# In-Field Load Acquisitions on a Variable Chamber Round
## 1 Introduction  
Fuel consumption represents one of the main costs for agricultural companies [1, 2, 3]. Being able to measure the external loads to which an agricultural machine is subjected during usage may contribute to avoid unnecessary over-sizing and, consequently, to reduce fuel consumption. Many authors have used commercial load cells to measure the external loads of agricultural machinery [4, 5, 6, 7, 8]. Other authors used properly calibrated strain gauge bridges to correlate the measured strains to the applied forces [9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24]. [PERSON] et al. [25] determined the operational loads during a grass-cutting process on a green harvesting machine using strain gauges placed in stress concentration regions. [PERSON] et al. [26] developed an instrumented connection between the tractor and agricultural equipment that was capable of measuring draught and vertical forces up to 20 kN. The system showed high linearity between the output of the strain gauges and the applied forces. [PERSON] et al. [27] developed a three-point hitch equipped with a force transducer to measure the horizontal towing loads between the tractor and the driven agricultural implement during soil tillage operations. The authors measured towing loads up to 16.0 kN and 19.9 kN on partiallytilled and untilled fields, respectively. Some investigations focused on the loads acting onthe bearingsings of the tractor's Power Take-off (PTO) [28; 29; 30]. In particular, [PERSON] at al. [30] developed an octagonal ring dynamometer [31], consisting of eight strain gauges connected to form two complete Wheatstone bridges, and measured the axial and radial loads acting on the outer-side ball bearing supporting the PTO shaft. A dedicated PTO shaft for acquisitions was designed. The authors demonstrated that the depth of soil tillage, the size of the agricultural implement wheels, and the PTO transmission ratio settings influenced both the radial and axial loads acting on the bearing. [PERSON] et al. [32] measured the PTO torque using strain gauges during soil tillage and baling operations at different tractor ground speeds and PTO rotation speeds. During the acquisitions, a 75 kW L7040 tractor by LS Mtron Ltd. was used. The Authors demonstrated that the load on the PTO is greater during soil tillage operations and that the PTO rotation speed has a greater impact on the required torque compared to the tractor speed. Similar results were found during soil tillage operations with a rotary tiller [33; 34]. [PERSON] et al. [35] obtained the load spectra during operation of the rear axle of a dump truck using strain gauges. Moreover, the accumulated damage in operation was calculated according to the Palmgren-Miner hypothesis [36; 37; 38]. Similar fatigue monitoring [39] investigations were carried out on railway axles [40], truck crane jib structures [41], and bogie frames of railway trains [42]. In particular, [PERSON] et al. [40] measured the bending stress spectra of railway axles using an instrumented powered wheelset over a 22-month period, while [PERSON] et al. [41] and [PERSON] et al. [42] derived the load or stress spectra from smaller sample data collected over shorter periods: 30 days in [PERSON] et al. 's [41] case, and approximately 3.5 h in [PERSON] et al. 's study [42]. In all three above-mentioned investigations, the fatigue life assessment was also reported. In the present investigation, the load spectra acting in the vertical direction on the hub carriers and in the horizontal longitudinal direction on the drawbar of a variable chamber trailed round bader were measured. To this end, a 3940 kg baler was equipped with a specially designed dynamometric towing pin used to measure the horizontal loads acting on the drawbar of the baler during in-field load acquisitions. Furthermore, the hub carriers of the baler were instrumented with properly calibrated full bridge channels in order to measure the vertical loads on each hub carrier.