brake failure

Michael Press

In article
<95308713-af30-4933-9ab5-3b9911f4d725@f63g2000hsf.googlegroups.com>,
velodancer <commerce48@yahoo.com> wrote:

> There are several reasons why "linear" brakes now own the market.
> Considerably easier setup, slightly better overall leverage ratios
> leading to a lighter feel, useful for mountain bikes. (Lighter feel is
> also the primary reason for increasing disc sizes on mountain bikes.)
> And the leverage ratio is almost completely unchanged throughout the
> lever stroke, which is something maddening about cantilever brakes as
> can easily be ascertained with Sheldon's discussion of straddle cable
> setup. As a downside to the higher overall leverage ratio, pads do
> have to be set closer to the rim. This does have one beneficial effect
> of reducing pad dive under the rim.
>
> Large amounts of braking force are lost in the cable and housing
> system. Thus doubling of cable travel halves this lost force, also
> increasing braking efficiency and contributing to the rapid conversion
> to "linear" pull brakes over cantilevers. This is the same effect used
> by SRAM in their "1:1" rear derailleur shifting system to halve the
> effect of friction on shifting precision. Lost force reduction also
> accounts for the popularity of hydraulic disc brakes versus cable
> activated disc brakes despite their complexity.

There a many solutions to replace single pivot calipers,
but none of them measure up. Adding up advantages and
disadvantages, single pivot calipers are the best. When
you need to improve some aspect of brake performance
over single pivot calipers, then you must compromise
others. Typically one of the advantages we abandon when
we abandon single pivot calipers is the minimal maintenance.
Nobody here writes in with questions on setting up and
maintaining single pivot calipers. (of course they are
not produce any more except BMX 75-90 mm reach.)

For me there are three improvements in brakes in the
last fifty years: lined cable housing, aerodynamic
brake levers, and orange brake pads. The rest is
optimization of exactly one component of brake performance.

--
Michael Press

Michael Press

In article <4835c236$0$34549$742ec2ed@news.sonic.net>,
jobst.brandt@stanfordalumni.org wrote:

> someone wrote:
>
> > I'm having trouble figuring out what is being argued, er discussed,
> > in this thread...
>
> > 1. 'Linear' is a perfectly obvious concept and one I've seen Jobst
> > embrace in previous posts. The horizontal displacement of the
> > brakes pads of a V brake move in fixed proportion (MA of the
> > calipers) to the horizontal displacement of the cable anchor points.
>
> > 2. All brakes are probably close to linear in the distance between
> > pad contact and pad deforming, caliper bending, fork twisting full
> > application. However, figuring out what that is, is complicated by
> > yoke configuration.
>
> > 3. High profile cantilevers, set near horizontal (i.e. MAFAC's) are
> > not only linear in the above sense, but of fixed MA as they are
> > indifferent to changes in yoke length.
>
> > 4. Cantilevers don't dive down much more than center pivoted brakes
> > in their immediate ranges. This is easily determined by running a
> > string from the fork center to a cantilever mount and observing it
> > passes pretty close to the rim. (Dual pivots have some advantage
> > here.)
>
> Dive is given by the position of the pivot around which the brake arm
> rotates. In the sidepull single pivot, the pivot is centered over the
> rim and has essentially zero cosine error (foreshortening as it
> articulates). The cantilever has large cosine error, arcing at close
> to 45 degrees from the contact area. V-brakes, using the same pivot
> points do likewise.
>
> > 5. All brake systems (okay not hydraulics) change their geometry
> > with pad wear. There is no need for V brakes to have thin pads.
> > The correct solution is to maintain the pad surface in the same
> > plane - hence the shaft mount of traditional cantilevers.
>
> Not true. With classic sidepull brakes, pads can be worn to the metal
> (pad holder) without changing enough to require adjustment. I do it
> all the time with my brakes.
>
> I take it trigonometry is no longer taught in schools.

I do not know how well it was ever taught. We had a physics
teacher who one day said "Today I teach you trigonometry",
and he did. Of course he had our attention 'cause he used
to tell us war stories, and about what it was like for a
17 year old to steep in a south Pacific foxhole all night
while Japanese soldiers screamed at you and promised to
inflict abominations upon your flesh. The rest of the
hour after he taught us trigonometry he told war stories.

