Stepper Motors and resolution
Hello, I am back
I am going to offer my opinions on stepper motors and resolution.
My friends often ask me "What resolution do you get with your 3d Printer?". I know what they ask, but I do not know how to answer them, the question is two pronged.
Using the ruler, we measure the block, since the measurement precision of the ruler is limited to whole mm, we HAVE TO ROUND to comply with the precision of the ruler. In this case the answer is either 49 or 50, depending on your opinion of the location of the lines.
I would be inclined to use 50 here, but again, that is somewhat my opinion.
Taking the same block and measuring it with a Caliper, we get a more precise answer....
Looks like 49.74mm. Not a bad result from an item printed on a $250 Sainsmart A8 with pretty variable PLA filament (that is another rant... for later) (no comments on how I am using the calipers please - the image is for illustration purposes only and not indicative of correct use. You never measure on the flats, only the bevel section)
Now we can see that both tools gave us roughly the same answer, witch leads me to believe the are both accurate - though one is obviously much more precise.
So where does that leave us on precision?
Well, the STL file, and the slicer are very precise and accurate - they will run out to multiple decimal points for every position call.
Where it gets interesting is when we look at the stepper motor and gearing setup. The type of stepper motor you use, how the drives work, and the gearing all conspire together to drive precision.
A standard setup with say a 2mm belt, a 20 tooth gear and a 400 step per revolution motor will yield you a resolution of 50 micron (0.050mm). See the Prusa Calculator. Obviously, we can change the gearing and microstep the drive to get much finer, however, it does illustrate a point. The answer to that overwhelming question , "What is the resolution?" in this case is 50 micron (0.050mm).
Lets be honest, for most all of us, this is pretty stinking good and we should not complain. And I am not complaining.
I have an opportunity, however, to use some very amazing drives and motors that I have acquired over the years:
These are Oriental Motors Vexta drives with a 5-phase stepper motor. The pair can drive step rates down to 0.00288degrees per step (125,000 steps per revolution). CRAZY! I am not going to use that insane of a step rate, because I am worried clock rates on the board will limit my speeds.
I will, however, set my step rates to achieve about 5 microns of resolution. (0.005mm).
Stay tuned! More to come!
I am going to offer my opinions on stepper motors and resolution.
My friends often ask me "What resolution do you get with your 3d Printer?". I know what they ask, but I do not know how to answer them, the question is two pronged.
- Are they asking about precision, resolution or accuracy? Though at first glance they seem similar, they are actually two separate topics.
- Precision is, essentially, the number of decimal points behind a number.
- for example, 10.0000000 is much more precise than 10 - and in an engineering sense they are treated quite differently.
- Resolution is the lowest number that an instrument can discern.
- So for example, a millimeter scale ruler will typically have mm gradients - so it's resolution will be 1 mm. A caliper, however, will have typically sub-millimeter resolution and enable a reading down to 0.01mm (that is 10 micron).
- Accuracy is how close to the TRUTH a number or measurement is. This is why we calibrate - which is another rant all on it's own. For the sake of this discussion , we will assume accuracy.
Using the ruler, we measure the block, since the measurement precision of the ruler is limited to whole mm, we HAVE TO ROUND to comply with the precision of the ruler. In this case the answer is either 49 or 50, depending on your opinion of the location of the lines.
I would be inclined to use 50 here, but again, that is somewhat my opinion.
Taking the same block and measuring it with a Caliper, we get a more precise answer....
Looks like 49.74mm. Not a bad result from an item printed on a $250 Sainsmart A8 with pretty variable PLA filament (that is another rant... for later) (no comments on how I am using the calipers please - the image is for illustration purposes only and not indicative of correct use. You never measure on the flats, only the bevel section)
Now we can see that both tools gave us roughly the same answer, witch leads me to believe the are both accurate - though one is obviously much more precise.
So where does that leave us on precision?
Well, the STL file, and the slicer are very precise and accurate - they will run out to multiple decimal points for every position call.
Where it gets interesting is when we look at the stepper motor and gearing setup. The type of stepper motor you use, how the drives work, and the gearing all conspire together to drive precision.
A standard setup with say a 2mm belt, a 20 tooth gear and a 400 step per revolution motor will yield you a resolution of 50 micron (0.050mm). See the Prusa Calculator. Obviously, we can change the gearing and microstep the drive to get much finer, however, it does illustrate a point. The answer to that overwhelming question , "What is the resolution?" in this case is 50 micron (0.050mm).
Lets be honest, for most all of us, this is pretty stinking good and we should not complain. And I am not complaining.
I have an opportunity, however, to use some very amazing drives and motors that I have acquired over the years:
I will, however, set my step rates to achieve about 5 microns of resolution. (0.005mm).
Stay tuned! More to come!
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