Re: [Emc-users] Closed loop control of air motors.

[John Dammeyer]

Andy
If I was only running TTS or something with a pull stud like yours that would 
be a no brainer.  

However I want the ability to use both TTS (no more than two turns either 
direction) and R8 (engaged thread number of turns to release and capture).

The idea of tap on the button to force two turns and press and hold for 
continuous would work if I could get the socket to line up and the motor to not 
over speed to thousands of RPM.

I'll take a longer look at guiding the socket but in the end not all R8 tooling 
starts the thread at the same point.  So the draw bar engages at a different 
angle into each R8 collet so even if the spindle were at the index position 
where the nut ends up when tight will be different.  

Now if I had a slotted disk or reflective mark on the nut I could turn the 
spindle until that was detected and stop there.  Now we know where the flat is. 
 A tab on the socket that stops the socket turning in the up position would 
then allow a short blip on the air wrench to locate the socket close enough so 
when it then goes down is guided over the drawbar bolt head.   

Hence my other question about turning the spindle with the MESA 7i92H step/dir 
module in position mode or catching an index position.

John


> -Original Message-
> From: andy pugh [mailto:bodge...@gmail.com]
> Sent: November-22-21 5:26 AM
> To: Enhanced Machine Controller (EMC)
> Subject: Re: [Emc-users] Closed loop control of air motors.
> 
> On Mon, 22 Nov 2021 at 05:23, John Dammeyer  wrote:
> 
> > As it is the nut is getting pretty trashed so until the 12 point socket 
> > arrives I think this part of the project is on hold.
> 
> Is it time to cut your losses and go with a Bellville washer stack?
> It works for Tormach: https://tormach.com/power-drawbar-pcnc-1100-31706.html
> (and, for that matter, for me: https://youtu.be/mZWQvq-X7DQ )
> 
> --
> atp
> "A motorcycle is a bicycle with a pandemonium attachment and is
> designed for the especial use of mechanical geniuses, daredevils and
> lunatics."
> � George Fitch, Atlanta Constitution Newspaper, 1912
> 
> 
> ___
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> https://lists.sourceforge.net/lists/listinfo/emc-users



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Re: [Emc-users] Closed loop control of air motors.

[Gene Heskett]

On Monday 22 November 2021 07:07:45 Gregg Eshelman via Emc-users wrote:

> How about an eddy current brake that uses a thick copper washer, a
> disk with some strong magnets, and use a small air cylinder to push
> the copper washer away from the magnets and springs to pull or push it
> close to the magnets when the air is cut off so the wrench stops fast.

Since eddy currents are speed sensitive, I see no need to disengage. what 
I do see is a lack of space to build it in since its effect would need a 
larger diameter copper disk than there is room for in Johns wrench 
mount. Lurking in the back of my mind is a very short pulse of air in 
fwd to stop the overspin once its unlocked.

The air valve I am using to switch the mister air on the 6040 may be 
different from the one John is using, this one stops by venting the 
pressure in the out port to atmosphere with a pop, and I got it from 
some outfit that specializes in air horns for large cars. It may be that 
the venting would stop most of the overspin. Its only problem is that I 
don't think the coil maker figured on CCS operation as it runs way 
hotter than that famous little red wagon when its been on for 45 
minutes. I've no clue if a bidir valve that does that is available.

Something else for John to investigate. I think a 2 spool could do it, 
one to control the air, feeding one to do the reversal. My guess is that 
the one doing the reversal probably can't switch while the pressure is 
on. Oneshots in the hal file can fix that so I don't see that as a real 
problem. 

But you get that eddy current braking effect for free by using the 
battery impact screwdriver because the bts-7960 crowbars the motor in 
the off mode. You can turn it by hand, but not very fast. From wide open 
to stopped is about 1 turn.

