I have encountered a similar problem recently, and I am trying to solve it.

Thanks for your useful advice. I think I'll try it

OK, so it seems that the shift registers were the problem again.

Thanks for satisfying my curiosity :)

Trying to figure out how to run 3 shift registers in series. I couldn't figure out how to send the bytes to separate shift registers. The sketch robot builder put together for me worked great for the first shift register, but I couldn't get it to go for the other two unless I wired them in parallels, which defeats the purpose of saving room on the Arduino. I bought the mega and can control the dc motors and the stepper motors with simple Arduino libraries, however I am struggling to write functions and use serial communications from the esp32 cam to call functions. Ill reply over on the project with my test code (that is not working) maybe someone can tell me where I am going wrong

I'm curious about why you gave up on the steppers via shift registers. I thought you had a working sketch that drove two steppers that way, what convinced you that six at a time wouldn't work ?

Good, nice to see you back :)

@will

Thanks I will do! I had a few life matters come up so I had to take a break, things are looking up again so I am back at it, I just ordered a Arduino Mega off amazon, should make life a lot easier, and it was only $20 Cad so I figured why not. Im sure there has to be a way to do this with shift registers, I look at it like its just like lighting up led's in a sequence and being able to call up that sequence and run it in reverse if necessary. I dont have the knowledge in coding to be able to figure it out, so Im just going to use this easier approach with the Mega, It should be here by Saturday, so Ill let you know how it goes. 

Have you abandoned this project or just decided to leave it alone for a while ?

Do keep us up to date if you continue developing a robotic arm.  I have just ordered two more stepper motors for another project which will need the stepper motors to move independently but also simultaneously.  Although I will not be using shift registers it should be easy replace any direct pin output solution to a shift output.

Feeling a bit burnt out on this project so I will have to give it a rest.

Found this that uses the same stepper motors and controllers.
https://www.thinker-talk.com/post/how-to-control-multiple-bipolar-stepper-motors-in-parallel-using-an-arduino-nano
It suggests if you need even more pins you can try using a shift register chip (e.g. the 595).
You can find the source code at GitHub here: https://github.com/nenovmy/arduino

Another example
https://www.thinker-talk.com/post/how-to-extend-the-number-of-digital-pins-of-an-arduino-or-nodemcu-using-shift-registers
https://github.com/nenovmy/arduino/tree/master/control_stepper_motors_with_shift_registers