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Article

Pilot Performance Testing of a Battery-Powered Salamander Micro-Skidder in Timber Harvesting

by
Grzegorz Szewczyk
1,*,
Jozef Krilek
2,
Paweł Tylek
1,
Ján Hanes
3,
Slavomír Petrenec
3,
Miłosz Szczepańczyk
1 and
Dominik Józefczyk
1
1
Department of Forest Utilization and Forest Technic, Faculty of Forestry, University of Agriculture in Krakow, Al. Mickiewicza 21, 31-120 Kraków, Poland
2
Department of Environmental and Forestry Machinery, Faculty of Technology, Technical University in Zvolen, T.G. Masaryka 24, 960 01 Zvolen, Slovakia
3
WIM s.r.o., 962 61 Podzámčok, Slovakia
*
Author to whom correspondence should be addressed.
Forests 2025, 16(5), 753; https://doi.org/10.3390/f16050753 (registering DOI)
Submission received: 24 February 2025 / Revised: 11 April 2025 / Accepted: 22 April 2025 / Published: 28 April 2025
(This article belongs to the Section Forest Operations and Engineering)
Browse Figures
Versions Notes

Abstract

:
The objective of our research was to ascertain the time intensity of timber skidding with a prototype ATV Salamander 600 4 × 4 micro-skidder and to characterize the operator’s field of view. The time intensity of skidding amounts to approximately 20 min/m3 at a distance of 20 m when skidding timber from the forest stand and approximately 10 min/m3 when skidding along the skid trail for a distance of 80 m, which is comparable to other machines of this type, despite reported problems with raw material causing jamming on rugged terrain in the first phase of the skidding process. The significant discrepancy (6%) in wheel slippage between the front and rear axles was particularly pronounced during the process of pulling timber up to the skid trail. This can be attributed to the transport hitch being positioned excessively high, thereby relieving the force on the hitch and causing the front axle to be affected. The observed difficulties in skidding resulted in the need to scan a wide visual scene when working in the stand. The initial phase of timber skidding in the forest stand exhibited a deficiency in its smooth flow, which led to an augmentation in mental workload, as indicated by the elongation of saccades. On average, these saccades were approximately 80% longer compared to those in work conducted on the skid trail.