> Automatic brake release and fail safe engagement, but zero contact so
> there's nothing to wear out or jam up.
>
>   On Sunday, November 21, 2021, 07:57:34 AM MST, Gene Heskett
>  wrote: Close to the truth, However there might
> be a salvation in a viscous greased disk that would absorb the rapid
> spin, trapped between two other disks. It would allow the initial slow
> unlocking but seriously impede the following rapid spin. Or an eddy
> currant brake but that would take burn it up power so it would need to
> be applied only when the air is applied, and possibly for half a
> second after the air valve was turned off. I like the suicide braking
> idea, but there is limited space and it needs more diameter than you
> have room for. A coil spring anchored to the tool that would allow
> maybe three turns of the socket before winding tight against the
> socket OD might be a softer stop. Or a pile of interlocking disks that
> were screw driven like the rear brakes on an old Schwinn bicycle? 
> That was fairly compact and lasted close to forever.
>
> Just tossing out ideas to see if one sticks.
>
> Cheers, Gene Heskett.
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> https://lists.sourceforge.net/lists/listinfo/emc-users


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
Genes Web page 


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Re: [Emc-users] Closed loop control of air motors.

[andy pugh]

On Mon, 22 Nov 2021 at 05:23, John Dammeyer  wrote:

> As it is the nut is getting pretty trashed so until the 12 point socket 
> arrives I think this part of the project is on hold.

Is it time to cut your losses and go with a Bellville washer stack?
It works for Tormach: https://tormach.com/power-drawbar-pcnc-1100-31706.html
(and, for that matter, for me: https://youtu.be/mZWQvq-X7DQ )

-- 
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1912


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Re: [Emc-users] Closed loop control of air motors.

[andy pugh]

On Sun, 21 Nov 2021 at 07:45, John Dammeyer  wrote:
>
>  I'd like to be able to limit the number of turns to 2.

OK, here is a possible arrangement that will fit in the existing packaging.

Press a sleeve onto the outside of the socket with a spiral groove
machined into it (actually two grooves, a 2-start thread)
Sliding on the two uprights is a part that engages with the groove on
both sides.  We will call it "the slider"
The slider will initially travel down with the socket on engagement.
When running clockwise the grooves lift the slider up into a
continuous run-out groove at the top, so that clockwise rotation is
not restricted.
When running anticlockwise the slider is biased down (spring?
gravity?) into the spiral and descends for the full two / three turns
before getting to the end of the groove.

What happens then is open to development.

I can see that the slider could operate a switch to turn off the air
somewhere in its travel.
The slider could operate a friction disc at the bottom of travel. In
that embodiment the bottom would also have a continuous run-out groove
(but then the spring bias needs to be a collar top and bottom)

Alternatively the slider could just hit the ends of the grooves and
stop. Or the spiral ramp could be friction-coupled to the socket,
still with a hard-stop at the end of the ramp.

-- 
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1912


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Re: [Emc-users] Closed loop control of air motors.

[Gregg Eshelman via Emc-users]

How about an eddy current brake that uses a thick copper washer, a disk with 
some strong magnets, and use a small air cylinder to push the copper washer 
away from the magnets and springs to pull or push it close to the magnets when 
the air is cut off so the wrench stops fast.

Automatic brake release and fail safe engagement, but zero contact so there's 
nothing to wear out or jam up.

  On Sunday, November 21, 2021, 07:57:34 AM MST, Gene Heskett 
 wrote: 
Close to the truth, However there might be a salvation in a viscous 
greased disk that would absorb the rapid spin, trapped between two other 
disks. It would allow the initial slow unlocking but seriously impede 
the following rapid spin. Or an eddy currant brake but that would take 
burn it up power so it would need to be applied only when the air is 
applied, and possibly for half a second after the air valve was turned 
off. I like the suicide braking idea, but there is limited space and it 
needs more diameter than you have room for. A coil spring anchored to 
the tool that would allow maybe three turns of the socket before winding 
tight against the socket OD might be a softer stop. Or a pile of 
interlocking disks that were screw driven like the rear brakes on an old 
Schwinn bicycle?  That was fairly compact and lasted close to forever.

Just tossing out ideas to see if one sticks.

Cheers, Gene Heskett.  
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Re: [Emc-users] Closed loop control of air motors.

[John Dammeyer]

An update...
I spent the afternoon tweaking software and air pressure etc.  Still haven't 
been able to get the 3/8" impact deep socket from falling off. The dimple in 
the drive is deeper and the set screw definitely locks tight but after a few 
cycles the screw is loose again.  Eventually the socket flies off.

