A TRUE DOBSON WITH AN OLD TUBE
==============================
The essence of a true Dobson

What is the main characteristic of a Dobson telescope?? The response to this
question is that a Dobson telescope is moved by hand (not gears, no mechanics
stuff), and that this movement has a special "touch": neither too soft nor too
hard; using the same force both to start the movement as to keep it; letting go
of a star drift easy and accurately...
A Dobson telescope there is not a true Dobson if theirs movements aren't as
described in the last paragraph, so the only manner of recognizing a true Dobson
is to move it.
Be careful about web pages when the author seem to talk about make a Dobson.
Usually, the author make anything that SEEM to be a Dobson and LOOKS like a
Dobson... but if the author don talk about the special movement of a Dobson,
perhaps is because there is not a true Dobson.
Controlling the friction

The secret for the special movement characteristics of a Dobson telescope flow
from a design when the friction in both altitude and azimuth axes is taking into
account.
My main font about how to calculate the friction of a Dobson comes from the
book "The Dobsonian telescope: A Practical Manual for Building Large Aperture
Telescopes", by D. Kriege & R. Berry (thanks to Pablo Canedo for talk me about
this book).
###Using the right materials
A lot of materials was tested by experienced people, finding for the right
material to use in order to get the necessary friction. The static and dynamics
friction coefficient must be similar. The friction must be higher enough for
compensate tremors, inertia or wind effects, and small enough for can move the
telescope in an easy manner.
Unless you know exactly what you're doing, you must use virgin Teflon and some
concrete laminate models as frictional material. For this combination of
materials, the static friction coefficient is 0.10, and the dynamic one is 0.08,
according the "Kriege & Berry" book.
These recommended laminates are both "Ebony Star #4552" from Wilsonart Inc. and
"Stardust #1782" from Formica Inc. Perhaps some other laminates will work, but
you MUST use one of these for ensure the correct friction.
The force to move the tube depends on the position of the Teflon pads, and the
these forces must be similar in both axes. On the other hand, the position of
the pads don't must affect to the stability. So the position (and size) of the
Teflon pads must be calculating carefully.
The main parameters to consider are the weight of some parts. One is the weight
of the complete tube, including the side bearings. Let label this weight "p".
The second is the weight of the complete tube (including the side bearing) plus
the rocker box (without the ground board). Let label this weight "P".
###Calculate the force necessary for move the telescope
For make a design that match the before considerations,we must calculating the
forces that is necessary for moving each axis (altitude and azimuth). These
calculations are specified in the following diagram, made by "pulgaril", a
member of the "Constructores de telescopios" Yahoo group
(http://es.groups.yahoo.com/group/ConstructoresTelescopios/)
![Axis forces](true_dobson_old_tubeimg/Axis_forces_by_pulgarilVersion2.png)
We have for the altitude axis:
Fa = [r * k * p] / [L * sen(a)]
Where:
 "r" is the ratio of the altitude bearings.
 "k" is the friction coefficient.
 "p" is the weight of the tube plus the tube support with bearings.
 "a" is the angle between the horizontal and the position of the altitude
Teflon pads.
 "L" is the distance from the bearing centre and the point when you hold the
tube for move it.
And for the azimuth axis:
Fz = [R * k * P] / [L * cos(h)]
Where:
 "R" is the distance between the pivot to the Teflon pads of the azimuth axis.
 "P" is the total weight of the tube plus the tube support with bearings plus
the rocker box.
 "h" is the altitude where the tube points to.
 The others coefficients are the same that in the altitude axis case.
Designing a Dobson

