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View Full Version : Gantry/two motors per axis...how to configure



chozo
08-26-2004, 09:26 PM
I'm new to CNC, but I'm in the planning stages of building a machine.

I was going to have two rails for the X-axis, with a single rail mounted across for the Y-axis, which will hold the Z-axis.

I've been reading the manual for Mach2, and it talks about running two motors/screws per axis. It says the second motor will need its own axis to slave to the main drive.

I was planning on purchasing the FET-3 system from stepperworld.com
On their site, it says: "As an example of what you can do with the extra power, the FET-3 can easily run two motors in unison off each axis. (Two motors slaved together making identical or mirrored rotations is an economical way to drive a single axis with increased torque.)"

So, how will all of this work? It's a 3-axis controller, and the Mach2 needs an axis per motor? Will I have to ignore the Mach 2 statement, and run the X-axis pair as a single axis? Or do I need to purchase a 4-axis controller?

Will the hardware and software work together, or are they doing the same thing?

Anyone have experience in this? Thanks a bunch!

InventIt
08-26-2004, 10:18 PM
I can tell you from my own experience, using 2 motors to drive your gantry is not the best way. I had many headaches trying to do this on my build. A mechanical connection of the two leadscrews is a better way to go! it may be more complicated and a little more costly but the end result is much better.

Do you need the space under your gantry to be open? Is your machine wide? Can you use one leadscrew under the table? Tell us more about your design, size etc...

Checkout my build...and my problems with running two motors
http://cnczone.com/forums/showthread.php?s=&threadid=2249&perpage=10&pagenumber=1

chozo
08-26-2004, 10:41 PM
What type of control system did you use? You think using the hardware or software I mentioned would've helped?

Yep, I need clearance under the gantry.

I'm mounting this to a SS table, and it's going to be 24x36" in size.

The 36" X-axis is the dual-screw axis, with the Y-axis floating in between.

What type of mechanical connection would be best if I went with a single motor? A belt?

You never showed any pics of your timing belt setup.


Thanks.

ger21
08-26-2004, 11:04 PM
http://website.lineone.net/~rmtucker/

2nd row, 3rd picture. There is a thread here on this machine, the builder is rmtucker I believe.

You won't get very good performance from the FET board, btw. You'll get much higher speeds with a Xylotex or the new Hobby CNC board.

If you do want to use two motors, you will need a 4 axis drive. There are a lot of machines that use 2 motors per axis that work fine, they just have to be well designed and setup. You want to make sure you NEVER miss any steps or you could cause some damage to your machine.

chozo
08-26-2004, 11:12 PM
Wow, where can I get the hardware to set that type of belt system up?

Also, thanks for the info on the FET board, and reminding me to check back on the HobbyCNC site.


If you do want to use two motors, you will need a 4 axis drive. There are a lot of machines that use 2 motors per axis that work fine, they just have to be well designed and setup. You want to make sure you NEVER miss any steps or you could cause some damage to your machine.
So, the 4-axis controller from HobbyCNC would do well?

Graham S
08-27-2004, 07:05 AM
This sexy machine:

http://www.rainnea.com/cnc_5axis.htm

Uses two motors, at least the older version did.

Apparently it is not a good idea as the motors can tend to fight each other however I understand he had no problems although I don't think he was taking heavy cuts.

Balendo who is a bit of an expert on these things suggests belts are better so that is what I intend to do.

Graham

DSL PWR
08-27-2004, 09:12 AM
That is a sexy machine!

chozo
08-27-2004, 04:54 PM
Has anyone here actually tried using two motors, where the second motor is slaved to the first?
I want know if that configuration can work with no problems, if properly set up. I know there are problems with treating the two motors as one.

ger21
08-27-2004, 09:50 PM
Yes, it can work. I've seen quite a few machines on various sites and groups that have 2 motors per axis. But I think the only one I've seen here was InventIt's, and he had problems with his. It also depends on what software you use to run your machine. Mach 2 has a slave function so the second axis will do exactly what the first one does. It also allows the two motors to be rest independantly in case you do happen to lose a few steps.

All ShopBot's use two motors for their x-axis. http://www.shopbottools.com

I plan on using 2 motors on my X-axis, but my machine is still a few months away from construction.

If this is your first machine, and you're new to CNC, I would recommend going with either a single motor and leadscrew, or the single motor/ belt drive/ 2 leadscrew method desribed above. Much simpler to build and get working properly. And a lot cheaper than having to rebuild if the 2 motor design won't work correctly. Just about everyone here will tell you when you're starting out, Keep it Simple.