Restricting the air exhaust did slow down the full speed but not enough without 
some major mechanical changes.  With that in mind I took another look at the 
PWM approach but this time I followed the suggestion to do PWM which was 10% 
and 20% of 100mS.  The valve still has time to open and supply enough so the 
motor doesn't turn super fast (although too fast still) but also has torque.

The problem is when using a torque wrench to set 18 ft-lbs the 10% wouldn't 
budge it.  The 20% setting does but once it's a tiny bit loose it will turn 4 
or 5 turns.  It was reliable enough to not drop the R8 most of the time.  But 
it would take a lot of tries at 1 second per cycle to move it a tiny bit, then 
another tiny bit, and so on.

And if it's lifted a touch and the magnet isn't at the right height because it 
didn't sit fully on the head of the draw bar then it spins for the entire 
timeout period.  Make that time too long and once again the R8 drops out.  

Would be better if the indexing was on the drawbar nut but that raises other 
issues with the quill moving down and the nut descending downwards into the 
center of the drive pulley.  Reflective sensor on the round bottom of the nut 
would work.  As it is the nut is getting pretty trashed so until the 12 point 
socket arrives I think this part of the project is on hold.

John


> -Original Message-
> From: ertleyd--- via Emc-users [mailto:emc-users@lists.sourceforge.net]
> Sent: November-21-21 12:04 PM
> To: 'Enhanced Machine Controller (EMC)'
> Cc: ertl...@yahoo.com
> Subject: Re: [Emc-users] Closed loop control of air motors.
> 
> 
> you could try putting the air valve "very close" to the inpact.
> this will reduce the air volume betwen the valve and inpact.
> a valve that closes when off, creating a vacuum in the inpact input line.
> this vacuum may help control the inpact over run.
> low input hose volume and a vacuum when shut off.
> 
> the use of 2 valves in the inpact input line would be able to control the 
> volume
> of air that is avable to releace the collet. you may need a small adjustable
> accumulator or longer/larger line between the 2 valves to increace the air 
> volume
> so as to start the inpact hitting hard.
> 
> good luck
> Happy Thanksgiving
> And Be Safe
> 
> dale
> 
>  On Sunday, November 21, 2021, 01:12:19 PM EST, John Dammeyer 
>  wrote:
> 
>  Thanks everyone.� Definitely something to think about.� As it turns out, 
> sitting on a shelf somewhere, I have an old RIGID 14.4V
> impact driver with a failed battery pack.� When the pack failed a new pack, 
> only available by mail but not allowed to be shipped by
> mail due to lithium issues, was more expensive than a replacement impact 
> driver kit on sale.
> 
> The video here shows a slow motion behaviour of the internals of an impact to 
> drill adaptor.
> https://youtu.be/f0gSJa3L_7c
> 
> So that opens up possibilities.
> 
> I will try my existing impact driver on the draw bar with a TTS holder and 
> then use a torque wrench to see what it takes to undo it.
> 
> As I recall, using the larger 3/4" torque wrench 20 ft-lb was way more than I 
> ever tighten the system now which is why the stepper
> motor and 10:1 planetary drive looked interesting.� Especially since my 
> electronic lead screw has a built in 3A stepper driver (Z axis)
> and encoder index sensing circuit (Spindle Index).�
> 
> I had thought about using my ELS as a remote Pendant for Drawbar Control and 
> Tool Changing etc.� One of the reasons I used this
> GIM module as the tool changer controller as I now have indictors on the LCNC 
> screen showing the status of the draw bar all with
> CAN bus and CANopen protocol.� And in place of the X axis drive my ELS has 
> CAN bus too but it didn't have enough outputs for relay
> driving without an additional expansion board or BoB.� In fact I can send CAN 
> messages to my GIM tool changer to trigger the load
> release feature too so it could be done from LCNC or the ELS.
> 
> The GIM has two DIP relays and two relay drivers and an optically isolated 
> input connected to the PIC30F5011 interrupt input.� Plus
> some inputs for the switches so all in all enough for the pair of pneumatic 
> valves and the other I/O.� It lets me test it and program it
> on the bench without the need for LCNC running or connected.� Being able to 
> set break points etc. is very handy for embedded
> systems development.
> 
> And I do have the 

Re: [Emc-users] Closed loop control of air motors.

