View Full Version : Motion control, Servos - Where to start?

02-04-2005, 09:41 AM
Question for you motion/servo/stepper experts...

I'd like to start using servos in a few projects, but haven't worked with anything like that in the past. I've got the basic concept of servo systems and the mechanical part I can handle. The servo motors and drives/amplifiers I could probably manage to select on my own also, but what's a good controller to use as a starting point?
PC with software, PLC, HMI panel?
Any suggestions would be great, because I don't have any idea where to begin when it comes to controlling the thing.

I don't have an unlimited budget, but I don't mind buying things as neccessary either. I just want to get a good solid starting point and then learn from there... If that's possible.


02-04-2005, 10:14 AM
Dear Sir:

What are you controlling? We need to know what you want to accomplish with a good amount of details about number of axes, speed desired, accuracy wanted, force needed per axis etc!

Jack C.

02-04-2005, 10:37 AM
well if you got a mill or lathe you might want some gecko drives, or a kit such as the one from industrialhobbies

02-04-2005, 11:05 AM
I may be wrong on this, but what I'm looking for is information on the control end of it moreso than the mechanical end or a specific application. Speed, force and things like that I could work out for the particular application. The control/programming/feedback loop is where I'm lost. How do I get a signal to the amplifier? How do I make use of the feeback, wether it's a tach, encoder, resolver, etc?
For instance, if I had a 2-axis system that I wanted to electronicly gear together or a 3-axis system that would move from one position to the next with a pause for operator input before continuing, what's the best way to accomplish that?
Certain controls will work better for a particular application, but at the moment I'm just looking for someplace to start making things move.

I don't know if that helps or not, but I hope it does.


02-04-2005, 02:32 PM
I think Elnino is right, get a Gecko servo drive US$114 , then get a servo or make one from a dc motor an a rotary encoder.

The Gecko looks after all the tricky stuff you tell it which direction and how many encoder steps to turn. This is easily done with a connection to the parallel port of your pc.

I suggest you download Turbocnc from Dakeng.com so you will have a no brainer way to control your servo with accelleration decelleration etc. It is not expensive to register it if you find it to be usefull.

Good luck

02-04-2005, 02:35 PM

[This message has been edited by Stanko (edited 02-04-2005).]

02-04-2005, 03:59 PM
Learning is not always cheap.

Most the robotic classes at the college will cost you in money and time, or you can tinker and self educate.

I'd buy one servo drive, one stepper drive and play. You can get a parallel cable and just cut the printer end off, wire it up to the drives.

Research all you can. www.geckodrive.com (http://www.geckodrive.com) has some of the best documentation. www.rutex.com (http://www.rutex.com) www.dakeng.com (http://www.dakeng.com) the Yahoo groups also have lots online.

Nobody is born knowing everything, you learn from each thing you accomplish, each opened door showes you unseen doors to open. (knowledge) Having a open mind allows you to learn and not be blinded by thinking you "know it all".

Are you bad about taking things apart? I picked up a old plotter for $5. Not sure if I want to use it for a plotter or butcher it for all the goodies in it.
Some people use them for cutting vinyl signs with a rotating knife.

Have you seen the harmoicat and other "cheapie" cnc learning experiences? He used to use tip120 transistors tied to a chip that decodes it into two signals like a gecko does *(step and direction) otherwise you have to use 4 bits on the port, one for each transistor base. His plans are cheap and easy to build.
A simple cnc can be built for less than $100. If you find the parts laying around in "junk" a lot cheaper than that. there is enough parts in this plotter to make a cnc plasma cutter table to carry the torch.

There is no "one right way" but many ways to do the same thing.

02-05-2005, 09:45 AM
Thanks for the info.

I do like to self educate/tinker with alot of things, while not always the most efficient or cost effective way - it's usually fun.

Taking things apart is another problem I have. I think that goes hand-in-hand with the tinkering. Sometimes they go back together sometimes not.

Learning is a never ending battle, but the only way to loose is by thinking that you won.

Off I go for another adventure...

02-05-2005, 11:30 AM
Involute, I also like to tinker with things, but I have a really short attention span. If you haven't seen this website:
take a look. There are some tutorials on motor control, and some really neat stuff.

02-05-2005, 02:59 PM
My first cnc? A old craftsman table top drill, a drill cross x-y slide I put xl gears on to double drive. Motors were too Weak to pull the slide on thier own, so I doubled up the gear ratio.

Finding out you can cast gears with the www.synair.com (http://www.synair.com) resin makes it mucho cheaper. You can buy One gear, then copy it. I posted pictures at one time. Not sure where they ended up. Evan redid them since they were so dark.

That lil cnc was not good for much except drilling circuit boards.

A better plan would be a gantry machine. Build it and make it work, sell it on ebay for 3x your investment, then build something more elaborate. They are good for 2 dimensional text engraving, torch cutting, light carving. A local trophy shop bought one off ebay, has been making trophies now for about a year. They load it up and take it to the sports events and karate tournaments. Engrave peoples name on them trophies right there. They make a killing just doing Competitor badges.