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'[EE] Looking for 12VDC high-torque motor'
2006\10\19@142144 by Gerhard Fiedler

picon face
Hello,

we're currently using this gear motor in a servo-type application:
http://www.casaferreira.com.br/pdf/CEP453042.pdf

12VDC, 57W, nominal 9Nm/75rpm/18A, stall 36Nm/50A, idle speed 100rpm, gear
63:1

There are two problems I need to solve. One is that the stall torque is not
enough. Ideally it would have 50 Nm. The idle speed is not critical and may
be lower, so a similar power motor with a different gearing should be ok.

The other problem is that this particular motor has a plastic gear that is
designed as a "mechanical fuse" to prevent burning out of the motor. The
connection between that gear and the output shaft sometimes strips off,
probably when there's a mechanical backlash on the output shaft.

So I'm looking for a gear motor (or a gear + motor combo) in that power
range (should not be less power, but may be somewhat more) with a higher
stall torque, a solid gearing (ideally some kind of metal) and an idle
speed that's at least 80 rpm or so.

The final purpose is to move a push/pull cable back and forth. We generate
this linear movement through a lever mounted to the motor shaft. So in
theory a linear actuator could also do it. The problem with most actuators
we have is twofold: one is the overall length; they tend to be much longer
than we have space for. We need a total movement of ~70mm and have around
160mm space, lengthwise. Linear actuators tend to be longer. The other
problem is that most of them are much slower. In the current application,
the mounting point at the lever moves the distance in some 200 ms (at half
load). But one that fits and that is fast enough could be even better.

And of course I don't have several hundred dollars to spend on that :)  The
one we're using now costs around $50. Small production quantities (several
hundred per year). Final destination is USA.

Does anybody know where I can find such a gear motor or gear+motor combo
(or linear actuator)? I've looked a lot, but they either are made for
different voltage (24+V or AC), are much slower (<10rpm) or faster (and
therefore weaker), or much more expensive.

Thanks for any hints,
Gerhard

2006\10\19@171304 by Richard Prosser

picon face
Gerhard

Windscreen wiper unit from a car wrecker?
RP

On 20/10/06, Gerhard Fiedler <spam_OUTlistsTakeThisOuTspamconnectionbrazil.com> wrote:
{Quote hidden}

> -

2006\10\19@174833 by alan smith

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what about an electric winch motor?  

Richard Prosser <.....rhprosserKILLspamspam@spam@gmail.com> wrote:  Gerhard

Windscreen wiper unit from a car wrecker?
RP

On 20/10/06, Gerhard Fiedler
wrote:
{Quote hidden}

> -

2006\10\19@175628 by Gerhard Fiedler

picon face
Richard Prosser wrote:

> Windscreen wiper unit from a car wrecker?

Yes, comes close :)

But from what I can see, we're already using the strongest gear motor Bosch
has available here in that range. So chances are that most others are not
stronger either -- you don't need 50 Nm for running a windshield wiper. But
if someone has a good source of such motors (which includes datasheets),
I'd like to check that out.

The other thing is that we may have difficulties securing several hundred
of the same type from a typical car wrecker :)

Thanks,
Gerhard

2006\10\19@180856 by Mark Rages

face picon face
On 10/19/06, Gerhard Fiedler <listsspamKILLspamconnectionbrazil.com> wrote:
> Richard Prosser wrote:
>
> > Windscreen wiper unit from a car wrecker?
>
> Yes, comes close :)
>
> But from what I can see, we're already using the strongest gear motor Bosch
> has available here in that range. So chances are that most others are not
> stronger either -- you don't need 50 Nm for running a windshield wiper. But
> if someone has a good source of such motors (which includes datasheets),
> I'd like to check that out.
>
> The other thing is that we may have difficulties securing several hundred
> of the same type from a typical car wrecker :)
>
> Thanks,
> Gerhard


http://www.allelectronics.com/cgi-bin/item/DCM-249/400200/POWERFUL_WINDSHIELD_WIPER_MOTOR_.html


--
You think that it is a secret, but it never has been one.
 - fortune cookie

2006\10\19@191312 by Gerhard Fiedler

picon face
Mark Rages wrote:

>>> Windscreen wiper unit from a car wrecker?

>> But if someone has a good source of such motors (which includes
>> datasheets), I'd like to check that out.

> http://www.allelectronics.com/cgi-bin/item/DCM-249/400200/POWERFUL_WINDSHIELD_WIPER_MOTOR_.html

This is a very good price :)

Unluckily they don't provide much useful data. There are many wiper motors
out there, but so far I've been unable to locate datasheets for most of
them.

