I saw a real fast one armed robot. I was wondering if stepper motors was used or closed-loop control. I know NC machines use stepper motors but I heard the torque isn't as good as dc motors.
Stepper motors or servos?
Started by ●March 15, 2017
Reply by ●March 15, 20172017-03-15
On Wed, 15 Mar 2017 10:49:13 -0700, gyansorova wrote:> I saw a real fast one armed robot. I was wondering if stepper motors was > used or closed-loop control. I know NC machines use stepper motors but I > heard the torque isn't as good as dc motors.* Stepper motors are bigger for the torque that they'll deliver, and getting the most torque out of them requires trickery. Well known and established trickery, but still trickery. * _Some_ NC machines use steppers, some use servo motors. For a time (and possibly still, I haven't been paying attention recently), most of the DIY NC machine software was targeted to stepper outputs. However, it is very common to have a servo motor controller that takes the same "direction + step" commands that a stepper motor driver does. If you want maximum speed for the motor size, then you want a servo motor. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com I'm looking for work -- see my website!
Reply by ●March 16, 20172017-03-16
On Thursday, March 16, 2017 at 7:09:09 AM UTC+13, Tim Wescott wrote:> On Wed, 15 Mar 2017 10:49:13 -0700, gyansorova wrote: > > > I saw a real fast one armed robot. I was wondering if stepper motors was > > used or closed-loop control. I know NC machines use stepper motors but I > > heard the torque isn't as good as dc motors. > > * Stepper motors are bigger for the torque that they'll deliver, and > getting the most torque out of them requires trickery. Well known and > established trickery, but still trickery. > > * _Some_ NC machines use steppers, some use servo motors. For a time > (and possibly still, I haven't been paying attention recently), most of > the DIY NC machine software was targeted to stepper outputs. However, it > is very common to have a servo motor controller that takes the same > "direction + step" commands that a stepper motor driver does. > > If you want maximum speed for the motor size, then you want a servo motor. > > -- > > Tim Wescott > Wescott Design Services > http://www.wescottdesign.com > > I'm looking for work -- see my website!Do position servos work 360 degrees nowadays. In the old days we had pots that limited the travel though ac servos using synchros could go right round
Reply by ●March 16, 20172017-03-16
On Wed, 15 Mar 2017 20:55:37 -0700, gyansorova wrote:> On Thursday, March 16, 2017 at 7:09:09 AM UTC+13, Tim Wescott wrote: >> On Wed, 15 Mar 2017 10:49:13 -0700, gyansorova wrote: >> >> > I saw a real fast one armed robot. I was wondering if stepper motors >> > was used or closed-loop control. I know NC machines use stepper >> > motors but I heard the torque isn't as good as dc motors. >> >> * Stepper motors are bigger for the torque that they'll deliver, and >> getting the most torque out of them requires trickery. Well known and >> established trickery, but still trickery. >> >> * _Some_ NC machines use steppers, some use servo motors. For a time >> (and possibly still, I haven't been paying attention recently), most of >> the DIY NC machine software was targeted to stepper outputs. However, >> it is very common to have a servo motor controller that takes the same >> "direction + step" commands that a stepper motor driver does. >> >> If you want maximum speed for the motor size, then you want a servo >> motor. >> >> -- >> >> Tim Wescott Wescott Design Services http://www.wescottdesign.com >> >> I'm looking for work -- see my website! > > Do position servos work 360 degrees nowadays. In the old days we had > pots that limited the travel though ac servos using synchros could go > right roundIf you're talking RC servos, yes, they're still limited in travel. If you're talking industrial servo motors, most of them come with shaft encoders. As long as your mechanism can stand doing a "home" cycle on startup, you can get as many turns out of them as you wish. (AFAIK, the current trend is servo motors with built-in drives, so you're not even driving the motor externally -- you're just supplying it with power and commands. But I'm usually involved in things that are more deeply embedded than that, at least at the moment.) -- Tim Wescott Control systems, embedded software and circuit design I'm looking for work! See my website if you're interested http://www.wescottdesign.com
Reply by ●March 16, 20172017-03-16