1. Introduction

European forests cover about 33% of its surface and are owned by some 16 million private and public owners, with 60% of the EU forest area being privately owned and 40% publicly owned. The proportion of privately owned forests is particularly high in the Scandinavian countries and in France and Italy, where, in many areas, up to 100% of the forest area is in private hands. The average size of a private forest holding in the EU is around 13 hectares. However, it should be noted that approximately two-thirds of private owners have holdings of less than three hectares [1,2,3]. This is also the case in central European countries, where large areas are dominated by state ownership, yet the proportion of private owners is considerable. The type of ownership of forest land greatly influences how forest stands are managed. In forests with larger areas, harvesters and forwarders have been used in logging operations for a number of years [4,5,6,7,8]. Small forest owners often set up consortia where specialized machinery is used, but SSF (small-scale forestry) technology is also of great interest. This system is most prevalent in Sweden and other Nordic countries, as well as in Austria and North America [9,10]. Interest in so-called small-scale production technologies started to develop in European forestry circles in the 1980s [11] and in Slovakia, especially, after the change of political system in the early 1990s, when parts of the forests were transferred into private hands.
In Slovakia, forests cover 1955.5 thousand hectares of the total area (41.3%), of which 7.3% is privately owned and 42.1% is owned by associations, municipalities, etc. [12]. Chainsaws are used for harvesting in these forest stands and agricultural tractors with self-loading trailers are used for skidding or, more rarely, horses or small forwarders are used [13]. Although ATVs are available, they are not widely used. This situation is in line with trends prevailing in other Central European countries. It is particularly hard to carry out harvesting operations on small farms. A number of factors influence this finding, including the age of the woodland (mostly younger), the spatial structure of the forest stands (which are quite scattered) and the relatively small size of the trees [14,15]. It is in such forest stands that SSF technologies are particularly important for adequate productivity [9]. SSF technologies use small-scale machinery and equipment [16,17,18,19] and ATVs (all-terrain vehicles) [9,20,21,22]. Timber skidding with ATVs is carried out in a number of ways. These include overhead methods [23,24,25], skidding [21], or forwarding using skidding arches [26,27].
The all-terrain vehicle (ATV) is a motorized off-highway vehicle designed to travel on four low-pressure or non-pneumatic tyres. The first ATV models were marketed in the 1970s when the Honda Motor Corporation launched the ATC90 model [22,28]. The integration of advanced suspension systems, all-wheel drive and electronic control systems has led to significant advancements in the performance, safety and comfort of modern ATVs [29]. In recent years, the popularity of ATVs has increased considerably among extreme sports enthusiasts and in professional applications. Their excellent handling characteristics and high stability enable them to navigate a wide variety of low load-bearing surfaces in rugged terrain that is characterized by ruts, stones and tree roots. As a result, micro-skidders and ATVs have long found applications not only in leisure but also in agriculture [30], in forestry [25,31,32,33] and even in rescue operations [29]. In the UK, several thousand ATVs were sold every year for small private forestry operations in the late 1990s [34]. In Sweden, where the tradition of logging and skidding in smallholder forests based on small-scale forestry technologies is deeply rooted, there has been a continuous increase in ATV sales. This trend is evident in both the sales of ATVs themselves (exceeding 3200 units annually) and the number of trailers adapted for ATV use (surpassing 1700 units per year) [10].
The Salamander 600 4 × 4 electric micro-tractor was showcased at the 2024 Brno trade fair. The manufacturer, First Green Industries a.s., which is based in Velká Dobrá, Czech Republic, cites a comprehensive range of business applications spanning from agriculture, through municipal services, to forestry (small-scale forestry) [35]. In the context of forestry, the Salamander’s use is associated with skidding operations, where performance testing and operator field-of-view analyses are crucial for machine stability assessments, particularly in challenging terrain conditions and when handling timber loads of relatively limited thickness. The aim of our research was to determine the time-consuming nature of timber skidding with a prototype ATV Salamander 600 4 × 4 micro-skidder and to characterize the field of view of the vehicle operator.

2. Materials and Methods

2.1. Salamander 600 Micro-Skidder

In our research, we used a prototype of a small electrically driven wheel skidder with a Salamander 600 4 × 4 front loader (Figure 1 and Figure 2). We have summarized the basic technical data of the Salamander 600 skidder in Table 1.
The skidder’s low weight and compact dimensions allow it to be transported to work areas using a trailer with ramps that is towed by a passenger car.
The three-component skidder frame, designed for securing the vehicle’s axle, powertrain and machinery components, is compatible with powertrains employing either internal combustion engines or electric motors (Figure 3). The skidder frame is protected by intellectual property rights in the form of a utility model, registered under No. 9769. The intellectual property rights for this model are held by Prof. Ing. Jozef Krilek, PhD. from the Zvolen University of Technology (Department of Environmental and Forestry Technology, Faculty of Technology), Ing. Slavomír Petrenec and Ján Hanes from the company WIM s.r.o [36]. The skidder frame consists of three parts: the front frame, the centre frame and the rear frame. The front frame is structurally identical to the rear frame but is connected to the centre frame by a pivot joint, with a hydraulic cylinder in the centre frame enabling the rotation of the front frame. The rear frame is connected to the centre frame by a rotary joint, which provides rotation of the frames in a transverse direction.
The skidder is powered by a pair of modular electric axles manufactured by Benevelli, with one axle driving the front frame and the other the rear frame. The electric motor is of a permanent magnet asynchronous (PMAC) type and includes a speed sensor and electromagnetic parking brake. Torque transfer from the electric motor to the axle hubs is provided by a gearbox, which also includes a differential with mechanical locking. Both axles are fitted with liquid disk brakes and a double wheel assembly, which can be modified to provide separate wheels, and the dual mounting provides higher lateral stability and superior traction capabilities.
The hydraulic oil is supplied under pressure by a gear pump driven by a 3 kW Benevelli electric motor, with an operational pressure of 150 bar and a flow rate of 25 L · min−1 (in the basic setting). This pump unit drives the Danfoss manufacturer’s steering system servo and the brake frame’s linear hydraulic cylinders, as well as the linear hydraulic cylinders of the front loader and the rear three-point linkage. These components are controlled by a 4-sectional distributor with 3 levers.