Now, we have the mathematical expressions that can help us for design a dobson
telescope. Never the less, there are more parameters that equations, so we
can't calculate all the design parameters we need.
To avoid this difficulty, we use a double approach.
First, we fix some of these parameters according to empirical values recommended
by experienced Dobsons constructors or to a compromise value.
This empirically fixed parameters are:
 "k", the friction coefficient is determinate by the material used. If we use,
as experience said, Teflon and one of the recommended laminate, the value
of this parameter will be the adequate one. From "Kriege & Berry" book, this
value is 0.08.
 "a" is the angle between the horizontal and the position of the altitude
Teflon pads. The "Kriege & Berry" book talk about the empirical separation of
the two Teflon pad for each bearing must be 60 degrees, so the angle between
the vertical and each pad will be 30 degrades, so the angle "a" must be
9030=60 degrades.
 "h" is the altitude where the tube points to. Obviously, this parameter varies
when we are using the telescope... the solution to this issue is use a value
for "h" that will be approximately the more usual one. The experienced
observer report that this value is 60 degrades.
Second, we will use and iterative method for tune the design. Firstly, we make
a very first design an according to it, we will ESTIMATE the values of "L"
(distance from the bearing centre and the point when you hold the tube),
"p" (tube plus bearings weight), "P" ( p plus rocker box weight) and
"R" (distance between the pivot to the Teflon pads of the azimuth axis).
When you have estimated all this parameters, you can CALCULATE the last
parameter "r" (the ratio of the altitude bearings). This can be calculated by
equate both the forces necessary to move the tube both in altitude and azimuth
axis.
This diagram show the flux of estimating and calculating:
+·······················································+
· ·
· ++ ++ ++ ·
·  ESTIMATE   ESTIMATE   ESTIMATE  ·
·       ·
·  Tube plus   Tube plus   Pivot to  ·
·  altitude   bearings   azimuth  ·
+> bearings > (p) plus > teflon +
 ·  weight (p)   rocker box   pads  · 
 ·  and the   weight (P)   distance  · 
 · longitude (L)    (R)  · 
 ·  (1)   (2)   (3)  · 
 · ++ ++ ++ · 
 · · 
 +·······················································+ 
 
 ++ 
  CALCULATE  
   
  Ratio of the  
+ altitude <+
 bearings (r) 
 
