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
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_______________________________________________
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Emc-users@lists.sourceforge.net
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.
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
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