Indexer B moves are doubled.

[norm]

Good morning all,

I'm trying to set up an indexer. I have a PRT Bot running 3.4.27 software. When I got the Bot, I bought an extra VEXTA A6497-9412KTG motor which I would like to use on the indexer direct until I can get pulleys and belts. The current VU are X/Y-733.386 and Z/A-916.7324. When I give a MB90 the motor moves 180, MB180 goes 360, MB360 goes 720, etc. It would seem that I need to divide the A value in half to get the correct moves. Do I also have to half the XYZ values also or do they stay the same? Thanks for your help.

Norm
Appling, GA

[Brady Watson]

Halve the UV for the A/B only. My guess is that you have a 3.6:1 motor in place of the factory standard 7.2:1 motor that came with PRT indexers. You UV will stay the same for all other axes.

Going forward you might want to look for a higher reduction stepper since 3.6:1 is really too coarse for indexing in fine increments, especially if you are not running a 4G board with higher resolution.

-B

[norm]

Thank you Brady. Do I also half the current B value of 16.000 to 8.000? When I can get pulleys and belts, I will contact you for help computing the new values again. Many thanks again.

Norm

[Brady Watson]

Yes - The lower number (16) is the number of steps to go 1 degree of movement. This is the value for a 7.2:1 motor. If you set it to 8, it will be correct.

FYI - From the SB Command Ref PDF:


Computing the Unit Value for an indexer would be done as follows, assuming you want to express the rotary
motion in degrees. With an indexer having a 10:1 gearbox and with the alpha driver set at 500 steps/rev, we
would have: (10 * 500) / 360 = 13.8889 [or, 13.8889 steps per degree].

So...Let's proof it out:

(3.6 * 800) / 360 = Rotary UV (8)

Where 3.6 is your stepper gearbox ratio, 800 is the number of steps per revolution of the stepper (you have a 200 full steps per rev motor & you are 1/4 stepping with your 3G PRT box; so that is 200 X 4 = 800)

You can use the same formula when you change the gear ratio on the headstock. Just plug in the numbers.


-B

[norm]

Brady,

Thanks again for the information. I've ordered gearbelt pulleys and belt. Should get a 4:1 ratio with these. Will work on the math later......

Norm