Gerry Chu wrote: > I'm new to motion controllers, and I'd like to ask the newbie question > of which motion controller I should get. They all seem about the same to me. > > Maybe the better question to ask is what's the difference between > controllers, esp. given their price range. > > Requirements: 4+ axis, less than 1ms servo loop, extra inputs/outputs, > nice to have windows driver.
You don't mention things like "analog outputs" (as compared to step/dir, or PWM). For EMC, the "motion controller" is EMC itself. Any board that you buy is basically an I/O device. Not all I/O is created equal of course. Simple I/O devices like the parallel port or an 8255 board only handle individual bits. More sophisticated boards provide more sophisticated I/O devices such as encoder counters, PWM generators, step/dir generators, digital-to-analog converters (DACs), analog-to-digital converters (ADCs), etc. What matters for EMC (and non-EMC related HAL based applications) is simply what mix of I/O devices the board provides, compared to what you need. > I've read the list archives, and have seen similar questions asked, but > I haven't seen the question answered to my satisfaction. If you'd like, > you can respond by emailing me directly. > > Here's my impressions on a few of them given my lack of knowledge of the > subject: > > ==Servo-To-Go== > Good: I know someone who's had good experiences with it, 8axis, seems > well-documented, windows driver > Bad: ISA bus, all the software seems to be kinda outdated, expensive Provides analog DACs and encoder counters, plus some plain digital I/O. I don't know offhand how many DACs or encoder channels, probably 4 or 8 of each. > ==Mesa== > Good: Seems like a lot of people on the list use it. Nice that they sell > an H-bridge amp that plugs in. Cheap! > Bad: I don't really care about the FPGA. I want a motion controller, not > an anything I/O card. Is FPGA slower? Existing config+driver provides 4 encoder counters and 4 (maybe 8?) DACs, plus plain digital I/O. (The DACs are implemented as a high frequency PWM that is filtered and converted into an analog voltage on a breakout board). Work is in progress on a new FPGA config+driver that will provide any combination up to 8 encoder counters, 8 pwm generators (can be used as DACs), and 8 step/dir generators, with unused pins as plain I/O. That config will probably be available in a month or two. > ==Vital MotencLite== > Good: Seems well documented, professional, windows driver. At this point > in my mind, this seems like the best. > Bad: Someone on the list a while back said he had some trouble with it. Regular Motenc is 8 channels encoder, 8 channels DAC, and I think 8 channels ADC, plus some plain I/O. (To my knowledge its the only board with ADC, but I could be wrong.) Motenc Lite is cheaper and has only 4 channels of encoder. Not sure if it has 4 or 8 DACs and/or ADCs. > ==Pico== > Good: Cheap. Sells amps too. > Bad: Parallel port seems kinda iffy. Multiple flavors. USC has 4 step/dir generators, and 4 encoder counters that can be configured to count the steps, or count an external encoder. UPS has 4 PWM generators and 4 encoder counters. Both have some plain I/O, with provisions for using Opto-22 modules. > If I understand right, I can use EMC as a controller-independent > interface to do PID control. Is this correct? Yes. EMC's motion controller module simply outputs commanded position every millisecond for each axis. Those commands go either to a software based step/dir generator for budget systems, or to software PID loops. The PID loops get their feedback from any input device (almost always an encoder counter), and send their output to any output device (usually either a DAC or a PWM generator). For moderate performance needs, HAL has software based encoder counters and PWM generators that can be used with plain I/O pins. > > My application is haptic devices (touch/force feedback) for user > interfaces. Also maybe CNCs, which I'd love to build in the future. > Sounds like you might need ADCs to measure force? or are the signals digitized in the sensors? In any case, I think the first step in picking a board is coming up with a list of all the I/O that you need. If you need ADCs for example, you can immediately rule out any boards that don't have ADC channels. Regards, John Kasunich ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys-and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