For this one, the only thing they say is "65 RPM @ 12 Vdc, 2.5 Amps
(no-load rating)". The no-load current is not really that helpful; the
stall current would be better. (FWIW, the one we're using now draws around
3.5 A no-load current and some 45 A stall current. So if this is any
indication, this one is probably weaker than our current motor.)

One thing I forgot to mention is that we're using it bidirectionally. I'm
not sure how relevant that is. Most wiper motors seem to be speced for
unidirectional only.

Thanks,
Gerhard

2006\10\19@191312 by Gerhard Fiedler

picon face
Mark Rages wrote:

>>> Windscreen wiper unit from a car wrecker?

>> But if someone has a good source of such motors (which includes
>> datasheets), I'd like to check that out.

> http://www.allelectronics.com/cgi-bin/item/DCM-249/400200/POWERFUL_WINDSHIELD_WIPER_MOTOR_.html

This is a very good price :)

Unluckily they don't provide much useful data. There are many wiper motors
out there, but so far I've been unable to locate datasheets for most of
them.

For this one, the only thing they say is "65 RPM @ 12 Vdc, 2.5 Amps
(no-load rating)". The no-load current is not really that helpful; the
stall current would be better. (FWIW, the one we're using now draws around
3.5 A no-load current and some 45 A stall current. So if this is any
indication, this one is probably weaker than our current motor.)

One thing I forgot to mention is that we're using it bidirectionally. I'm
not sure how relevant that is. Most wiper motors seem to be speced for
unidirectional only.

Thanks,
Gerhard

2006\10\19@192716 by Gerhard Fiedler

picon face
alan smith wrote:

> what about an electric winch motor?  

That might be another venue. I started a quick search, and so far
everything I've seen was way too heavy, way too strong and most of it also
way too expensive. But there probably are some in the range I'm looking for
-- "just" a matter of finding them :)

Thanks,
Gerhard

2006\10\20@035131 by Pearce, AB (Alan)

face picon face
>So I'm looking for a gear motor (or a gear + motor combo)

Your local motor vehicle dealer scrap yard?

A starter motor initially came to mind, but a windscreen wiper motor
would do. After finding a suitable unit then see if the appropriate car
manufacturer will cut you a deal on them, or point you at their supplier
for a bespoke version of it.

2006\10\20@073741 by Gerhard Fiedler

picon face
Pearce, AB (Alan) wrote:

>>So I'm looking for a gear motor (or a gear + motor combo)
>
> Your local motor vehicle dealer scrap yard?
>
> A starter motor initially came to mind,

I think they are too fast and too big. I'd need a gear, for which I don't
yet have a cheap enough solution.

> but a windscreen wiper motor would do.

Something like this is what we're using now. The problem I'm seeing is that
our torque requirements seem to be just a bit above what most wiper motors
produce, so I probably have to try many of them until I find one -- if I
find one.

Anybody knows where to find datasheets of windshield wiper motors? What
would get me started is stall torque and idle speed... Ideally a list of
all the motors of one of those replacement parts manufacturers with that
data :)

Thanks,
Gerhard

2006\10\20@075432 by Tamas Rudnai

face picon face
Try to buy some motors preassembled with gears used by robotics projects.
Some of them has a very large torque.

Something like these:

http://www.active-robots.com/products/motorsandwheels/gearhead-motors.shtml

Tamas


On 20/10/06, Gerhard Fiedler <.....listsKILLspamspam.....connectionbrazil.com> wrote:
{Quote hidden}

> -

2006\10\20@081335 by Tony Smith

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{Quote hidden}

What about a winch?  Like on the front of 4-wheel drive vehicles?

Tony

2006\10\20@093811 by Gerhard Fiedler

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Tamas Rudnai wrote:

> Try to buy some motors preassembled with gears used by robotics projects.
> Some of them has a very large torque.
>
> Something like these:
>
> http://www.active-robots.com/products/motorsandwheels/gearhead-motors.shtml

What this site seems to call "high torque" is a magnitude or more below
what we need. But checking out robotics sites may lead to something...

Thanks,
Gerhard

2006\10\20@094013 by Gerhard Fiedler

picon face
Tony Smith wrote:

> What about a winch?  Like on the front of 4-wheel drive vehicles?

