Help, confirm my mach servo calc's please

[Sparky_NY]

I am beginning to retrofit a bridgeprort mill that already has servos. I ordered new AMT encoders that are capacitive and have selectable resolution.

The servo drives and motors I am using should be able to propel the mill at 250-400 ipm but I am just now looking if mach can drive it that fast using the parallel port and get reasonable resolution.

The hardware: Servo motor, adjustable resolution encoder, mach running at 45khz kernel speed, 2:1 belt drive to 5tpi ballscrews.

Using a formula I found and assuming 500 encoder res:

Mach kernel / 500 line encoder @ quad encoding = Rotations per sec.
45000/2000=22.5 rotations per sec

Using a 2:1 belt drive that gives 11.25 rotations/sec at the ballscrew

And with a 5 tpi screw (11.25/5) gives 2.25 inches per second or 135 inches per minute.

Am I doing this correctly? The results are not good. I could go lower encoder resolution than 500 to gain more speed at the cost of lower resolution but imagine that is not a good approach. Or, do I have to go to something like the smoothstepper to get the speed up?

Thanks for any help, I have done stepper retrofits but this is the first time playing with servos.

[jeffery71]

Your math looks right to me... Lets look at it another way.

2000 steps per revolutioin of the motor

That makes it 4000 steps per revolution of the lead screw

Your lead screw is 5 tpi. so 5x4000steps = 20,000 steps per inch of movement

1inch divided by 20,000 = resolution of 0.00005

I think that is more resolution than you will need for a mill.

If you went to a 250 encoder you would have 1000 steps per revolution of motor and you will double your speed and still have 0.0001 resolution


Jeff T.

http://www.3dcarvestudio.com

[ger21]

If your PC is fast enough, newer versions of Mach3 can do 100Khz, which would double your max speed plus some.

[Sparky_NY]

Posted the same question on the yahoo mach group. Opinion there is that although on paper Mach can do 100khz, it won't in the real world. 45khz is the max recommended speed for stable operation. The opinion there is that a smoothstepper is the hardware of choice for this application. (4mhz max pulse train)

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