Let's try not to add to any confusion. The original post was Stepper versus Normal DC. Once this is answered we can move to Servo Motors. We need to go sloooow here. No harm done yet folks, just staying on top of things.
DC motor move in a continuous rotation. Stepper moves in steps caused by electric impulses. Simple as that???
"Billy G" :thumbsup:
I think the group may have moved on but I wrote this yesterday and did not wasn't to just throw it away ...
Ok, here is my take on it.
First, lets talk about how any electric motor works.
Lets start with just a very simple bare shaft inside a very simple empty housing. Add bearings on the end of the shafts as necessary so the shaft can easily spin.
Great prototype, except it doesn't do anything because it is just a shaft and a housing. We need to improve on this design. Setting the prototype aside for a moment go back to our childhood days and think about the fun we had with two magnets. We thought it was magic that if we had two magnets and tried to push the two 'N' of the magnets together they would repel one another and if put the 'N' and 'S' ends together it would take some force to pull them apart.
The interesting part was that the 'force' was invisible and therefore somewhat magic. If we used used a lever or a pry bar to push things apart it was not magic as we could see the lever or pry bar touching the two items and therefore it was obvious what was pushing them apart. The same way if we used a bolt and a nut to pull two things together ... it was obvious what was happening. But these magnets and this thing called magnetism ... able to push thing apart and pull thing together without the need for a physical connection between the two items. It was an invisible magic force with the only minor constraint being that both items had to be magnetic.
"the only minor constraint being that both items had to be magnetic" ... lets address that immediately. There are two common ways to "be magnetic". One is to be a magnet in the first place ... like the kind you were playing with as a kid. The other way would pass electricity thru a strand of any conductive material. Around this strand of conductive material will be a magnetic field ... i.e. be a magnet. Great, we now have a magnetic we can can control by simply turning the electricity on or off.
But our solution to the 'we need a magnet' has a minor problem. The magnetic field around a single conductive strand is relatively weak. It can be measured ... has been since the early 1800's ... but it is not strong enough be of much use. But again, we can resolve that issue by taking a long strand of our conducting material, covering it with an insulating material that does not conduct electricity then wind the strand up in to a coil. Note that we need to use an insulated conductive material to keep the conductive material in each wind of our from touching each other. If the conductive material of one winding touches the conductive material of another winding you have what is called a 'short' and very shortly will utter the words "where did that smoke come from".
Anyway, now that we have a coil we will notice that when we pass electricity thru the conductor the magnetic field is much stronger and something that we may be able to put to use. Of course we can improve on this basic design by winding the coil around a suitable material ... like an iron core ... and being very careful and creative about the exact winding of the core, but at least we have a basic understanding of what id going on.
So now, back to our prototype shaft and housing. What would happen if we put a magnet ... either the static kind we used as a kid or our second generation controllable "electromagnet" on the shaft and also put another magnet ... again static kind we used as a kid or our second generation controllable "electromagnet" on the housing. If we put the magnets on the shaft and the housing in the proper orientation we would see that the magnets would attract or repel each other and in the process turn the shaft.
Great, we now have a "magnetic" motor in that the shaft will turn ... with a minor issue to be resolved. The shaft turned part way and then stopped. Not exactly what we had planned but at least it is progress. What has happened is that our design has a magnetic field on the shaft and a magnetic field on the housing that are static ... they do not change. So the two magnetic fields did what they were designed to do ... either were attracted or repelled each other and caused the shaft to turn ... but the shaft quickly reached a point of equilibrium and stopped turning.
Think about it for a minute. Lets assume the magnet in the housing and the shaft repelled each other. The magnet on the shaft would start turning away from the magnet on the housing but as the shaft rotated it would eventually rotate far enough that the magnet on the shaft would start going back towards the magnet on the housing ... and that can not happen because the magnets are set up to repel one another. So the shaft would turn and stop at a point where it was "happy" because it had turned as far away from the housing magnet as it could but also was "happy" because the magnet was not moving towards the housing magnet.
Note that we can apply the exact same logic if the magnets attract each other, just the shaft would "be happy" in a different location ... probably 180 degrees from where it "was happy" if they repelled each other.
At least our shaft was happy even if we aren't happy with our motor. We have to resolve this minor issue.
It would seem that if we could exert come control on the magnetic field we might be able solve this problem. Given that we have no control over the magnetic field if we use the static "kids" magnets we will throw out that design. No control means no improvement so to the trash with that one. But we are still left with three alternatives ... controlled magnetic field on the housing and static magnets on the shaft; static magnetic field on the housing and controlled magnetic field on the shaft; controlled magnetic field on both the housing and the shaft.
Now that we have agreed we will used a controlled magnetic field, what will we do with it. The obvious 'control it' but how. We saw that the shaft turned until it reached an equilibrium point. What would happen if we then altered the magnetic field in such a way that this equilibrium point changed. Maybe we put in a second coil mounted in a different location and orientation in either the housing or the shaft. We then turn on the original configuration and as soon as the shaft reach its equilibrium we turn off the original configuration and turn on the second set of coils. The shaft would then try to seek a "happy" spot based on the new magnetic field.
Our first try at this was not quite what we hope. When we mounted the second set of magnets Murphy intervened and the location was such that when the second set of coils were engaged the "happy" spot for this configuration was "behind" the "happy" spot for the first configuration so our shaft would rotate part of a turn clockwise and then part of a turn counter clockwise as it sought out the "happy" spot with each change. The shaft did not go around, just oscillated back and forth between the two position. But at least it is progress in that the shaft no longer just sat there. It was doing something, just the wrong thing.
We noodle over this minor issue for a little while and decide that if Murphy does not intervene, and we put the magnetic coils in the correct locations, and possibly add more magnetic coils, and then make sure the the timing electricity to of each of the coils is right, we can come up with a scheme where we energize and de-energize the coils in such a way as to keep the "happy" spot just a little bit in front of where the shaft is at any moment in time and therefore the shaft continually turns in the "correct" direction seeking out ... or chasing if you will ... the happy spot that is always just out of reach.
Note that we have not talked about steppers, servos, AC or DC up to this point. Just "how do electric motors work" ... at least from my perspective.
Assuming I am not banned from the board for being too long winded, too basic, etc., I can move on from this starting point to AC, DC, steppers and servos as we talk about how we can orchestrate or synchronize the "happy spot just out of reach" that we think will solve our problems. Or you can PM me and tell me to go away ... or publicly tell me to go away. I've been married for 28 years so I am use to harsh criticism.