[ertleyd--- via Emc-users]

 
you could try putting the air valve "very close" to the inpact. 
this will reduce the air volume betwen the valve and inpact. 
a valve that closes when off, creating a vacuum in the inpact input line. 
this vacuum may help control the inpact over run. 
low input hose volume and a vacuum when shut off.

the use of 2 valves in the inpact input line would be able to control the volume
of air that is avable to releace the collet. you may need a small adjustable
accumulator or longer/larger line between the 2 valves to increace the air 
volume
so as to start the inpact hitting hard. 

good luck
Happy Thanksgiving
And Be Safe

dale

 On Sunday, November 21, 2021, 01:12:19 PM EST, John Dammeyer 
 wrote:  
 
 Thanks everyone.  Definitely something to think about.  As it turns out, 
sitting on a shelf somewhere, I have an old RIGID 14.4V impact driver with a 
failed battery pack.  When the pack failed a new pack, only available by mail 
but not allowed to be shipped by mail due to lithium issues, was more expensive 
than a replacement impact driver kit on sale.

The video here shows a slow motion behaviour of the internals of an impact to 
drill adaptor.
https://youtu.be/f0gSJa3L_7c

So that opens up possibilities. 

I will try my existing impact driver on the draw bar with a TTS holder and then 
use a torque wrench to see what it takes to undo it.

As I recall, using the larger 3/4" torque wrench 20 ft-lb was way more than I 
ever tighten the system now which is why the stepper motor and 10:1 planetary 
drive looked interesting.  Especially since my electronic lead screw has a 
built in 3A stepper driver (Z axis) and encoder index sensing circuit (Spindle 
Index).  

I had thought about using my ELS as a remote Pendant for Drawbar Control and 
Tool Changing etc.  One of the reasons I used this GIM module as the tool 
changer controller as I now have indictors on the LCNC screen showing the 
status of the draw bar all with CAN bus and CANopen protocol.  And in place of 
the X axis drive my ELS has CAN bus too but it didn't have enough outputs for 
relay driving without an additional expansion board or BoB.  In fact I can send 
CAN messages to my GIM tool changer to trigger the load release feature too so 
it could be done from LCNC or the ELS.

The GIM has two DIP relays and two relay drivers and an optically isolated 
input connected to the PIC30F5011 interrupt input.  Plus some inputs for the 
switches so all in all enough for the pair of pneumatic valves and the other 
I/O.  It lets me test it and program it on the bench without the need for LCNC 
running or connected.  Being able to set break points etc. is very handy for 
embedded systems development.

And I do have the Pi4 with LCNC and a Lawicel CANUSB to test the CAN side.  I 
used the CANUSB rather than a HAT for the Pi4 so I could also use CAN on the 
Mill PC in the shop.

Really the only reason I went with the pneumatic butterfly wrench is because I 
bought it and paid for the drawings document over 10 years ago.  That's where 
the basic design came from.  I just redid them in Alibre and then cast the 
parts and machined them with LCNC after first testing with 3D printed parts.

John




> -Original Message-
> From: Gene Heskett [mailto:ghesk...@shentel.net]
> Sent: November-21-21 7:54 AM
> To: emc-users@lists.sourceforge.net
> Subject: Re: [Emc-users] Closed loop control of air motors.
> 
> On Sunday 21 November 2021 03:24:24 John Dammeyer wrote:
> 
> > Actually that is along the lines of what I've asked.  Some sort of
> > brake that could limit the speed.
> >
> > If you go back to steam engines the two weights swung out and shut off
> > the pressure to the engine to keep it from running away.  I'm not sure
> > I could fit something like that in that space but I had an idea like
> > that.
> >
> > Occasionally, until I solve that problem the socket goes flying off
> > too.  The square shaft of the wrench is hardened and I've used a
> > Dremel to create a dimple but it's not deep enough yet.  Adding a
> > guard around the socket for safety is a good idea then.  And if
> > centrifugal force causes two arms with brake pads to fly out and run
> > against the guard to slow it down that would work.  But seems overly
> > complex.
> >
> > Using that same guard idea but with pads that apply load to the socket
> > to keep it from spinning away might be easier.  If you think about the
> > sound of an impact wrench it spins up and only when it hits a load do
> > you get the hammering sound.
> >
> > I've been considering this as a solution instead.
> > https://www.aliexpress.com/item/4000220757109.html
> >
> > John
> >
> Even at 10/1, I doubt it could generate enough closing torque. The air
> wrench is probably too much anyway. It can probably strip t