Trigonometry only gets a bit complicated/interesting
when you would like to figure the angles on a complex mitre
for carpentry, or two twisted eighth bends while plumbing,
or the geodesic distance given latitude and longitude
of two points.

--
Michael Press

Larry Dickman

jobst.brandt@stanfordalumni.org wrote in news:48347bea$0$34514
$742ec2ed@news.sonic.net:

> To make up for that, their long thin pads wear out faster and have no
> benefit other than being different from other brakes.
>
> Jobst Brandt

V brake pads are much easier to install and align than any canti brake I
had before.


--
Larry Dickman <LDickman@comcast.net>

jobst.brandt@stanfordalumni.org

Michael Press wrote:

>> There are several reasons why "linear" brakes now own the market.
>> Considerably easier setup, slightly better overall leverage ratios
>> leading to a lighter feel, useful for mountain bikes. (Lighter
>> feel is also the primary reason for increasing disc sizes on
>> mountain bikes.) And the leverage ratio is almost completely
>> unchanged throughout the lever stroke, which is something maddening
>> about cantilever brakes as can easily be ascertained with Sheldon's
>> discussion of straddle cable setup. As a downside to the higher
>> overall leverage ratio, pads do have to be set closer to the rim.
>> This does have one beneficial effect of reducing pad dive under the
>> rim.

>> Large amounts of braking force are lost in the cable and housing
>> system. Thus doubling of cable travel halves this lost force, also
>> increasing braking efficiency and contributing to the rapid
>> conversion to "linear" pull brakes over cantilevers. This is the
>> same effect used by SRAM in their "1:1" rear derailleur shifting
>> system to halve the effect of friction on shifting precision. Lost
>> force reduction also accounts for the popularity of hydraulic disc
>> brakes versus cable activated disc brakes despite their complexity.

> There a many solutions to replace single pivot calipers, but none of
> them measure up. Adding up advantages and disadvantages, single
> pivot calipers are the best. When you need to improve some aspect
> of brake performance over single pivot calipers, then you must
> compromise others. Typically one of the advantages we abandon when
> we abandon single pivot calipers is the minimal maintenance. Nobody
> here writes in with questions on setting up and maintaining single
> pivot calipers. (of course they are not produce any more except BMX
> 75-90 mm reach.)

> For me there are three improvements in brakes in the last fifty
> years: lined cable housing, aerodynamic brake levers, and orange
> brake pads. The rest is optimization of exactly one component of
> brake performance.

A problem with single pivot brakes is that the caliper return spring
has significant cosine error causing spring sliding at contact points
on its brake arms. The spring rotation centers are in the two ram's
horn coils on either side of the brake anchor. With a return spring
having a single coil wrapped around the anchor about which brake arms
rotate has no cosine error. This makes a reliable self centering
caliper that does not need "dual pivot" remain centered and prevent
one sided brake drag.

On conventional single pivot brake calipers, drag can only be avoided
keeping spring contact points clean and lubricated. I am amazed that
brake designers missed that point. This is apparent on the dual pivot
brake because it has greater cosine error than prior single pivot
brakes and uses a special plastic slider bearing to accommodate that
greater spring-to-brake-arm motion.

Are we making any progress yet?

Jobst Brandt

JG

No, the angle a centerpull makes to the rim is roughly the same as a
cantilever does... However, the radius of the centerpull is about
twice as long, so it will dive twice as much as the neglible
centerpull dive. Of course, I cheated and actually looked at a
bike...

One reason for thin V brake pads is that while thick pads are
perfectly viable, a 2.5 MA would mean the arms would have to be
adjusted through 2.5 x 2 pad thicknesses, which would be rather
inelegant...

JG

jobst.brandt@stanfordalumni.org

Larry Dickman wrote:

>> To make up for that, their long thin pads wear out faster and have
>> no benefit other than being different from other brakes.

> V brake pads are much easier to install and align than any canti
> brake I had before.

Why? I don't see what their length and thinness has to do with
installation. My Kool-Stop Continental pads are as simple as can be
and they last a long time.

Jobst Brandt

jim beam

jobst.brandt@stanfordalumni.org wrote:
> Larry Dickman wrote:
>
>>> To make up for that, their long thin pads wear out faster and have
>>> no benefit other than being different from other brakes.
>
>> V brake pads are much easier to install and align than any canti
>> brake I had before.
>
> Why? I don't see what their length and thinness

jobst, precisely /where/ do you see "length and thinness" in the words:
"V brake pads are much easier to install and align than any canti brake
I had before."???

what makes them easier to install and align is the design of mounting
post. nothing to do with "length and thinness".