Alan Smith already suggested this. What I answered to him is still valid:

"That might be another venue. I started a quick search, and so far
everything I've seen was way too heavy, way too strong and most of it also
way too expensive. But there probably are some in the range I'm looking for
-- "just" a matter of finding them :)"

Thanks,
Gerhard

2006\10\20@094845 by Tamas Rudnai

face picon face
An advise to myself: read before speak :-)

Tamas


On 20/10/06, Gerhard Fiedler <EraseMElistsspam_OUTspamTakeThisOuTconnectionbrazil.com> wrote:
{Quote hidden}

> -

2006\10\20@095816 by Pearce, AB (Alan)

face picon face
>What this site seems to call "high torque" is a magnitude or more below
what
>we need. But checking out robotics sites may lead to something...

Maybe what you need are the sort of motors that used to used on reel to
reel mag tape units on computers, but all the ones I saw were operated
on 24V.

2006\10\20@104320 by Gerhard Fiedler

picon face
Pearce, AB (Alan) wrote:

>> What this site seems to call "high torque" is a magnitude or more below
>> what we need. But checking out robotics sites may lead to something...
>
> Maybe what you need are the sort of motors that used to used on reel to
> reel mag tape units on computers, but all the ones I saw were operated
> on 24V.

This is what I'm also finding with the robotics sites. Most of them have
only motors that are way below my specs. (To summarize quickly: 12 V DC,
stall torque >50 Nm = 450 lbf in = 7200 ozf in, electric power ~60 W, stall
current probably ~50 A, idle speed >80 rpm).

The ones that fall into this range are almost all speced for 24 V or more.
Which makes sense -- but not in an automotive application :)

Gerhard

2006\10\20@110159 by Tony Smith

picon face
Yes, but it helps if you get the message to read it!  :)  Hmmm, mail must
acting up.

There are some fairly cheap winches (Chinese) around, but cheap is relative
and weight may still be a problem.

The only other source (as in available at your local hardware store) I can
think of is from cordless tools, like a drill.  (Gearbox, clutch and speed
control as a bonus.)  Most will be underpowered (I guess), but there are a
few hefty ones out there.  Still a few 12v ones out there.

Largish stepper motors can be had fairly cheaply.  At the RPM you're after
they'd work nicely.  Downside is you need to make drivers for them.  Not
hard, but a bit of a nuisance and pushes the cost up somewhat.  The simplest
driver is for unipolar motor (6 wire) and is 4 fets and a bit of logic.  I'm
sure James would be happy with orders for a few hundred LiniSteppers.

Someone mentioned car starter motors, but motorcycle ones are smaller &
lighter.  Like the windshield wiper moters, good luck getting a few hundred
matching ones!  Can't hurt to ask though.

Tony


(Cheap cordless drills are my favorites, I get the motor, and a mate gets
the batteries to destroy in his model aircraft.)


{Quote hidden}

2006\10\20@115236 by Tamas Rudnai

face picon face
I think a brushless outrunner has the better torque / efficiency, however,
I could not find any that would meet your needs. The motors I use for my
airplanes are very strong, needs no more than 40A @12V, rotates more than
10K and you can put a gear on it... but even though when I took a look at
the specs of the special motor section it turned out that the NM is less
than your needs @~50A (in stall). And I did not even calculate with the loss
of the gear! The better I could find produces 37NM (probably it would be
30-33 with the power losses on the gear). That's much less than your specs.
With 70A you can get the desired power and speed, but then it is much higher
power consumption you wanted -- it is not that bad if you do not use it for
too long and too often.

Have a look at the manufacturer's site of my motor, you may find something
that useful:
http://www.megamotor.cz/new/script/mega.php?ref=products&sid=b29fe216bbc849dbd58e61559b1a59eb

You may find other manufacturers or may be able to build your own motor
using stronger neodymiums or better stators / windings, but you might get to
go up with the current limit or lower with the power / rotation speed. Also
for brushless you would need a more sophisticated speed controller than for
a DC motor, but I am sure it is no problem for you to build ;-)

Sorry, I can't help any further on this.
Tamas




On 20/10/06, Gerhard Fiedler <@spam@listsKILLspamspamconnectionbrazil.com > wrote:
{Quote hidden}

> -

2006\10\20@174617 by Lee McLaren

flavicon
face
Check out the geared 250W motor.

http://www.oatleyelectronics.com/motors.html


Gerhard Fiedler wrote:
{Quote hidden}

2006\10\22@115444 by Tony Smith

picon face
I thought about scooter motors after I sent my other message.  Oatley have
been selling them for a while, but I think Gerhard might baulk at the
shipping cost!  Treadmill motors come up surplus a lot as well, but I don't
know if they are 12v.  

The joy of buying stuff in small quantities...