On 16.3.17 17:20, Tim Wescott wrote:> On Wed, 15 Mar 2017 20:55:37 -0700, gyansorova wrote: > >> On Thursday, March 16, 2017 at 7:09:09 AM UTC+13, Tim Wescott wrote: >>> On Wed, 15 Mar 2017 10:49:13 -0700, gyansorova wrote: >>> >>>> I saw a real fast one armed robot. I was wondering if stepper motors >>>> was used or closed-loop control. I know NC machines use stepper >>>> motors but I heard the torque isn't as good as dc motors. >>> >>> * Stepper motors are bigger for the torque that they'll deliver, and >>> getting the most torque out of them requires trickery. Well known and >>> established trickery, but still trickery. >>> >>> * _Some_ NC machines use steppers, some use servo motors. For a time >>> (and possibly still, I haven't been paying attention recently), most of >>> the DIY NC machine software was targeted to stepper outputs. However, >>> it is very common to have a servo motor controller that takes the same >>> "direction + step" commands that a stepper motor driver does. >>> >>> If you want maximum speed for the motor size, then you want a servo >>> motor. >>> >>> -- >>> >>> Tim Wescott Wescott Design Services http://www.wescottdesign.com >>> >>> I'm looking for work -- see my website! >> >> Do position servos work 360 degrees nowadays. In the old days we had >> pots that limited the travel though ac servos using synchros could go >> right round > > If you're talking RC servos, yes, they're still limited in travel. > > If you're talking industrial servo motors, most of them come with shaft > encoders. As long as your mechanism can stand doing a "home" cycle on > startup, you can get as many turns out of them as you wish. > > (AFAIK, the current trend is servo motors with built-in drives, so you're > not even driving the motor externally -- you're just supplying it with > power and commands. But I'm usually involved in things that are more > deeply embedded than that, at least at the moment.)Before the shaft encoders, there were sin/cos potentiometers and resolvers (rotating I/Q transformers), also synchros, which were three-phase versions of the resolvers. -- -TV
Reply by ●March 16, 20172017-03-16
On Friday, March 17, 2017 at 7:26:19 AM UTC+13, Tauno Voipio wrote:> On 16.3.17 17:20, Tim Wescott wrote: > > On Wed, 15 Mar 2017 20:55:37 -0700, gyansorova wrote: > > > >> On Thursday, March 16, 2017 at 7:09:09 AM UTC+13, Tim Wescott wrote: > >>> On Wed, 15 Mar 2017 10:49:13 -0700, gyansorova wrote: > >>> > >>>> I saw a real fast one armed robot. I was wondering if stepper motors > >>>> was used or closed-loop control. I know NC machines use stepper > >>>> motors but I heard the torque isn't as good as dc motors. > >>> > >>> * Stepper motors are bigger for the torque that they'll deliver, and > >>> getting the most torque out of them requires trickery. Well known and > >>> established trickery, but still trickery. > >>> > >>> * _Some_ NC machines use steppers, some use servo motors. For a time > >>> (and possibly still, I haven't been paying attention recently), most of > >>> the DIY NC machine software was targeted to stepper outputs. However, > >>> it is very common to have a servo motor controller that takes the same > >>> "direction + step" commands that a stepper motor driver does. > >>> > >>> If you want maximum speed for the motor size, then you want a servo > >>> motor. > >>> > >>> -- > >>> > >>> Tim Wescott Wescott Design Services http://www.wescottdesign.com > >>> > >>> I'm looking for work -- see my website! > >> > >> Do position servos work 360 degrees nowadays. In the old days we had > >> pots that limited the travel though ac servos using synchros could go > >> right round > > > > If you're talking RC servos, yes, they're still limited in travel. > > > > If you're talking industrial servo motors, most of them come with shaft > > encoders. As long as your mechanism can stand doing a "home" cycle on > > startup, you can get as many turns out of them as you wish. > > > > (AFAIK, the current trend is servo motors with built-in drives, so you're > > not even driving the motor externally -- you're just supplying it with > > power and commands. But I'm usually involved in things that are more > > deeply embedded than that, at least at the moment.) > > > Before the shaft encoders, there were sin/cos potentiometers and > resolvers (rotating I/Q transformers), also synchros, which were > three-phase versions of the resolvers. > > -- > > -TVYes, the military used a lot of them, maybe for gun turrets and the like, you can still buy them.