> has to do with
> installation. My Kool-Stop Continental pads are as simple as can be
> and they last a long time.

your experience buffer overran 30 years ago. you comprehension buffer
is "status unknown".

jim beam

jobst.brandt@stanfordalumni.org wrote:
> Michael Press wrote:
>
>>> There are several reasons why "linear" brakes now own the market.
>>> Considerably easier setup, slightly better overall leverage ratios
>>> leading to a lighter feel, useful for mountain bikes. (Lighter
>>> feel is also the primary reason for increasing disc sizes on
>>> mountain bikes.) And the leverage ratio is almost completely
>>> unchanged throughout the lever stroke, which is something maddening
>>> about cantilever brakes as can easily be ascertained with Sheldon's
>>> discussion of straddle cable setup. As a downside to the higher
>>> overall leverage ratio, pads do have to be set closer to the rim.
>>> This does have one beneficial effect of reducing pad dive under the
>>> rim.
>
>>> Large amounts of braking force are lost in the cable and housing
>>> system. Thus doubling of cable travel halves this lost force, also
>>> increasing braking efficiency and contributing to the rapid
>>> conversion to "linear" pull brakes over cantilevers. This is the
>>> same effect used by SRAM in their "1:1" rear derailleur shifting
>>> system to halve the effect of friction on shifting precision. Lost
>>> force reduction also accounts for the popularity of hydraulic disc
>>> brakes versus cable activated disc brakes despite their complexity.
>
>> There a many solutions to replace single pivot calipers, but none of
>> them measure up. Adding up advantages and disadvantages, single
>> pivot calipers are the best. When you need to improve some aspect
>> of brake performance over single pivot calipers, then you must
>> compromise others. Typically one of the advantages we abandon when
>> we abandon single pivot calipers is the minimal maintenance. Nobody
>> here writes in with questions on setting up and maintaining single
>> pivot calipers. (of course they are not produce any more except BMX
>> 75-90 mm reach.)
>
>> For me there are three improvements in brakes in the last fifty
>> years: lined cable housing, aerodynamic brake levers, and orange
>> brake pads. The rest is optimization of exactly one component of
>> brake performance.
>
> A problem with single pivot brakes is that the caliper return spring
> has significant cosine error causing spring sliding at contact points
> on its brake arms. The spring rotation centers are in the two ram's
> horn coils on either side of the brake anchor. With a return spring
> having a single coil wrapped around the anchor about which brake arms
> rotate has no cosine error. This makes a reliable self centering
> caliper that does not need "dual pivot" remain centered and prevent
> one sided brake drag.
>
> On conventional single pivot brake calipers, drag can only be avoided
> keeping spring contact points clean and lubricated. I am amazed that
> brake designers missed that point.

jobst, have you looked at /any/ form of brake equipment inside the last
three decades??? single pivot brake manufacturers use a plastic sleeve
that has precisely this function. sheesh.


> This is apparent on the dual pivot
> brake because it has greater cosine error than prior single pivot
> brakes and uses a special plastic slider bearing to accommodate that
> greater spring-to-brake-arm motion.

just like single pivot. see above.


>
> Are we making any progress yet?

have you been to a bike shop yet?

seriously jobst, as one that pretends to be an expert, the onus is on
YOU to stay current and buy/use the equipment on which you so freely
express opinion. then you might even get stuff right. on occasion.

_

On 23 May 2008 05:09:52 GMT, jobst.brandt@stanfordalumni.org wrote:

> Michael Press wrote:
>
>>> There are several reasons why "linear" brakes now own the market.
>>> Considerably easier setup, slightly better overall leverage ratios
>>> leading to a lighter feel, useful for mountain bikes. (Lighter
>>> feel is also the primary reason for increasing disc sizes on
>>> mountain bikes.) And the leverage ratio is almost completely
>>> unchanged throughout the lever stroke, which is something maddening
>>> about cantilever brakes as can easily be ascertained with Sheldon's
>>> discussion of straddle cable setup. As a downside to the higher
>>> overall leverage ratio, pads do have to be set closer to the rim.
>>> This does have one beneficial effect of reducing pad dive under the
>>> rim.
>
>>> Large amounts of braking force are lost in the cable and housing
>>> system. Thus doubling of cable travel halves this lost force, also
>>> increasing braking efficiency and contributing to the rapid
>>> conversion to "linear" pull brakes over cantilevers. This is the
>>> same effect used by SRAM in their "1:1" rear derailleur shifting
>>> system to halve the effect of friction on shifting precision. Lost
>>> force reduction also accounts for the popularity of hydraulic disc
>>> brakes versus cable activated disc brakes despite their complexity.
>
>> There a many solutions to replace single pivot calipers, but none of
>> them measure up. Adding up advantages and disadvantages, single
>> pivot calipers are the best. When you need to improve some aspect
>> of brake performance over single pivot calipers, then you must
>> compromise others. Typically one of the advantages we abandon when
>> we abandon single pivot calipers is the minimal maintenance. Nobody
>> here writes in with questions on setting up and maintaining single
>> pivot calipers. (of course they are not produce any more except BMX
>> 75-90 mm reach.)
>
>> For me there are three improvements in brakes in the last fifty
>> years: lined cable housing, aerodynamic brake levers, and orange
>> brake pads. The rest is optimization of exactly one component of
>> brake performance.
>
> A problem with single pivot brakes is that the caliper return spring
> has significant cosine error causing spring sliding at contact points
> on its brake arms.

This would easy to fix - have the arms connected via a pivoting link to the
ends of the spring.

Of course, to completely* eliminate sliding friction you'd have to have
ball- or roller-bearings at each end of the link, but superfluous
complexity in cycle components has never been an obstacle to marketing.

* completely here not meaning ABDSOLUTELY completely, as even in rolling
contact bearings there may be some minute amount of sliding friction, but
hey, we're not jim beam claiming that cut threads NEVER are used on qr
skewers...

jim beam

_ wrote:
<snip for clarity>

> we're not jim beam claiming that cut threads NEVER are used on qr
> skewers...

only an someone unfamiliar with the concept of fatigue would sanction
production of such a component. i therefore ask you to show one single
example of one that is!

bear in mind, a lot of prior debate on rolled/cut threads had people
citing as example rolled threads under the mistaken impression that they
were cut. not understanding what is being looked at leads to all kinds
of mistakes. and not just for thread forming.

for the unfamiliar, this is a highly simplistic description of why
rolled threads are used:
http://www.precisionscrewthread.com/ptroll.html

dabac

I've done that myself, on 2-3 occasions. Worked rather well for the front brake. Brake got a bit more powerful, but that frequently warned for lock-up and endo repeatedly failed to happen.
Set-up for the rear was considerably more questionable, with extreme care needed to keep the slack down enough to get both a drag free resting position and a satisfying wheel lock w/o the lever bottoming out against the bar.

You're quite right in that mismatched systems works, but at the cost of becoming more finicky.
I've toyed with the idea of trying the set-up again using Nokon cables, see if that would offer any improvement.
I also considered using the shifter cable from an old Positron RD to see if that would reduce the slack enough to get decent performance out of the rear brake, as according to the yachting world a solid wire is less springy than a multi strand wire(for a given diameter).
Now when I've got matching sets it doesn't seem worth the effort merely for satisfying my own curiosity though.

As a curiosity I can mention that my brother had a bike equipped with a set of brake levers that had a set intermediate stroke length. Long enough to let them work with rear linear brakes w/o bottoming out too badly, but short enough not to be impossibly stiff when used with cantis. Only seen that one pair though.

Gary Young

On Fri, 23 May 2008 05:09:52 +0000, jobst.brandt wrote:

> Michael Press wrote:
>
>>> There are several reasons why "linear" brakes now own the market.
>>> Considerably easier setup, slightly better overall leverage ratios
>>> leading to a lighter feel, useful for mountain bikes. (Lighter feel
>>> is also the primary reason for increasing disc sizes on mountain
>>> bikes.) And the leverage ratio is almost completely unchanged
>>> throughout the lever stroke, which is something maddening about
>>> cantilever brakes as can easily be ascertained with Sheldon's
>>> discussion of straddle cable setup. As a downside to the higher
>>> overall leverage ratio, pads do have to be set closer to the rim. This
>>> does have one beneficial effect of reducing pad dive under the rim.
>
>>> Large amounts of braking force are lost in the cable and housing
>>> system. Thus doubling of cable travel halves this lost force, also
>>> increasing braking efficiency and contributing to the rapid conversion
>>> to "linear" pull brakes over cantilevers. This is the same effect
>>> used by SRAM in their "1:1" rear derailleur shifting system to halve
>>> the effect of friction on shifting precision. Lost force reduction
>>> also accounts for the popularity of hydraulic disc brakes versus cable
>>> activated disc brakes despite their complexity.
>
>> There a many solutions to replace single pivot calipers, but none of
>> them measure up. Adding up advantages and disadvantages, single pivot
>> calipers are the best. When you need to improve some aspect of brake
>> performance over single pivot calipers, then you must compromise
>> others. Typically one of the advantages we abandon when we abandon
>> single pivot calipers is the minimal maintenance. Nobody here writes
>> in with questions on setting up and maintaining single pivot calipers.
>> (of course they are not produce any more except BMX 75-90 mm reach.)
>
>> For me there are three improvements in brakes in the last fifty years:
>> lined cable housing, aerodynamic brake levers, and orange brake pads.
>> The rest is optimization of exactly one component of brake performance.
>
> A problem with single pivot brakes is that the caliper return spring has
> significant cosine error causing spring sliding at contact points on its
> brake arms. The spring rotation centers are in the two ram's horn coils
> on either side of the brake anchor. With a return spring having a
> single coil wrapped around the anchor about which brake arms rotate has
> no cosine error. This makes a reliable self centering caliper that does
> not need "dual pivot" remain centered and prevent one sided brake drag.

Judging from online photos, it looks as if the new Bontrager single-pilot
brakes have a spring that's wound around the central mounting bolt:

http://bontrager.com/model/06693/en


>
> On conventional single pivot brake calipers, drag can only be avoided
> keeping spring contact points clean and lubricated. I am amazed that
> brake designers missed that point. This is apparent on the dual pivot
> brake because it has greater cosine error than prior single pivot brakes
> and uses a special plastic slider bearing to accommodate that greater
> spring-to-brake-arm motion.
>
> Are we making any progress yet?
>
> Jobst Brandt

jobst.brandt@stanfordalumni.org

Jay Taylor wrote:

>>>> There are several reasons why "linear" brakes now own the market.
>>>> Considerably easier setup, slightly better overall leverage
>>>> ratios leading to a lighter feel, useful for mountain bikes.
>>>> (Lighter feel is also the primary reason for increasing disc
>>>> sizes on mountain bikes.) And the leverage ratio is almost
>>>> completely unchanged throughout the lever stroke, which is
>>>> something maddening about cantilever brakes as can easily be
>>>> ascertained with Sheldon's discussion of straddle cable setup.
>>>> As a downside to the higher overall leverage ratio, pads do have
>>>> to be set closer to the rim. This does have one beneficial
>>>> effect of reducing pad dive under the rim.

>>>> Large amounts of braking force are lost in the cable and housing
>>>> system. Thus doubling of cable travel halves this lost force,
>>>> also increasing braking efficiency and contributing to the rapid
>>>> conversion to "linear" pull brakes over cantilevers. This is the
>>>> same effect used by SRAM in their "1:1" rear derailleur shifting
>>>> system to halve the effect of friction on shifting precision.
>>>> Lost force reduction also accounts for the popularity of
>>>> hydraulic disc brakes versus cable activated disc brakes despite
>>>> their complexity.

>>> There a many solutions to replace single pivot calipers, but none
>>> of them measure up. Adding up advantages and disadvantages,
>>> single pivot calipers are the best. When you need to improve some
>>> aspect of brake performance over single pivot calipers, then you
>>> must compromise others. Typically one of the advantages we
>>> abandon when we abandon single pivot calipers is the minimal
>>> maintenance. Nobody here writes in with questions on setting up
>>> and maintaining single pivot calipers. (of course they are not
>>> produce any more except BMX 75-90 mm reach.)

>>> For me there are three improvements in brakes in the last fifty
>>> years: lined cable housing, aerodynamic brake levers, and orange
>>> brake pads. The rest is optimization of exactly one component of
>>> brake performance.

>> A problem with single pivot brakes is that the caliper return
>> spring has significant cosine error causing spring sliding at
>> contact points on its brake arms.