Tony


> {Original Message removed}

2006\10\22@132333 by Austin

flavicon
face
>Gerhard Fiedler
>everything I've seen was way too heavy, way too strong and most
>of it also way too expensive. But there probably are some in
>the range I'm looking for -- "just" a matter of finding them :)"

ATV winches.

One site I came across with a few specs:
http://www.gorillawinches.com

Austin


{Original Message removed}

2006\10\22@153908 by Gerhard Fiedler

picon face
Austin wrote:

>> everything I've seen was way too heavy, way too strong and most of it
>> also way too expensive. But there probably are some in the range I'm
>> looking for -- "just" a matter of finding them :)"
>
> ATV winches.
>
> One site I came across with a few specs:
> http://www.gorillawinches.com

Thanks for the pointer. What I saw was not encouraging, though...

http://tinyurl.com/y84se9 : At $130 that could almost fit into the budget,
6 kg might be bearable. The data provided was not too extensive, other than
that it is a 1 hp (750 W) motor. That is plenty for my application,
actually quite an overkill. I found a bit more data for a sister-winch:

http://tinyurl.com/upxjm : Here they have a load/speed table. I don't know
the spool diameter, but I estimated with at least 10 cm. This gives an idle
speed of max. 22 rpm -- which is too slow. Probably there are not many
winches that are much faster: I'd need it around 80 rpm, four times the
speed.

Am I wrong with this estimation? Are there winches that rotate at 80 rpm? I
don't have a lot of experience with ATV winches.

Thanks,
Gerhard

2006\10\22@154602 by Gerhard Fiedler

picon face
Lee McLaren wrote:

> Check out the geared 250W motor.
>
> http://www.oatleyelectronics.com/motors.html

If you're talking about the SC250G, it's a 24V motor -- like so many others
in this class that I've come across. I'm not sure how the torque/speed
curve behaves when halving the voltage. Does anybody have experience with
this, or pointers?

Thanks,
Gerhard

2006\10\22@154941 by Tamas Rudnai

face picon face
How much amper they take?

Tamas


On 22/10/06, Gerhard Fiedler <KILLspamlistsKILLspamspamconnectionbrazil.com> wrote:
{Quote hidden}

> -

2006\10\22@155110 by Gerhard Fiedler

picon face
Tony Smith wrote:

> I thought about scooter motors after I sent my other message.  Oatley have
> been selling them for a while, but I think Gerhard might baulk at the
> shipping cost!  

The cited motor is 79AUD, shipping is around 35AUD. That's a total of
114AUD or 85USD -- not too bad if it solves the problem.

> Treadmill motors come up surplus a lot as well, but I don't know if they
> are 12v.  

The ones I've seen so far I don't even remember too well -- they were all
around 130VDC, IIRC.

> The joy of buying stuff in small quantities...

What would be my options with bigger quantities?

Gerhard

2006\10\22@183133 by Rich

picon face
Did you check out Oriental Motor?
----- Original Message -----
From: "Austin" <RemoveMEpiclistTakeThisOuTspamaustinm.net>
To: "Microcontroller discussion list - Public." <spamBeGonepiclistspamBeGonespammit.edu>
Sent: Sunday, October 22, 2006 1:23 PM
Subject: Re: [EE] Looking for 12VDC high-torque motor


{Quote hidden}

> --

2006\10\22@194014 by Austin

flavicon
face

Gerhard,

I don't recall you saying exactly what you're pulling/lifting, but it's
worthwhile to note that most winch specs you'll find are on the
first layer of rope.  Because the drums are fairly small in diameter,
pulling power quickly decreases and speed quickly increases as
you add layers of rope.  Winches in this range will likely have
3/16" or 5/32" wire rope.

For instance, A 1.6HP Warn 12vdc winch, 1700lb on the first
layer of wire, 1500 on the second, 1350 on the 3rd, etc.
Here is a link to a manual for the 1700DC, with some specs:
www.warn.com/works/dcwinches/images/868/73054CO.pdf
Sounds like the 1700DC will be too large for your purpose.

Another one from Warn to consider is the 1.5ci.  Weighs 5.2kg.
1500lb pulling power on the first layer.
http://www.warn.com/atv/winches/15_ci.shtml
Manual for the 1.5ci:
http://www.warn.com/atv/winches/images/541/69009A1.pdf

The 1.5 has a 1.5" drum, 1.77" circumference, unloaded line
speed of 15 feet/min, which should yield just over 100rpm
with no load.

You could also consider using a snatch block (backwards)
to double pulling speed/halve pulling power.