Re: [Emc-users] Closed loop control of air motors.

[Gene Heskett]

On Sunday 21 November 2021 03:24:24 John Dammeyer wrote:

> Actually that is along the lines of what I've asked.  Some sort of
> brake that could limit the speed.
>
> If you go back to steam engines the two weights swung out and shut off
> the pressure to the engine to keep it from running away.  I'm not sure
> I could fit something like that in that space but I had an idea like
> that.
>
> Occasionally, until I solve that problem the socket goes flying off
> too.  The square shaft of the wrench is hardened and I've used a
> Dremel to create a dimple but it's not deep enough yet.   Adding a
> guard around the socket for safety is a good idea then.  And if
> centrifugal force causes two arms with brake pads to fly out and run
> against the guard to slow it down that would work.  But seems overly
> complex.
>
> Using that same guard idea but with pads that apply load to the socket
> to keep it from spinning away might be easier.  If you think about the
> sound of an impact wrench it spins up and only when it hits a load do
> you get the hammering sound.
>
> I've been considering this as a solution instead.
> https://www.aliexpress.com/item/4000220757109.html
>
> John
>
Even at 10/1, I doubt it could generate enough closing torque. The air 
wrench is probably too much anyway. It can probably strip the drawbolt

I use a 20 volt battery powered Porter Cable impact screwdriver which has 
plenty of closing torque due to its impact, and my reflexes are fast 
enough to prevent the overspin and r8 collet drop. I don't see why that 
idea couldn't be timed to turn it off when the magnet comes by the 
second time. An H bridge such as the $7 ebay thing I used to drive that 
BS-1 clone can switch 25 volts at 43 amps, shouldn't have a problem 
replacing the trigger switch and would also serve as the reversing 
switch without having to punch the direction button. Total electric 
conrol by a pair of signals from the bob, crowbarring the motor to stop 
it quick. Controls for that are a 30 minute edit and test in linuxcnc. 
Unless busier than that cat on that famous tin roof, charge/swap the 
battery about monthly. On my g0704, about a seconds hammering and theres 
no tool slippage, 10 seconds would likely strip or break the drawbolt. 
Put the H bridge right on the tool so 10 gauge leads are short for low 
loss. Since you have the air rigged to drop/lift it, keep that but I'd 
tally the down position and interlock the logic so the only thing you 
could do when its up, is position it to put the magnet in the correct 
position for the next unlock cycle.

Your pix gives me an idea to make the engagement slider out of an old 
plunge router base, printing a collar to adapt the impact tool to the 
router base.  All I'd need is the giddyup to get off my duff and do it.
But first, straighten the crooked post on that BBLB POS. Until I do that, 
its looking to be replaced and used for salvage.

