hey everyone, so I'm designing a project that requires some precise movement via stepper motors. Before continuing i'd like to address some of priorities for the project:
In building the driver electronics i do NOT want to by an all-in-one chip. I'd like to learn as much as possible throughout the project, while keeping on a reasonable time line. For this reason I want to attack the stepper motor driver on a modular level. I thought about using lower level components even, but it would throw me way off my intended finish date. But segregating different function to different chips will make it fun to design my own software architecture and probe around with a scope.
I'd like to either microstep 1/8 or 1/16. That being said, I dont need to move extremely fast. More to come about my motor/load setup so far.
Constant chopper current driver. Because, well, efficiency, and microstepping ability.
I admit i haven't done as many calculations as i originally wanted to, but i'm willing to approach the motor on a test basis. I do know that my load will require be about 16-25 ozin of torque. Since microstepping will quickly bring down my torque to overcome load friction, i've chosen a bipolar stepper rated for 51ozin. I took into account my low speed and microstep size to get that hold torque rating. Might be a bit overkill, but if i do plan to microstep down to 1/8th it'll be on the money. I chose a .9 deg/step res, because in my application, the higher res the better. It's rated for 9A/phase
Disclaimer, The picture of my eagle schematic is a very rough draft, mainly a block diagram, chips will change, and values haven't really been put inn yet.
I want to put about 8 times the voltage that will get me .9A/phase through the chopper driver for good ramp times. This means about 45 volts.
The driver starts with a dual DAC that will get signals for an arduino. It will follow the sin/cosin drive patterns, and my lookup tables will be in the code for me to switch resolutions. Then that stage moves to a voltage comparator that compares the DAC value with the current sense value of my classic L298n dual full bridges. The diodes on the phases will be fast switching schottkys.
My questions for you guys:
Do you see any foreseeable issues with my attack strat. on the driver?
Will the L298n handle the the high switching times that microstepping requires? (I know it's dependent on my speed and resolution, but just to gain a note of feasibility.
Should i try to rig up some type of RAM to not bog down the arduino processor with outputting all the serial data to the DAC
I've read a bit about how inductor pushes the current after the switches shut down, and that's why we need the diodes. But that means the currents flows through the power supply. Do i need a capacitor somewhere? And what's a safe power supply to use.
I guess that's all for now. Let me know what you think! thanks!