# Manual Wheelchair Equipped with a Planetary Gear-Research Methodology and Preliminary Results
## 2 Materials and Methods
### Test Conditions and Statistical Analysis  
In order to carry out the experiments, the appropriate methodology and research plan were developed and its diagram is shown in Figure 5. The study consisted of two phases: the preparation phase (A1-A3) and the actual tests (B1-B4). In the first step, the person being examined was prepared by attaching measuring electrodes (A1) and performing exercises necessary to perform MVC normalization on the test results (a commonly used amplitude analysis technique for EMG signals) [32] (A2). Subsequently, the person was placed with the wheelchair on the dynamometer (A3) and the test was started (B1). After completing the task, the wheelchair operator rested for 15 min (B2). At the same time, the wheelchair gear ratio and/or inclination (B3) were changed. The inclination angle change, thanks to the used test stand, was performed in such a way that the larger wheel did not change its position in relation to the support rollers. The tests were repeated successively, until all variants were exhausted and they came to an end (B4). The test consisted of performing a series of 30 propulsion phases, i.e., pushing off the wheels of a wheelchair. This number was selected so that it was possible to carry out all the defined variants of the experiment without the participant's physical discomfort (so as not to lead to excessive muscle exhaustion). Tests were performed for each of the 27 system configurations. They were obtained by changing: the gear ratio of the planetary propulsion system (p1-3) and the angle of inclination of the wheelchair together with the patient (k1-3). Such measurements were repeated in three series (s1-3). The push frequency (occurrence of the propulsion phases) was \(f=40\) BPM (occurrence approximately every 1.5 s) and it was sonically imposed with the use of a metronome--the examined person's task was to  
Figure 4: View of the dynamometer, the examined wheelchair with the participant and the arrangement of electrodes; 1—planetary gear integrated in the hub of a larger wheel, 2—test stand (wheelchair dynamometer), 3—support rollers for the propelled wheel, 4—measuring electrodes, 5—mounting arm (enables changing the angle of inclination of the wheelchair) and 6—servo drive. follow the impact rhythm as accurately as possible. Thanks to this, the average speed of the wheelchair was controlled. It was hypothesized that the participant's muscle effort would change with the gear ratio of the drive system and angle of inclination of the wheelchair. Table 1 shows variants of the markings and input values for the performed experiments. The markings assumed according to it are consistently preserved throughout the paper. The measured EMG signals were rectified and then smoothed using RMS algorithms with a window width of 150 ms. Later, a maximum voluntary contraction test (MVC) was performed. This post-processing method utilizes a reference value to normalize the subsequent EMG data series (Figure 5, marking A1). The output is displayed as a percentage of the MVC value, which can be used to easily establish a common ground when comparing the data between repetitions and subjects. A set of five dedicated exercises were carried out to test the maximum contraction of any one, which were selected on the basis of the previous studies [31]. The recorded data were successively normalized, using the arithmetic mean of the amplitude of the highest signal segment with a constant duration of 1000 ms as the reference value. Subsequently, each experiment was divided into individual propulsion phases. On the basis of the measurements, the surface area (\(SA\)) was determined numerically, using the trapezoid method, under each obtained graph and the signal amplitude (\(MVC_{MAX}\)), separately for each propulsion cycle. Out of 30 values determined in this way (\(n\)), the 3 largest and the smallest ones (the most deviating from the average) were rejected, assuming that they were burdened with a large error.