> > -Original Message-
> > From: Roland Jollivet [mailto:roland.jolli...@gmail.com]
> > Sent: November-21-21 12:14 AM
> > To: Enhanced Machine Controller (EMC)
> > Subject: [Emc-users] Closed loop control of air motors.
> >
> > It's not what you asked, but what about a centrifugal
> > clutch/limiter? Above say 200RPM it could swing outwards and lock,
> > only releasing again once the torque is removed.
> >
> > On Sun, 21 Nov 2021 at 09:45, John Dammeyer  
wrote:
> > > Has anyone ever tried any sort of closed loop control of an air
> > > motor similar the one on this butterfly impact wrench.
> > > https://www.penntoolco.com/52-424-9/
> > > In order to not have both the TTS and R8 collet drop out of the
> > > spindle I'd like to be able to limit the number of turns to 2.
> > >
> > > What I've found however, is that 10mS pulses to the valve
> > > supplying air for CCW rotation barely move it until it's unloaded
> > > and then it immediately spins up very fast and does at least 4 to
> > > 8 turns.  That's way too many.
> > >
> > > I've only got a one pulse per rev hall sensor detecting a magnet
> > > on the socket.  But I suspect between reaction time of the valve,
> > > the compressibility of air and the rotary inertia of the motor
> > > that unless there is some sort of constant load that control is
> > > pretty well impossible.
> > >
> > > With servos, if the motor is loaded and then suddenly totally
> > > unloaded, it too might turn a number of revolutions before the
> > > control system could bring it back down to the original speed.
> > >
> > > Short of adding some sort of mechanical brake am I trying to do
> > > the impossible?  Oh and to avoid another 1000 words to explain
>

Re: [Emc-users] Closed loop control of air motors.

[ertleyd--- via Emc-users]

 
electric baby. 
$99 + shipping
https://www.ebay.com/itm/Black-Decker-2211-Type-6-Electric-Impact-Wrench-Yamazen-CNC-Vertical-Mill/124224993932?epid=17039113677=item1cec62fa8c:g:3MwAAOSw7P1e6KY9=fbda9f54-d12f-4a6f-b70c-dd849f2ac1b7=mobile
 On Sunday, November 21, 2021, 02:43:55 AM EST, John Dammeyer 
 wrote:  
 
 Has anyone ever tried any sort of closed loop control of an air motor similar 
the one on this butterfly impact wrench.
https://www.penntoolco.com/52-424-9/
In order to not have both the TTS and R8 collet drop out of the spindle I'd 
like to be able to limit the number of turns to 2.  
 
What I've found however, is that 10mS pulses to the valve supplying air for CCW 
rotation barely move it until it's unloaded and then it immediately spins up 
very fast and does at least 4 to 8 turns.  That's way too many.
 
I've only got a one pulse per rev hall sensor detecting a magnet on the socket. 
 But I suspect between reaction time of the valve, the compressibility of air 
and the rotary inertia of the motor that unless there is some sort of constant 
load that control is pretty well impossible.
 
With servos, if the motor is loaded and then suddenly totally unloaded, it too 
might turn a number of revolutions before the control system could bring it 
back down to the original speed.
 
Short of adding some sort of mechanical brake am I trying to do the impossible? 
 Oh and to avoid another 1000 words to explain I've added a picture.
John
  
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Re: [Emc-users] Closed loop control of air motors.

[Gene Heskett]

On Sunday 21 November 2021 02:40:39 John Dammeyer wrote:

> Has anyone ever tried any sort of closed loop control of an air motor
> similar the one on this butterfly impact wrench.
> https://www.penntoolco.com/52-424-9/
> In order to not have both the TTS and R8 collet drop out of the
> spindle I'd like to be able to limit the number of turns to 2.
>
> What I've found however, is that 10mS pulses to the valve supplying
> air for CCW rotation barely move it until it's unloaded and then it
> immediately spins up very fast and does at least 4 to 8 turns.  That's
> way too many.
>
> I've only got a one pulse per rev hall sensor detecting a magnet on
> the socket.  But I suspect between reaction time of the valve, the
> compressibility of air and the rotary inertia of the motor that unless
> there is some sort of constant load that control is pretty well
> impossible.
>
> With servos, if the motor is loaded and then suddenly totally
> unloaded, it too might turn a number of revolutions before the control
> system could bring it back down to the original speed.
>
> Short of adding some sort of mechanical brake am I trying to do the
> impossible?  Oh and to avoid another 1000 words to explain I've added
> a picture. John

Close to the truth, However there might be a salvation in a viscous 
greased disk that would absorb the rapid spin, trapped between two other 
disks. It would allow the initial slow unlocking but seriously impede 
the following rapid spin. Or an eddy currant brake but that would take 
burn it up power so it would need to be applied only when the air is 
applied, and possibly for half a second after the air valve was turned 
off. I like the suicide braking idea, but there is limited space and it 
needs more diameter than you have room for. A coil spring anchored to 
the tool that would allow maybe three turns of the socket before winding 
tight against the socket OD might be a softer stop. Or a pile of 
interlocking disks that were screw driven like the rear brakes on an old 
Schwinn bicycle?  That was fairly compact and lasted close to forever.

