Maximum move speed?

[richards]

It looks like there is an artificial 12-ips limit on the move speed of an axis. Changing the VS parameters in the appropriate Shopbot_PRS96x48alpha.sdb file to 30-ips still had the 12-ips limit (version 3.6.38).

I'm using non-alpha motors geared 1:1.5 which can easily run at 60-ips in Mach3 with a top speed of over 80-ips with a pulse train set at 45,000 pulses per second. (This is a non-cutting application, which would be similar to constant jogging.)

Assuming a pulse train of 30,000 pulses per second from the Shopbot controller, we were hoping for speeds of over 40-ips but that 12-ips limit may force us to switch to other software.

Does anyone know how to get around the 12-ips limit?

[ken_rychlik]

I don't know the answer to your question directly, but can't you just use a jog command in the file?

[Gary Campbell]

Mike...
I dont have a dog in this fight, but is there a limit due to pulse/comm max rate? To enable the faster jog speeds, steps/in (resolution) is decreased on the current alpha.

IS it possible that the bottleneck is the USB comm rate and the software is set to max out somewhere below that number to ensure reliability?

[danhamm]

Is it the "RBK" drivers smooth drive function, from 1/8 step to full step that gives the alpha that speed.? Mike maybe you need those drivers with the Micor card..?

[richards]

Thanks everyone. We've thought about replacing the MX, MY, commands with JX, JY, etc. That would let the machine run at 30-ips (in theory). The higher jog speeds on the PRS-alpha is mostly due to the alpha motors and the electronic switching capabilities of the Alpha stepper drivers, so I'm not sure what the pulse rate actually is when a jog command is running.

The math shows that the PRS-alpha with 1:7.2 motors installed requires about 18,300 pulses per second to run at 12-ips:

1.5" pinion gear diameter X PI / 7.2 gear ratio / 1000 steps per rev = 0.0006545 inches per step.

12 inches / 0.0006545 = 18,334 steps per second.

The new machine uses PK299-F4.5A steppers driven by Gecko G203v stepper drivers. It also uses a 30 tooth pinion gear. It has a 1:1.5 belt drive transmission to increase torque to 80 lb*in (which gives it the same torque as the motors/gearboxes used on the PRS-alpha).

1.5" pinion gear diameter X PI / 1.5 gear ratio / 2000 steps per rev = 0.0015708 inches per step.

0.0015708 X 18,334 steps per second = 28.8-ips.

So, if I've done the math correctly, using the same number of pulses per second would give us at least 28.8-ips.

I know that there is a limit caused by the USB interface; however, several years ago at the Maker Fair in San Mateo, Ted, Bill Y., Bill P. and I talked about the V201 microcontroller and its possibilities. For that Maker Fair, I built a demo machine, using the V201 microcontroller and SB3 software, that duplicated the three-color exposure mechanism used in a $35,000 Durst photo printer. That little demo machine had faster filter to filter rotation times and finer exposure time resolution than the very expensive photo printer. Anyway, at that time the magic number of 30,000 pulses per second was discussed as the practical pulse per second limit available with the USB interface. We discussed the possibilities of using the V201 board and SB3 software for non-CNC applications. Bill Y. had several non-CNC machines doing some very impressive things for the visitors at the fair.

That's basically what we are trying to do. The PRS-alpha machine and PRS-alpha controller are the basis for a robotic non-CNC router application. The application requires move speeds over 30-ips. The motors supplied with the PRS-alpha are limited by the gearbox to 20-ips, so I was asked to build a auxiliary controller that would take the step pulses from the PRS-alpha controller to run other motors.

Those motors can easily spin at 1,200 RPM using the other software that I use at my test bench. That gives a move speed of 60-ips. I've run them at 100-ips through a parallel port on a Windows XP computer. The smooth-stepper option (USB) would give a pulse rate much higher than those motors could use.

So, it seems that the 12-ips is an artificial limit that doesn't relate to the pulse rate possible with the PRS-alpha controller. For instance, if someone replaced the 1:7.2 alpha motors with 1:3.6 alpha motors, they would still be limited to 12-ips even though the 3.6 motors could move at 24-ips using the same number of pulses. (I'm ignoring the Oriental Motor maximum speed for their gearboxes which would limit the speed of the 3.6 alpha motor.)

I'm thinking that removing the 12-ips limit would allow the controller to be used with non-CNC applications.

[richards]

Frank, at Shopbot solved the problem. My customer just emailed me to say that he talked with Frank and that Frank told him that the speed parameter could be changed by modifying the /bin/ShopbotW.prn file.

That modification works!

Thanks Frank.

I should have called Shopbot first.