2.2. Field Measurements

We took field measurements in the forest stands of Mestské Lesy, s.r.o Krupina (N 48.34097; E 19.06703), in section 621 (Figure 4). Table 2 summarizes the basic taxonomic characteristics of the forest stand.
We established a research site within a section of the forest stand that was homogeneous, both structurally and species-wise. Longwood skidding (the long length system, or LLS) was conducted using a Salamander micro-tractor. We analysed two skidding phases: skidding from the stand to the skid trail at an average distance of 20 m; and skidding along the skid trail at a distance of 80 m. Skidding was carried out down the slope, which had an average incline of 18% in the first scenario and 14% in the second scenario. The work was carried out with the LLS logging system, skidding logs with an average length of 8 m and an average volume of about 0.3 m3. Trailing skidding was carried out, with the harvested timber being hitched to the rear frame of the tractor using a PES 2T/3M loop belt sling. In the stand in which we conducted the study, a skidding trail had been predetermined and prepared. The micro-skidder operator had two years of experience in forestry operations and two years of experience in operating micro-skidders.

2.3. Time Intensity of Timber Harvesting

We established the time intensity of timber harvesting and skidding at the analysed workstations for the recurrent work cycles (productive time, or PW) measured during this study [37,38]. TIMER PRO PROFESSIONAL footage analysis software ver. 11.1.22.2015 (Applied Computer Online Services ACOS, 2901 Moorpark Ave, Suite 100, San Jose, CA 95128, USA) was used to perform the timber skidding duration studies. Boundary points defining precisely the beginning and end of each activity were superimposed onto the film track. The timber skidding observed in the study plots was smooth, with no interruptions associated with repairs, maintenance activities, or rests. Chronometers were employed with an accuracy of 1 s. The following limiting points of the activities observed within the work cycles were distinguished:
(a)
Hooking, unhooking (supportive time)—from the moment the operator grasps the hauling rope until it is hooked or unhooked from the timber to be harvested;
(b)
Passages during loading (supportive time)—the act of hooking and unhooking the load, from the moment the operator moves forwards until he stops;
(c)
Skidding (work time)—from the time the skidder starts to move from the loading spot until it stops at the next timber loading spot in the forest stand or after the timber has been detached at the landing;
(d)
Drive-through (supportive time)—from the start of the unloaded skidder until the skidder has arrived at the next loading point.
The amount of growing stock harvested in the resulting work cycle was calculated for each piece of timber harvested, on the basis of its central length diameter.
Statistical analyses of the time intensity of work were carried out using Statistica 13 software (StatSoft, Kraków, Poland). The study of differences in time intensity recorded during timber skidding in the stand and on the trail was carried out, due to the normality of the distribution of the analysed characteristics. This was determined using a parametric form of Student’s t-test.

2.4. Analysis of the Operator’s Vision Scene

We analysed the variable eye activity of the micro-skidder operator using a Tobii Pro Glasses 2 Reflective Eye Tracker (Tobii AB Karlsrovägen 2D Box 743 S-182 17, Danderyd, Stockholm, Sweden), along with the Tobii Pro Glasses Controller software ver. 1.83.11324-RC1 (Figure 5 and Table 3). The micro-skidder operator had no diagnosed sight impairment. The almost contactless interface created minimal distraction for the work contractor. We recorded the reflection of infrared light from the eye and then processed it digitally in real time, allowing us to identify the points to which the machine operator was paying attention. After calibrating the glasses, we started the recording session, which lasted approximately 30 min.
A single recording lasted 5 min. In the context of eye-tracking testing, it is recommended that the exposure time be longer than 1 min to allow participants to make average fixations of 200 to 300 milliseconds [39,40]. Following each session, we concluded our analyses, completed data recording and, after recalibrating the device, initiated another recording session. The footage obtained during the fieldwork was processed using Tobii Pro Lab—Analyzer Edition 1.102 software ver. 1.102.16417.
We carried out eye-tracking analyses in two ways. Firstly, we determined the spatial resolution, i.e., the ability to distinguish between those areas of the visual scene at which the machine operator was looking. Secondly, we determined temporal resolution, i.e., the duration of gaze fixation points.
In order to identify those parts of the vision scene most strongly attracting the attention of the operator, we created heat maps. In order to identify those parts of the vision scene that were characteristic due to their content or context, we identified areas of interest (AOI) on snapshots representing the vision scene: the forest stand, skid trail, machine and timber (Figure 6).
For individual AOIs, we generated standard measures of the location and the variability of fixation points: mean, median, size and total duration.