Just tossing out ideas to see if one sticks.

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
Genes Web page 


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Re: [Emc-users] Closed loop control of air motors.

[ken.strauss]

Rather than the hard to control air wrench have you considered using a small DC 
motor with an encoder and gear reduction? Some years ago there was a lengthy 
series of posts on CNCZONE about such a system.

-Original Message-
From: John Dammeyer  
Sent: November 21, 2021 2:41 AM
To: Enhanced Machine Controller (EMC) 
Subject: [Emc-users] Closed loop control of air motors.

Has anyone ever tried any sort of closed loop control of an air motor similar 
the one on this butterfly impact wrench.
https://www.penntoolco.com/52-424-9/
In order to not have both the TTS and R8 collet drop out of the spindle I'd 
like to be able to limit the number of turns to 2.  
 
What I've found however, is that 10mS pulses to the valve supplying air for CCW 
rotation barely move it until it's unloaded and then it immediately spins up 
very fast and does at least 4 to 8 turns.  That's way too many.
 
I've only got a one pulse per rev hall sensor detecting a magnet on the socket. 
 But I suspect between reaction time of the valve, the compressibility of air 
and the rotary inertia of the motor that unless there is some sort of constant 
load that control is pretty well impossible.
 
With servos, if the motor is loaded and then suddenly totally unloaded, it too 
might turn a number of revolutions before the control system could bring it 
back down to the original speed.
 
Short of adding some sort of mechanical brake am I trying to do the impossible? 
 Oh and to avoid another 1000 words to explain I've added a picture.
John
  



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Re: [Emc-users] Closed loop control of air motors.

[Gregg Eshelman via Emc-users]

How about an eddy current magnetic speed brake? Powerful magnets moving close 
to a thick piece of copper ought to do it. 
https://www.youtube.com/watch?v=sENgdSF8ppANo power required, the right design 
should bring the impact wrench to a fast stop once the air is off.

   On Sunday, November 21, 2021, 01:26:32 AM MST, John Dammeyer 
 wrote:  
 
 Actually that is along the lines of what I've asked.  Some sort of brake that 
could limit the speed.

If you go back to steam engines the two weights swung out and shut off the 
pressure to the engine to keep it from running away.  I'm not sure I could fit 
something like that in that space but I had an idea like that. 

Occasionally, until I solve that problem the socket goes flying off too.  The 
square shaft of the wrench is hardened and I've used a Dremel to create a 
dimple but it's not deep enough yet.  Adding a guard around the socket for 
safety is a good idea then.  And if centrifugal force causes two arms with 
brake pads to fly out and run against the guard to slow it down that would 
work.  But seems overly complex.

Using that same guard idea but with pads that apply load to the socket to keep 
it from spinning away might be easier.  If you think about the sound of an 
impact wrench it spins up and only when it hits a load do you get the hammering 
sound.  

I've been considering this as a solution instead.
https://www.aliexpress.com/item/4000220757109.html  
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Re: [Emc-users] Closed loop control of air motors.

[andy pugh]

On Sun, 21 Nov 2021 at 07:45, John Dammeyer  wrote:

> In order to not have both the TTS and R8 collet drop out of the spindle I'd 
> like to be able to limit the number of turns to 2.

How about an end-stop in the draw bar? It would be fairly easy to have
something that simply "catches" the collet as it drops off the end of
the thread.
But you could also consider leaving the thread engaged and pulling up
against an internal collar (this is assuming that the drawbar thread
is smaller than the ID of the collet)

There is some risk of this jamming up, though, and it might put some
stress on the alignment pin if it is a pin rather than a key.

There are a number of rotation limiting designs onYoutube. This one
looks like it might work for your application, with only 2 or 3
layers:
https://www.youtube.com/watch?v=3airCg2Xd-4


Does a restrictor in the exhaust limit the wrench speed?

-- 
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1912


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Re: [Emc-users] Closed loop control of air motors.

