7.2 gearhead z axis

[jon]

Hi all, I just subbed my old z axis motor (alpha, non gearhead) with a 7.2 gearhead motor. I have the same 30 tooth gear on the shaft, and all is identical to my other axis x and y. However when my unit value is set the same as the other axis my z axis moves a very small distance. The unit value is 2482.8171 for the other axis, which is default for the PRS. I have a PRT with the x and y motor upgrade, and I have another 7.2 motor and driver fitted to a custom z axis I made. I would love to get cutting again!!! Has anyone else done this to their machine? I need to know how to figure the correct unit value out, I have the resolution multiple set to 5 like the others.

cheers,

[ssflyer]

Hi Jon,

I have a PRSAlpha, and my x and y values are the same as yours, however, my z is set to 2979.3805

Hope this helps,
Ron

[ken_rychlik]

I changed my z to a 7.2 and was told the driver and motor both had to be changed. They used different drivers with the geared motors.

[jon]

Thanks guys, the problem is that I purchased a driver motor combo directly from Oriental motors, which is something that you should not do! The drivers that Shopbot uses are CUSTOM programmed. I am having to set my unit value higher than normal to get the z axis to move the distance that it says it is moving. I actually have not done this correctly yet, as I am trying to determine what that value is.
My system; Prt Alpha 96, with four 7.2 gearhead motors, and appropriate drivers, one of which (z axis) is directly from Oriental Motors, the other three are from Shopbot.

This is what I am going to do;
1)run z zero routine
2)measure the distance it actually is from the bed
3)compare that distance with the value displayed (1.0 inches)
4)take that value and apply it in either division or multiplication of the current unit value in my software.

I have a unit value that is near 10000 right now, which should get me close to the number required. Then I will apply the above technique. I still believe that it will perform better than the old asm911aadc2.65v non geared motor, but the computer will have to work harder to operate the machine, and I will be more susceptible to micro crashes and stuttering due to communication errors between PC and control box.

Again, learn from my lesson here, do not use a driver directly from Oriental Motors, it will not perform as you expect it should!

I should note that I have a communication cable from Oriental motors and have been inside the driver looking at the settings in Hyperlink, (which is a modem communication software), and I did not detect any difference with the driver from them, and the Shopbot drivers, so I am stumped as to what they have modified. I might have another look if I cannot get my system to function properly.

[ken_rychlik]

I had them program one for me and it wasn't to expensive.

Give em a call.

[jon]

Thanks, they know about it, I've been talking to both parties trying to get them to provide a number. I've sent a request for quotation to Shopbot, waiting to hear back. Did you do the same thing I did?

[ken_rychlik]

No, I ran across a spare driver for cheap and bought it. I just wanted an extra on hand. They said it was a five minute job, and shipping it back and forth was the biggest expense.

[jon]

Well that's what I'll do then, in the meantime I'm running the unit value at 7649.3829 for those who might encounter this same situation. I suppose the reason for the unit value for z being different from the other axis on the PRS is that there is a different gear ratio in the motor's gearbox, or the pinion is different.

My method worked out pretty well, and I managed to find the magic number with only three attempts, each attempt bringing it closer to accuracy. I started with a value of 5000 and applied the corrected ratio after each measurement. I used a calibrated set of Vernier calipers to measure the distance and it is bang on now.

I still need to do tests on how it performs cutting a three dimensional file at high speed with these parameters, but it sure moves a lot smoother than with the old motor on there!

thanks for attempting to help me with this.

[jon]

Actually, that number didn't work. It's still not running correctly, I'm wondering if anyone else has any ideas.

[blackhawk]

You mentioned that you bought a "communications cable" from Oriental Motor. Are you referring to the ribbon cable that goes between the driver and the control board or the long round cable that goes between the motor and driver? I set up a motor and drive from Oriental for my homemade indexer. I bought both the ribbon and motor extension cable from Shopbot. I don't think the motor extension cable directly from Oriental will work correctly. This could be one problem. Maybe you could switch out the cable from the X or Y axis to your Z to check?

Also have you measured the distance that your Z travels in both Jog and Move modes? In my original setup, I found that these were different by a factor of exactly 10.