You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
This invention relates to a wagon of the kind that has a main frame carried by mutually oscillatable wheel frames or crawler frames and it relates particularly to crawler drill wagons that have a feed beam for a rock drill mounted on the distal end of a boom. 
     When such a crawler drill wagon is used the feed beam is used as a support to make a three point support. If the direction of the feed beam need to be adjusted during drilling, the entire rig tends to move since the feed beam forms one of the three supports. The adjustment will therefore be difficult and will take time. 
     When using a drill wagon according to the invention, it will be easier for the operator to position the wagon and the feed beam and the wagon will stand more stable. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a drill wagon. 
     FIG. 2 is a top plan view of the drill wagon shown in FIG. 1. 
     FIG. 3 is a side view of a modified drill wagon. 
     FIG. 4 is a top plan view of the drill wagon shown in FIG. 3. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The drill wagon according to FIGS. 1-2 comprises a main frame 11 that carries a body 10. Two crawler frames 12, 13 are journal-mounted on two coaxial trunnions 14, 15 on the main frame. The crawler frames are also coupled to brackets 16, 17 on the main frame by means of two hydraulic cylinders 18, 19 that are pivotably mounted to a respective crawler frame and to the main frame. These two hydraulic cylinders 18, 19 are hydraulically connected together so that one of them extends when the other contracts. Therefore the main frame will always take up a middle position between the swing positions of the crawler frames. Each crawler frame carries an individually operable motor and gearing unit 20, 21 that drives the crawler treads 22, 23 through drive wheels 24, 25. Each motor and gearing unit includes a friction brake or a locking device to lock the respective drive wheel. A boom 26 is pivotably mounted on the main frame to pivot about two perpendicular axes in order to be laterally swingable by means of a hydraulic cylinder 27 and vertically swingable by means of a hydraulic cylinder 28. On the outer free end of the boom 26, a holder 29 for feed beam 30 is pivotably mounted to be swingable vertically about a trunnion 31 by means of a hydraulic cylinder 32 and to be swingable about a trunnion 33 that is perpendicular to the trunnion 31 by means of a hydraulic cylinder 34. The feed beam 30 is axially displaceable in its holder 29 by means of a hydraulic cylinder 35 and it has a spur 36. A percussive rock drill 45 is slidably mounted on the feed beam 30. A drill rod is designated by 46. 
     A pair of support legs 37, 38 are pivotably mounted about pivots 39, 40 on the brackets 41, 42 on the crawler frames. The support legs 37, 38 are swingable by means of hydraulic cylinders 43, 44 which are pivotably coupled between the brackets and the support legs so that the support legs 37, 38 and the cylinders 43, 44 form together hydraulic support jacks. 
     In FIG. 1, the drill wagon is shown in drilling position. The crawler frames are supported on the one hand by the support legs 37, 38 and on the other hand on the crawler treads at the ends of the treads that mesh with the lockable drive wheels 24, 25. This four point support is very stable since the crawler treads are effectively locked at their contact area to the ground and since there will be a statically determined four-point-system due to the crawler frames being swingable about the trunnions 14, 15. The swingability of the crawler frames permits a stable support in rough terrain. By means of the cylinder 35 the feed beam can be advanced against the rock until its spur 36 will take up a suitable force against the rock and reduce the force that is taken up by the support legs without unloading the legs completely. Then, if the spur 36 of the feed beam is retracted off the ground, the wagon will still stand stable. 
     In FIGS. 3 and 4 an alternative embodiment is shown in which the support jacks 43, 44 are not mounted in the same end of the wagon as the feed beam. In this embodiment, the support jacks 43, 44 are mounted on extensions of the crawler frames so that they are located behind the crawler tracks. This permits a higher force on the spur 36 than should be the case if the support jacks would be located nearer the trunnions 15 about which the crawler frames oscillate. A drill wagon can alternatively also be provided with four support jacks, that is, the crawler frames can have two jacks each; one at each end.

Summary:
A drill wagon has oscillatable crawler frames. Each crawler frame has a hydraulic ground engaging support jack at one end.