The 1700DC went for $170 on one site I found.
The 1.5ci was priced at ~$250 on another site.

Hope some of that helps,

Austin


{Original Message removed}

2006\10\23@030938 by Lee McLaren

flavicon
face
While I can't give you figures it seems to work fine, I have the geared
version and am planning on using it on a gate opener, I will be using it
on 12v as that is more that fast and strong enough for my needs.

Gerhard Fiedler wrote:
{Quote hidden}

2006\10\23@042114 by Pearce, AB (Alan)

face picon face
>> The joy of buying stuff in small quantities...
>
>What would be my options with bigger quantities?

Well, I would have thought the quantities you have mentioned so far
would be large enough to go talking to a motor manufacturer to get a
bespoke design. Biggest problem is probably finding a suitable
manufacturer.

2006\10\23@050834 by Tony Smith

picon face
> > The joy of buying stuff in small quantities...
>
> What would be my options with bigger quantities?
>
> Gerhard


Manufacturers don't hang up when you call them  :)  

Cheaper too, ever tried to buy a windscreen motor new?

All those winch & scooter motors come out of China (maybe India), but
minimum order might be a container load or two.

E.g. those little lathe & mills (google 7x12 or mini-mill) have the motors
readily available as a spare part (12v, but maybe too big / fast for your
purposes as is, they have electronic speed controls).  Worth a look.

Wheelchairs?

Tracking down the maker is possible, but placing an order is much harder.  A
bit like Maxim, you can either get 1 or 1 million, nothing in between.

You need to find someone who uses the motors you need, they'll be happy to
sell you a few.  Or get lucky in the surplus market, like the Oatley ones.

You can also get them made to spec.  I've had motors rewound (done a couple
myself), same as transformers, you can get them wound to whatever you like.
The RC plane crowd rewind CD-ROM motors for more torque.

Custom made can be a bit expensive, as I found out once.

Tony

2006\10\23@125802 by Gerhard Fiedler

picon face
Tony Smith wrote:

> Largish stepper motors can be had fairly cheaply.  At the RPM you're
> after they'd work nicely.  Downside is you need to make drivers for
> them.  Not hard, but a bit of a nuisance and pushes the cost up
> somewhat.  The simplest driver is for unipolar motor (6 wire) and is 4
> fets and a bit of logic.  

I've trouble finding a stepper motor that can produce 50 Nm (7000+ ozf.in).
The biggest I found have a holding torque of 40 Nm (5700 ozf.in), which is
a bit more than what we have now (as stall torque).
http://www.anaheimautomation.com/hightorque.htm

Are there stronger stepper motors?

How does the holding torque of a stepper motor relate to the stall torque
of a DC motor? One site says that "dynamic torque" is about 70% of holding
torque. Is "dynamic torque" what I have available to move something? (I
know that the available torque goes down with speed, but since I'm working
at around 1 rot/s, it seems that is very slow for a typical stepper motor
and it develops its maximum torque.)


> I'm sure James would be happy with orders for a few hundred LiniSteppers

Probably :)  However, it seems that the circuit as-is won't be able to
handle the currents I suppose will be necessary for 40...50 Nm torque.

Thanks,
Gerhard

2006\10\23@141101 by Tony Smith

picon face
{Quote hidden}

Ok, your definition of 'largish' is different to mine :)

There are bigger steppers, the next size up from a NEMA42 is a NEMA66, but
it starts getting a bit silly.  The body of that is bigger than a CD-ROM!
You could bolt a gearhead to the stepper, at low RPM you tend not to loose
too much torque.  Given the prices on this page
<www.powerdrives.com/superior/order/nema42gearheads_rtplanetary.htm>,
that's probably not an option.

Not sure what they mean by dynamic torque, as you say torque varies with
speed.  Most steppers have a torque curve that remains fairly flat up to a
certain speed, and then falls off rapidly, a bit like a knee.  Maybe the 70%
refers to that point.

Looks like your stuck with trading speed for torque, get a motor and gear it
down.  Servos on CNC machines are usually geared down (say 1:5), so pulleys
& belts are common.

50Nm is a lot of torque, what are you making?

Tony

2006\10\23@162236 by Tamas Rudnai

face picon face
dynamic vs static torque: is that something like when you start the motor
you can stop spinning it with an X power but you can't stop it with the same
once it spinning?

Tamas


On 23/10/06, Tony Smith <ajsmithEraseMEspam.....rivernet.com.au> wrote:
{Quote hidden}

> -

2006\10\23@181258 by Gerhard Fiedler

picon face
Tamas Rudnai wrote:

> dynamic vs static torque: is that something like when you start the motor
> you can stop spinning it with an X power but you can't stop it with the same
> once it spinning?

