Control 4x Nema 23, 24v 3A steppers

Hi, Im building a large aluminium saw cut line, at the moment im planning on using 4x linear rails driven by nema 23 motors. (24v 3A)

Nema 23 - Linear rail

And 4x TB6560 3A motor drivers.

TB6560 Motor driver

This is my first time controlling multiple steppers and I wonder if there's anyone with experience of Nema 23's and TB6560s?

The workflow is like this:

Init:

  • All steppers will reverse until they hit their limit switches and find their home position. One at the time.

Program:

  • An aluminium profile will be locked sideways with an aircylider mounted on rail 1, (24v relay + air solenoid)
  • Rail 1 goes 300mm forward to its position
  • Rail 2 is mounted vertically with a drill, - drills a hole into the profile
  • Rail 1 moves 200 mm forward
  • 3x air cylenders will go down from the top and lock the profile on three places while cutting
  • Rail 3 holds / directs a cutting saw motor and moving it forward, then backward.
  • Rail 4 holds another cutting saw motor and moving it forward, then backward (two angle cut)
  • The cycle repeats

Thats the workflow pretty roughly. Since the program is pretty simple i thought id just program the steppers using digital high / low signal with delay between and no external library. Is that good or bad? What would you recommend?

If this works i might extend the line even further.

Is this duable using the equipment i described above? Any input is appreciated.

Thanks in advance!
// H

For 3 amp motors I would use a stepper driver that can handle 4amps or 5 amps.

I have no experience of stepper driver boards with TB6560s but there have been some reports of poor quality control on the boards - not what you want with a dangerous saw. If you are going to use them I suggest you get them from a reputable supplier.

Programming the steppers should be straigtforward. The real challenge will be in the mechanical system. And I have no idea how much torque that will require from the motors.

You may find some useful stuff in
Stepper Motor Basics
Simple Stepper Code

Have you checked with your insurers to see if they are happy with DIY controls on a dangerous tool?

…R

Always ramp up steps with big heavy systems or you'll immediately lose lock at
startup (unless limited to very slow speeds). Thus the AccelStepper library is your first port of
call, learn how it works and experiment. Use a modest level of microstepping (x8 or so)
as a first guess - you can experiment with this too.

If you don't know how much torque/speed you require from the motors then don't choose the motors!
You probably need to make some measurements to see what forces are involved. Remember
you can choose the drive mechanism too (leadscrew, belt) and that affects the effective gearing
a lot.

You will need to find this out before buying motors (this is called common sense).

And if you don't know how big the motors need to be, don't choose motor drivers yet either.

And stepper motors don't have a voltage rating, only a current, resistance, inductance. There
is also a maximum voltage rating for the insulation, but that ought to be more than 24V!

Robin,
Thanks for great input and two interesting posts. That was my main concern, poor quality and loss of steps on the TB6560. I found another driver a TB6600, here, it's rated up to 5A and microstepping aswell. The line will have supervision all the time, and will have protection sheilds around the saw area.

Mark,
Yeah, I read some about the AccelStepper library and I think thats the way to go since im dealing with a pretty high load and will probably need acceleration to prevent step loss. Your're right, i dont know the exact torque or speed and i will do some more exact measurements tomorrow, but since the rail comes with a motor alredy installed i thought that would be pretty good and easy to use, even if the rail can handle 50kg horizontal load and my load is approximately 10-15kg. But I havent seen any 800mm rails that comes with a smaller motors.

// H

For high current motors you would normally use a discrete MOSFET driver design, which doesn’t need
anything like the heatsinking of a single-chip stepper driver - discrete MOSFETs have about 2 orders of
magnitude less heat dissipation than ones that are integrated on a single chip due to the current
flow geometry. Checkout the Geckodrives and similar budget designs.

For comparison the TB6600 has 0.4 ohms per switch, ie more heat would be dissipated in the
TB6600 than in the motor for decent sized NEMA23! Modern MOSFETs are available down to a few
milliohms on resistance, not 400!

You will definitely need acceleration, no CNC system gets away without it.