2.5. Skidder Wheel Slip

Slippage on the vehicle’s drive wheels is an undesirable phenomenon that can be detrimental to productivity, increase fuel consumption and tyre wear (especially on soil with a high content of quartz grains) and negatively impact the soil [41]. However, it is an unavoidable phenomenon. To determine the amount of slippage, the number of revolutions of all the tractor wheels on a 20-m measuring section was recorded using cameras. The recordings were made during skidding work and when the vehicle was driving unloaded, which made it possible to determine the theoretical number of wheel revolutions, taking into account the dynamic radius of the driving wheels. Slippage was calculated by comparing the theoretical distance with the actual distance. Measurement accuracy was derived from recordings of the angular velocity of the wheels. The tyres had 15 rows of tread blocks, resulting in a measurement error of 24° of wheel rotation. Considering the wheel radius, this led to an accuracy of 0.11 m in determining the travelled distance.

3. Results

We analysed a total of 18 complete skidding cycles, with 9 carried out in the forest stand and 9 on the operational trail.
On average, it took twice as long to skid the timber from the forest stand to the skid trail as it did to move along the trail (21 min/m3; Table 4, Figure 7). The differences in skidding duration were statistically significant (t = 4.20; p = 0.00). We observed a lower variation of about 10% in the time taken during timber hauling to the skid trail, this being 27% during forest stand hauling and 37% during skidding on the skid trail.
Significant differences were observed in the structure of the lengths of skidding cycles during timber skidding in the stand and on the skid trail. Working in the forest stand resulted in longer durations of all work activities. Hooking and unhooking in the forest stand took approximately twice as long as when performed on the skid trail, while passages during loading (preparations for timber hitching) took even longer (Figure 8). Statistically significant differences were found between hitching and unhitching times for the scenarios tested (t = 2.28; p = 0.04) (Figure 9).
As illustrated in Figure 10, the heat maps provide a visual representation of the operator’s field of view during timber skidding operations in the forest stand and on the skid trail. It is evident that the view was more expansive when working in the stand, with the operator’s gaze directed towards the ground in front of the skidder and the direction of travel. His field of view primarily covered the area on the sides of the skidder, where the front wheels would travel, along with the driving zone approximately 3 m in front of the skidder. However, scans of the working area also included the area through which skidding was to take place, at a distance of several meters in front of the skidder. In the case of skidding along the skid trail, the visual inspection of the foreground concerned almost exclusively the zone located in the direction of travel, at a distance of approximately 3 to 4 m.
As shown in Table 5, the mean duration of fixation during skidding in the forest stand and on the skid trail was similar, at approximately 255 ms. However, differences between the tested scenarios were observed between the distinguished AOIs. Shorter fixation times for skidding in the stand compared to skidding on the trail were recorded for the machine and trail AOI areas, at 15% and 18%, respectively. The longest fixation time for both options was for the AOI regarding trail observations, which was 16% longer than the mean trail and machine observation time for skidding in the forest stand and 42% longer for skidding on the skid trail.
Slip is a key economic and environmental indicator for skidders, as this is the basis for interpreting the interaction of the traction system with the ground. If it is too high, there are significant energy losses. In fieldwork, a slippage of 20% is acceptable, but the optimum value is 12 to 15%. During testing, analyses of the skidder’s wheel slippage during skidding operations were carried out separately for the front and rear axle wheels, and the results are shown in Table 6.
The mean slip values are high, with noticeably higher values when the tractor is working in the stand, due to the specific nature of the work in the non-cleared area. The variability of the slip parameters for subsequent passages during loading is also clearly discernible in this case. The significant difference between the slip values for the front and rear axle wheels is a cause for concern. While the absolute values for the rear axle wheels were within acceptable limits, the front wheels demonstrated excessive slippage, reaching almost 40% during skidding in the stand. This issue is likely attributable to the elevated placement of the transport hitch (Figure 11), which was positioned well above the centre line of the rear wheels. Consequently, the front axle load was relieved by the force on the hitch. In the case of maximum tractive forces, there was even a complete separation of the front axle wheels from the ground, which, in addition to a sharp increase in slippage, led to a loss of manoeuvrability.