Sounds like that would be mechanical momentum (if that's the word...)

You have to overcome the inertia of the rotational movement when you want
to stop a motor. When holding while the motor is rotating at speed, the
rotor inertia works against you, while at the moment it tries to start
moving, it works in favor of you (you being the one trying to stop the
motor).

Gerhard

2006\10\23@191657 by Gerhard Fiedler

picon face
Tony Smith wrote:

> Given the prices on this page
> <www.powerdrives.com/superior/order/nema42gearheads_rtplanetary.htm>,
> that's probably not an option.

Yes, that's what I'm seeing a lot too :)  As Alan said, finding a suitable
manufacturer is probably the biggest problem. The ones I've seen so far are
either way too expensive already with their stock parts or are working in
quantities where they are really not interested in making a custom part for
us.

> Looks like your stuck with trading speed for torque, get a motor and gear it
> down.  Servos on CNC machines are usually geared down (say 1:5), so pulleys
> & belts are common.

I'm leaning towards using my current motor (which is relatively inexpensive
for the torque and power it provides) together with a belt or chain.

> 50Nm is a lot of torque, what are you making?

Basically a servo drive for moving push-pull cables, with forces up to 800+
N and a throw of 7 cm. So far we're moving the cables with levers mounted
to the motor, but the belt/chain drive would give more freedom in the
translation of the rotation into a linear movement. That way, I could
increase the force without losing throw (as I do with the lever).

Gerhard

2006\10\24@052324 by Gerhard Fiedler

picon face
Tamas Rudnai wrote:

>>> http://www.gorillawinches.com

>> http://tinyurl.com/y84se9

>> http://tinyurl.com/upxjm

> How much amper they take?

They don't say. But they are 1hp (750W) motors, so probably a lot. My 57W
motor pulls 45A stall current...

Gerhard

2006\10\24@053610 by Gerhard Fiedler

picon face
Austin wrote:

> The 1700DC went for $170 on one site I found.
> The 1.5ci was priced at ~$250 on another site.

The 1.5ci motor has the mechanical specs I need, even though I'd have to
beef up my drivers. But unluckily it's way out of my price range.

Thanks for the help,
Gerhard

2006\10\24@054652 by Gerhard Fiedler

picon face
Rich wrote:

> Did you check out Oriental Motor?

http://www.orientalmotor.com/

No, I hadn't -- thanks for the pointer, nice selection. Unluckily they
don't seem to have anything for 12VDC operation: everything is for 24VDC or
more or mains. Which seems to be the preference for most industrial
manufacturers. (Understandably, considering the currents at 12V.)

Gerhard

2006\10\24@055642 by Gerhard Fiedler

picon face
Gerhard Fiedler wrote:

{Quote hidden}

Thanks to all who responded. I got a lot of interesting ideas, some of
which I had tried earlier that got a new momentum. Unluckily, it also
confirmed that it's not as easy as selecting an opamp... There is not
really a "market" for this type of equipment in my quantities, and
datasheets for the mass-market products are difficult to find. Or the
market that exists is way out of my price range.

My current thought is to use a normal 12VDC ~60W motor and drive a threaded
bolt, making a custom linear actuator. The linear actuators I found that
work this way are usually too slow. I'll see whether there's a reason for
that... I need at least 10 cm/s, ideal would be 20 cm/s.

Another possibility would be to continue using my gear motor and drive a
belt. That would also get me more force on the cable than I have now.

Gerhard

2006\10\24@094536 by Tony Smith

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Another reason plastic gears are used is that they are quieter than metal
ones, not really an issue in a low RPM application.

Threaded rod isn't all that efficient, but there's different grades.
Ballswcrews work the best, but are expensive by comparison.

Another method to get linear movement is to have the cable in a loop, with
one end wound around the threaded rod, the other around a pulley.  Cable is
tensioned by a spring.  Rod turns, cable winds 'on' one end, and 'off' the
other.  Old timers would say "just like old radio tuners!" but I've seen the
same setup in photocopiers.

Tony

2006\10\24@143757 by Gerhard Fiedler

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Tony Smith wrote:

> Another reason plastic gears are used is that they are quieter than metal
> ones, not really an issue in a low RPM application.

It seems we don't really have a problem with the plastic gear per se, but
with the way it is connected to the output shaft. This connection
apparently strips (and is designed to do so) with higher torque shocks like
backlashes.

