Author Topic: Controller Hardware  (Read 2004 times)

Offline Will_D

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Controller Hardware
« on: July 23, 2016, 02:33:22 PM »
So as not to hijack an existing thread:

Whilst idlly searchin ePray I came acroos this package:

http://www.ebay.ie/itm/Upgraded-3Axis-CNC-Kit-Professional-TB6600-Controller-Box-Nema23-2-5Nm-Motor-PSU-/401143910418?hash=item5d660a5012:g:ghIAAOSwbYZXdrfk

So it looks a good price for 3 big steppers and their drivers. Also you get a PSU to power the system.

Also their is the controller. This is the bit I am not clear about. There is vague reference to a computer downloading g-code which can then nbe run, there is also manual jogging type control or even the ability to write and edit g-code in the controller.

Any one got one? Any comments?
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Offline Joules

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Re: Controller Hardware
« Reply #1 on: July 23, 2016, 03:00:07 PM »
Quite a bit worries me over that advert Will.  You still need a PC to feed that setup g-code.  They never show the screen being used and "WHAT" it really shows.  The picture of the control box in the top photo has two ports, then the photo of the PCB lower down shows 3 ports.  The LCD has a ribbon cable and no obvious connection for the screen on the PCB.   They might just be incompetent at producing an advert....  OR not...
Just get doing and make swarf, you can decide what its going to be later.   :thumbup:

Offline Will_D

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Re: Controller Hardware
« Reply #2 on: July 23, 2016, 06:08:19 PM »
I agree Joules, Its a bit vague as to what it can interface with.

Price is tempting tho!

Similar price as compared to the stand alone controllers (with USB g-code i/f)  but WITHOUT: driver interface, Steppers and the PSU
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Offline PK

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Re: Controller Hardware
« Reply #3 on: July 23, 2016, 07:27:47 PM »
Others have commented on the control aspect of the device. So I'll just chip in on the drives.

TB6600 drive IC's are everywhere these days. They are actually OK little devices, certainly they are dirt cheap.
You just need to be aware of their limitations. 
The big one is voltage. They are rated to 42V, but because steppers act like generators on deceleration and there is nothing to clamp the voltage, then you'd be ill advised to run them above about 30VDC (I have one running at 36V). 

This is important because (baring some issues with motor inductance) stepper max speed is a function of voltage.  As an example, I run the little NEMA23 motors in my mill at 75V and (with 5mm pitch screws) get 4m/min rapids. Our full sheet router at work runs NEMA42s at >100VDC.

The other thing is that these cheap drives have no protection against common problems. A broken wire in a stepper cable will destroy the drive.

Like I said, I'm not bashing these things, I think the last TB6600 drive I bought cost about AU$15 landed. At that price I keep a few in stock for projects..

Offline raynerd

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Re: Controller Hardware
« Reply #4 on: July 24, 2016, 12:25:43 AM »
For what it's worth, I Would be wary! After going down dodgy eBay adds twice before and a cheap TB6560, I paid the price for my latest cnc adventure and purchased 3 separate drivers, new motors, break out board from cnc4you. You can't compare...just my opinion but it's worth waiting a few weeks/months and getting something that works well. Cheaper will only ending up costing when you want to upgrade, and You will do. Just from my limited experience....
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Offline Imagineering

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Re: Controller Hardware
« Reply #5 on: July 24, 2016, 06:37:23 AM »

Offline Will_D

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Re: Controller Hardware
« Reply #6 on: July 24, 2016, 06:10:53 PM »
Regarads this package: I have asked the seller for a manual explaining how to dowload the g-code!

In general buying this CNC stuff is a nightmare.

Quality UK (or .EU) stuff is VERY expensive (like over 100 for a 300 Ncm stepper and its driver board - Multiply by 3 and WTF?)

500 mm C7 ballscrew?

[adopt Monty Python Accent] "Ballscrews Sir, You should see ours, They are the absolute best, Wink, Wink, Nudge Nudge . Buy these and its as good as a nod to dead donkey!

500 mm ball screaws and nuts for 100 plus??

For the real link:

https://www.youtube.com/watch?v=AGrvQ1c5khU&list=RDAGrvQ1c5khU#t=16
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Offline joshagrady

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Re: Controller Hardware
« Reply #7 on: July 25, 2016, 04:57:52 AM »
I can't speak as to the quality of the product, since I've never actually purchased anything from him, but a German member of a local forum is very highly regarded for the quality of his controllers.  Among those who know, he is considered on par with Gecko.

Benezan-Electronics.de

Offline John Stevenson

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Re: Controller Hardware
« Reply #8 on: July 25, 2016, 06:53:06 AM »
I can't speak as to the quality of the product, since I've never actually purchased anything from him, but a German member of a local forum is very highly regarded for the quality of his controllers.  Among those who know, he is considered on par with Gecko.

