24 
CARLO TROMBETTI 
The syncro-transmitters are grouped together in the two boxes 41 and 42 
(the former for X and the latter for Y) which are connected with X carriage 43 and 
Y carriage 44 respectively. Figs. 23 and 24 clearly show the boxes, hg. 22 the car 
riages. 
To transform the rectilinear movement of the carriage into the rotating move 
ment of the synchro-transmitters we employ two precision racks : 
— precision rack 45 (fig. 23) is fixed into the back beam of the Y carriage ; 
a cog-wheel engages therewith, transmitting the movement to the shaft of the 
fast-synchro-transmitter of X, 
— a second precision rack 46 (fig. 24) is fixed to the left-hand Y beam 
(joined with the plotting instrument base ; on this beam rests the Y carriage); 
this rack meshes with a similar cog-wheel operating the fast-synchro-transmitter 
shaft of Y. 
The transmission ratios between rack and synchro-transmitters are worked 
out so that one turn of the fast synchro-transmitter corresponds to a linear displa 
cement of 10 mm of the relative carriage. This has been arrived at as follows. 
The rack meshes with pinion R t with a number of teeth Z = 52 and modulus 
m — 0,3 ; therefore the primitive circumference corresponds to 49 mm plus 0,00896 
mm {p = 7T m = 0,94 248 m, c = p. Z = 49,00896 mm). 
On the axis of pinion R l is joined a wheel R 2 meshing with pinion R 3 of the 
synchro-transmitter with a ratio 49/10; therefore R z completes one turn every 10 mm 
displacement of the carriage, less the residual 0,00896 mm. 
To correct this residual error the stator of the synchro rotates, so as to per 
form a small angle a every turn of the rotor, by means of a connecting rod pro 
vided with a contact roller against a slidebar set along the rack, forming therewith 
a suitable angle (T 
Considering that, for a carriage displacement of 49 mm the correction angle 
referred to pinion R 1 is 4', the corresponding angle in the stator results as being 20'. 
Consequently for the whole stroke of the 800 mm carriage the correction angle 
is approximately a = 5 0 . 
As the rod connected to the stator is about 30 mm long, the contact slidebar 
should be inclined, with regard to the rack, of about (3 = 12' therefore the distance 
difference between slidebar and rack is of 2,8 mm in its largest point. 
The correction slidebar is flexible and held by several adjusting screws, which 
allow to set right any errors of the rack by comparing the readings effected by means 
of microscopes on the X and Y graduations engraved on glass rules. 
No particular problem is to be faced as far as the Z transmission is concerned : 
it takes place by direct connection of the Z synchro-transmitter with the Z axis 
coming from the altitude meter, rather than by mechanical transmission. 
The connectors joined with the cables starting from the three transmission 
groups are inserted in their respective connectors by means of a panel in the bra 
nching box 51 (fig. 22) set near one back leg of the plotting instrument ; this box 
has, for each coordinate, two output connectors, so that two instruments may be