[vertcnc]

I am currently getting ready to Cnc a MTW Md001. This will have sevos and rolled ballscrews all axis. Looking for opinions on whether to use direct drive for the servos or belt reduction.

I currently have a rf45 with belt reduction and servos that works great, just thought direct drive would be cleaner and maybe simpler.
If I use direct drive for the Z axis is a brake on this servo required?

[recordingwhiz]

I went with direct drive, for simplicity and lower part count. I do wish for the space savings and compactness the belt drive method offers.

just my reasoning.

GG

[SCzEngrgGroup]

Deleting the belt reducer from a servo system will require much larger, more powerful, and expensive, motors and drivers, and you'll end up using only a small portion of the available dynamic range, unless you plan to run your machine with 1000 IPM rapids (which is completely useless on a small machine). For stepper and servo motors of rougly comparable size/cost, the servo motor will have MUCH higher usable RPM (up to 4X or more), and MUCH lower torque. The belt reducer compensates for this, by increasing torque, and reducing speed at the ballscrew, allowing you to use the full dynamic range of the motor. This will give you a smaller, cheaper, more efficient drive system, with essentially identical performance, as compared to a large servo with no belt reducer. The larger motor will work, but is rather like shoe-horning a 500 HP V8 into a Toyota Corolla - you'll have a car that is very quick to accelerate in a straight line, but handles like a Mack truck, and sucks fuel like a 747.

Regards,
Ray L.

[vertcnc]

Thanks for the coments. Looks like most of 400-750 watts servos on the reasonable priced side max out at 1000 rpm. Which on a direct drive system would give just under 200 ipm with a 5mm turn screw.(if my math is correct) On a belt reduction system of coarse less. Was looking for something in the 180-200 ipm range and this maybe a problem unless I go with more expensive drives.

[SCzEngrgGroup]

I don't know where you're shopping, but I don't think I've ever seen ANY servo that "maxes out" at only 1000 RPM. Hell, even a stepper motor will do better than that! The 850W DC servos on my 9x49 knee mill run 4200 RPM @ 72V, and will push the machine around at 350 IPM. You must be mis-interpreting the specs.

Regards,
Ray L.

[vertcnc]

I should have clarified, they were depended on the drive and power supply. I was looking at the DMM servos and drives. With the DYN2 drive was 1000 rpm, but the dyn3 drive was 3000rpm.

[mactec54]

vertcnc

You will be fine at 1:1 with the low voltage Drive Dyna2 750W motors 1000 rpm, if you went with the 400W motors 3000 rpm you could use them around 1.5 :1 or. 2:1 for the Z axes 2:1, & best to use the 750W motor & the Dyna3 Drive for the Z axes

With the high voltage Drive Dyna3, the 750W motor runs at 3000 rpm Plus, depending on what input Voltage you use

[TiagoSantos]

I'm VERY happy with my 400w DMM servos, through a 3:1 belt drive reduction on all 3 axis. I get 200ipm easily on my RF-45, including the head with a 145 frame 2hp motor. The acceleration will also go much higher than I'm willing to run (I tried it at 200ipm, 90 acceleration - a little too violent for my taste..!).

I think I could have gotten away with a 2:1 reduction too, for 300ipm travels, but I felt the extra torque reserve was more beneficial to me than the increased rapids. In fact, I'm running my machine with 150ipm rapids right now, still not quite used to working on something this fast.

The main reason I went with the belt drive reduction though, was packaging. I have limited room in my basement and having to mount the motors directly on the ballscrew would have severely limited my X travel. I don't think the Z axis motor would have fit on top of the column either, the ceiling is too low.

[vertcnc]

Probably stick with belt reduction drives on this build also. Not sure if I will stick with DMM drives or not, although they seem to work ok, they are a little slow to respond to inquires on support.

[TiagoSantos]

They're normally very good with support, but Tianyu (who normally responds to emails and deals with sales) has been in China for a few weeks. If I remember right, he'll be there until the end of April, maybe May? I would hope that didn't discourage you, but I understand what it may seem like. The last time he was in China, he did take a day or two to get back to my emails, but I haven't been in touch recently.

They are local to me (20 minute drive) and they let me pick up basically a "1 axis" kit to test, no charge. I tried it, loved it and bought the rest of the kit. In the meantime their prices had gone up, but they sold me everything for the initial quote. A few weeks later, when I finally tried to run my machine for the first time, one of the drives was dead. I thought it had been DOA, so called DMM (at 4pm on a Saturday) and Hui asked me to meet him at the shop 30 minutes later. He replaced the drive no questions asked and apologized (even though he probably suspected it had been my fault). I went home, replaced the drive on the controller, flipped the switch and.. *puff*. Yeah, I had a short in the motor wire. I ended up fixing the second drive myself and offered to pay or buy back the first dead drive, but they graciously told me to forget about it.

Obviously much of my experience has been different because they're local and I can drive there to buy or pick things up, but I have zero reservations recommending them to anyone.