Benezan-Electronics.de

That doesn't say a lot as Gecko is old hat now, no new products in a market that changes monthly.
The Chinese have had closed look steppers out for months now and even their Servo motor / driver combinations are very, very competitive.
You can get a 1.8Kw servo motor and driver which would make an ace spindle motor on something like a X3 or WM16 for 280
John Stevenson

Offline nrml

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Re: Controller Hardware
« Reply #9 on: July 25, 2016, 07:21:56 AM »
Sorry if this is a rather stupid question. Is the loop closed between the servo motor and driver or does it pass through the machine controller? Can a closed loop servo system be used as a spindle motor on a lathe to enable basic thread cutting function with a controller that does not accept encoder feedback?

Offline sparky961

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Re: Controller Hardware
« Reply #10 on: July 25, 2016, 04:39:52 PM »
Sorry if this is a rather stupid question. Is the loop closed between the servo motor and driver or does it pass through the machine controller? Can a closed loop servo system be used as a spindle motor on a lathe to enable basic thread cutting function with a controller that does not accept encoder feedback?

I can answer the question of closed vs. open loop in a broad sense, but not specifically for any given system.  It's a bit simplified but hopefully gives enough info for the purposes here.

Open Loop:

Typically used with steppers because they have explicit angular "steps" where they may be held in position.  The controller assumes that when it sends out a pulse (with direction signal), the motor achieves the desired position.  With a correctly specified system that is functioning within designed parameters, this is a perfectly valid assumption. 

However, with "hobby CNC" you typically try to buy the cheapest or most readily available components.  Little or no design/engineering is performed to make sure that things have proper specs, so you usually end up with under-powered motors that can't be relied upon to position the system under load or high speed.

Closed Loop:

Any system that has a control signal and feedback.  In terms of CNC, we're usually talking about servos - which are essentially a motor that can be energized to spin either direction at various speeds/torque.  In a working system, the speed/torque is dictated by the controller, which figures out how much speed/torque and in which direction.  It does this by looking at the feedback signal, most commonly a rotary encoder of whatever flavour you prefer.  The rotary encoder enables the controller to know how far the motor (servo) has rotated

It's still possible to under-power the system, but it becomes obvious very quickly when you're trying to tune the system.  If an axis falls behind where it's supposed to be (similar to "missed steps" when talking about stepper motors) the controller knows and can flag an error and/or shut down the system.

--

Answering your thread cutting question, the controller needs to have feedback to coordinate all axes involved in the motion.  So I'd say that coordinated thread cutting would not be possible without feedback to the controller.  There may be a TACH/RPM input that could provide some limited functionality.

Offline PK

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Re: Controller Hardware
« Reply #11 on: July 25, 2016, 05:58:34 PM »
Sorry if this is a rather stupid question. Is the loop closed between the servo motor and driver or does it pass through the machine controller? Can a closed loop servo system be used as a spindle motor on a lathe to enable basic thread cutting function with a controller that does not accept encoder feedback?

Not a stupid question. 'Normally' the loop is closed in the drive. But there are cases where you want to close the loop in the machine controller.
Here's one I prepared earlier:
<a href="http://www.youtube.com/watch?v=KH1eaS56UvI" target="_blank">http://www.youtube.com/watch?v=KH1eaS56UvI</a>

So the black rack mount case just contains a power supply and some PWM amplifiers. The PC has an FPGA card in it with the drive and loop closing logic programmed into it (google MESA IO).
The encoders wire directly back to that card.
Why do it this way?
Because it lets us turn the PWM amps and brakes off on the motors, move the arm manually and still read the encoder positions. We use this mode to teach a series of points that we later 'play back'
 

Offline nrml

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Re: Controller Hardware
« Reply #12 on: July 25, 2016, 06:26:05 PM »


Not a stupid question. 'Normally' the loop is closed in the drive. But there are cases where you want to close the loop in the machine controller.

Is my understanding then correct in the following scenario?
If I have a CNC lathe  with a servo motor spindle  and stepper motors on the X and Z axis, I can feed it G code to keep the spindle RPM at a certain number (automatically compensating for cutting forces within reason) while moving the z and X axis to cut threads without the machine controller doing anything but spitting out G code. This 'open loop threading' would be susceptible to errors but would still work with a basic Chinese control box.

Offline John Stevenson

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Re: Controller Hardware
« Reply #13 on: July 25, 2016, 07:12:16 PM »
Not going to work, the error would be too great and IF you were able to do one pass correctly and keep in pitch, when you went back for the second pass there is no way of starting at the same point.

Threading definitely need a closed loop from spindle to controller even if it is only a simple index pulse.
John Stevenson

Offline PK

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Re: Controller Hardware
« Reply #14 on: July 25, 2016, 09:52:58 PM »
John is right. The controller needs some kind of indication of the spindles position and speed.

It's surprising how well a single pulse per rev works for this though.
So long as your cuts are light (which they should be for small threads) then you can do some amazing stuff.
<a href="http://www.youtube.com/watch?v=I6cu9SC876Y" target="_blank">http://www.youtube.com/watch?v=I6cu9SC876Y</a>

I don't have any pictures of it, but I used to have this 'party piece' code that turned a 25x6mm, dual start, tapered ACME thread in some PVC bar. It was good to watch...