Reply by ●March 17, 20172017-03-17
On Wednesday, March 15, 2017 at 2:09:09 PM UTC-4, Tim Wescott wrote:> On Wed, 15 Mar 2017 10:49:13 -0700, gyansorova wrote: > > > I saw a real fast one armed robot. I was wondering if stepper motors was > > used or closed-loop control. I know NC machines use stepper motors but I > > heard the torque isn't as good as dc motors. > > * Stepper motors are bigger for the torque that they'll deliver, and > getting the most torque out of them requires trickery. Well known and > established trickery, but still trickery.what's the trickery? like quadrature sinusoids applied to the two windings with frequency/phase synchronized to the movement of the rotor? otherwise, i can't imagine what you can do. r b-j
Reply by ●March 17, 20172017-03-17
On 16.3.17 21:49, gyansorova@gmail.com wrote:> On Friday, March 17, 2017 at 7:26:19 AM UTC+13, Tauno Voipio wrote: >> On 16.3.17 17:20, Tim Wescott wrote: >>> On Wed, 15 Mar 2017 20:55:37 -0700, gyansorova wrote: >>> >>>> On Thursday, March 16, 2017 at 7:09:09 AM UTC+13, Tim Wescott wrote: >>>>> On Wed, 15 Mar 2017 10:49:13 -0700, gyansorova wrote: >>>>> >>>>>> I saw a real fast one armed robot. I was wondering if stepper motors >>>>>> was used or closed-loop control. I know NC machines use stepper >>>>>> motors but I heard the torque isn't as good as dc motors. >>>>> >>>>> * Stepper motors are bigger for the torque that they'll deliver, and >>>>> getting the most torque out of them requires trickery. Well known and >>>>> established trickery, but still trickery. >>>>> >>>>> * _Some_ NC machines use steppers, some use servo motors. For a time >>>>> (and possibly still, I haven't been paying attention recently), most of >>>>> the DIY NC machine software was targeted to stepper outputs. However, >>>>> it is very common to have a servo motor controller that takes the same >>>>> "direction + step" commands that a stepper motor driver does. >>>>> >>>>> If you want maximum speed for the motor size, then you want a servo >>>>> motor. >>>>> >>>>> -- >>>>> >>>>> Tim Wescott Wescott Design Services http://www.wescottdesign.com >>>>> >>>>> I'm looking for work -- see my website! >>>> >>>> Do position servos work 360 degrees nowadays. In the old days we had >>>> pots that limited the travel though ac servos using synchros could go >>>> right round >>> >>> If you're talking RC servos, yes, they're still limited in travel. >>> >>> If you're talking industrial servo motors, most of them come with shaft >>> encoders. As long as your mechanism can stand doing a "home" cycle on >>> startup, you can get as many turns out of them as you wish. >>> >>> (AFAIK, the current trend is servo motors with built-in drives, so you're >>> not even driving the motor externally -- you're just supplying it with >>> power and commands. But I'm usually involved in things that are more >>> deeply embedded than that, at least at the moment.) >> >> >> Before the shaft encoders, there were sin/cos potentiometers and >> resolvers (rotating I/Q transformers), also synchros, which were >> three-phase versions of the resolvers. >> >> -- >> >> -TV > > Yes, the military used a lot of them, maybe for gun turrets and the like, you can still buy them.Not only military, also heavy civilian use. -- -TV
Reply by ●March 17, 20172017-03-17
