referring to fig1 and 2 , note that the invention consists of a spool 1 with two adjacent relatively deep grooves 4 , 5 and strings 2 , 3 wound in opposite directions in the two grooves . groove 5 is shallower and thus has a larger radius ( the radius is the distance from the center of gravity of the body to the bottom of the groove ) than the other groove and is wound with the downward - pulling string . when the strings are pulled in opposite directions the greater leverage applied at the larger radius groove 5 causes the spool body to rotate and climb the other string 2 . reducing tension on the strings allows gravity to pull the body downward , unwinding the upper string and winding the lower string . an important difference between the present invention and the prior art is that the strings are wound in deep , narrow grooves -- rather than on relatively wide and shallow winding surfaces . the deep , narrow grooves guide the string and also absorb the tilting moment , which as explained before , is normal to the spool &# 39 ; s axis . in addition , the deep , narrow grooves control the axial position of the strings . this permits placing the strings close together to minimize the tilting moment . in practice it has been found that the invention works best when the groove depth is three to ten times greater than its width . in the example of fig1 through 3 the shallower ( larger radius ) groove is 0 . 10 inches wide and 0 . 50 inches deep while the deeper ( smaller radius ) groove is the same width and 0 . 75 inches deep . the two grooves are separated by a narrow web 6 which should be just as narrow as the practical considerations of the material strength and stiffness will permit . ( in the example the web is 0 . 050 inches wide .) the example shown in fig1 through 4 all embody an additional advantage over the prior art . as previously described , tension in the strings caused an undesireable tilting moment which is absorbed by the string - guides of the farnum type toy or can be absorbed by the deep grooves of the present invention . however , by axially offsetting the the grooves , as shown in fig1 through 4 , the tilting moment due to string tension can be counterbalanced by the opposite tilting moment caused by gravity acting on the axially offset center of mass of the spool body . referring to fig3 note that the radii of the two grooves are shown as r 1 and r 2 and the difference between them is designated δr . the axial distances from the center of gravity ( or center of mass ) to the center of each of the respective grooves are designated x 1 and x 2 , and the difference is δx . an analysis of the forces shows that the tilting moment will be counterbalanced when the following geometric conditions are fullfilled : ## equ1 ## in practice the radii vary somewhat depending on the amount of string wound in the grooves . however , experience has shown that good performance is acheived if the device satisfies the above equation when in the unwound state . small departures from perfect counterbalancing ( due to the thicknesses of the string windings ) are easily dealt with by the ability of the sides of the deep grooves to absorb the tilting moment . tension in the string can also be analysed by a simple equation : ## equ2 ## it is desireable to keep the tension below 0 . 5 lbs while still maintaining a high ratio of r 2 / δr ( which causes a rapid and pleasing climb of the spool body ). this necessitates making the spool body light in weight . low weight can be acheived by choosing a lightweight material , such as plastic or foam , or wood , and / or by making the body hollow , as shown in fig3 and 4 . in these figures the body is shown as being comprised of two parts 1a and 1b , joined together by a snap lock joint 8 . a pair or radial holes 7 are used to connect the strings to the body . the strings may be separate and retained by knotting them inside of the holes , or a single continuous string may pass in through one hole and out through the other hole in order to retain it to the body . although considerable discussion has been devoted to the benifits of the counterbalanced configuration as shown in fig1 through 4 it is emphasised that a non - counterbalanced configuration , such as is shown in fig5 also works well provided that the deep , narrow grooves of the present invention are employed . note that the mouths of the grooves should always be rounded and smooth in order to guide the string and reduce friction . this is particularly desireable in the non - counterbalanced configuration . the counterbalanced condition can be acheived , if desired , by attaching a balancing appendage to a non - counterbalanced body . this appendage might take the form of a figure or it might be allowed to move with respect to the body in order to create some further visual effect . non - circular bodies ( and groove paths ) will also climb the string quite well . fig6 and 7 illustrate elliptical and square planforms respectively . although both of these examples are regular shapes , irregular shapes or polygons will also climb well provided that the radius ( distance from the center of gravity ) of the point of tangency of the downward - pulling string is always greater than the radius of the upward - pulling string . furthermore , the grooves may be eccentric , provided that the above rule of the radii is met . of course , both counterbalaced and non - counterbalanced configurations of the non - circular versions can be made . one interesting possibility is to combine eccentric or non - circular groove paths and varying axial spacing between the grooves in a manner which acheives counterbalancing . while in the foregoing specification embodiments of the invention have been set forth in considerable detail for purposes of making a complete disclosure thereof , it will be apparent to those skilled in the art that numerous changes may be made in such details without departing from the spirit and principles of the invention .
a climbing toy including a body with two circumferential grooves of different depth . strings are wound in opposite directions in the two grooves . the toy climbs when tension is applied to the two strings . the toy contains no axles , bearings or other mechanisms .