[John Dammeyer]

Actually that is along the lines of what I've asked.  Some sort of brake that 
could limit the speed.

If you go back to steam engines the two weights swung out and shut off the 
pressure to the engine to keep it from running away.  I'm not sure I could fit 
something like that in that space but I had an idea like that. 

Occasionally, until I solve that problem the socket goes flying off too.  The 
square shaft of the wrench is hardened and I've used a Dremel to create a 
dimple but it's not deep enough yet.   Adding a guard around the socket for 
safety is a good idea then.  And if centrifugal force causes two arms with 
brake pads to fly out and run against the guard to slow it down that would 
work.  But seems overly complex.

Using that same guard idea but with pads that apply load to the socket to keep 
it from spinning away might be easier.  If you think about the sound of an 
impact wrench it spins up and only when it hits a load do you get the hammering 
sound.  

I've been considering this as a solution instead.
https://www.aliexpress.com/item/4000220757109.html

John


> -Original Message-
> From: Roland Jollivet [mailto:roland.jolli...@gmail.com]
> Sent: November-21-21 12:14 AM
> To: Enhanced Machine Controller (EMC)
> Subject: [Emc-users] Closed loop control of air motors.
> 
> It's not what you asked, but what about a centrifugal clutch/limiter?
> Above say 200RPM it could swing outwards and lock, only releasing again
> once the torque is removed.
> 
> 
> 
> On Sun, 21 Nov 2021 at 09:45, John Dammeyer  wrote:
> 
> > Has anyone ever tried any sort of closed loop control of an air motor
> > similar the one on this butterfly impact wrench.
> > https://www.penntoolco.com/52-424-9/
> > In order to not have both the TTS and R8 collet drop out of the spindle
> > I'd like to be able to limit the number of turns to 2.
> >
> > What I've found however, is that 10mS pulses to the valve supplying air
> > for CCW rotation barely move it until it's unloaded and then it immediately
> > spins up very fast and does at least 4 to 8 turns.  That's way too many.
> >
> > I've only got a one pulse per rev hall sensor detecting a magnet on the
> > socket.  But I suspect between reaction time of the valve, the
> > compressibility of air and the rotary inertia of the motor that unless
> > there is some sort of constant load that control is pretty well impossible.
> >
> > With servos, if the motor is loaded and then suddenly totally unloaded, it
> > too might turn a number of revolutions before the control system could
> > bring it back down to the original speed.
> >
> > Short of adding some sort of mechanical brake am I trying to do the
> > impossible?  Oh and to avoid another 1000 words to explain I've added a
> > picture.
> > John
> >
> > ___
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> > Emc-users@lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/emc-users
> >
> 
> ___
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[Emc-users] Closed loop control of air motors.

[Roland Jollivet]

It's not what you asked, but what about a centrifugal clutch/limiter?
Above say 200RPM it could swing outwards and lock, only releasing again
once the torque is removed.



On Sun, 21 Nov 2021 at 09:45, John Dammeyer  wrote:

> Has anyone ever tried any sort of closed loop control of an air motor
> similar the one on this butterfly impact wrench.
> https://www.penntoolco.com/52-424-9/
> In order to not have both the TTS and R8 collet drop out of the spindle
> I'd like to be able to limit the number of turns to 2.
>
> What I've found however, is that 10mS pulses to the valve supplying air
> for CCW rotation barely move it until it's unloaded and then it immediately
> spins up very fast and does at least 4 to 8 turns.  That's way too many.
>
> I've only got a one pulse per rev hall sensor detecting a magnet on the
> socket.  But I suspect between reaction time of the valve, the
> compressibility of air and the rotary inertia of the motor that unless
> there is some sort of constant load that control is pretty well impossible.
>
> With servos, if the motor is loaded and then suddenly totally unloaded, it
> too might turn a number of revolutions before the control system could
> bring it back down to the original speed.
>
> Short of adding some sort of mechanical brake am I trying to do the
> impossible?  Oh and to avoid another 1000 words to explain I've added a
> picture.
> John
>
> ___
> Emc-users mailing list
> Emc-users@lists.sourceforge.net
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>

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