Research methods

An Improved Recorder of the Bar’s Vertical Displacement, Velocity and Acceleration

V. I. Frolov, A. N. Furaev, State Central Institute of Physical Culture (GTsOLIFK)

English summary of Tyazhelaya Atletika. Ezhegodnik 1982 (Moscow: Fizkultura i Sport, 1982), pp. 66–68: the text is paraphrased, not translated; figures are the original images.

Purpose

Model: the V. A. Klynin and S. I. Lelikov instrument (1972), the best so far, but transistor-based, heavy and bulky.
Goal: same principle, compact electronics (by V. A. Klynin), simple reliable mechanics. No mechanical part precise enough for electronic differentiation, especially of acceleration, had existed before.

Electronics (Fig. 1)

Multi-turn potentiometer R1 (PPML-M, 10 kΩ), stabilised supply via contacts 3 and 8. Its output voltage, proportional to turns, i.e. bar travel, enters at contact 1.
MS1 (1UT401B IC), power amplifier: displacement at contact 2.
MS2, MS3 (K284UD1 series), differentiating amplifiers: velocity (dx/dt) at contact 4, acceleration at contact 5.
Power via contacts 6 and 7. Ground is the centre point (contact 3), the reference for all outputs.
Board 160 × 70 mm. Any supply with a centre tap and low ripple. Everything except R1 fits a 245 × 110 × 110 mm metal box.

Circuit diagram with potentiometer and three integrated-circuit amplifiers — Fig. 1. Electrical part of the instrument.

Mechanics (Fig. 2)

Shaft: a 40 mm drum plus a 10 mm section for the return mechanism (multi-strand rubber and an elastic metal plate).
A nylon thread runs from the drum over a pulley to the bar.
Plastic-sleeve coupling to the potentiometer slider. It must be exactly coaxial, so mount the potentiometer carefully on the side wall.
Records up to 2.5 m of bar height (from the bar centre).
A light plastic shaft gives low inertia and a reliable return. Load on the bar up to 100 g.

Dimensioned drawing of the drum shaft, return spring and potentiometer — Fig. 2. Mechanical part of the instrument. The multi-strand rubber is fixed to the flexible metal return plate; the nylon thread to the bar.

Use

Tested repeatedly on elite lifters, including USSR team members.
Accurate acceleration gives the force on the bar, which is useful compared with platform forces.

The acceleration is printed as “d²x/dt”.