On Wednesday 30 September 2009, Sven Wesley wrote: >2009/10/1 Gene Heskett <[email protected]> > >> ... > >Based on the if it walks & quacks like a duck theory, do you have any idea > >> what the pullup resistors are for that TTL circuitry? If there is any >> resistive load on those lines that goes back to ground instead of to VCC, >> it >> will play all sorts of tricks on you because the internal pullup of a TTL >> circuit is very weak. Often under 100 microamps. This means that you >> may not be getting a good logic one, and in that state, its very >> sensitive to induced noise. >> >> To check, try tying about a 4.7k to 10k 1/8 to 1/2 watt resistor from >> those data lines up to the 5 volt buss. The TTL circuitry can easily >> pull that down even if its only a few hundred ohms, but it might make all >> the difference in the noise immunity. The voltage at a logic 1 s/b >> higher than 3 >> volts, and 4 won't hurt a thing. A full 5 gets iffy again because there >> are >> TTL chips about that don't like an input at or above the VCC rail. >> >> This you can measure with a digital multimeter while everything is hot by >> turning the lathe spindle very slowly by hand, and you should see less >> than +0.150 volts when its low, and more than +3 volts when its high. >> This will give a noise margin of at least half a volt when low (and being >> low means the >> driver is turned on tight and it will gobble up most noises there that >> are not ground loop induced, and at 3 volts, a 0.6 volt noise margin >> since the guaranteed logic 1 to a TTL input is normally 2.4 volts. >> ... > >Mystery solved. :) >I made the cable right away and did the test run. Both Z and Y stop at dead >zero measured with a micrometer. > >Thanks Gene, I may try it, it seems it works now though. I was thinking of >getting the same encoder like the new one for the other servo's as well, > and after all this mess I maybe invest in a couple of new motor's as too. > They seem to be pretty strong but I wanna be on the safe side. > >Super thanks to everyone involved giving all the suggestions and ideas. You >have been the best support! >It's 4:11 in the morning, lets go home...
I'd say, but its only 10:52 pm yesterday as I start this reply here. :) I am glad you got it going Sven, but my curiosity bump is still sticking up. I'd love to see what your noise margins really are. My gut reaction is that either the old encoder was flaky, or that the new cable may follow better shielding and grounding methods than the old one. When push comes to real shoving, bear in mind that the cables with the mylar foil as a covering aren't just cheap cable. The best braided shielding, a 98% cover, will attenuate noise by maybe -55 db, the cheap foil cabling can easily attenuate noise to -110 db, in other words since the db is a log function, 55 additional db of shielding means its close to 1000 times better! That is why all of my machine except for the spindle motor, is wired with a microphone cable known as 'star-quad', when Belden sells it, a 4 conductor cable with a foil cover and about a 96% tinned copper braid over that. And the motors wired each coil to the opposite corner of the square pattern the wires are laid up in, with the whole square rotating a full 360 about every inch or so. With that fast a twist, even the magnetic shielding is very good. That cable is available in gauges as large as 20 I think, I'm using 24 gauge with my xylotex kit & motors. -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) The NRA is offering FREE Associate memberships to anyone who wants them. <https://www.nrahq.org/nrabonus/accept-membership.asp> Be careful! UGLY strikes 9 out of 10! ------------------------------------------------------------------------------ Come build with us! The BlackBerry® Developer Conference in SF, CA is the only developer event you need to attend this year. Jumpstart your developing skills, take BlackBerry mobile applications to market and stay ahead of the curve. Join us from November 9-12, 2009. Register now! http://p.sf.net/sfu/devconf _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