4. Discussion

The analysis revealed that in both tested skidding scenarios, 60% of the operating time of the Salamander 600 micro-skidder comprised skidding and non-loading passes, both in the forest stand and on the trail. Comparable yet slightly higher results were reported by Savelli et al. [21], who estimated the proportion of these times at a similar skidding distance to be 74%. When the skidder manoeuvring times and operator passes associated with load formation (passages during loading) (13%–14%), as included in our experiment, are added, these figures are almost identical. Kincl’s [24] study shows that the skidding and non-loading pass times of an ATV with a self-loading trailer account for 60% of the working time, while skidding and non-loading passes account for 40%. Given that Kincl’s study [24] reported approximately twice the timber volume being skidded during the skidding cycle that was studied in our experiment, the similarity in time structures is noteworthy. The results of our experiment revealed that the shares of skidding time and non-loading trips were almost identical, indicating optimal skidding conditions that did not necessitate the ATV operator reducing the skidding speed due to machine load. The impact of soil moisture on skidding speed was previously observed by Kincl [24], who noted an increase of up to 50% in the share of skidding time compared to non-loaded driving, which could be attributed to a reduction in ground-bearing capacity. The traction parameters of the Salamander skidder are, therefore, adequate for the loads we tested, and the reduction in time intensity that we observed could be based on a reduction in the substantial share of load-hitching time in the forest stand.
The high proportion of load-hooking time in the forest stand (30 per cent) corresponds to the equally high proportion of over 40 per cent reported by Savelli et al. [21]. This additional time was due to the need to accurately select the direction of the skidder so that the extracted timber did not become jammed when traversing rugged terrain, in view of the often insufficient towing power of the skidder. The ability of the skidder to overcome operating resistance while working with the machine is not only due to the adequate delivery of power and torque, but also to the technical and operational parameters affecting the towing power. This includes the type and condition of the tyres and the type of ground, but especially the weight resting on the drive wheels [42,43]. The optimum weight of a working vehicle should be approximately 50 kg per hp of traction engine power [44,45,46]. However, the current development of traction engines has resulted in the weight of the base design of operational vehicles being too low, requiring appropriate ballasting. Speaking from our experience, the ballasting of the skidder was achieved by a set of heavy-duty batteries, which measurably improved the traction properties while dispensing with conventional solutions. The 12.8%–38.3% slippage of the front axle wheels recorded in our experiment indicated the need for more weight on the front of the tractor and the reconstruction of the location of the load skidding hitch. Savelli et al. [21] reported that the pulling force of the ATV when the tractor’s front and rear axles were weighted at 40–50 kg each increased from approximately 230 daN to as much as 355 daN. In our experiment, the pulling force varied between 1.6 and 4.9 kN. The use of specialized equipment for skidding logs, skidding plates, skidding arches or tongs, as recommended by Stringer [18], is likely to reduce skidding resistance and improve the observed situation.
It is very important to keep a steady, even position while moving forward and backward, especially when traversing rugged terrain [47,48]. Uneven terrain, especially when it is sloping, can significantly reduce the stability of vehicles. This is because it can cause parts of the machine’s running system to lose traction [49,50,51]. The ability to move over obstacles depends on where the obstacle is in relation to the slope and the machine’s settings, like how close it is to the ground, how stable it is on the side and where the obstacle is in relation to the slope. It is crucial to determine lateral and longitudinal stability in the context of changing terrain conditions during operation [52], which are generally assessed in an approximate, visual manner. Stability assessment is particularly important for ATVs operating in harsh forest conditions, due to the unfavourable ratio of the skidding weight to the machine weight. Fixation duration has been shown to be a significant indicator of visual attention and cognitive processes, thereby serving as an indicator of learning [53]. In our study, we observed that fixation time in challenging terrain, specifically when observing the passing zone (AOI forest stand), was approximately 90% longer compared to trail-based work. This underscores the importance of careful observation of the ground and the recognition of the potential risks associated with reduced machine stability when traversing rugged terrain. A similar phenomenon was observed by Szewczyk et al. [54,55], who studied the reactions of forest machine operators when working in difficult mountainous conditions and in post-disaster areas. Fixation times went up by 80% when working on steep slopes and by 83% when working in damaged forest stands. In contrast, faster skidding trips on the trail required careful scanning of the terrain in front of the machine (AOI trail), resulting in significantly longer fixation durations of around 80%. This finding indicates that prolonged fixation durations may be indicative of extensive data processing within the visual field [56] and could potentially signify information assimilation challenges [57,58].
Our estimate of the time intensity of the work of skidding carried out on the trail was approximately 10 min/m3 over a skidding distance of 80 m. Such a result should be considered reliable in the light of previously published articles. Similar results were recorded in a study using a Honda Foreman TRX300FW ATV with a logging arch [20]. Under similar terrain conditions (10% slope) and with an average log volume of 0.21 m3 and an average distance from the logging yard of 100 m, the skidding efficiency was 9 m3/hrpt. It is likely that these slight differences were influenced by the use of a logging arch, which caused the heads of the logged wood to be raised. In contrast, the operational tests of the ATV CF Moto Gladiator X8 V-twin 800 EFI with a Vahva Jussi 1500/320 log skidder, as conducted by Kincl [24], yielded a skidding time intensity of approximately 15 min/m3, thereby aligning with the average skidding time from a stationary position and on the trail as established in our experimental study. The time-intensity values obtained in our experiment were also similar to the data published by Savelli et al. [21]. Under similar field conditions, with longer skidding distances of 150–200 m, they obtained an ATV skidding time intensity of 23 min/m3. The lower time consumption compared to our results could have resulted from the use of a winch. The operator did not need to drive up next to each piece of wood that was to be torn off, which was time-consuming in an area with many obstacles.

