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Author Topic: Electrically preloaded Dual motor drive for Rack & Pinion  (Read 3662 times)

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Hi all,

 i'm researching building a 4' x 8' cnc router for a woodshop.


I was wondering if Mach3 has the capability to drive 2 stepper motors per side of X axis ( 2 pinions per rack for reduced backlash, electrically preloaded ).




That would be 4 motors for the X axis.

 Motor A would drive in one direction while motor B would have less torque (dragging) to keep the pinion engaged.

When switching direction, the motors would switch  also to B driving and A preloading.





Thanks,
Radu
« Last Edit: May 22, 2014, 09:27:14 AM by raadu »

Offline ger21

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Re: Electrically preloaded Dual motor drive for Rack & Pinion
« Reply #1 on: May 22, 2014, 11:54:16 AM »
No, Mach3 can't do that.
Gerry

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Re: Electrically preloaded Dual motor drive for Rack & Pinion
« Reply #2 on: May 22, 2014, 12:42:29 PM »
        First question :

       Could Mach4 be configured to do that?

  
       Second question:

Could it work with Mach3  if there's a programmed micro-controller  between the breakout board and the stepper drivers?

       It would read the signal from Mach 3 and drive the steppers accordingly.

        Is that worth looking into or would it conflict with the way Mach 3 operates?


Thanks,
Radu



  
      
Re: Electrically preloaded Dual motor drive for Rack & Pinion
« Reply #3 on: May 23, 2014, 08:31:11 AM »
I guess the answers are no and no ? :)

Offline Tweakie.CNC

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Re: Electrically preloaded Dual motor drive for Rack & Pinion
« Reply #4 on: May 23, 2014, 09:20:40 AM »
Don't be too hasty, I am sure others will be thinking about this.  ;)

I am certain that your suggestion of a microprocessor is something that should be investigated as I think that could work.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline stirling

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Re: Electrically preloaded Dual motor drive for Rack & Pinion
« Reply #5 on: May 23, 2014, 10:27:07 AM »
Even if you could get this to work (and I have my doubts) why would you?

Surely, you'd end up with exactly the same effect that is achieved far more simply and cheaply by the old trick of using two pinions fixed slightly out of phase on the same shaft.

Ian

Offline Chaoticone

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Re: Electrically preloaded Dual motor drive for Rack & Pinion
« Reply #6 on: May 23, 2014, 10:30:41 AM »
Oh boy!, This is not supported by any stretch of the imagination...................................... but ;D I do not see why you could not have 2 drives and two motors for the backlash comp by sharing the step and direction signals to 2 drives. Maybe even drive 2 motors from the same drive. I think I would go with a single motor, some belts and pulleys and 2 gears myself since the backlash comp would not be electrical preload. The separate pinions would still have to be separated or opposing mechanically (spring, shock, spacer etc).  However, the best solution would be to use precision parts with precision placement, set up correctly to eliminate backlash. I do think any of the three options above would work (each with benefits and drawbacks) but they are elaborate workarounds for inferior components IMO.

Brett
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Offline mc

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Re: Electrically preloaded Dual motor drive for Rack & Pinion
« Reply #7 on: May 23, 2014, 11:02:44 AM »
Precise and Rack & Pinion don't really go together, certainly not in your typical home built machine.

Regardless, the OPs idea would be best acheived with a microcontroller, however it would also need stepper drivers that are capable of having the motor current varied on the go, which I think would be the biggest stumbling block.
Any delay in changing current levels could result in a jolt as backlash changes direction (motors would go from pulling apart to pushing together, or vice versa), which could lead to missing steps/jumping issues.

Just spring loading the pinion onto the rack, or using a anti-backlash pinion are far simpler solutions.

Offline stirling

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Re: Electrically preloaded Dual motor drive for Rack & Pinion
« Reply #8 on: May 23, 2014, 01:10:58 PM »
Precise and Rack & Pinion don't really go together, certainly not in your typical home built machine.

Regardless, the OPs idea would be best acheived with a microcontroller, however it would also need stepper drivers that are capable of having the motor current varied on the go, which I think would be the biggest stumbling block.
Any delay in changing current levels could result in a jolt as backlash changes direction (motors would go from pulling apart to pushing together, or vice versa), which could lead to missing steps/jumping issues.

Just spring loading the pinion onto the rack, or using a anti-backlash pinion are far simpler solutions.

Exactamundo - in every respect. Plus - a stepper with less current, whilst having less torque, will still step, because the other motor will release the load - so - no drag anyway.

Offline BR549

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Re: Electrically preloaded Dual motor drive for Rack & Pinion
« Reply #9 on: May 23, 2014, 04:01:17 PM »
The answer is NO and NO. Nor would you really want to ;)

NOW you COULD use a DC motor and use a low current to feed it creating a small counter force. But that does not really solve your problem.

(;-) TP
« Last Edit: May 23, 2014, 04:07:27 PM by BR549 »