On Thu, 16 Mar 2017 20:26:13 +0200, Tauno Voipio wrote:> On 16.3.17 17:20, Tim Wescott wrote: >> On Wed, 15 Mar 2017 20:55:37 -0700, gyansorova wrote: >> >>> On Thursday, March 16, 2017 at 7:09:09 AM UTC+13, Tim Wescott wrote: >>>> On Wed, 15 Mar 2017 10:49:13 -0700, gyansorova wrote: >>>> >>>>> I saw a real fast one armed robot. I was wondering if stepper motors >>>>> was used or closed-loop control. I know NC machines use stepper >>>>> motors but I heard the torque isn't as good as dc motors. >>>> >>>> * Stepper motors are bigger for the torque that they'll deliver, and >>>> getting the most torque out of them requires trickery. Well known >>>> and established trickery, but still trickery. >>>> >>>> * _Some_ NC machines use steppers, some use servo motors. For a time >>>> (and possibly still, I haven't been paying attention recently), most >>>> of the DIY NC machine software was targeted to stepper outputs. >>>> However, it is very common to have a servo motor controller that >>>> takes the same "direction + step" commands that a stepper motor >>>> driver does. >>>> >>>> If you want maximum speed for the motor size, then you want a servo >>>> motor. >>>> >>>> -- >>>> >>>> Tim Wescott Wescott Design Services http://www.wescottdesign.com >>>> >>>> I'm looking for work -- see my website! >>> >>> Do position servos work 360 degrees nowadays. In the old days we had >>> pots that limited the travel though ac servos using synchros could go >>> right round >> >> If you're talking RC servos, yes, they're still limited in travel. >> >> If you're talking industrial servo motors, most of them come with shaft >> encoders. As long as your mechanism can stand doing a "home" cycle on >> startup, you can get as many turns out of them as you wish. >> >> (AFAIK, the current trend is servo motors with built-in drives, so >> you're not even driving the motor externally -- you're just supplying >> it with power and commands. But I'm usually involved in things that >> are more deeply embedded than that, at least at the moment.) > > > Before the shaft encoders, there were sin/cos potentiometers and > resolvers (rotating I/Q transformers), also synchros, which were > three-phase versions of the resolvers.Yup. Those work great. They're still used where a homing cycle on startup is out of the question. -- Tim Wescott Control systems, embedded software and circuit design I'm looking for work! See my website if you're interested http://www.wescottdesign.com
Reply by ●March 17, 20172017-03-17
On Thu, 16 Mar 2017 23:03:20 -0700, robert bristow-johnson wrote:> On Wednesday, March 15, 2017 at 2:09:09 PM UTC-4, Tim Wescott wrote: >> On Wed, 15 Mar 2017 10:49:13 -0700, gyansorova wrote: >> >> > I saw a real fast one armed robot. I was wondering if stepper motors >> > was used or closed-loop control. I know NC machines use stepper >> > motors but I heard the torque isn't as good as dc motors. >> >> * Stepper motors are bigger for the torque that they'll deliver, and >> getting the most torque out of them requires trickery. Well known and >> established trickery, but still trickery. > > what's the trickery? like quadrature sinusoids applied to the two > windings with frequency/phase synchronized to the movement of the rotor? > > otherwise, i can't imagine what you can do.Running them at their rated current, even if it means running them above their rated voltage (so torque doesn't go down with speed). Ramping the speed up and down so that the torque required to accelerate the armature doesn't exceed the maximum. Microstepping may help, to -- I dunno about that one, but I'm willing to believe it. I'm not the world's foremost expert on steppers -- I usually try to deal with them by not using them. So others will probably give better, or at least more thorough, answers. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com I'm looking for work -- see my website!