5. Conclusions

Field testing of the Salamander 600 4 × 4 ATV micro-skidder has shown that it is possible to use the machine in forestry activities under the conditions described in this experiment, with the time taken to skid longwood being comparable to other machines of this type. However, problems have been noted with the raw material jamming on rugged terrain in the first phase of skidding. The issue of high wheel slippage of the front axle, as identified in our study, may be mitigated through the implementation of drag skidding enhancement devices, such as skidder caps, and by adjusting the attachment point of the load skidding hitch. The combination of the field of view described herein by eye movement analyses with aspects of work efficiency related to the terrain difficulties of timber skidding in the stand and on the skidding route constitutes the originality and innovation of the current research.
The complex transmission system used in internal combustion engines has been streamlined by the integration of an electric motor. In addition to its environmental benefits, such as the elimination of exhaust fumes, noise reduction and the prevention of environmental pollution by consumable fluids, this type of drive offers numerous advantages, including fast, precise and stepless speed control, very high torque during vehicle start-up and at extremely low speeds, higher efficiency under partial load and the capacity for energy recuperation during braking.
The skidder’s original three-component frame, which is used to mount the drive axles, control and powertrain components, and to aggregate attachments and machinery, is suitable for internal combustion engine or electric motor powertrains.
Further operational field tests are planned, following the implementation of appropriate design modifications.

