I've been fussing over this constant-torque clutch solution for my fuse
spinning machine for a few weeks.

The sprag clutch on the takeup reel solved a lot of problems --
primarily, it removed the "letoff" that was occurring when the mechanical
friction clutch slipped.

However, it still didn't solve the problem of the clutch sticking and
slipping, thus varying tension on the roving as it passed through the
machine. It was a minor thing, but resulted in cosmetic problems where
the final over-wrap on the fuse was not uniform.

Mag-fluid clutches were too expensive, and multi-plate clutches still had
the stiction problem. I even enquired of one multi-plate outfit that
claimed "static friction is less than dynamic friction", which not only
defies the rules of physics, but when they were challenged to produce
torque curves, the could (would) not.

So, what to do? Hydraulics. Constant pressure on a pump (disregarding
bypass losses) equals constant torque.

So I bought a re-furbished power steering pump, and set to making it into
a constant pressure pump -- thus constant torque.

I modified the pump by locking the internal relief valve. It could have
been made to relieve at the correct pressure, but had two drawbacks -- it
had a large throw, and caused oil to recirculate IN the pump, rather than
drawing from the reservoir during bypass. I also modified the pump by
adding a port to the top of the relief valve chamber to add my own custom
poppet-style relief valve.

This was a bit tricky, not for the easy machining of the cast iron, but
for keeping chips out of the work. To do that, I filled the chamber with
beeswax, draped a cloth over the entire pump, with a hole through which
to do the boring and tapping, then surrounded the work area with lots of
little rare-earth magnets. That worked. Kept ever trace of swarf out of
the body of the pump.

I didn't know the displacement of the pump, and couldn't find it in any
specs, so the selection of the relief valve spring had to be empirical.

I finally got the thing producing a smooth, jitter-free torque of 15
ft.lb. by cutting a miniature die spring down 1/2 coil at a time until
the torque fit the spec.

Now the only things left to do are to build a driving boss for the pump
housing, and a takeoff coupling for the shaft -- and we'll see how it
works on the fuse machine.

It's been a three week "off-the-clock" learning exercise for me, but
worth the time. I can see all sorts of uses for such a mechanism. The
torque varies only about 15% from 2rpm to 7rpm, and that's well within my
needs.

LLoyd

--I hope you're taking lotsa photos; this is fascinating!

--
"Steamboat Ed" Haas : A human without a critter
Hacking the Trailing Edge! : is incomplete..
www.nmpproducts.com
---Decks a-wash in a sea of words---

steamer fired this volley in news:4c4f1586$0$1673
:

--I hope you're taking lotsa photos; this is fascinating!

Just a few, but it's pretty self-explanatory.

When it's all done (and works as planned G) I'll document it.

LLoyd

On Jul 26, 7:40*pm, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:
I've been fussing over this constant-torque clutch solution for my fuse
spinning machine for a few weeks. *

The sprag clutch on the takeup reel solved a lot of problems --
primarily, it removed the "letoff" that was occurring when the mechanical
friction clutch slipped. *

However, it still didn't solve the problem of the clutch sticking and
slipping, thus varying tension on the roving as it passed through the
machine. *It was a minor thing, but resulted in cosmetic problems where
the final over-wrap on the fuse was not uniform.

Mag-fluid clutches were too expensive, and multi-plate clutches still had
the stiction problem. *I even enquired of one multi-plate outfit that
claimed "static friction is less than dynamic friction", which not only
defies the rules of physics, but when they were challenged to produce
torque curves, the could (would) not.

So, what to do? *Hydraulics. *Constant pressure on a pump (disregarding
bypass losses) equals constant torque.

So I bought a re-furbished power steering pump, and set to making it into
a constant pressure pump -- thus constant torque.

I modified the pump by locking the internal relief valve. *It could have
been made to relieve at the correct pressure, but had two drawbacks -- it
had a large throw, and caused oil to recirculate IN the pump, rather than
drawing from the reservoir during bypass. *I also modified the pump by
adding a port to the top of the relief valve chamber to add my own custom *
poppet-style relief valve.

This was a bit tricky, not for the easy machining of the cast iron, but
for keeping chips out of the work. *To do that, I filled the chamber with
beeswax, draped a cloth over the entire pump, with a hole through which
to do the boring and tapping, then surrounded the work area with lots of
little rare-earth magnets. *That worked. *Kept ever trace of swarf out of
the body of the pump.

I didn't know the displacement of the pump, and couldn't find it in any
specs, so the selection of the relief valve spring had to be empirical.

I finally got the thing producing a smooth, jitter-free torque of 15
ft.lb. by cutting a miniature die spring down 1/2 coil at a time until
the torque fit the spec.

Now the only things left to do are to build a driving boss for the pump
housing, and a takeoff coupling for the shaft -- and we'll see how it
works on the fuse machine.

It's been a three week "off-the-clock" learning exercise for me, but
worth the time. *I can see all sorts of uses for such a mechanism. *The
torque varies only about 15% from 2rpm to 7rpm, and that's well within my
needs.

LLoyd

I'm sure I missed something, but why wouldn't a DC ( Permanent
Magnet ) motor driven by a current source be a lot simpler?

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote:

I've been fussing over this constant-torque clutch solution for my fuse
spinning machine for a few weeks.

I wonder, could you have employed a viscous fan drive for automotive applications? The
silicon fluid is moderated by a valve that is either actuated by a bimetal snap disk, a
bimetal temperature sensing coil, or some electronics depending on the design.

