Learn how electrical resistance training improves peoples lifes.

At a Glance

Client Information
2019 - Today

Originally two engineers at Akrodyn - both very active - wanted to replace steel discs in gym training machines with electrical motors. They asked themselves

“What if we could use electronics to integrate a gym buddy into the machine so that I can push myself to the limit every time, to save time, progress faster and  improve safety”.

status quo

Weight stacks were invented in the 1970s and are still the most common choice for setting the training weight. However, the training sciences have known about electrically generated resistance for well over 25 years and the advantages of this technology for the end user - safe training until total muscle exhaustion - must be emphasized. Training progress is greater and time is saved at the same time, as the system is able to dynamically adjust the weight within each repetition. In the past, however, such systems were not only very expensive and large, but also too slow, as the bandwidth of the bus systems was too small and the algorithms were not executed on the motor controllers.


The weight of a steel disc is constant. However, biomechanics tell us that the maximum force we have depends on the angle of our bones, we are specially “weak” at a 90° angle. In addition, we are stronger when lowering weights rather than raising (eccentric). Sounds complex, isn’t it?

What if we could use dynamic weight that adjust to you in real time using electronics and an electric motor rather than complex mechanics?

Technical implementation

Based on our self-developed modular X1 control system, an additional plug-in board was developed that offered connectivity for the CAN bus system and a touch panel. Wireless communication via Bluetooth® Low Energy (BLE) was integrated. The fitness algorithms were programmed directly into the microcontroller of the motor drive, which offered previously unattainable dynamics and adaptability of the training resistance. In a later step, the system was expanded to include a synchronized multi-motor setup offering up to 1’500 kg of simulated weight! Enough even for professionals.

Training modes

Depending on your training program or machine, different training modes can be activated or super positioned.

  • Normal (feels like steel plates, simulated gravity)

  • Constant Resistance

  • Eccentric Overload

  • Isokinetic

  • Elastic (feels like a rubber band)

  • Stability (random weight changes)

  • Viscous (movements in water)

  • Force map (force adjustable on position during exercise)

  • Flywheel (Inertia)

On top a so called “Spotter” can be configured. It is your personal gym buddy. If you are struggling to perform an exercise, the system will detect it and ramp down the weight. So you can always train to your limit or use the spotter to ramp up your weight once in the start position ready to start your workout.


Depending on the purpose of the training machine, different training modes are activated. On a physiotherapy machine safe low force applications are more important. For example the modes elastic and isokinetic are good for joints while the stability mode improves coordination and core strength.

In a commerical or home strength machine, maximum force is more important. We recommend the modes Normal, Eccentric Overload and Isokinetic.


Using an electric motor for cardio equipment enables a more immersive training experience, as for instance the behaviour of spinning bikes, can be synchronized with the playback of the video. Example: Braking force is increased on the uphill, downhill slightly self-spinning when descending. Other features include new equipment designs with a lower transport weight and increased training safety.

The big challenge was to realistically reproduce the moment of inertia of a flywheel in conjunction with a freewheel and a bicycle brake.

reference Use Cases

Your project

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2. Let’s meet

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3. Quote

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