 (4) 
++
___

 Break the
 loop

`'
++
 CALCULATE 
 
 Pivot to azimuth teflon pads 
 distance (R) 
 (5) 
++
More details in estimating "L", "p", "P", "R" and calculating "r" in the
following subsections.
When the tube, the bearings and the rocker box was building, you can weight the
real things... and you can now calculate (instead estimate) the pivot to azimuth
teflon pads distance (R).
More details in calculating "R" in the following subsection.
###(1) Estimating tube plus bearings weight (p) and the longitude (L)
We must make a very first design of the tube and the altitude bearings. As a
first approximation, we can use a size for the bearings equal to the mirror
size. There are no magic in this: but we need a first value.
By using the density of the used materials, and calculating the amount of it,
we can estimate the weight "p". Estimate "L" is immediate from the design, and,
probably, it must not be changed from iteration to iteration.
As the end of the iteration, we will calculate a new bearing size, so a new "p"
value must be estimate...
###(2) Estimating tube plus bearings weight (p) plus rocker box weight (P)
Analogue to the before point, by using the density of the used materials, and
calculating the amount of it, we can estimate the weight of the rocker box.
This weight plus the value "p" from the before point, will produce a value for
"P".
As before, after a complete iteration, we will calculate a new bearing size, so
"p" value change and, consequently, the "P" value also must be reestimated...
###(3) Estimating pivot to azimuth teflon pads distance (R)
As a first approach, our first design must have the "legs" of the ground board
as separate between them as possible. In this way, all the structure is as
stable as possible. The azimuth teflon pads must, ideally, lay just where the
legs of the ground board (but, evidently, in the other side). This rule have us
a first value for the "R" parameter.
This value "R" must not be changed between different iterations, and, ideally,
it must not be changed in the final design.
But, in practical, a final recalculation of "R" must be done AFTER break the
loop. See subsection about the calculating of "R" for more about this.
###(4) Calculating the ratio of the altitude bearings (r)
For found an expression for calculate "r" (the ratio of the bearings), we can
equate both altitude an azimuth axis force. This is:
Fa = Fz => [r * k * p] / [L * sen(a)] = [R * k * P] / [L * cos(h)] =>
=> r * p / sen(a) = R * P / cos(h) => r = [R * P * sen(a)] / [p * cos(h)]
And, by using the assumed values for "a" (60 degrees) and "h" (also 60 degrees),
we can write:
r = [R * P * sen(60)] / [p * cos(60)] => r = [R * P * 1.73205] / p
By using this last equation, we can calculate a new value for the ratio of the
bearings (r), and continuing the loop...
###(5)Break the loop: calculating pivot to azimuth teflon pads distance (R)
In practical, a final recalculation of "R" must be done AFTER break the loop.
This can be necessary by different factors. Perhaps is not possible an arbitrary
size for the bearings (if we use some precast material for it, for example); or
simply, AFTER construct the tube, bearing and rocker box, we note that our
estimations about the weight was very bad ones.
So, after we have been build the tube, bearing, and rocker box, we have now a
fixed value for the weights "p" and "P" and for the bearing ratio "r". And a
final tuning must be done before build the ground board. For this tuning, we
will new calculate (instead estimate) a definitive value for "R", the distance
between the pivot and the azimuth teflon paths...
This can be done with the following equation:
r = [R * P * 1.73205] / p => R = [r * p] / [P * 1.73205]
Please note that, due the considerations about structure stability commented
before, the new calculate "R" value should not be very different from the first
estimated one, according with the cited considerations.
An, if we must change a little the positions of the azimuth teflon pads,
perhaps we must also reconsider repositioning the legs of the ground board
for put it just in the opposite side that the teflon paths. In this way, we
reduce the vibrations, especially is the telescope is a big one...
###Calculating teflon pads sizes
theoretically, the friction DON'T depends on the area of contact of both
materials. But in "Kriege & Berry" book they claims that the area of contact
between both teflon and laminate should have a concrete value, determined
empirically from the experience of advanced Dodson constructors. These value
can be consulted in 3.5 table from the book.
In this table, according the materials used, the pressure (weigh by area unit)
is listed. For the usual materials (teflon and laminate), this value must by,
according the authors, 15 PSI (pounds per square inch). In the metric system
this is equivalent to 0.0105462 Kg/mm2 (10.5462E3 Kg/mm2).
Please note: theoretically the friction between materials don't depends on the
area of contact. Never the less, I agree with that for some unknown (for me)
reason, we MUST respect the "Kriege & Berry" book criteria and use the
correspondent area of contact.
Due the considered pressure value, and the weights, calculate the teflon pads
sizes is easy.
And, as last note, the force necessary for move the tube in both axis should be
about 0.15 ~ 0.20 Newtons. For a value of this force too low or too big,
perhaps you could consider a drastic redesign, or the use of nylon instead
virgin teflon, as suggested in the "Criticism and lessons learned" subsection
of the case study part, later in this document.
