Is the New PRS Standard Controller a Step Up?

[gerryv]

To users of the new PRS standard machines with the new (non-Gecko) OM controller.

I'm considering buying either a recent vintage used PRS with Gecko drivers but am wondering if the new PRS controller WITHOUT Oriental Motor (Vexta) drivers does indeed offer smoother operation and cuts doing compound curves, arcs, circles, etc. and also if it is a faster machine than the 2008-09 PRS standard models? Also is it likely to cut any more quickly doing 3D carving?

What would be nice would be if you've had experience with both of course but if not and you have the new one, are there still any jaggies issues that some noticed with older machines? Also any of the random issues some have had that seem to relate to shielding?

Thanks much.

[richards]

Gerald,

The secret to getting good performance out of a stepper motor is to match the motor to a stepper driver and then to give that stepper driver the right voltage and the right current.

As far as I have read, the new controller does exactly that. The Oriental Motor stepper motors are matched to an Oriental Motor stepper driver and a power supply suited to that combination makes everything work.

Personally, I have used Geckodrive G202 and G203v stepper drivers extensively with motors that are matched to those stepper drivers (PK296-F4.5, PK299-02AA, PK299-F4.5, PK268-02AA, PK2962A-SG3.6). All of those motors have low to moderate inductance. The amount of inductance dictates the power supply voltage. Motors with 1.5mH inductance run extremely well with a 35VDC power supply. Motors with higher inductance need more voltage. The Geckodrive stepper controllers that I use can handle up to 80VDC. All of the motors that I use are rated to use a power supply less than 80VDC, so the match is excellent.

The next point that keeps me locked into Geckodrive is their 1/10th microstepping. That means that it takes 2,000 steps for the motor's shaft to revolve one time. Using a 1.25" spur gear (25-tooth) gives 0.0019" per step. I use either a belt-drive transmission or a gearbox on the motor to reduce that distance by 3.6X. That gives me a resolution of 0.000545, which is exactly the resolution that I would get on my PRT-Alpha with the 7.2:1 motor upgrade if I used 25-tooth spur gears. (The Alpha motor uses 1,000 steps per revolution, so a 7.2:1 gearbox with the 1,000 step per revolution motor/driver gives the same resolution as a 3.6:1 gearbox and a 2,000 step per revolution motor/driver.)

I haven't studied the new stepper driver/motor manual enough to know all of its features; however, there are many options available. I believe that Shopbot would choose the Oriental Motor settings that would allow the new controller to get the most performance out of those components.

As far as I'm concerned, any stepper motor, if run at its proper speed (so that it doesn't miss steps) will do an excellent job. Because Shopbot has chosen to buy both the motors and the stepper motor drivers from the same source, everything should match properly.

(Some of the disappointment that some users may have had with the 4g upgrade was due to the original motors. Those motors, which were wired bipolar series, had high inductance. They were electrically equivilent to the Oriental Motor PK296A1A motor. A much better motor for use with the Geckodrive stepper drivers is the PK296A2A motor wired half-coil. But, replacing four motors would add another $1,100 to the price of the upgrade.)

EDITED:
I should have read your post more carefully. You asked about the controller without motors.

The software determines how many steps it takes to make any move. Except for the resolution (the distance traveled per step), a properly tuned motor/driver should give the same results. The software commands the motor to turn its shaft a specified distance and the stepper driver makes that command possible.

Jaggies have many causes. Ramping is one cause. Non-tuned stepper drivers is another cause. Insufficient torque is another cause (one motor "pushes" the other axis when that secondary axis is in standby mode).

3-D cutting is slow. Most of my 3-D cutting has very short line segments, so the software is always running in the ramping mode. On my machine, that's just the way it works. My Alpha is fast when cutting 2-D, but 3-D imposes severe limitations.

Most of the "jaggies" were eliminated when I added a belt-drive transmission to my original machine. The replacement 7.2:1 motors eliminated the need for belt-drives. The cut quality is the same with the geared motors as it was with the belt-drive transmission.