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Author Topic: ATC Macro Help  (Read 4622 times)

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Offline stirling

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Re: ATC Macro Help
« Reply #10 on: September 13, 2014, 03:41:16 AM »
OK "ratcheting back into the pawl". Let's see if we really need to do this.

In the original system - they used a "regular" DC motor and they reversed it into the pawl with half current to hold it. Yes?

So - in that system the pawl stopped it moving ONE way and the "holding" torque of the motor stopped it moving the other way. Is that correct?

If we do exactly the same with the stepper, then the pawl will again stop it moving ONE way and the holding torque of the stepper motor will stop it moving the other. HOWEVER - here's the difference. Unlike DC motors, the stepper will resist movement in BOTH directions. So if the holding torque is good enough one way - it must be good enough the other way - so why do we need the pawl to hold it. Or am I missing something?

Put more simply - if you were to use it "as is" is the holding torque of the stepper not sufficient to resist cutting forces without using the pawl?

BTW - a video would help me see what's going on so far.
« Last Edit: September 13, 2014, 03:59:55 AM by stirling »
Re: ATC Macro Help
« Reply #11 on: September 13, 2014, 05:45:18 AM »
I'll try and get a vid done later,

It will need to drive against the pawl as there is mechanical play in the drive train which is a worm gear, resolution 40:1 results in just under 1/8" play at the tool tip. allthough the script we have thus far indexes correctly i wouldn't be confident maching with it.


I think its better suited to incremental motion, and possibly reset of dro according to input configuration if thats possible.


I really cant get my head around VBscript but is it not possibble to get it to rotate 45 degrees, check pins and rotate another 45 if not correct configuration of the 3 sensors and continue to do this until the correct config is reached. then obviously reverse at the end to lock.
« Last Edit: September 13, 2014, 05:47:23 AM by speckled »

Offline stirling

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Re: ATC Macro Help
« Reply #12 on: September 13, 2014, 06:41:52 AM »
It will need to drive against the pawl as there is mechanical play in the drive train which is a worm gear, resolution 40:1 results in just under 1/8" play at the tool tip. allthough the script we have thus far indexes correctly i wouldn't be confident maching with it.

I think this is where we're going to run into "issues".

Steppers are not the best choice of motors for applying force against stationary objects.

If you run a steady current DC motor up against the end stops it will just sit their nice and quite - pushing. However a stepper motor will tend to vibrate like crazy. THEN when you stop supplying steps it will tend to jump 2 steps backwards and THEN sit there quietly. However it's now - no longer - pushing against the stationary object. Just bear in mind that using a stepper MAY turn out to be not a good choice.

I think its better suited to incremental motion, and possibly reset of dro according to input configuration if thats possible.
Don't follow you - what problem are you trying to solve? I'm not against incremental but I can't see any particular advantage - please explain.


I really cant get my head around VBscript but is it not possibble to get it to rotate 45 degrees, check pins and rotate another 45 if not correct configuration of the 3 sensors and continue to do this until the correct config is reached. then obviously reverse at the end to lock.

You're still thinking servo. When we incorporate the positional info (pins), we'll know where we are so we'll know how to get where we want. Why "hunt" for something when we know where it is?
Re: ATC Macro Help
« Reply #13 on: September 14, 2014, 04:27:19 AM »
I think its better suited to incremental motion, and possibly reset of dro according to input configuration if thats possible.
Don't follow you - what problem are you trying to solve? I'm not against incremental but I can't see any particular advantage - please explain.

only advantage I see is that it won't care for the missed steps driving back on the pawl.

I really cant get my head around VBscript but is it not possibble to get it to rotate 45 degrees, check pins and rotate another 45 if not correct configuration of the 3 sensors and continue to do this until the correct config is reached. then obviously reverse at the end to lock.

You're still thinking servo. When we incorporate the positional info (pins), we'll know where we are so we'll know how to get where we want. Why "hunt" for something when we know where it is?
I'm just leading towards the original way it worked, it worked really well but it was so darn slow, I'd estimate around 8-10 seconds per index, approx 1 minute per full rotation.