Advice on buying servos.

[Robin Hewitt]

servos should be inertia matched to their load for best performance... the best positional accuracy I can get before things go unstable is about 200 encoder counts

To a lay idiot like me, you seem to be saying that there is some complicated matching that needs to be done on each axis before purchasing a servo system to avoid it being a huge disappointment. My steppers suddenly start to seem like God's gift to His chosen few. Am I misunderstanding?

[Boyan Silyavski]

To a lay idiot like me, you seem to be saying that there is some complicated matching that needs to be done on each axis before purchasing a servo system to avoid it being a huge disappointment. My steppers suddenly start to seem like God's gift to His chosen few. Am I misunderstanding?

Just a bit maybe. I went from steppers to servos and dont think i will ever look back. The other day i had here a vinyl plotter, was looking to buy. What stopped me was it was not servos but steppers, and somehow the noise put me off.

I got help from knowledgeable members of forum at the time which did the calcs for me what i need for my machine. So 100% here people will help you. Now i know more and can do that myself but surely will ask for advice if i am not sure. That's what the forum is for.

Anyway, as i have concluded many times, servos are a must for a metal working machine, production machine and hi resolution micro mill. All else could be done from steppers



PS. what put me off for the plotter was not only the noise but the ability of the plotter to track correctly longer lengths of vynil, if it was servo

[Robin Hewitt]

PS. what put me off for the plotter was not only the noise but the ability of the plotter to track correctly longer lengths of vynil, if it was servo

I think it was Calcomp had the patent on using grit for the driving rollers and everyone else looked jealous. I used to repair these things, a long time ago

[m_c]

To a lay idiot like me, you seem to be saying that there is some complicated matching that needs to be done on each axis before purchasing a servo system to avoid it being a huge disappointment. My steppers suddenly start to seem like God's gift to His chosen few. Am I misunderstanding?

Just apply some common sense. Don't go bolting a high inertia motor to a X1, and don't try using a small inertia servo on a quarter ton table. Use something a reasonable size.

Given what Agathon has posted links to, I would of though 400 or 750 watt servos would work nicely.
The smaller machine you've posted a photo of, I would of thought 200 or 400 watt.
To give some idea, IIRC Denford Triacs with servos, came with 200W servos, however they'd be conservatively sized due to being aimed at education. They perform well enough, however 400W would give a good boost to performance and work just as well.

[Agathon]

Just apply some common sense. Don't go bolting a high inertia motor to a X1, and don't try using a small inertia servo on a quarter ton table. Use something a reasonable size.

Given what Agathon has posted links to, I would of though 400 or 750 watt servos would work nicely.
The smaller machine you've posted a photo of, I would of thought 200 or 400 watt.
To give some idea, IIRC Denford Triacs with servos, came with 200W servos, however they'd be conservatively sized due to being aimed at education. They perform well enough, however 400W would give a good boost to performance and work just as well.

Yes, I think the 200W Omron drivers I've just bought will be too small, but will try them geared at 3:1. They were very cheap, so I'm not worried if I have to put them back on the market. I shall be keeping an eye out for 400W which is what they currently fit to the very slightly larger version of my machine.

Do you know what the ratio was on the Triac servos?

[Boyan Silyavski]

Yes, I think the 200W Omron drivers I've just bought will be too small, but will try them geared at 3:1. They were very cheap, so I'm not worried if I have to put them back on the market. I shall be keeping an eye out for 400W which is what they currently fit to the very slightly larger version of my machine.

Do you know what the ratio was on the Triac servos?

I am moving a 200kg gantry with 2x400w servos / via rotating nuts which have smaller inertia than spinning a screw / 3000 mms2 acceleration and judjing from the servo tuning and initial calculations, its the perfect thing. Exact sizing. geared 1.5, not 3. So with 200W servos geared 1.5 you could do a lot of things. No need to gear them up so if not needed. As gearing up will increase the spinning mass so maybe you will not benefit as you think ... 20/30 tooth is an ideal relation and pulley size. For lighter load you could go down as 16t but mind the servo shaft size. I would say for 200W servos, 18t pulley will be right, start thinking from there...

I am not sure also how Chinese servos stand up to brand servos. If 400w is 400w really? What i know is that the brand servos stand up to what they say. Thats why i preferred 230V AC servos , for all that benefits. If i buy a chinese servo i will always Up it one level of power so just to be sure. 750W isntead of 400

[m_c]

Do you know what the ratio was on the Triac servos?

I've only got the parts list for the stepper version, and it uses 12:30. Chaz has a servo version, but I don't think there would be much room to go for a higher ratio.

[Agathon]

What size timing pulleys would you suggest for 200 or 400 watt servos? I was thinking that 5M 9mm wide belt should be about right. Centres should be around 100mm.

[Ger21]

I'd say 15mm belt width minimum.

[m_c]

If you download the Gates DF software, it will generate suitable drive options.