With the bi-metal coil operated device, you can set your amount of drag by rotating the
valve the coil is attached to, it is often adjustable.

Wes
--
"Additionally as a security officer, I carry a gun to protect
government officials but my life isn't worth protecting at home
in their eyes." Dick Anthony Heller

Cross-Slide fired this volley in news:128b7a25-
:


I'm sure I missed something, but why wouldn't a DC ( Permanent
Magnet ) motor driven by a current source be a lot simpler?

It certainly would have been. I would loved to have built a current-
varied takeup with a dancer arm to regulate.

But it wouldn't fit in the (existing) machine without big-time mechanical
changes to both the drive train and the chassis.

This is an in-service machine that can't have major structural
modifications without taking it out of service for a considerable (and
unacceptable) time.

LLoyd

"Lloyd E. Sponenburgh" wrote:

Cross-Slide fired this volley in news:128b7a25-
:


I'm sure I missed something, but why wouldn't a DC ( Permanent
Magnet ) motor driven by a current source be a lot simpler?

It certainly would have been. I would loved to have built a current-
varied takeup with a dancer arm to regulate.

But it wouldn't fit in the (existing) machine without big-time mechanical
changes to both the drive train and the chassis.

This is an in-service machine that can't have major structural
modifications without taking it out of service for a considerable (and
unacceptable) time.

LLoyd

Still don't want to try the dancer arm - band brake mechanical tension
control I suggested?

Wes fired this volley in
:

I wonder, could you have employed a viscous fan drive for automotive
applications? The silicon fluid is moderated by a valve that is
either actuated by a bimetal snap disk, a bimetal temperature sensing
coil, or some electronics depending on the design.



That's an excellent guess, because I tried that first. I don't know if
it was the clutches I was testing, but I suspect it is the design, which
has a fairly small surface area of interleaving grooves and channels --
but the maximum torque I could get out of one at 2rpm was about .5 ft.lb.
At 2K rpm, they produce a lot more.

I even scavanged a used one, and filled it full of 1000Cps oil in an
attempt to nullify the effect of the thermostatic relief valve. Same
deal. Even with all the channels full of oil all the time, it wouldn't
produce useful torque at low speeds.

LLoyd

Wes fired this volley in
:

With the bi-metal coil operated device, you can set your amount of
drag by rotating the valve the coil is attached to, it is often
adjustable.

Oh.. forgot to mention, the effect of a fluid shear clutch is not linear at
all speeds. The torque increases almost linearly with speed up to the
shear stripping force of the oil, then flattens.

I need constant torque at _super_low_ rpms. (got it, too! g)

LLoyd

"Pete C." fired this volley in news:4c4f5ea6$0
:

Still don't want to try the dancer arm - band brake mechanical tension
control I suggested?


Pete, that would be fine, but there simply is not any room for the
dancer. I've got about 5" from the winding shuttle to the spool. I can
build such a brake easily, but I cannot (personally) see how to fit it
into the existing structure without a lot of chassis and drive-train
changes. If I were to "remote" the dancer to some other part of the
chassis, it would complicate things in other undesirable ways.

The problem isn't "can it be done?", it's "can it be done without taking
the machine out of service?" (except overnight).

I wasn't in love with having to "invent". I looked for a long time for a
solution off-the-shelf that would fit the budget. 'Just couldn't find
it.

The basic nature of this problem is an old one -- fit an "improvement"
into the same space occupied by the old, unacceptable mechanism. As an
example, the "Ingenious Mechanisms" book set is full of 'em.

LLoyd

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote:

Wes fired this volley in
:

I wonder, could you have employed a viscous fan drive for automotive
applications? The silicon fluid is moderated by a valve that is
either actuated by a bimetal snap disk, a bimetal temperature sensing
coil, or some electronics depending on the design.



That's an excellent guess, because I tried that first. I don't know if
it was the clutches I was testing, but I suspect it is the design, which
has a fairly small surface area of interleaving grooves and channels --
but the maximum torque I could get out of one at 2rpm was about .5 ft.lb.
At 2K rpm, they produce a lot more.

I even scavanged a used one, and filled it full of 1000Cps oil in an
attempt to nullify the effect of the thermostatic relief valve. Same
deal. Even with all the channels full of oil all the time, it wouldn't
produce useful torque at low speeds.


Large truck models have even more torque. Some use 23,000cps fluid (bitch to pump). We
test those things with 30+ inch fans and 75 hp drive motors in our test cells.

Wes

"Lloyd E. Sponenburgh" wrote:

"Pete C." fired this volley in news:4c4f5ea6$0
:

Still don't want to try the dancer arm - band brake mechanical tension
control I suggested?


Pete, that would be fine, but there simply is not any room for the
dancer. I've got about 5" from the winding shuttle to the spool. I can
build such a brake easily, but I cannot (personally) see how to fit it
into the existing structure without a lot of chassis and drive-train
changes. If I were to "remote" the dancer to some other part of the
chassis, it would complicate things in other undesirable ways.

The problem isn't "can it be done?", it's "can it be done without taking
the machine out of service?" (except overnight).

I wasn't in love with having to "invent". I looked for a long time for a
solution off-the-shelf that would fit the budget. 'Just couldn't find
it.

The basic nature of this problem is an old one -- fit an "improvement"
into the same space occupied by the old, unacceptable mechanism. As an
example, the "Ingenious Mechanisms" book set is full of 'em.

LLoyd

Perhaps you can post a picture of the relevant portion of the machine in
the metalworking dropbox so all the brilliant minds here can better see
what might work?