####Teflon pads size for the altitude axis
Let me show how to make the calculation for the altitude teflon pads by using an
example.
If the tube plus bearings weight is, for example, 15.5 Kg the TOTAL area for the
needed teflon will be:
15.5 / 10.5462E3 = 1470 mm2
But for the altitude axis we must use 4 teflon pads, so for EACH altitude
teflon pads the area must be:
1470 / 4 = 367.5 mm2
Now, one of the dimensions of the teflon pads will be equal to the used wood
thickness (suppose it is 15 mm), so the other dimensions of the teflon pad will
be:
367.5 / 15 = 24.5
So, for the example, the size for each one of the 4 altitude teflon pad could
be 15 x 24.5 mm
Perhaps these values can be improved by take in account some issues as a
possible hole for screw them to the wood or some cut down in the sides that
attack the laminate in the direction of movement (this is, the sort sides). But
this tuning is a problem of elementary geometry.
####Teflon pads size for the azimuth axis
In a similar manner, the size for the pads of the azimuth axis can be
calculate. But here there are to possibilities: the simple case, with 3 square
teflon pads, and an enhanced case, with 3 square pads plus a tiny circular pad
around the central pivot hole.
The enhanced case with central pivot teflon pad is recommended for hight weight
(related to the wood thickness used for the bottom part of the rocker box).
For both possibilities, the very first step is calculate the TOTAL area for the
need teflon. As an example, lets consider a weight for the tube, plus bearings,
plus rocker box of 21 Kg, so the total area must be.
21 / 10.5462E3 = 1991 mm2
Now, the methodology for calculation are a few different for the simple case
(3 teflon paths) or the engagement one (3 teflon pads plus a central pivot pad).
#####Simple case (3 pads)
Due we have 3 pads, the area for each of them must be:
1991 / 3 = 663.7 mm2
and, due we considered square pads, the size for each side must be:
SQRT(663.7) = 25.8 mm
So, for the example, the size for each one of the 3 azimuth teflon pads would
be 25.8x25.8 mm. As in the previous case, the calculation can be improved by
take in account a possible cut down for the teflon pads, now in all the sides.
#####Engagement case (3 teflon pads plus a central pivot pad)
For this case, we must subtract the area of the central pivot pad before
calculate the size of the 3 square ones. As an example, consider a central
circular pad of 15 mm of radius and a pivot hole of 10 mm of diameter (5mm of
radius), so instead use the total area of used teflon (1991 mm2), we subtract
the area of this circular pad:
1991  [PI * (15^2  5^2)] = 1363 mm2
And the following calculations are similar to the simple case, but use this
modified total area, so the area of each each square pad would be:
SQRT(1363 / 3) = 21.3 mm
So the squared pads size would be 21.3x21.3 mm
As in the previous case, the calculation can be improved by take in account a
possible cut down for the squared teflon pads (and maybe in the circular one),
in all the sides.
Please note that the presence of a central pivot pad don't change the
calculation of the force for the azimuth axis. This is because the pivot pad
MUST be small, so the distance of every superficial points of the pivot pad is
near 0 apart the pivot itself, so them can be obviated in the practice. A small
size for the pivot pad is also necessary for maintain the size of the square
pads not too few.
So be careful: a central pivot pad always must be small...
###The azimuth pivot
The "Kriege & Berry" book talk about the making of the azimuth pivot in extent.
I refer to the book if you are planning a Dobson.
Never the less, I design my own azimuth pivot. My design only have value when
the thickness of the wood used for make the ground board is about 1.5 or 2 Cm.
In this design, a "packing ring" like piece of thin (about 0.2 mm) virgin
teflon is adhered surrounding the pivot hole at the rocker box (at top side).
The ground board is worked for embed a nut in the manner showed in the
correspondent section of the case study part.
The pivot components are also showed at the case study part of this document,
and its description is the following:
A M10 screw has adhered a packet ring in its head. This packet ring has also
adhered a thin teflon sheet at side opposed to the head of the screw. A piece
of teflon tape is applied to the body of the screw, from the head to a length
that must be equal to the thickness of the wood used for make the rocker box.
The hole for the pivot at the rocker box should be lined with a piece of steel
pipe.
Other pieces of the pivot are: a free "packet ring" of thin teflon, a "packet
ring" of felt, a normal steel packet ring and a nut.
Once the pivot is mount, this is the list of all components, in the order its
lies:
1. The head of the screw.
2. A steel packet ring adhered to the head of the screw.
3. A thin packet ring made of teflon, adhered to the before metal packet ring.
4. A free thin packet ring made of teflon.
5. A thin packet ring made of teflon, adhered to the top of the rocker box.
6. The bottom of the rocker box.
7. The ground board. The ground board has a embedded nut.
8. A free packet ring made of felt.
9. A steel packet ring.
10. A nut. This last nut product a countersunk effect with the other embed in
the rocker box.
When the pivot is in the corresponded site, the countersunk effect must be
adjusted. The force between the teflon pads fixed to the ground board and the
laminate fixed to the rocker box must be near zero, but without clearance. A
periodic readjustment of this stuff is recommended.

