The Best Steppers/Servos Setup Thread

[m_c]

but the machine doesn't need the worlds biggest servos, its not like it will take massive heavy billets. are there no small decent servos?

the table doesn't need to move at 1000mph.

There are, but gearing is the problem.
Stock steppers are 1.1Nm stall, with a gearing ratio of 12:30, giving roughly 2.75Nm at the screw.

A 50W 3000rpm servo, which from Kinco is 83mm long (should fit in a similar place to the steppers), gives 0.16Nm. So to get similar torque you need in the region of 17:1 gearing, and you limit screw speed to 176RPM (roughly 880mm/min).
Move to a 100W version, which from Kinco is 110mm long (I think this was very borderline for fitting to the X, and wouldn't fit on the Y), gives 0.32Nm. Ratio needed is about 8.5:1, and you'd get 1.6m/min speed. If you could manage the gearing ratio, this size would probably be a good match specification wise, but 8.5:1 involves a very big pulley. A gearbox would be a good option, but you add cost, and length.
A 200W 3000RPM servo, again from Kinco is about 120mm long, and gives 0.7Nm continuous torque. You need a ratio of about 4:1, which is very achievable., and you'd be up over 3m/min if you ran it at full speed.

Off course all those figures are based around the continuous/rated torque of the motor. Instantaneous/peak torque is typically 2-3x the continuous figure, but you normally rely on that for acceleration, which is where you should get the real benefit over steppers. If you were to run the figures above using the peak torque, then you would have to limit acceleration, and performance gains would be far more limited.

IIRC, the servo Triacs used about 200W DC servos. I'm sure I read the Y servo stuck out the back of the machine, but I've got no idea how the X was fitted.

[andy_con]

I'm guessing all the leadshine and other Chinese AC servos on ebay are naff?

[m_c]

I'm guessing all the leadshine and other Chinese AC servos on ebay are naff?

Some of them are perfectly good. Kinco is Chinese. Leadshine is good.
The big thing is making sure whatever you buy will do what you expect it to, and comes with reasonable documentation.

[Skiprat]

I bought a full set up of hybrid closed loop stepper motors and associated drivers etc (Purelogic and leadshine) from Zappautomation a few years back and have had nothing but praise for the setup and zappautomation.
Closed loop does exactly what i wanted and i think i oversized the hybrid steppers but at least i can sit on the machine and take a ride...obviously only done under the influence of alcohol ..

Tommy

[andy_con]

there are lots of things like this over ebay

http://www.ebay.co.uk/itm/CNC-AC-Ser...gAAOSwMgdXyS7x

and even cheaper stuff??

http://www.ebay.co.uk/itm/EU-Stock-N...4AAOSwoBtW58KV

I don't mind spending a few quid to get good results

[m_c]

there are lots of things like this over ebay

http://www.ebay.co.uk/itm/CNC-AC-Ser...gAAOSwMgdXyS7x

and even cheaper stuff??

http://www.ebay.co.uk/itm/EU-Stock-N...4AAOSwoBtW58KV

I don't mind spending a few quid to get good results

750W would be overkill for a Triac. I'd aim for 200W, or maybe 400W.

The second link is actually a closed loop stepper system. Technically it is servo system, however it won't have the same performance as what's more commonly referred to as a servo system.

I had been hoping DaveK would of chimed in with his views on the generic Chinese servo systems, but I guess he's too busy playing with his new toy...

[Davek0974]

Hi all,

I got my servo's from AliExpress direct from China, they are fitted to a Bridgeport mill(ex manual style machine) I got 700W on X&Y and 400W on Z.

Having only used steppers until this job, i was not expecting them to be as good as they were as the Nm figures do not compare with steppers at all. I used a CSMIO IP-A with 10-0-10v control.

The issues i had/have are all tuning related really - the manual i was sent by the guy was in strong Chinglish so not really much use to a beginner like me. To get a really good tune i am convinced i need to alter the parameters in the drives but cannot do this.

The tuning in CS Labs plugin is all i have so worked with that. It is a time consuming process, forget the auto-tune ;) Apart from a slight resonance on the Z drive I have it running really well now, very little following error and good acceleration, top speed is pretty low at 2500mm/min but this is only an old Bridgeport so no point in flogging her to death. Acceleration was more important to stop corner-rounding in Mach 3's trajectory planner.

I must admit that i had the 400W on the bench to play with and even running at maybe 5 rpm i could not stop the shaft rotating no matter how hard i grabbed it, the torque is phenomenal and start / stops at speed are sharp enough to make the motor jump off the bench!

I could probably have fitted smaller motors on the mill, they have 2:1 reduction drives but this size seemed a good price :) I think they were about £400 for 700W with drive and 5m cables.

I would love to fit them to the plasma cutter, may do one day.

[Zeeflyboy]

I bought a full set up of hybrid closed loop stepper motors and associated drivers etc (Purelogic and leadshine) from Zappautomation a few years back and have had nothing but praise for the setup and zappautomation.
Closed loop does exactly what i wanted and i think i oversized the hybrid steppers but at least i can sit on the machine and take a ride...obviously only done under the influence of alcohol ..

Tommy

I'm also running closed loop leadshine steppers and drivers, very happy with them.

[andy_con]

so these?

http://www.ebay.co.uk/itm/CNC-Leadsh...EAAOSwsN9XA89p

[Zeeflyboy]

Yes, looks to be the same as what I'm using.

They are nice, work great for me... but then I've never used servos so can't comment on that front. Even if you just view them as normal steppers they are a good (if not the cheapest) option in my opinion, they are quite literally plug and play with no tuning required at all and are very quiet, smooth at all speeds, stay very cool in operation and have the must-have features such as stall detection and error signal.

It was quite fun playing around with the closed loop system before installing them. You can fit a coupling to the shaft and then try to prevent it from rotating as an experiment. Long before it will throw a fault and disable the drive, you can see a sort of rubber band effect.... where a normal stepper would have thrown steps, these keep trying to fight you and then just ping back into place once you release them.

In theory the closed loop stuff also has better torque curves, acceleration and speed due to the controller having a better idea of what position the motor is actually in, along with higher efficiency and lower noise.

Edit:

Quite an interesting read on closed vs open loop steppers where they've actually done some lab testing http://www.motioncontroltips.com/tor...epper-systems/