> Threaded rod isn't all that efficient, but there's different grades.
> Ballswcrews work the best, but are expensive by comparison.

Yes, that's true. I've read that ballscrews are more sensitive WRT
lubrification than normal screws. Is this true?

> Another method to get linear movement is to have the cable in a loop, with
> one end wound around the threaded rod, the other around a pulley.  Cable is
> tensioned by a spring.  Rod turns, cable winds 'on' one end, and 'off' the
> other.  Old timers would say "just like old radio tuners!" but I've seen the
> same setup in photocopiers.

But probably not pushing/pulling 800...1000 N?

Gerhard

2006\10\25@122445 by Tony Smith

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> > Threaded rod isn't all that efficient, but there's different grades.
> > Ballswcrews work the best, but are expensive by comparison.
>
> Yes, that's true. I've read that ballscrews are more
> sensitive WRT lubrification than normal screws. Is this true?
>
> > Another method to get linear movement is to have the cable
> in a loop,
> > with one end wound around the threaded rod, the other
> around a pulley.  
> > Cable is tensioned by a spring.  Rod turns, cable winds
> 'on' one end,
> > and 'off' the other.  Old timers would say "just like old radio
> > tuners!" but I've seen the same setup in photocopiers.
>
> But probably not pushing/pulling 800...1000 N?
>
> Gerhard


Ballscrews don't like getting dirty.  On machinery they are usually placed
out of harms way, and have wipers fitted to keep them clean.  Grit still
manages to get into everything.

You'd be surprised at how well the cable setup works.  If you get slippage,
you just wind the cable around the rod a couple more times.  Not sure of the
efficiency or mechanical advantages, but the force is really only limited by
the strength of the cable.  You don't really need a spring to keep tension,
you can attach the ends of the cable to whatever it is you're moving.

As a complete aside on simple ideas, I recently discovered how the tracks
are kept taut on bulldozers, not that I'd ever wondered.  On most
motorcycles, to remove slack in the chain you loosen the rear axle, slide
the wheel back, and re-tighten.  On a bulldozer, it's hydraulic.  Rather
than pressure being applied by air or springs, it's by grease.  When the
track becomes loose, you just pump in more grease.  The grease can't be
compressed, so the tension is maintained.  Rather neat, I thought.  I've
contemplated making this work on a bike.

Tony

2006\10\25@135514 by Gerhard Fiedler

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Tony Smith wrote:

> You'd be surprised at how well the cable setup works.  If you get slippage,
> you just wind the cable around the rod a couple more times.  Not sure of the
> efficiency or mechanical advantages, but the force is really only limited by
> the strength of the cable.  You don't really need a spring to keep tension,
> you can attach the ends of the cable to whatever it is you're moving.

Sounds like what I was planning with a belt. The problem is the tensioning,
with both approaches. Bi-directional pull/push of 1000 N... I don't
understand when you say that I don't need a spring to keep the tension. Of
course I can use a screw or something and re-tension when needed, but
something needs to be adjustable (or self-adjusting), doesn't it?

> As a complete aside on simple ideas, I recently discovered how the tracks
> are kept taut on bulldozers, not that I'd ever wondered.  On most
> motorcycles, to remove slack in the chain you loosen the rear axle,
> slide the wheel back, and re-tighten.  On a bulldozer, it's hydraulic.
> Rather than pressure being applied by air or springs, it's by grease.
> When the track becomes loose, you just pump in more grease.  The grease
> can't be compressed, so the tension is maintained.  Rather neat, I
> thought.  I've contemplated making this work on a bike.

Calling a grease-driven mechanism "hydraulics" is stretching it a bit :)

On a bike, you'd probably have the problem of having to synchronize the
movement on both sides of the axle. Not a problem for bulldozers.

Gerhard

2006\10\26@022717 by Tony Smith

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> > Not sure of the efficiency or mechanical advantages, but
> the force is
> > really only limited by the strength of the cable.  You don't really
> > need a spring to keep tension, you can attach the ends of
> the cable to whatever it is you're moving.
>
> Sounds like what I was planning with a belt. The problem is
> the tensioning, with both approaches. Bi-directional
> pull/push of 1000 N... I don't understand when you say that I
> don't need a spring to keep the tension. Of course I can use
> a screw or something and re-tension when needed, but
> something needs to be adjustable (or self-adjusting), doesn't it?