=====================================================================

A case study: refurbished old newton tube

My very first Dobson experience was aborted based on a old Newton 200mm tube.
My goal was learn about the dobson mount and use the this old tube for
starhopping technique with Dobson telescope (until then I always used a
equatorial telescope for starhopping.
I don't intend a detailed description of the work, but only show it and present
ideas that I hope become useful for other people.
###The bearings
My idea was to attach the tube to the bearings by using pressure The device used
for attach the altitude bearing to the tube is easily released from the it in
order to place the tube easily in a convenient manner for balancing it or put
the eyepiece in the best side depending on the sky zone we are observing.
The bearing themselves are formed by two 20cm diameter PVC pipe caps. Stardust
ribbon is adhered in the frictional surfaces of the bearings by using epoxy
adhesive.

![bearings close](true_dobson_old_tubeimg/true_dobson_old_tubebearings_close.jpg)
Here the bearings attached to a device that can be fixed to the tube. The
bearings are 20 cm diameter, with an skin of Stardust. A soft material is used
when the device contact with the tube. A mechanism permit a easy relaxing the
device from the tube for fine tuning of its position.

![bearings open](true_dobson_old_tubeimg/true_dobson_old_tubebearings_open.jpg)
Here the device that support the bearings opened for introduce the tube and
attach it.

![bearings on rocker](true_dobson_old_tubeimg/true_dobson_old_tubebearings_on_rocker.jpg)
Here the bearings presented in the rocker box.

![bearings lock](true_dobson_old_tubeimg/true_dobson_old_tubebearings_lock.jpg)
Thus mechanism permit easily fix and relax the device to the tube.

![bearings side](true_dobson_old_tubeimg/true_dobson_old_tubebearings_side.jpg)
This is the lateral side of the bearings, fixed to the device and with the
tube attached. Note the little legs that permit put the structure on the floor.

![bearings with tube](true_dobson_old_tubeimg/true_dobson_old_tubebearings_with_tube.jpg)
This perspective show the tube attached to the bearings.

###The rocker box is conceptually simple, but it must be resistant and made with
precision, specially the semicircles when the bearings will lie.
Please note the special feature for support the tube in order to adjust the
placement between the tube and the device that support the bearings.
In the down, the rocker box has a hole for the azimuth pivot.
The stardust surface is adhered by use contact cement. There are contact cement
of different viscosity. You should use one with low viscosity.
A guide must be used for align the rocker pivot hole with the laminate hole
for the pivot. The laminate must be bigger that the rocker base. When the
adhesive run dry, the excess of laminate can be rasped.
After the rocker box was completed, a thin adhesive felt was added for avoid
accidental damage of surface when the bearing is placed.

![rocker perspective](true_dobson_old_tubeimg/true_dobson_old_tuberocker_perspective.jpg)
A perspective of the rocker box.

![rocker front](true_dobson_old_tubeimg/true_dobson_old_tuberocker_front.jpg)
Here we can appreciate the rocker box structure.

![altitude both teflon pad](true_dobson_old_tubeimg/true_dobson_old_tubealtitude_both_teflon_pad.jpg)
The altitude teflon pads attached to the rocker box. They are 60 degrees apart

![rocker down](true_dobson_old_tubeimg/true_dobson_old_tuberocker_down.jpg)
The Stardust base adhered to the bottom of the rocker box.

![rocker with adhesive felt for protection](true_dobson_old_tubeimg/true_dobson_old_tuberocker_with_adhesive_felt_for_protection.jpg)
The finished rocker box. A adhesive protection was added.

![tube on rocker](true_dobson_old_tubeimg/true_dobson_old_tubetube_on_rocker.jpg)
Here we can see how the tube can be hold by the rocker box, for and easy tube
manipulation and setup...

