Gosh this was almost 2 years ago. Don't even remember why I was asking. John
> -----Original Message----- > From: Chris Albertson [mailto:albertson.ch...@gmail.com] > Sent: February 23, 2024 10:30 AM > To: Enhanced Machine Controller (EMC) > Subject: Re: [Emc-users] Acceleration question. > > It is very easy to compute the rotational momentum of a complex-shape > flywheel. Let�s use a simplified case as an example: You have a 100 mm > diameter steel disk with an 80 mm hole. This looks like a ring made of 10 mm > thick metal. > > First compute the momentum as if there was no hole, for a solid 100 mm > disk, Next compute the same for an 80 mm disk. Subtract the 80mm disk > momentum from the 100 mm disk momentum. > > If you want to account for the spokes, figure out their �average thickness� as > if the spokes were replaced by a thin sheet of metal and add that back in. > > There is a more complex way to do this but it requires Calculus. I think > they > showed us the hard way just so that they could come back and show us > students that you could decompose any complex wheel into a set of simple > disks and then add and subtract them. > > +++++ > > Stepper motors CAN work. But not if you use the simple Step/Direction > interface most drivers offer. The step/dir convention is NOT a function of > the motor. It is a function of the motor driver. The motor itself as A+/A-, > B+/B- leads and takes analog voltages. It is nothing more than a two-phase > BLDC motor with many pole pairs. You can drive a stepper in �continuous > and smooth non-stepping� mode if you like, if you get a smarter driver that > can continuously vary the input voltages. The more sophisticated controller > can driver the motor in �torque mode� so that it supplies a specified torque. > > > > > > > On Feb 23, 2024, at 10:05�AM, gene heskett <ghesk...@shentel.net> > wrote: > > > > On 6/16/22 21:57, John Dammeyer wrote: > >> Hi Gene, > >> Quite right. That link I posted used a table while in fact, as you pointed > out, the mass is mostly on the outside of a flywheel with spokes. I would > imagine at there is some average where if it's a 300 lb disk that is 24" > might be > the same as a 36" disk that is 400 lbs. > >> Think of a fly press for example with a clutch that engages the tooling. > Even if it does take 5 seconds to get up to speed, the clutch engages, the > tool > moves down and punches and moves up and the clutch releases. Even if the > speed slowed down by 20% when the clutch released then assuming linear > acceleration now only 1 second is required to bring the speed back up. At 50 > RPM (0.83 seconds per rev) then you could do another punch stroke 1 > second later and so possibly run 30 strokes per minute. > >> That jpg chart I included suggests with 100% efficiency and no real > >> friction > that 45 oz-in are required. Seems very low to me hence the questions. Even > if I did use a stepper motor and went 16:1 to bring the RPM down to 800 RPM > the motor could easily be a size 23 300 oz-in. > >> Could that actually bring a flywheel up to that speed in 5 seconds? > > > > The closest I could come, assuming no frictional losses, would still be > > just a > SWAG. But it sure seems to me a decimal point got moved or left out > someplace. > > > > A stepper would be a poor choice of power unless the stepper drive also > started at zero. A stepper unable to stay synced with the incoming step rate > has next to zero torque. A vfd makes far more sense as you could set it for 2 > or 3x the motors FLA and the vfd would then throttle the current, using > seriosly more drive currant immediately after a strike to get it back to > speed, > but the average would still be only maintenance unless it was striking with > every revolution. EG 50 strikes a minute. Given the time to extract and > replace the next work piece is going to be at least a second, that would be > one heck of a busy machine. Much the same could be said of a hirez encoder > whose output was compared to the desired speed and a 1 horse treadmill > motor being run by one of Jon's pwm-servos. Both solutions would need far > less electrical power to get the job done than a steeper could do. > >>> -----Original Message----- > >>> From: gene heskett [mailto:ghesk...@shentel.net] > >>> Sent: June-16-22 6:34 PM > >>> To: emc-users@lists.sourceforge.net > >>> Subject: Re: [Emc-users] Acceleration question. > >>> > >>> On 6/16/22 20:54, John Dammeyer wrote: > >>>> OK. I realize this will be a dumb question but please bear with me > especially since I've included the ability > >>> to accelerate in my Electronic Lead Screw project. > >>>> > >>>> A friend and I were discussing bringing a 300 pound flywheel up to > speed. > >>>> Vz=0 RPM, Vf=50 RPM. Reduction drive to the flywheel shaft is 32:1 so > final speed of motor is 1600 RPM. > >>>> > >>>> Assume we're happy with 5 seconds to accelerate for Tz to Tf. Motor > voltage is 12V. > >>>> > >>>> We have the mass, we have the velocity, we have the time and motor > voltage. The question is what are > >>> the calculations to determine how much current the motor will require > to create this acceleration? > >>> Assuming of course the motor is 100% efficient. > >>>> > >>>> We're getting all confused with F=ma and 1/2*a*t^2 etc. > >>>> > >>>> What size motor is actually needed to do this? > >>>> > >>>> Thanks. > >>>> John > >>>> > >>> That John, is going to be determined by where that weight is. > >>> If 270 lbs of it is in a rim 4 feet in diameter and the other 30 > >>> is in the spokes supporting that rim, its going to take a lot > >>> more torque to get it up to speed in 5 seconds than it would > >>> take if its only 2 feet in diameter, its the linear speed of the > >>> outer diameters major mass that has to be moved to twice > >>> as many feet per second needing 4x the torque to do it for > >>> the 4 foot example, and Einstiens E=m*v*v comes into the > >>> picture, cuz v=2*2 is 4, but v=4*4 is 16, not 8. > >>> > >>> That's as close as I can get to the math, sorry. I'd have to > >>> ask someone else for a SWAG or more knowledgeable > >>> answer too. This is a case also, of doing a bit of cheating > >>> with a bigger vfd running at a higher voltage and the low > >>> speed current boost could, if enough line voltage is present, > >>> bang a 1 horse motor hard enough to natch a 3 or 4 horse > >>> motor, knowing the overdrive will only last a few seconds. > >>> > >>> But, if going to machine cut with that motor, I'd have an > >>> amprobe or equ watching the motor currant to make sure > >>> the steady load is within the FLA on the motors nameplate. > >>> > >>> I hope the real answer means you've a motor and vfd in > >>> stock that will do it. > >>> > >>> Cheers, Gene Heskett. > >>> -- > >>> "There are four boxes to be used in defense of liberty: > >>> soap, ballot, jury, and ammo. Please use in that order." > >>> -Ed Howdershelt (Author, 1940) > >>> If we desire respect for the law, we must first make the law respectable. > >>> - Louis D. Brandeis > >>> > >>> > >>> > >>> _______________________________________________ > >>> Emc-users mailing list > >>> Emc-users@lists.sourceforge.net > >>> https://lists.sourceforge.net/lists/listinfo/emc-users > >> _______________________________________________ > >> Emc-users mailing list > >> Emc-users@lists.sourceforge.net > >> https://lists.sourceforge.net/lists/listinfo/emc-users > >> . > > > > Cheers, Gene Heskett, CET. > > -- > > "There are four boxes to be used in defense of liberty: > > soap, ballot, jury, and ammo. Please use in that order." > > -Ed Howdershelt (Author, 1940) > > If we desire respect for the law, we must first make the law respectable. > > - Louis D. Brandeis > > > > > > > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
