On 08/02/2013 03:08 PM, Greg Bentzinger wrote: > It is often "uncomfortable" to pay too much ( or what you may > preceive as too much ) but it is usually far worse to not pay > enough. > > A real DC servo, and a 4 brush more specifically will turn smoothly > with as little as the power supplied by a single "D" cell battery > with no visual or audio signs of "cogging". Try this on a "treadmill > motor" and it will be a big eye opener. That big ol fan unit which is > usually mounted on the tread mill motor shaft serves double duty as a > flywheel to soften this cogging, also the cogging is lessoned by the > reduction belt drive, the belts help damp out the vibration.
I'll agree that a cog free motor is more desirable, but with a feedback controlled motor, there seems to be very little advantage. For the difference in cost, I've found that cog-rich treadmill motors work pretty well. I think putting the savings into getting rid of backlash is more important. I could be convinced to change my opinion, but so far I haven't been. > I like those Mitsubishi units Andy linked to - but Buyer beware - > There are servos, and there are sever duty servos - you need a good > sealed unit that can handle running in coolant if the servo is > mounted in an area subject to chips and coolant. A prime example > would be the motor used for a 4th axis sitting on a mill table. That > unit will get practically submerged in some cases when run in a > common VMC type machine. A treadmill motor could be well protected by using a full enclosure: http://www.wallacecompany.com/machine_shop/bridgeport/00047-1a.jpg I made the above table end plate large enough to fit a box over the motor, encoder, et al. (This was a jury rig. If I ever build it for real, the encoder would go on the screw end, and the motor fitted with billet end caps and bearings upgraded.) Now, if a machine is being used used to put one's kids through college, I would agree that spending a few buckets of money on known-good hardware and saving downtime may make a lot more sense. " Cost Time \ / | Quality " -- Kirk Wallace http://www.wallacecompany.com/machine_shop/ http://www.wallacecompany.com/E45/ ------------------------------------------------------------------------------ Get your SQL database under version control now! Version control is standard for application code, but databases havent caught up. So what steps can you take to put your SQL databases under version control? Why should you start doing it? Read more to find out. http://pubads.g.doubleclick.net/gampad/clk?id=49501711&iu=/4140/ostg.clktrk _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
