Sorry for not getting back earlier but I was only able to reply quickly before because I was home sick. Reading through what you've written it sounds like the approach I was taking in my initial post is mostly correct and maybe I just didn't explain what I was doing very well. Initially I assumed that the supply voltage would be the voltage used to do the calculations which made sense that a 24v supply would allow faster speeds than a 12v at the same torque. I understand that the way the drivers work is that you set the desired current limit but I was working from the perspective of using a desired step rate and then figuring out what maximum current could be achieved within that time period and consequently the torque produced because I also assumed that current and torque were linearly related. For example with the motor we've been using I assumed that when a .5 amp current was flowing through the coil(s) it produced it's rated holding torque of 4.2kg-cm. Part of my reason for asking if I should de-rate the holding torque value by 20% was because I assumed the max torque produced when actually moving would be somewhat less than the holding torque value. De-rating also made sense because of the website I mentioned before that had a holding torque and 'rated torque' rating. For example if they had a motor with 20 n-cm 'rated torque' then it's holding torque was 25 n-cm.
After looking at the datasheet graphs more closely I see what you mean about the pulse from the micro-controller not relating to much of anything. All I can tell is that the only things that appear to correspond is the initial receiving of the pulse and the rise or fall of the current. Looking at the Smoothieboard there appears to be 2 lines between the controller and the driver; step and direction. The way I understand it is that the controller tells the driver how fast to step and which way to spin the motor. From there the driver has it's own internal tables to determine how to power the coils in order to achieve the instructions sent by the controller. What I'm still a bit confused on is if the driver only see's the on pulse from the controller as the point in time to turn the current on to whatever value it's tables says to, how does it decide when to start the decay if it doesn't know when the next step pulse will arrive and the driver doesn't derive any information from the step pulse other than to try and reach a certain current level and hold it until the next pulse signal?
Anyway I will have to look over your responses some more later, I just got home and still have some stuff to take care of. Thanks again :)
After looking at the datasheet graphs more closely I see what you mean about the pulse from the micro-controller not relating to much of anything. All I can tell is that the only things that appear to correspond is the initial receiving of the pulse and the rise or fall of the current. Looking at the Smoothieboard there appears to be 2 lines between the controller and the driver; step and direction. The way I understand it is that the controller tells the driver how fast to step and which way to spin the motor. From there the driver has it's own internal tables to determine how to power the coils in order to achieve the instructions sent by the controller. What I'm still a bit confused on is if the driver only see's the on pulse from the controller as the point in time to turn the current on to whatever value it's tables says to, how does it decide when to start the decay if it doesn't know when the next step pulse will arrive and the driver doesn't derive any information from the step pulse other than to try and reach a certain current level and hold it until the next pulse signal?
Anyway I will have to look over your responses some more later, I just got home and still have some stuff to take care of. Thanks again :)