Handwritten calculation notes: pedal car, cable and propeller (1940)

In this document

Page 3 — the pedal car: cable, drum, foot pressure

The sheet details the kinematic chain of a pedal system connected to a cable and a drum. One can read a "Devel[opment], 7 m" to be obtained, with the indication "Must be 3 m 50 per pedal stroke" p. 3.

The geometric data set out are:

• Cable travel: 400 (mm, not specified)
• Φ wheel = 550
• l = 1.730

The number of wheel turns per pedal stroke is calculated by the ratio 3.5 / 1.730 = 2.2 p. 3.

A winding calculation follows: "400 m of cable winding on a Drum of φ = 25.7. l: 80 make. 400/80" — the value obtained is crossed out and replaced by another, difficult to read p. 3.

A reduction is noted: 22/50 = 44/100 p. 3.

Finally, the foot pressure is quantified: "Foot pressure. 50 kg. x 2 [times] = 100 kg", with a "Foot travel" of 320 and a "Cable travel" of 400. The resulting cable tension is: 100 x 32/400 = 8.0 kg for a development of 7 m; then 160 kg for 3.5 m and 320 kg for 1.75 m p. 3.

A small table in the right margin mentions "clinda[?] steel", "l:25 c=80/[?]", "S=5m²", and a series "Tang simple work / devil" with the pairs of values 16/8, 32/16, 64/32 kg p. 3.

Page 4 — propeller calculations and sketches

The second sheet concerns a propeller, with several sets of dimensions:

• Φ: 25, pitch = 800, circumference length: 82 p. 4
• Φ 20, pitch 800, circumference length: 63 p. 4

A calculation of "1/4 propeller" is started, accompanied by a right-angled triangle diagram dimensioned "H", "16" (or 160, uncertain reading) and "200" p. 4.

The formula H = √200² + 16²... is set out then abandoned, replaced by a second crossed-out calculation (√20² + 8² = 400+64 = √164), then by √20² + 2² = √404 = 20 (final value uncertain), followed by figures that are difficult to read p. 4.

A second diagram represents a rectangle with a diagonal annotated "Propeller", dimensioned 200 and 20 p. 4.

Context

These handwritten calculations most likely fall within the broader context of Paul Magès's experiments during the year 1940, a period when several side projects — including a pedal car — apparently occupied his notebooks, alongside his automotive engineering work for Citroën.

The propeller calculation, without explicit context in the document, could refer to more general mechanical reflection (propulsion, transmission) common among engineers of the time faced with DIY or personal experimentation needs, outside of any demonstrated link with the automobile.

Archivist's perspective

This diptych of calculations illustrates Magès's working method well: figures thrown down quickly, values crossed out and corrected in the course of reasoning p. 3-4, revealing a process of trial and error rather than a fixed result.

The consistency with the series of sketches and technical diagrams of the pedal propulsion mechanism and with the 1940 folder on the pedal car project suggests that this sheet indeed belongs to this same experimental file.

The transition to the propeller p. 4, without apparent transition in the document, seems to be a personal technical digression; it is difficult to affirm a direct link with the pedal project without another piece from the file to shed light on it.