This difference with a cable is that you can attach it to whatever is
moving.  You still need to tension it somehow, and a screw type adjuster is
best as you don't get problems with the spring stretching.  Of course, you
can move the motor itself to adjust tension.  If the ends of the cable are
attached to the driven rod itself, then a bit of slack can be tolerated, but
you get positioning problems.  Possibly too much hassle for your case,
unless you find a similar setup running and learning about it's
advantages/failing.  

Threaded rod doesn't have those problems, of course.


{Quote hidden}

You're right about the bike, keeping the wheel aligned is rather important,
one of the reasons it didn't get past the  contemplation phase.  You'd need
to equalise the pressure, etc.  No doubt someone has tried it.  Can't beat a
couple of bolts on pricing though.

Hydraulic is a bit of a stretch, but that's what they called it.  A piston
with the cylinder full of grease.  Grease is a liquid, I suppose...  I asked
about it, and was told the 'getting the grease back out' bit could be fun.
It's a very old idea apparently, and no-one is in a hurry to change it.

Tony

2006\10\26@053345 by Howard Winter

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Gerhard,

On Tue, 24 Oct 2006 15:37:03 -0300, Gerhard Fiedler wrote:

>...
> I've read that ballscrews are more sensitive WRT
> lubrification than normal screws. Is this true?

No I don't think it is, the "nut" unit is well lubricated during manufacture and I'm not aware of any maintainance lubrication requirements.  What they
are sensitive to is dirt on the track - you need to shield them from dust, swarf, and so on, or they will start to jam as the balls try to roll over the
contamination.  If you can afford it, and can stop them picking up dirt, they are an excellent solution to producing linear motion from rotary,
accurately.

Cheers,


Howard Winter
St.Albans, England


2006\10\26@073635 by Gerhard Fiedler

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Tony Smith wrote:

> Possibly too much hassle for your case, unless you find a similar setup
> running and learning about it's advantages/failing.  

This would definitely be interesting :)

> I asked about it, and was told the 'getting the grease back out' bit
> could be fun.

I thought they might have a bigger hole in the cylinder that only gets
opened then. But probably this happens too rarely for them to spend even
that on it.

Gerhard

2006\10\26@074041 by Gerhard Fiedler

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Howard Winter wrote:

> No I don't think it is, the "nut" unit is well lubricated during
> manufacture and I'm not aware of any maintainance lubrication
> requirements.  What they are sensitive to is dirt on the track - you
> need to shield them from dust, swarf, and so on, or they will start to
> jam as the balls try to roll over the contamination.  

Ah, makes sense. I didn't know they were so well lubricated for life.

> If you can afford it,

Yes, I've seen this problem already :)

Gerhard

2006\10\26@131147 by Tony Smith

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> > Possibly too much hassle for your case, unless you find a similar
> > setup running and learning about it's advantages/failing.
>
> This would definitely be interesting :)
>
> > I asked about it, and was told the 'getting the grease back
> out' bit
> > could be fun.
>
> I thought they might have a bigger hole in the cylinder that
> only gets opened then. But probably this happens too rarely
> for them to spend even that on it.
>
> Gerhard


I got interested in cable drive when thinking of building a CNC router.
Cable was cheap, fast, needed smaller motors and fairly accurate with the
light loads it needed.  Basically a large flatbed plotter, which are cable
as well.  The test rig I built worked very well, far better than the
threaded rod version.

I'm not sure how it would scale up (bigger load in your case).  As you know,
double any variable and the amount of aggravation goes up four-fold.  You'd
need to build a test rig.  At it's simplest, it's a motor with a (long) worm
gear, some steel cable (even thin stuff can handle a few hundred kilos) and
a pulley.  I do need to finish grinding some mirrors...

For the 'dozers, the grease came out just like you thought.  Open a valve,
and out it squirts.  What a fun job that would be.  Happens fairly
regularly, the larger machines (like in mines) run almost non-stop (easily
22 hours a day), and some enviroments (sand, coal etc) are quite harsh.
Much time and effort is spent trying to make tracks, buckets etc last
longer.  Interesting stuff.  I could ask if they have any spare engines
around, would a 16-cyclinder 46-litre diesel be ok?  :)

Tony

2006\10\26@154842 by Gerhard Fiedler

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Tony Smith wrote:

> I'm not sure how it would scale up (bigger load in your case).  As you
> know, double any variable and the amount of aggravation goes up
> four-fold.  

Oh, yes... :)

> You'd need to build a test rig.  At it's simplest, it's a motor with a
> (long) worm gear, some steel cable (even thin stuff can handle a few
> hundred kilos) and a pulley.  

I may just try this. This or a belt. (I'm a bit partial towards the belt.
Probably easier to avoid slipping.)

Gerhard

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