###The ground board concept is really simple. The only difficult is to put a nut
in the right manner for the azimuth pivot and mark the position for the teflon
azimuth pads and for the foots.
For mark the position for the teflon azimuth pads and for the foots, we will use
cardboard templates, made accord with our calculations.
The nut for the pivot is punting as showed in the pictures. Please note that for
a more resistant mount, the foots must be put in the same side when the nut
was aligned, and the teflon pads in the other.
For a optimal stability and resistance, the foots must be put in the manner
that they was at the most distance one of another, and the teflon pads must be
over the foots, in the other side of the ground board.
Please note that THIS LAST POINT IS NOT ACCOMPLISHED in my design This WAS
CAUSED BY A ERROR DESIGN I must improvise a compromise solution for maintain
the force to manage the azimuth axe about similar to the altitude one.

![ground board preparation 1](true_dobson_old_tubeimg/true_dobson_old_tubeground_board_preparation_1.jpg)
This partial hole was done with an adequate Forstner drill.

![ground board preparation 2](true_dobson_old_tubeimg/true_dobson_old_tubeground_board_preparation_2.jpg)
The nut must fit in the partial hole.

![ground board preparation 3](true_dobson_old_tubeimg/true_dobson_old_tubeground_board_preparation_3.jpg)
With a normal drill, the hole is completed as showed.

![ground board preparation 4](true_dobson_old_tubeimg/true_dobson_old_tubeground_board_preparation_4.jpg)
The nut is fixed by using an epoxy based putty.

![ground board hole for pivot](true_dobson_old_tubeimg/true_dobson_old_tubeground_board_hole_for_pivot.jpg)
The close part of the hole if reinforced by fits a piece of steel pipe.

![template mark foots on ground board](true_dobson_old_tubeimg/true_dobson_old_tubetemplate_mark_foots_on_ground_board.jpg)
This carton template was used to mark the holes for screw the legs of the
ground board.

![mark foots on ground board](true_dobson_old_tubeimg/true_dobson_old_tubemark_foots_on_ground_board.jpg)
Here the position for the screws of the legs are marked.

![foots on ground board](true_dobson_old_tubeimg/true_dobson_old_tubefoots_on_ground_board.jpg)
And here, the legs of the ground board.

![template mark for teflon pads on ground board](true_dobson_old_tubeimg/true_dobson_old_tubetemplate_mark_for_teflon_pads_on_ground_board.jpg)
Other carton template was used for mark the position of the azimuth teflon pads.

![mark for teflon pads on ground board](true_dobson_old_tubeimg/true_dobson_old_tubemark_for_teflon_pads_on_ground_board.jpg)
The marks for the azimuth teflon pads in the right position.

![ground board](true_dobson_old_tubeimg/true_dobson_old_tubeground_board.jpg)
Here, the finished ground board.

###Teflon pads
The teflon pads size was calculated in the manner described before. For the
altitude teflon pads a hole was drilled for use a screw for keep it in place.
The contact surface missing by this hole and by some reduction of material in
the shorter sides was considered when the size of pads was calculated
For hold the altitude teflon pads in their places we will use screws as showed
in the pictures. The screws heads must be buried into the teflon pads. It is
very important that the head of the nails don’t touch the laminate when it slide
over the teflon pads.
For hold the azimuth teflon pads, a double sided adhesive ribbon plus tiny nails
was used. The nails heads was buried inside the pads by using a punch. It is
very important that the head of the nails don’t touch the laminate when it slide
over the teflon pads.

![teflon pads](true_dobson_old_tubeimg/true_dobson_old_tubeteflon_pads.jpg)
The teflon pads. The four altitude teflon pads at up, the azimuth ones are the
others.

![altitude teflon pad](true_dobson_old_tubeimg/true_dobson_old_tubealtitude_teflon_pad.jpg)
Detail of one of the altitude pad.

![teflon pads on ground board](true_dobson_old_tubeimg/true_dobson_old_tubeteflon_pads_on_ground_board.jpg)
The azimuth pads.

###The Pivot
![pivot components](true_dobson_old_tubeimg/true_dobson_old_tubepivot_components.jpg)
The pivot components are showed in the picture.

