Mariss, Some day do the 11 to 99. I will save this email for reference. Very valuable information. Thanks Jim ----- Original Message ----- From: "Mariss Freimanis" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Friday, December 17, 2004 11:12 PM Subject: [CAD_CAM_EDM_DRO] Re: Best source for Servo's ??
> > > My 2 cents on the subject, no particular order: > > 1) Never mind torque, never mind RPM. Think Watts. Watts is power and > power is what gets things done. > > 2) Power is torque times RPM or linearly, force times velocity. > Specifically, Watts = RPM * in-oz / 1351 or linearly, Watts = IPM * > Lbs / 531 > > 3) 1 Watt can push (or lift) 1 LB at 531 inches per minute or it can > push (or lift) 531 Lbs at 1 inch per minute. Mix or match; you see > the point. > > 4) 1 horse-power is 746 Watts. > > 5) Steppers or servos? A stepper (NEMA34) tops out at 200 to 250 > Watts (1/4 to 1/3 HP) mechanical. A servo goes past 1,000 Watts > (Using 80VDC rated drives). Both are equally accurate and reliable as > positioning motors. > > My recommendations? If you need 100W or less, think steppers. If you > need 200W or more, you have to go with servos. In between, either > will do. > > 6) How do you estimate how many Watts you need? > > The best trained Olympic atheletes can generate a sustained 200 Watts > of power output. I'm talking about Marathon runners, long distance > swimmers or Tour de France bicyclists. This is documented in the lead- > up to the human-powered Gossamer Condor human powered flight across > the English Channel. > > I have in my experience been on the shop floor more than a few times. > The machinists I remember didn't look like Olympians and they weren't > working up a sweat running manual Bridgeports. It's safe to say less > than 200W was being put into the hand-cranks of these machines. > > Start by figuring what torque you need on the lead-screw. Measure the > diameter of the hand-crank of a manual machine. Use your experience > as a machinist of how much force you would apply to that handle > before you figured you are doing something wrong. 5 Lbs, 10 Lbs, or > both hands to get over 25 Lbs? > > Multiply that number by 16 to get ounces, then multiply that by the > radius of the hand-wheel. The result is the torque in in-oz you apply > to the lead-screw. > > If you apply 10 Lbs on a 5" diameter crank, you should get 400 in-oz > of torque. > > Calculate the screw RPM for the speed you want. If you have a 5 TPI > screw and you want 120 IPM, you get 600 RPM (IPM * TPI = RPM). > > Multiply screw RPM by in-oz, divide by 1351; that is the power you > need. Using the above, you get 177 Watts. > > 7) Steppers are better than servos for milling CNC applications. > > Steppers have a speed-torque curve that makes it ideal; lots of > torque at low speeds where work gets done, miserable torque for > rapids where nothing is needed of it. Think of a stepper as a motor > with an infinitely variable automatic transmission gearbox. Trade in > torque for speed. > > 8) Gearing is very imortant. Steppers or servos, each has > their "sweet point" for best power delivery to the load. Steppers > should be run between 900 to 1500 RPM to deliver max power. Servos > should always be run near 80% of no-load RPM for same. > > 9) Never have a power supply voltage higher than what you need when > using a stepper. It is absolutely insane to run a 5A NEMA34 step > motor at 80VDC when the motor will never turn faster than 500 RPM. > All you get for your trouble is a very hot motor that could deliver > decent power at 2,000 RPM but it never gets run there. What a waste. > Use a lower voltage. > > This particularly applies to people using rack and pinion > transmissions. > > 10) Don't replace a stepper with a servo of the same frame size and > expect things to work OK. They won't. > > Steppers are high torque, low RPM motors. Servos are the opposite. > They have little torque but they develop that at high RPM. They need > reduction gearing to to match the load. > > Think of being in a sports car with a manual transmission. The light > turns from red to green; which gear do you want to be in? 1st or 5th? > Same engine, same power. > > Were it a desiel, (stepper) the gearing would be different than if it > were a turbocharged 4-valve, 9,000 RPM red-lined 4-banger (servo). If > transmissions matter so much on cars, they matter just as much on > your choice of motors. Steppers and servos are entirely different > animals and must be treated that way. > > I could easily do (11) thru (99), there is so much territory to cover > but that's enough for now. > > Mariss > > > > > > > > > > > Addresses: > FAQ: http://www.ktmarketing.com/faq.html > FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/ > Post Messages: [EMAIL PROTECTED] > > Subscribe: [EMAIL PROTECTED] > Unsubscribe: [EMAIL PROTECTED] > List owner: [EMAIL PROTECTED], [EMAIL PROTECTED], [EMAIL PROTECTED] > Moderator: [EMAIL PROTECTED] [EMAIL PROTECTED] [EMAIL PROTECTED] [Moderators] > URL to this group: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO > > OFF Topic POSTS: General Machining > If you wish to post on unlimited OT subjects goto: aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if you have trouble. > http://www.metalworking.com/news_servers.html > > http://groups.yahoo.com/group/jobshophomeshop I consider this to be a sister site to the CCED group, as many of the same members are there, for OT subjects, that are not allowed on the CCED list. > > NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM. DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........ > bill > List Mom > List Owner > > > Yahoo! Groups Links > > > > > > > Addresses: FAQ: http://www.ktmarketing.com/faq.html FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/ Post Messages: [EMAIL PROTECTED] Subscribe: [EMAIL PROTECTED] Unsubscribe: [EMAIL PROTECTED] List owner: [EMAIL PROTECTED], [EMAIL PROTECTED], [EMAIL PROTECTED] Moderator: [EMAIL PROTECTED] [EMAIL PROTECTED] [EMAIL PROTECTED] [Moderators] URL to this group: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO OFF Topic POSTS: General Machining If you wish to post on unlimited OT subjects goto: aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if you have trouble. http://www.metalworking.com/news_servers.html http://groups.yahoo.com/group/jobshophomeshop I consider this to be a sister site to the CCED group, as many of the same members are there, for OT subjects, that are not allowed on the CCED list. NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM. DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........ bill List Mom List Owner Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
