PRSAlpha Indexer Unit Value

[lcolburn]

Hi all,

Just got our indexer set up yesterday, and started moving it around today. Everything seemed fine until I discovered that a MB 360 command didn't rotate the head through one full revolution- more like 1 1/2 revolutions.

I checked the unit value for the B axis, as recommended in the manual, but the 13.888 value is for PRTAlphas- no word in the manual on a value for the PRS machines.

By trial and error, I figured out that a value of 9.0250 is pretty close to accurate for one revolution, but I'm wondering if anyone has an exact number for the PRSAlpha B-axis unit value setting. If it helps, my indexer has the Oriental Motor ASM98AA-T10,- I used a little info from the Oriental Motor site to get my approximation, but I'd like to get it exact as I plan on using the indexer mostly for true 3D objects machined from four sides. Has anyone else run into this? Any tips would be great. Thanks!

-Lewis

[Brady Watson]

Lewis,
Your UV should be 13.889 with the selector switch on the motor driver in the '500' position. Check to make sure that this is the case.

-B

[dana_swift]

I measured 10 turns on my indexer with a laser level because everything was wrong according to the documentation. What I came up with is: 9.0275 I don't understand why it isn't the 13 value that the gear head "should" require. This one is a mystery, glad to know I am not the only one with the weird value. Personally I would like to know how that number could be predicted rather than measured. D

[lcolburn]

Dana, thanks for confirming my suspicions. Your 9.0275 value works beautifully- better than my guesswork, but I'm glad I was in the right ballpark. Brady, I'm stumped as to why the published values don't work- the selector switch on the driver is in the 500 position as you describe, but 13.889 is way to high for one revolution. In any case, this is enough to get me up and running- now let's see if I can make those cabriole legs I've been planning.

[Brady Watson]

Lewis,
It *could be* that ShopBot has enhanced the Alpha driver firmware - which would result in unit values different than what earlier tools are running. My 10:1 Alpha Indexer uses 13.889 as the UV. That is to say, it takes 13.889 micro steps to go one degree of revolution with 10:1 gearing.

-B

[frank]

I checked with Gordon. The formula is 325 steps per revolution times 10 (gear ratio) divided by 360 degrees. 9.0278

[Justin G]

And here's my unit value for the same motors: 140.0000 I know this is not the exact number but eyeballing a dot on the Chuck for the MB360 it gets pretty close. Any ideas? SB support is struggling.

[myxpykalix]

In any case, this is enough to get me up and running- now let's see if I can make those cabriole legs I've been planning.[/QUOTE]

When you get those legs cut make sure you post plenty of pictures.

[Gary Campbell]

For my friend Dana:
Of course, once the actual values are known, all is predictable! Here is a screen clip from my drive ratio calculator:

http://www.talkshopbot.com/forum/attachment.php?attachmentid=26657&stc=1

[Brady Watson]

Try 138.8889 for your VU. If that's right, I think I know why...

-B

[Justin G]

I'm curious to hear what you think is the culprit. I remember speaking with support a year or so ago when I got my indexer before erasing my setup by accidentally loading a different custom configuration and they told me the indexer motorwas not programmed at the factory. Or something to that effect.

This morning I turned on the indexer with the 140.0000 value I had been using. Typing a 360 command output about 180 degrees of rotation real world. So no idea why it magically changed but I doubled it so my b unit value was around 280.0000. I then proceeded to trial and error using a square and a couple notches on the top of the indexer motor bracket and Chuck. I started with mb 360 and made adjustments to the value until it was as close as I could detect. I then did a mb 3600, and then MB 5400, and every time fine tuning going back and forth between mb 0 and MB multiples of 360. This is obviously not the most scientific way but after 60 rotations or so, the marks are as close as I can tell dead on. Unit value isn't in front of me but it was somewhere in the 277.7500 range.

[Brady Watson]

Don't know about that one...Why would the UV suddenly change from around 140 to 280? Yes, multi-rotations for checking the UV is the proper way to sneak up on it.

-B

[Justin G]

yup neither do I. The only thing I could think would be some kind of VS command changed the speed so dramatically it threw the rotation off? I had managed to finish a whole slew of orders and had a day of downtime to mess with the indexer again. The only thing I changed between testing it was working on a custom zzero program so unless I am missing something (which anyone that knows me would say...) could it be that?