GRASSBOARD OR MOUNTAINBOARD

Abstract: The board (1) has transverse front and rear rollers (7 and 8). Each roller is symmetrical with a maximum diameter at its centre and has a length which is at least twice said maximum diameter. The front roller (7) is mounted to rotate about a vertical pivot axis against the action of a recoil spring incorporated in the mounting (5) such that by transferring his/her weight the roller automatically steers the board.

Description: GRASSBOARD OR MOUNTAINBOARD TECHNICAL FIELD OF THE INVENTION This invention relates to articles for use in board sports of the kind which are commonly known as "grassboards" or "mountainboards". BACKGROUND Skateboards comprising a board mounted on four wheels are well known, but they are generally only suitable for use on hard surfaces such as concrete, metalled, or plywood surfaces. Most skateboards have four wheels although a two-wheeled skateboard is disclosed in WO 90 00 428. The same restrictions regarding hard surfaces apply to roller skates and roller blades, (i.e. in-line skates). On the other hand, snowboards are capable of being used on snow and wakeboards on water, both soft surfaces, but are useless on hard surfaces. From a safety point of view, grass represents an ideal surface for board sports. A small number of grassboards and mountainboards are available which are intended to be used on soft surfaces such as grass in addition to hard surfaces. One such board has four large rather like pram wheels and another has three, including a single front or rear wheel. All have a mechanical steering type mechanism that does not allow the weight of the rider to be transferred to the steering side. Thus centrifugal forces allow the board to slide away from the rider especially in wet conditions. Another design uses rubber tracks similar to tank tracks, but this is again difficult to steer. In summary therefore, the existing forms of grassboard and mountainboards are cumbersome and often dangerous in that the pram like spoked wheels protrude above the front or sides of the deck standing, sitting or lying area allowing hands or fingers to be entangled. They have poor or no steerability and they are generally also expensive. It is therefore not surprising that grassboards and mountainboards have failed to achieve a significant level of popularity. The present invention seeks to provide a new inventive form of grassboard or mountainboard which is easy to manoeuvre both on soft grassed or hard concrete surfaces, which is relatively safe from the point of view of possible entanglement with wheels or rollers, is lightweight and practical in size with an affordable selling price. SUMMARY OF THE INVENTION The present invention proposes a grassboard or mountainboard comprising: - a generally horizontal support member presenting an upper ridding surface. - front and rear mountings; - a single roller associated with each mounting extending transversely of the support member to rotate about a rotational axis, each roller having a symmetrically curved outer surface with a maximum diameter in the mid region of the roller, at least one of said mountings being pivotally connected with the support member for pivotal movement about a substantially vertical pivot axis which substantially intersects said rotational axis in said mid region of the respective roller; - recoil means associated with the pivotal mounting to resiliently bias the respective roller towards a stable position extending transversely of the support member such that, in steering the board, the roller can rotate in opposite directions about said vertical axis to return to said stable position under the action of said recoil means. In order to achieve stable and accurate steering the axial length of each roller is preferably at least twice its maximum diameter. BRIEF DESCRIPTION OF THE DRAWINGS The following description and the accompanying drawings referred to therein are included by way of non-limiting example in order to illustrate how the invention may be put into practice. In the drawings: Figure 1 is a general view of a grassboard in accordance with the invention, viewed from the underside; Figure 2 is a is a vertical cross section through one of the mountings by which the grassboard is steered, taken in a front-rear direction; Figure 3 is a further vertical section through the mounting taken perpendicular to the section of Fig. 2; and Figure 4 is a plan elevation of the mounting showing the torsion recoil spring in its rest position. DETAILED DESCRIPTION OF THE DRAWINGS Referring firstly to Fig. 1 , the grassboard includes a generally horizontal support member in the form of a deck 1 which presents an upper riding surface 2 upon which the rider generally stands in use but upon which he/she could also sit or lie. The front and rear ends 3 and 4 of the deck may be slightly upturned as shown. Inset from said ends, respective front and rear steering mountings 5 and 6 