DDL / Direct Drive Linear Motors - anyone using them?

14 Dec 2016 03:50 - 14 Dec 2016 03:50 #84070 by FDP
I'm going into a new machine build and considering DDL, if I can get the cost to be worthwhile vs. ballscrew + servo that is.

Has anyone used DDL servos with LinuxCNC/have recommendations on motion controllers that work well well?

Since I'm new to LinuxCNC I probably won't go down this road if someone hasn't gone there before me.
Last Edit: 14 Dec 2016 03:50 by FDP.
14 Dec 2016 13:43 #84088 by Todd Zuercher
I have no experience with them, but my understanding is, it depends on what you want the machine to do, and how much you want to spend on it.
They can be amazingly fast, but can be very temperamental, and do not handle dirt and contamination well (especially the sort of mess associated with a metal working machine.)
I was looking at buying a slightly used very large wood working machine set up with a Fanuc control and linear motor system, and was discouraged from pursuing it by the manufacturer (they flat out told me don't buy one).
The following user(s) said Thank You: FDP
16 Dec 2016 22:38 #84293 by FDP
Thanks, I had a meeting with a sales rep from one of the larger firms who claimed that debris isn't that much of an issue. Still, I hadn't calculated the full power requirements until after our meeting and was pretty shocked by how far away they are from regular servos in power needs.
17 Dec 2016 02:19 #84303 by Todd Zuercher
What was shocking, that they need so much more power, or that it wasn't that much more?
I would not find it surprising if there is a huge difference, they have no mechanical advantage, and there has to be inefficiencies in the basic motor design compared to a regular motor.
17 Dec 2016 20:44 #84340 by FDP
They need about 3X the wattage of the servos we are looking at (with a relatively low lead pitch, giving a good deal of advantage to the servos). The DDL seems to be much easier to install (only a plus if you are building a bunch of machines, which we might be) and absurdly fast rapids. All in all the DDLs were much more competitive on paper than I had imagined going in. If we didn't have low-power as a criteria in our design I would seriously consider trying them on one axis of the prototype. Cost is ~1.25-1.5X of a good quality ball screw + servo combo.
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