[koenbro]

Hi,
I have bought B2 series servos, they have a 160,000 count per rev incremental encoder. They are effectively Deltas entry level model. You pay more for A2,A3 and the latest B3 series but is doubtful to me that I would get any great benefit over and above the B2 series which are truly impressive themselves. The A2 series (and possibly the A3 and B3 series)
has a dual feedback loop. Thus the principle feedback from the motor is still the rotary encoder, normal for any AC servo, but the drive can accept a second encoder input, say a linear scale attached direct to the axis and the position control loop incorporates both encoders. Very impressive, and only about $50 more than a B2 series. This is an example of 'load sensing position control' which all the top-flight servo manufacturers use in various guises. Clearpath dosen't even come close to that level of sophistication.

Clearpath servos are good quality and well supported but are expensive for their power output. For the same or less money than you would pay for a 400W Clearpath you can get a 750W Delta or DMM. Additionally in order to make Clearpaths as appealing to first time servo buyer as possible they have vey limited IO and control modes whereas Delta and DMM have vastly more IO and mixed control modes.

The sizing of a servo, or stepper come to that, is all about inertia. Contrary to popular belief the dominating component in the inertia equation is the rotating components, particularly the ballscrew.

I am using 32mm diameter C5 double nut ballscrews of 5mm pitch. The ballscrews represent 85% of the inertia with the servo armature contributing another 10% with the axis bed (at 115kg) contributes only 5%.

Thanks Craig, that is very helpful advice and helps me clarify my path. First, I decided to continue with Mach4 and will buy a second ESS (one is already installed for my CNC router. This way I can hopefully use the configuration for homing and limit switches and auto-zero from Avid CNC RouterParts. That will also save some money from returning the Acorn + software.

Second, I’d like go with servos and not steppers. It was very easy to find documentation on the Delta ASD-B2 series, which I think is the optimal choice for me, but I am having a very difficult time finding vendors. Where did you get yours? I saw some on eBay with "shipping from China" but I want to buy from a US vendor.

If you tell me what size, pitch and length ballscrews you are using I can tell you what size servos you will need, and surprisingly is less affected..... much less affected by axis mass than you might believe.

I do not know the size, pitch or length of the ball screws, as I have not yet received them, but from the documentation on the Precision Matthews size and the use of 7001 series ball bearing, I guess 1/2". From the description of the PM-728VT mill, the length of the x is probably about 19", y is maybe 10"; don't know the pitch.

The PM site also mentions that the attachments on x and y are for NEMA 23 and for z is NEMA 34. Does this change the choice of servo motor? Will 400W servos adapt?