Centroid Schematics

[Richards]

As a "process control engineer" with over forty years experience designing and building process control computers for industrial purposes, I found it very refreshing to see Centroid's extensive schematics. They had schmatics for Gecko drives, for Leadshine drives, for ClearPath servos and for DMM servos. In other words, they already had schmatics for everything that I planned to use. Piece by piece, I assembled my test bench. My routine is to test a single driver/motor on the bench before testing multiple drivers/motors. In every case, the single motor worked (although I missed the speed limitations of the Leadshine clone when I first tried that driver).

When I used multiple ClearPath motors, I had erratic problems. I checked and rechecked the schematics, the Acorn User's Manual, and documentation from Teknic/ClearPath. As far as I could tell, everything was wired properly. The problems really became apparent when I added a DMM/DNY4 driver to the mix. It's fault signal was opposite of the ClearPaths' fault signals.

Later on, Centroid released a new schematic for using multiple ClearPath motors. (Thank you Keith). Even though Centroid had followed ClearPath's documentation before revising the schematic, Centroid realized that ClearPath had erred. The new schematic using relays (just as Gary Campbell has earlier advised), solved the problem.

I also found a new problem when I used servos instead of steppers. With steppers, assuming that the enable signal is not used, the stepper has maximum torque when stopped (usually cut to 50% after a second or so by the driver). That "holding torque" held the axis position when the motor stopped. Servos don't do that. They require that the enable signal be active before they move. Unfortunately, the enable signal turned off when a job was finished, allowing the weight of an axis to move the servo out of position which required homing before starting the next job.

There were a few other minor things about how signals were handled that I prefered to do differently from the way that the schematics advised. (Please note that I'm absolutely not critisizing the schematics. I'm an old man who has picked up preferences on my journey through life. I'm more comfortable doing some things different from the way that others do them.)

The end result is that I looked outside the box and chose to handle signals in an unorthodox way.

My advice is to start with the schematics. If everything works the way that you want, you're ready to start cutting. On the other hand, if you're left scratching your head, don't be afraid to look outside the box. At $300, we shouldn't expect the Acorn to solve every possible problem. In the DIY world, sometimes we have to accept that "DO IT YOURSELF" can mean doing more than we though would be necessary. I can assure you that if you find yourself outside the box, that if you move slowly, test signals, take careful notes, do proper research and follow standard practices, that you will be able to build the machine of your dreams using the Acorn as the center point of the design.

[cnckeith]

thank you.

just to clarify...AC servos will and can hold position at the end of a job.

often where both servos and steppers get into trouble is with a weighted (not balanced) Z axis ...then when power is removed from the Z axis motor (estop condition or turn off the main power) the the axis 'falls' to the table. this can be fixed several ways.. 1.) counterbalance the Z axis (linear spring or gas strut or weight 2.) install an Axis Brake such as a electro mechanical unit (note: the wizard has Preprogrammed Axis Brake outputs in the Output drop down selections to make it easy to configure an axis brake that automatically comes on when power is removed from the axis motor)

[cnckeith]

and on the Centroid schematics.. we have a new schematics page up and running in Beta..there are a few dead links that we are fixing while we continue to populate and test the new page.. take a look..

https://www.centroidcnc.com/dealersuppo ... browse.php#

[Richards]

Thanks, Keith.

The problem on a CNC router is that the Z-axis moves with the gantry. That means that using counter-weights would put a lot of extra weight on the gantry. I've looked at gas shocks. I know that a lot of people use them. I have not used them, but it seems that the motor would have to fight the shock's resistance as well as the Z-axe's weight when moving up. I may be wrong about that. I've also checked into using electrical brakes ($$$).

I may have some setting wrong, but the ClearPath motor shafts freely spin after a job is completed. (I haven't upgraded to the new software yet.) I suppose that the ClearPaths would be DC servo motors because they use 75VDC as a power source. To get around that situation, I grab the "ready" signal on the Acorn's output, set a coil to hold enable ON until I manually turn it off or until the program exits. That may cause excessive heat in the ClearPath motor if run in a production environment. That's something that I will be watching when I get to that stage.

[cnckeith]

Thanks, Keith.

The problem on a CNC router is that the Z-axis moves with the gantry. That means that using counter-weights would put a lot of extra weight on the gantry. I've looked at gas shocks. I know that a lot of people use them. I have not used them, but it seems that the motor would have to fight the shock's resistance as well as the Z-axe's weight when moving up. I may be wrong about that. I've also checked into using electrical brakes ($$$).
.

<< if the Z axis weighs 50 pounds and the gas shock is a 40 lb unit the z axis motor would be moving 10 lbs up or dn, size the linear spring or gas / air cylinder slightly under the wight of the Z axis.>>

[Richards]

Thanks, Keith,

I'll try to find an appropriate gas shock today and try things out.

[Gary Campbell]

Mike...
A few points

ClearPath motors will not "free wheel" until power is removed or ENA signal is de-asserted. If yours do, something is wrong. That said, on a Z axis the weight can in some cases cause the motor to work to hard and actually fault. On my "Ultimate Woodworking Machines" I have been using double ended air cylinders, (one end under pressure the other vented to daylite) as a Z counterbalance. The ClearPath tuning software makes it very easy to set the regulator for the counterbalance as you can read onscreen in real time how much torque is required to hold a given position. You can watch the torque numbers go down as you increase pressure, then as you pass "neutral buoyancy" watch it increase.

Problem with gas springs is that they are not consistent thruout their range. And its hard to guess which you need.

[Richards]

Thanks, Gary

I just bought a gas strut and brackets and I have some double-ended air cylinders on hand that I can hook up to a regulator and compressor. Thanks for that tip. Other than needing to run an air compressor, which is essential when using a router, both solutions are in the same price ballpark, depending on whether you already have a regulator, hosing and fittings.

As for the enable/disable signal, mine goes OFF after a program has finished. Is there a setting that keeps the enable signal on?

[Gary Campbell]

In all honesty, I never connect to the onboard ENA signal. I usually go thru a relay (COM) (for control) and link to an Aux button. I had noticed a few instances when the ENA signal was not active when I wanted/needed to be and visa versa, so I've stopped using it.

Here's a couple pics of my Air CB setup:

[Gary Campbell]

Mike...
Can you make a quick sketch showing your enable circuit?