Author Contributions

Conceptualization, G.S., J.K. and P.T.; methodology, J.K., J.H., S.P., G.S. and P.T.; software, G.S., M.S. and D.J.; validation, G.S., J.K. and P.T.; formal analysis, G.S., J.K. and P.T.; investigation, G.S., J.K. and P.T.; resources, G.S., J.K. and P.T.; data curation, J.K. and P.T.; writing—original draft preparation, G.S.; writing—review and editing, J.K. and P.T.; visualization, J.K. and P.T.; supervision, P.T.; project administration, P.T. and J.K.; funding acquisition, J.K., S.P., J.H. and P.T. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Ministry of Education and Science of the University of Agriculture in Krakow in 2025: KEGA No. 007TU Z-4/2023 “Innovation and Educational Support of Subjects in the Field of Technical Diagnostics of Agricultural and Forestry Technology with an Orientation to Practice” and KEGA No. 012SPU-4/2025 “Implementation of modern methods in the Smart Farm 4.0 concept for sharing data in teaching for agricultural and forestry sciences”.

Data Availability Statement

The data used in the study are available from the corresponding author.

Acknowledgments

We would like to thank First Green Industries a.s., based in Velká Dobrá, Czech Republic, and the employees of Mestské Lesy, s.r.o. Krupina, for their assistance in conducting the fieldwork.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
EUEuropean Union
ATVAll-terrain vehicle
SSFSmall-scale forestry

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Figure 1. ATV Salamander 4 × 4 micro-skidder.
Figure 1. ATV Salamander 4 × 4 micro-skidder.
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Figure 2. Dimensions of the ATV Salamander 600 4 × 4 micro-skidder [36].
Figure 2. Dimensions of the ATV Salamander 600 4 × 4 micro-skidder [36].
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Forests 16 00753 g003
Figure 3. Three-part Salamander 600 skidder frame [36]. 1—Front frame; 2—rotary joint; 3—hydraulic cylinder; 4, 41—centre frame; 5—rotary joint; 6—rear frame.
Figure 3. Three-part Salamander 600 skidder frame [36]. 1—Front frame; 2—rotary joint; 3—hydraulic cylinder; 4, 41—centre frame; 5—rotary joint; 6—rear frame.
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Figure 4. Forest stand in Section 621, ML Krupina.
Figure 4. Forest stand in Section 621, ML Krupina.
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Figure 5. Eye-tracking device on the Tobii Pro Glasses 2.
Figure 5. Eye-tracking device on the Tobii Pro Glasses 2.
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Figure 6. Areas of interest (AOI) determined during timber harvesting in the forest stand.
Figure 6. Areas of interest (AOI) determined during timber harvesting in the forest stand.
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Figure 7. Box and whisker chart of timber skidding intensity times in the forest stand and on the skid trail.
Figure 7. Box and whisker chart of timber skidding intensity times in the forest stand and on the skid trail.
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Forests 16 00753 g008
Figure 8. Average share of time intensity according to the activities observed in the skidding cycle.
Figure 8. Average share of time intensity according to the activities observed in the skidding cycle.
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Forests 16 00753 g009
Figure 9. Box and whisker chart of timber hooking and passage during loading times in the forest stand and on the skid trail.
Figure 9. Box and whisker chart of timber hooking and passage during loading times in the forest stand and on the skid trail.
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Figure 10. Heat maps showing the length of driver fixation time during timber skidding in the forest stand (a) and on the skid trail (b).
Figure 10. Heat maps showing the length of driver fixation time during timber skidding in the forest stand (a) and on the skid trail (b).
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Figure 11. Positioning of the transport hitch during skidding.
Figure 11. Positioning of the transport hitch during skidding.
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Table 1. Technical specifications of the ATV Salamander 600 4 × 4 micro-skidder.