> This would easy to fix - have the arms connected via a pivoting link
> to the ends of the spring.

I already mentioned how that should have been fixed 50 years ago with
a spring whose coil lies around the caliper pivot. Your suggestion
involves mechanism and maintenance, something the spring I mentioned,
does not.

> Of course, to completely* eliminate sliding friction you'd have to
> have ball- or roller-bearings at each end of the link, but
> superfluous complexity in cycle components has never been an
> obstacle to marketing.

That's the brute force way, but designing a spring that has no cosine
error is far better but it requires an understanding of the problem,
something uncommon in the bicycle industry.

> * completely here not meaning ABSOLUTELY completely, as even in
> rolling contact bearings there may be some minute amount of sliding
> friction, but hey, we're not jim beam claiming that cut threads
> NEVER are used on qr skewers...

That doesn't matter. There is a solution and I have tried it.

Jobst Brandt

jobst.brandt@stanfordalumni.org

Gary Young wrote:

>>>> There are several reasons why "linear" brakes now own the market.
>>>> Considerably easier setup, slightly better overall leverage
>>>> ratios leading to a lighter feel, useful for mountain bikes.
>>>> (Lighter feel is also the primary reason for increasing disc
>>>> sizes on mountain bikes.) And the leverage ratio is almost
>>>> completely unchanged throughout the lever stroke, which is
>>>> something maddening about cantilever brakes as can easily be
>>>> ascertained with Sheldon's discussion of straddle cable setup.
>>>> As a downside to the higher overall leverage ratio, pads do have
>>>> to be set closer to the rim. This does have one beneficial effect
>>>> of reducing pad dive under the rim.

>>>> Large amounts of braking force are lost in the cable and housing
>>>> system. Thus doubling of cable travel halves this lost force,
>>>> also increasing braking efficiency and contributing to the rapid
>>>> conversion to "linear" pull brakes over cantilevers. This is the
>>>> same effect used by SRAM in their "1:1" rear derailleur shifting
>>>> system to halve the effect of friction on shifting precision.
>>>> Lost force reduction also accounts for the popularity of
>>>> hydraulic disc brakes versus cable activated disc brakes despite
>>>> their complexity.

>>> There a many solutions to replace single pivot calipers, but none
>>> of them measure up. Adding up advantages and disadvantages,
>>> single pivot calipers are the best. When you need to improve some
>>> aspect of brake performance over single pivot calipers, then you
>>> must compromise others. Typically one of the advantages we
>>> abandon when we abandon single pivot calipers is the minimal
>>> maintenance. Nobody here writes in with questions on setting up
>>> and maintaining single pivot calipers. (of course they are not
>>> produce any more except BMX 75-90 mm reach.)

>>> For me there are three improvements in brakes in the last fifty
>>> years: lined cable housing, aerodynamic brake levers, and orange
>>> brake pads. The rest is optimization of exactly one component of
>>> brake performance.

>> A problem with single pivot brakes is that the caliper return
>> spring has significant cosine error causing spring sliding at
>> contact points on its brake arms. The spring rotation centers are
>> in the two ram's horn coils on either side of the brake anchor.
>> With a return spring having a single coil wrapped around the anchor
>> about which brake arms rotate has no cosine error. This makes a
>> reliable self centering caliper that does not need "dual pivot"
>> remain centered and prevent one sided brake drag.

> Judging from online photos, it looks as if the new Bontrager
> single-pilot brakes have a spring that's wound around the central
> mounting bolt:

http://bontrager.com/model/06693/en

Great! It's nice to see that someone at TREK reads wreck.bike, but
then Damon Rinard, TREK's best engineer who got there after years of
good contributions to this newsgroup is aware of these problems.
Without a cross section of an assembly drawing it is hard to tell, but
from the enlarged picture I believe the brake will remain centered
without dual pivots or gratuitous and expensive hardware.

>> On conventional single pivot brake calipers, drag can only be
>> avoided keeping spring contact points clean and lubricated. I am
>> amazed that brake designers missed that point. This is apparent on
>> the dual pivot brake because it has greater cosine error than prior
>> single pivot brakes and uses a special plastic slider bearing to
>> accommodate that greater spring-to-brake-arm motion.

>> Are we making any progress yet?

Not at cramp-and-go-slow!

Jobst Brandt



Jobst Brandt