level controller to talk to. That was more than a couple years ago, and I guess I still have that memory in the back of mind. I'm just trying to keep it simple for this project.

Robin2 has does a great job getting this discussion started and I am hoping to fill in some of the blanks. the goal that I think being sought is a SIMPLE way for a newbie to get enough familiarity with steppers to make an educated decision. I can say with a high degree if certainty, that the number of formulas to truly understand these things will take a lot of study. I think this field breaks down with application. slow speed, low power. and then higher speed and higher power. the speed of a coil becoming energized 98% takes long time, voltage reduces that. at the cost of a higher voltage power supply and motor heat. but if you do not need speed, then your options are more open. if battery power is desired, then the lower voltage and h-bridge might be the simpler and more appropriate solution. assume the motor has a 1 inch circumference wheel driving a belt. then one rotation (200 steps) is 1 inch. a chess board is often a foot across. so, if one can deliver 200 steps a second, that would take 12 seconds to traverse the entire board. if one can deliver 2,000 steps a second, then 1.2 seconds to traverse the whole board. a slow move of a chess piece at 2 seconds to traverse the whole board may be acceptable. a note that it is really hard to talk about this without doing the math

Dave, as always, you make good points.

And then you say this: :smiling_imp:

dave-in-nj: and even worn pennies are better than a blind guess.

I don't think you lose that much weight from a worn penny. After all you're not really looking for an extremely precise value. When you get your weight, what are you going to do with it? Round it up and add some headroom, right? With that in mind, does the difference between 12.7 and 12.74 in-ozs really make that much difference?

The bigger question is where will our European, Asian, Australian, etc. brethren get a stack of pennies? ;)