Alternator Control; Mechanics; Control - Technogym Steprace Service Maintenance Manual

3.2. ALTERNATOR CONTROL

3.2.1. M
ECHANICS
The movement of the pedals imparts a rotation to the primary shaft via the chain connected to the 2
pedals. The chain turns on a sprocket which is attached to a slide that can move up and down along
2 guide bars. The other side of the slide is connected to 2 springs which provide an elastic
connection between the slide and the machine frame.
The primary shaft is coupled to the secondary shaft by means of a chain, and the secondary shaft is
coupled to the alternator by means of a belt. In this way, the movement of the pedals is transmitted
to the alternator.
The stepping mode selection knob determines the type of movement of the slide:
• mode A: the slide is free to move, with the springs acting as dampers. The downward movement
of a pedal causes a downward movement of the slide, which is damped by the action of the
springs. In this way neither pedal is affected by the changes in position of the other pedal.
• mode B: the slide is locked into place and the springs are not in use. The downward movement
of one pedal causes the upward movement of the other due to the fixed length of the chain.
3.2.2. C
ONTROL
To control the difficulty level of the workout, the machine adjusts the excitation of the alternator
which generates a resistance to the movement that is proportional to the excitation level. To do this,
the CPU board transmits a PWM (Pulse Width Modulation) signal to the alternator interface board
which the alternator interface board passes directly to the alternator itself. The alternator filters the
incoming PWM signal to extract its dc component: in other words, the alternator sees the PWM
signal as an analog voltage. The higher this voltage (corresponding to a duty cycle of the PWM
signal close to 100%), the higher the alternator excitation signal will be and hence the greater the
resistance.
The alternation rotates in the field produced by the excitation signal, generating electrical energy
which is dissipated by the power resistor.
The rotation of the alternator also generates a square wave signal proportional to its speed, with 6
pulses corresponding to one complete rotation of the alternator. This signal enters on the interface
alternator board where it is filtered and sent to the CPU board.
If the CPU board does not receive the speed signal, which means that the alternator is
not rotating, it does not transmit any PWM signal. Therefore the alternator does not
receive the excitation signal and there is no resistance at all.
The alternator control differs depending on the selected stepping mode:
• mode A: In this stepping mode, the user moves at a constant speed (which increases with
increasing difficulty level) in order to maintain a "floating" position on the pedals. By using the
Page 3.4
STEPRACE: Service & Maintenance Manual - rev. 1.2