###Car wax for better performance.
For a better performance, car wax was applied to the laminate. It must be
extended by using a cotton cloth. After it dry, remove the rests with a brush.
In the picture, the rocker laminate is showed after wax was applied and dry.
It must be brushed until no wax rest were appreciate.

![turtle wax](true_dobson_old_tubeimg/true_dobson_old_tubeturtle_wax.jpg)
The car wax used for optimize performance.

![turtle wax on stardust unbrushed](true_dobson_old_tubeimg/true_dobson_old_tubeturtle_wax_on_stardust_unbrushed.jpg)
Here can be seen the StarDust after the application of the car wax. The next
steep must be to brush the laminate after the car wax was dry.

![result](true_dobson_old_tubeimg/true_dobson_old_tuberesult.jpg)
This picture show the Dobson telescope finished.
###Car integration
For a portable telescope, the integration with the car is very important. The
following pictures show how the telescope is transported in my car. An adhoc
device made with a thermal insulation material used in construction and some
plastic ribbons is used for maintain the telescope in place.

![aict](true_dobson_old_tubeimg/true_dobson_old_tubeaict.jpg)
This device is used for integrate the telescope with the car for transportation.
It was made by using a thermal insulation material used in construction.

![result in car](true_dobson_old_tubeimg/true_dobson_old_tuberesult_in_car.jpg)
This picture show the telescope integrated with the car.

![result in car detail 1](true_dobson_old_tubeimg/true_dobson_old_tuberesult_in_car_detail_1.jpg)
The tube is hold by two cinch. The Rocker box is hold to the device where the
tube lies by two elastics ribbon, one to each side.

![result in car detail 2](true_dobson_old_tubeimg/true_dobson_old_tuberesult_in_car_detail_2.jpg)
The ground board is fixed to the rocker box by a elastic ribbon for
transportation.

![result in car detail 3](true_dobson_old_tubeimg/true_dobson_old_tuberesult_in_car_detail_3.jpg)
In my car, the copilot seat can be swing: perfect for the transportation.

Criticism and lessons learned

There are two failures in my telescope.
One is that the rocker box is 5 cm too taller. It was an implementation error,
not a design error. I added twice the 5cm extra, necessary for make the
appendices for hold the tube by the rocker box. Due this error, the rocker box
just fit in my car: too just... It also increases slightly the vibration of the
rocker box.
The other error is an authentic design error: the distance from the pivot hole
to the squared teflon pads in the ground board (R) is too small. Some people
ask me: Why simply do you put them more separate from the central pivot? The
answer to this question is that if I did that, then the force necessary for
move the tube in the azimuth axis would be too weak, and very different to the
force necessary in the altitude axis: this is precisely the situation that I
want to avoid.
The reason that a standard design does not work for this particular telescope
is that the tube is heavier than it would be a typical truss one (for a same
aperture).
For the case of a heavy design (a tube heaver than the truss one equivalent or
a very big tube in any case) like the mine, the value "r" should be bigger for
make the correspondent value of "R" big enough, and the forces in both axis
approximately equal. But then, the value of these forces can be too low. For
avoid this issue, you can consider using nylon instead virgin teflon to make
these values greater. This is because the friction coefficient for the nylon is
greater (0.19 dynamic, 0.20 static) that for the virgin teflon.
So a correct design for my telescope should have bigger bearing, so the
distance from the pivot to the azimuth teflon pads could be big enough to make
them be near the edge of the ground board. In this manner, the structure should
be stable, and the forces to move the tube in both axis should be approximately
equal. But these forces can be too small; so, in this case, we can use nylon
instead teflon for make the pads...
Never the less, when I was aware of these errors, the work was almost over...
so I decide continue with the design, but using a "R" a few bigger that the
theoretic value and close a few the legs of the ground board. In this manner,
I got an notsoworse stability...
When I tested the telescope at country, in a real observation, the results was
good, even due the cited errors... I am happy with the result and I learned a
lot making the work.
Clear skies.