How does belt drive help? Is the maximum of 19 lbf per stepper correct? Is that set by the controllers’ current limits or by the stall torques of the motors?
If your axis is screw driven and you drive it past the limits, it won’t just skip. It’ll tear itself apart.
Good question. In short no. The HDZ is strong enough to withstand the pressure of a ball screw driving into it. The coupler or motor will slip before damage is caused but it will make a loud noise. I did test a HDZ to destruction but you need a 1600oz nema 34 with glued couplers.
That’s good to hear! IMO it would be a rather poor design if it was that easy to break!
I still don’t understand how belt drives are supposed to help (unless something slips before the motors).
I assume that you didn’t use the S3 for your destructive testing, right? What was the corresponding force on the Z axis?
Correct, there isn’t even a way to fit a nema 34 to a HDZ.
I didn’t measure the forces but the motor is over 10x more powerful than that on a shapoko to cause damage and required a 60v power supply traveling at 10,000 mm a min.
Usually what happens is the belt starts skipping before something gives way — when it does it’s usually the Delrin V wheels. There’ve been some crashes where inertia was sufficient to keep things moving, so the V wheels gave way, in a couple of instances the rails have gotten gouged as well, but that’s not as common.
The Z axis stepper motor slips before the belt skips. Is that not the case on the other axes?
Good question. I haven’t tried to track that or differentiate. If anything, you’d think it would be the other way around since there’s less surface area engaged on the 6mm belts and the two 90 degree angles.
IMO the best way to limit CNC machine operating forces to safe levels would be to limit the torque available from the transport motors by limiting their drive currents. I’d be quite surprised if the S3 designers didn’t do that. Can you find out if that’s the case and what the resulting maximum forces are on each axis?
I suspect that this aspect of the machines is the same as the Sparkfun Stepoko:
Yes, current is limited, it’s one of the major functions of the stepper drivers. Each driver independently limits to 2A or less. The way that works is pretty interesting, but I won’t go there. No matter what the driver PSU voltage, the current is essentially fixed. The stock steppers are rated for 2A, 127 oz*in of torque (static). They get their 2A, at 20V but could be run at higher voltage, which would give them more running torque (but no more static torque). Again, increasing the voltage does not increase the current (because of the way the drivers work).
The drivers on the board (TI 8188) support 35V, but are run at ~20V. I went to change this with a different PSU and got sucked down the rabbit hole. Am now in the process of installing new drivers (4xMT524S), which required a new control board (Keyestudio GRBL), and 2x 48V PSU’s for no particularly good reason. I’ll write something up when I’m done.
Your posts on another thread suggest that you should get almost 3 times the torque (and force) with your motors than the standard S3 motors with the standard S3 control board/drivers. Are you? Do you think that it would be a good idea if you could/did?
I’m in the middle of the project, not quite to where I can answer that very well. Was just going to increase the motor voltage on the existing board, but got sidetracked. The S3 board should take ~30V and be fine. That would help a lot both with the stock steppers and the high torque ones. The high torque/low current ones have such high inductance that 20v just doesn’t drive them particularly well. For the single axis proto I did, yes, it’s much stronger. Good idea? Not so sure, more “huh, what’s this like” than any great reason at this point.
High speed machining- 200ipm/5000mm or bust
That looks like the “old” (three stepper motor driver) controller/diver with adjustable current limits. I’m going to assume that whoever designed the new ones set the “new” current limits to values that would prevent machine damage. IMO that would be the “right” thing to do.
Ha, that’s the kind of logic I can relate to…
Apparently its actually 22 lbf per stepper - at least for the Z-axis.
Does the HDZ increase the Z-axis force available from the standard S3 motors and controllers?
Yes, it does due to the way it converts the movement.
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