MesaCT config - Help

Hey,
I am trying to do a Mesa Config for Mesa board 7i95T. I have a Nema 34 stepper motor, and a CL86T-V41 stepper driver from Stepperonline. This is for X-axis on benchtop mill. I will use Mesa Hardware Stepgen. I also attached the manual for stepper driver.

Here are my specs:

• 2:1 gear reduction
• Ball screw pitch 4mm
• Fullstep = 200steps/rev
• 20 microstep, 4000steps/rev
• Driver has max 500KHz input frequency
• Recommended specs from driver manual:
  • Step space should not be less than 1us
  • Step length should not be less than 1us
• Duty cycle of PUL signal is recommended 50%

Question 1) Is step length + step space = step pulse?

Question 2) What does they mean with Duty cycle of PUL signal is recommended 50%? Do they mean that Step space should be 50% of Step length?

Question 3) Regarding Step scale (Which I believe is steps(step pulses) required per 1mm). Are my calculations correct?:

• (200steps/1rev)*(20microsteps/step)*(2revs/1ballscrew rev)*(1ballscrew rev/4mm)= 2000step pulse/1mm

Question 4) What is maximum linear velocity? Is this the max speed at the gear/pulley after reduction? Or is it the max speed at the stepper motor shaft? I assume it is after reduction, aka at the gear/pulley?

Question 5) What is the lowest step length and step width I can have? I know you shouldn't use max settings specified by the manual, but this is just for my understanding/learning. Stated by the driver: 500KHz max input frequency

• Maximum input Pulse Rate of stepper driver 500KHz = 1pulse/0.000002nano sec = 1pulse/2000nano sec  
• Since (I assume) Step pulse = Step length + Step space. I can Divide Step Pulse by 2 and get:
• Step length settings in Mesa CT: 1000nano sec
• Step space settings in Mesa CT: 1000nano sec

Question 6) Is the maximum linear velocity calculated by this formula?:

• Maximum input pulse rate of stepper / driver step scale
• (500000step pulse) / (2000step pulse/mm) = 250mm/s Maximum linear velocity? 

Question 7) What should my maximum acceleration be(For trapezoid linear motion)? And how do I calculate it? A formula with explanation would be appreciated.

Best regards
Caf

1. step_length+step_space = step_period
Maximum frequency = 1/ step_period
(so 500 KHz for 1000 ns step_length+1000 ns step_space)

2. They suggest 50% duty cycle. With the mesa hardware this would be true
only at the highest step rate, though this is probably not important.

3. Looks correct

4. Max linear velocity is after all reductions and ballscrew conversion to linear motion.

5. The shortest step_length on a 7I95T is 10 ns but you are limited to 1000 ns minimum by the drives
Note that it is better to leave some margin and not use the minimums.

6. If the speed was limited by the step timings, yes, 250 mm/S would be your maximum linear velocity.
at those microstep settings.
Practically, the maximum velocity will be much lower, as it will be limited by the step motors maximum
RPM which will be closer to 1500 RPM (= 50 mm/S) than the 7500 RPM that 250 mm/S requires.
This should allow you to increase the step_length and step_space to say 2000 ns so you have plenty of margin.

7. Really depends on the motor shaft/ballscrew/axis mass. A good guess to start is 5x the linear velocity.
If that is 50 mm/S, an accel of 250 mm/S^2 would be a good start. Too high will cause stalls, too low
will limit speed on curves.

 

PCW wrote:

1. step_length+step_space = step_period
Maximum frequency = 1/ step_period
(so 500 KHz for 1000 ns step_length+1000 ns step_space)

2. They suggest 50% duty cycle. With the mesa hardware this would be true
only at the highest step rate, though this is probably not important.

3. Looks correct

4. Max linear velocity is after all reductions and ballscrew conversion to linear motion.

5. The shortest step_length on a 7I95T is 10 ns but you are limited to 1000 ns minimum by the drives
Note that it is better to leave some margin and not use the minimums.

6. If the speed was limited by the step timings, yes, 250 mm/S would be your maximum linear velocity.
at those microstep settings.
Practically, the maximum velocity will be much lower, as it will be limited by the step motors maximum
RPM which will be closer to 1500 RPM (= 50 mm/S) than the 7500 RPM that 250 mm/S requires.
This should allow you to increase the step_length and step_space to say 2000 ns so you have plenty of margin.

7. Really depends on the motor shaft/ballscrew/axis mass. A good guess to start is 5x the linear velocity.
If that is 50 mm/S, an accel of 250 mm/S^2 would be a good start. Too high will cause stalls, too low
will limit speed on curves.

 

Thank you for the help PCW