wrong distances

[lutchman]

hi guys, our bot is off by 3/32" per 2 feet in the y axis, how do i correct this? we have prt alpha 96 if that helps

[barrowj]

Sounds like your unit values are wrong, check them by selecting "UV" from the Shopbot console. For the PRT Alpha (I have the late '04 PRT Alpha) the settings should be 1273.24 for all axis.

[lutchman]

hi joe, i just checked the values and they are all the same 1273.24. any other suggestions?

[barrowj]

I had similar issues a month ago and ended up reloading (UR) and even went so far as to do a reinstall of the control software. Hope you figure it out, it drove me nuts for a day messing with it.

[Brady Watson]

1273.2395 is the proper value for PRTAlpha tools running AS911 1:1 motors with 20 tooth pinions.

A) Are the values EXACTLY 1273.2395 (not rounded to 1273.24) ?

B) Are you running those motors & 20T pinions?

-B

[lutchman]

hi brady,
a/ the values are 1273.24, should i change them to the exact values u have listed?
b/ yes we are running 20T pinions.

[Brady Watson]

Yes - they should be 1273.2395 exactly.

-B

[donek]

I'll admit I'm no expert on unit values. I think Brady is far more knowledgeable.

Is it possible that your pinion gears are worn? When did you last replace them?

3/32" over 24in translates to a an error of 0.0039" per in.

If the unit values represent a number of steps per in, then the difference between 1273.2395 and 1273.24 represent a error of 0.00000039in per in. I believe that would only become measurable in a part that is over 1000in or 80ft long. If it represents a steps per mm, then it would become measurable at 393in or 32ft.

Unless I have the unit values concept all wrong, it is far more likely that some other problem exists, like worn pinions.