are secured to the underside of the deck. The mountings incorporate forks 9 and 10 which contain and shield respective rugby ball shaped rollers 7 and 8 extending across most of the transverse width of the deck. Purely by way of example, the deck may be 1 m long by 300mm wide by 10mm thick, and each roller may be about 275mm long with maximum diameter of 150mm and a minimum diameter at each end of 60mm. The front roller 7 and mounting 5 will now be described with reference to Fig.s 2 to 4. The steering mounting comprises a circular top plate 11 which is secured to the to the underside of the deck 1 by boltsl 6 or other means. A circular bottom plate 12 is pivotally secured to the underside of the top plate 11 by a centrally positioned threaded bolt 14 or similar component, thereby allowing the bottom plate 12 to pivot relative to the top plate 11 about a vertical axis A (Fig. 3) located substantially on the central fromt-rear axis of the deck 1. The plates are in mutual sliding contact by bearing plates 13 of PTFE (polytetrafluroethylene) or a similar polymer type plastic with a low coefficient of friction or by metal ball/needle bearings etc. The roller- mounting forks 9 may be integrally formed with the plate 12 and project downwardly from diametrically opposite edges of the plate 12, between which the roller 7 (Fig. 3) is rotatably mounted on an axle 24 secured to the forks by bolts, nuts or similar releasable fixings 20 and 21. Each roller may for example be injection or rotationally moulded of rubber, ethyl acetate, hytrel or similar material. The rollers are pneumatic and inflated with air through a valve 28 or similar, although they may also be filled with a foam or solid rubber for example, or moulded as a solid body. The rollers incorporate an external tread profile 25 and include an axial tube 22. Each end of the tube 22 is shaped to house bearings 26 and 27 which are mounted on the axle 24. More than two bearings may be located in the roller to spread the load and reduce wear. The bearings are spaced apart by spacer tubes 23 which line the tube 22. The roller is thus free to rotate about a substantially horizontal axis B which intersects or passes in close proximity to the vertical pivot axes A half way along the length of the roller. It will be noted that the two halves of the roller are substantially symmetrical, the roller having a curved outer surface, the maximum diameter being at the middle of the roller. Referring to Fig.s 2 and 4, it will be noted that the plate 11 defines an annular recess which is closed by the opposed face of the plate 12 and contains a coiled torsion recoil spring 15 or similar. One leg 15a of the spring is restrained by a restraint pin 18 fixed with the top plate 11 whereas the opposite leg of the spring 15b is restrained by restraint pin 19 fixed with the bottom plate, or vice versa depending on the direction of rotation of the bottom plate 12 about top plate 11. Under normal conditions the spring is balanced so that the bottom plate 12 attains a rest position with the rollers 7 and 8 parallel to each other extending across the width of the deck 1. However the front roller 7 can be rotated about its vertical axis A by about 30 degrees in opposite directions, as indicated in Fig. 4, by a rotational load which is produced by the rider transferring his/her weight from the centre of the deck to one of the sides of the deck enabling the roller 7 to roll on its convex surface 25. Since the circumference of the roller is greater at the centre of the roller than the circumference at the ends, during one revolution a further distance is moved at the centre than at the ends thus creating a rotational load forcing the spring 15 to coil and thus allowing the board to turn. (The friction between the type of roller material used and the surface terrain being ridden on is a factor in the steering response.) The limits of steering rotation are defined by the coiled strength of the spring 15 exceeding the obtainable load at 30 degrees away from the transverse centre line, and ultimately, buffering by 30 degree stops 29 and 30. The rear roller 8 and its axle are of the same in construction as the front roller 7 and axle 24. However the rear mounting has a single spacer plate 6 which is non-rotatably secured to the deck 1 by bolts 17 or the like (Fig. 1 ). The roller forks 10 project downwardly from diametrically opposite edges of the plate 6. However some models of grassboard or mountainboard may have steering mounting assembles at both front and rear rollers making the front and rear the same. In use of the grassboard, in order to move down an incline forward along a straight line the rider distributes his or her weight evenly on the deck 1 so that the middle regions of the rollers contact the ground. The shape of the rollers allows the weight of the rider to be spread sufficiently to prevent the board from sinking into the ground. Steering of the board is