# Dif between (C) and (A) movement help plz. Cannot find answer anywhere!!

• I need help figuring out the difference with a Circular (c) motion and anCircular arc (a) motion...

Ive recieved different responses from different people, and when i google the Key words I cannot seem to find the answer..

Just need an explanation of the differences bettween the two. Im attempting to weld a Nose cone with a Keel strip. Starts welding in a straight line for about 10 inches, then curves down hill..

As im going down hill, between the points there are little curves going away from the part, making sort of a "w" effect.

If i could get an explanation of the difference between the two motion types it might help me out with my problem. Thank you!

• ## HawkMEFeb 25th 2023

• They both produce the same motion shape (circle or part of a circle) but the syntax is different and have a few minor functional differences.

A circle command always has pairs of points. The starting point is whatever point is before the first C point. The first C point is a mid point. And the 2nd C point is an end of that segment. For every 2 C points you can do a max of 180 degrees.

An Arc makes exactly the same motion but instead of requiring pairs of C points you can have any number of A points, but a minimum of 3. The movement to the first A point will always be linear, then it will blend circle motions to each next A point.

They do the same exact thing but I prefer A because it is a little more flexible for a few reasons.

1. Not forced to have them in pairs.

2. Automatic linear approach to first point.

3. You can apply frame and tool offsets to A points at the same time.

You can't go more than 180 degrees between any 3 points with either method.

Your start and end point must always be Fine or your circle will be lopsided. In C your starting point is not the first C point but instead is the non C point before your first C point. With A your starting point is the first A point.

All mid points should be CNT100.

You can deviate a little from a perfect circle but not much or it will error.

To create a W shape you could use an A movement at each vertex of the W. Your movement will actual look like a sine wave, not a W.

If you need a non-circular arc movement then you actually need to use Spline, which is a newer option.

• Thank you very much. Exactly what I needed.

• Hey Hawk, I have a short-arm M-10 and R-30iA here and I am trying out Circular motion for the first time. I do not have the Circular Arc motion type available to me. Basically, I am trying to teach this thing to play cornhole for my company's big anniversary party this summer.

I am happy with the path I've taught, but the arm moves through the C points SOOOOO slowly. I have several speed modifiers available to me, including mm/sec, MAX_SPEED, etc.

Oddly, I have found that entering an extremely small MSEC value gives me much faster circular motion than MAX_SPEED does, however it is still not nearly as quick as I want it to be and nowhere NEAR the speed of every other move in my program.

Is there something I'm missing here? Would posture and/or orientation be limiting my speed (and if so, how?)? Do you have any tips for achieving super fast circular motion or am I better off teaching a bunch of short linear segments with CNT100 termination?

• Your start and end point must always be Fine or your circle will be lopsided. In C your starting point is not the first C point but instead is the non C point before your first C point. With A your starting point is the first A point.

Fine termination type isn't really ideal for most applications (arc welding, laser, sealing). Having 20 linear segments to create a single arc isn't ideal either. I've always attempted to make A or C moves work for these applications, but usually just end up with the linear segments because they end up providing the best motion. Are these motion types really applicable to these types of processes? Would there be any benefits (ex. more consistent TCP speed)? Even spline for sealer path. Just curious.

• It may not work for those applications. All I know is that the way the Fanuc motion planner works, if you don't start and end on Fine, or pretty close to it, you circle will turn into a lemon shape.