Table 1. Technical specifications of the ATV Salamander 600 4 × 4 micro-skidder.
SpecificationValue
Tractive force [kN]6
Weight [kg]650
Load capacity of front loader [kg]200
Load capacity of the three-point hitch [kg]250
No. of speeds2
Maximum speed [km/h−1]15
Tyres5.00 × 12
Service life [h] (depending on operation type)>4
Vanguard lithium battery [V/kWh]48/5
Battery charging speedThe charging time is 5 h, as the tractor is equipped with a 1 kW charger. With a higher charger power input, the charging time decreases, e.g., a 2 kW charger would reduce the charging time to 2.5 h. The charging time also depends on the type of charging station used.
Advantages over a traditional combustion engineLower operating costs, less maintenance, zero emissions, quiet operation and instant power.
Table 2. Taxonomic characteristics of the stand in Section 621.
Table 2. Taxonomic characteristics of the stand in Section 621.
Total Area [ha]Age [years]Species Share [%]Growing Stock [m3 · ha−1]
18.28110English oak (Quercus robur)40327
Common hornbeam (Carpinus betulus)30
European beech (Fagus sylvatica)20
Red oak (Quercus rubra)10
Table 3. Technical data for the eye-tracking Tobii Pro Glasses 2 device.
Table 3. Technical data for the eye-tracking Tobii Pro Glasses 2 device.
Sampling frequency50–100 Hz (with respect to eye movement trackers, the sampling frequency means the number of identified locations of fixation points per 1 second. This frequency determines the quality of the results and the accuracy of the measurements taken)
Eye Tracker
Cameras (in glasses frames)4
Scene camera FOV82° horizontally, 52° vertically
Scene camera parametersh.264; 1920 × 1080 pixels; @25 fps
Field of view160°
Diagonal of scene camera FOV90°; 16:9
Sound recordingYes
Weight45 g
Battery120 min.
Recording Station
ConnectionHDMI, Micro USB and 3.5 mm Jack
Frequency2.4 GHz and 5 GHz band
Dimensions130 × 85 × 27 mm
Weight312 g
Table 4. Time consumption of timber harvesting with an ATV Salamander 600 4 × 4 micro-skidder.
Table 4. Time consumption of timber harvesting with an ATV Salamander 600 4 × 4 micro-skidder.
Mean [min/m3]Median
[min/m3]		Minimum
[min/m3]		Maximum
[min/m3]		Std. Dev.Variation Coefficient
[%]
Skidding of timber from the forest stand to the skid trail20.7921.0714.8131.425.5926.87
Timber skidding on the skid trail10.1110.545.0915.693.7537.07
Table 5. Mean fixation time in the areas of interest (AOI).
Table 5. Mean fixation time in the areas of interest (AOI).
Fixation Time for AOI [ms]Mean [ms]Median [ms]
Forest Stand Machine Trail
Skidding in the forest stand 250240290260250
Skidding on the operational trail 130280350250280
Table 6. Wheel slippage during off-road operations using the Salamander 600 4 × 4 ATV micro-skidder.
Table 6. Wheel slippage during off-road operations using the Salamander 600 4 × 4 ATV micro-skidder.
Timber Harvesting Mean [%]Median
[%]		Minimum
[%]		Maximum
[%]		Std. Dev.Variation Coefficient
[%]
From the forest stand to the skid trail
-front wheels 23.121.0714.838.311.951.5
-rear wheels 17.118.812.822.46.940.4
On the skid trail
-front wheels 14.415.411.121.76.746.5
-rear wheels9.610.17.715.13.233.3
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Szewczyk, G.; Krilek, J.; Tylek, P.; Hanes, J.; Petrenec, S.; Szczepańczyk, M.; Józefczyk, D. Pilot Performance Testing of a Battery-Powered Salamander Micro-Skidder in Timber Harvesting. Forests 2025, 16, 753. https://doi.org/10.3390/f16050753

AMA Style

Szewczyk G, Krilek J, Tylek P, Hanes J, Petrenec S, Szczepańczyk M, Józefczyk D. Pilot Performance Testing of a Battery-Powered Salamander Micro-Skidder in Timber Harvesting. Forests. 2025; 16(5):753. https://doi.org/10.3390/f16050753

Chicago/Turabian Style

Szewczyk, Grzegorz, Jozef Krilek, Paweł Tylek, Ján Hanes, Slavomír Petrenec, Miłosz Szczepańczyk, and Dominik Józefczyk. 2025. "Pilot Performance Testing of a Battery-Powered Salamander Micro-Skidder in Timber Harvesting" Forests 16, no. 5: 753. https://doi.org/10.3390/f16050753

APA Style

Szewczyk, G., Krilek, J., Tylek, P., Hanes, J., Petrenec, S., Szczepańczyk, M., & Józefczyk, D. (2025). Pilot Performance Testing of a Battery-Powered Salamander Micro-Skidder in Timber Harvesting. Forests, 16(5), 753. https://doi.org/10.3390/f16050753

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