achieved by the rider shifting his or her weight onto his/her toes or heels to one side of the deck. By applying weight to one side or the other the area of ground contact is shifted towards one end of the rollers. Since the outer end of the rollers particularly the front roller 7 in contact with the ground is now rotating on a smaller circumference than the inner, larger circumference of the roller, the inner portion will cover a greater distance each revolution causing the front roller to rotate about its vertical axis A. The board is thus caused to steer a smooth curve, the radius of which depends upon which the board is tilted. With a little practice the rider can soon attain accurate control over direction simply by shifting his/her weight by an appropriate amount. When the riders weight is re-distributed in an even manner the rollers automatically achieve a parallel configuration due to the action of the spring 15 combined with the fact that the rollers are now rotating on their central regions. It is important to note that the axis A should substantially pass through the widest part of the roller 7 to achieve travel in a straight line when the rider's weight is evenly distributed. It is not necessary that the two axes A and B intersect but they should be of close proximity to each other along the centre line of the board. The re-coil torsion spring 15 is an important part of the design and without this device a castor-like effect will result leading to poor steering ability and a unstable board, rather like a supermarket trolley. The third requirement which is important to achieve smooth handling on soft or hard surfaces is a low coefficient of friction (bearing plate/s 13) in the pivotal mounting that can withstand large axial loads together with low friction 8 bearings 26 and 27 in the rollers 7 and 8. Although the term grassboard is used above the description would also apply to a mountainboard. The roller arrangement could be applied to other kinds of sideways or forward action sports rendering it suitable for use on grassed or concrete surfaces, for example skis or skates, windsurfing on flat areas by means of sail or kite, or transportation by means of the rear roller being powered by a battery or petrol driven motor. The board in most cases will be stood on. However it can also be operated in a lying or sitting position for example a lugeboard, (sledge/bobsleigh), or go-cart. It will be appreciated that the features disclosed herein may be present in any feasible combination. Whilst the above description lays emphasis on those areas which, in combination, are believed to be new, protection is claimed for any inventive combination of the features disclosed herein.

Claims: CLAIMS 1. A grassboard or mountainboard comprising: - a generally horizontal support member (1) presenting an upper ridding surface. - front and rear mountings (5, 6); - a single roller (7, 8) associated with each mounting extending transversely of the support member to rotate about a rotational axis, each roller having a symmetrically curved outer surface with a maximum diameter in the mid region of the roller, at least one of said mountings (5) being pivotally connected with the support member for pivotal movement about a substantially vertical pivot axis (A) which substantially intersects said rotational axis in said mid region of the respective roller; - recoil means (15) associated with the pivotal mounting to resiliently bias the respective roller towards a stable position extending transversely of the support member such that, in steering the board, the roller can rotate in opposite directions about said vertical axis to return to said stable position under the action of said recoil means. 2. A grassboard or mountainboard according to Claim 1 , in which the axial length of each roller (7, 8) is at least twice its maximum diameter. 3. A grassboard or mountainboard according to Claim 1 , in which said recoil means comprises a torsion spring (15) coiled about said axis or rotation. 10 4. A grassboard or mountainboard according to Claim 3, in which opposite ends of the torsion spring (15) act against a fixed stop (19) and a stop (18) that rotates with the roller. 5. A grassboard or mountainboard according to Claim 3, in which the torsion spring (15) is housed in a fixed plate member (11 ) fixed with the support member (1 ) and the roller is mounted on a rotatable plate member (12). 6. A grassboard or mountainboard according to Claim 5, in which bearing means (13) are interposed between the fixed and rotatable plate members. 7. A grassboard or mountainboard according to Claim 3, in which the rollers is mounted on an axle (24) between forks (9) extending downwardly on opposite sides of the rotatable plate member (12).

Inventors: RUSSELL RICHARD IAN, RUSSELL, RICHARD, IAN
Applicants: RUSSELL RICHARD IAN, RUSSELL, RICHARD, IAN
Application year: 1999
Main classification: A63C17
IPC codes: A63C5, A63C17