Jump-O-Bot DAT File About Lego trigger Capturing the power Completing the cycle Learning to land Instructions Video Brickshelf Gallery
I apologize in advance for the many blunders this explanation might contain. My lack of traditional technical background really gets in the way when it comes to explaining springs, equilibrium and mass in motion. As usual, feedback is encouraged and cherished. Lego trigger When I first began toying aroung, trying to figure out how to use Lego shock absorbers to make a robot jump, I quickly found a very handy relationship between Lego cams and small shock absorbers. The set-up shown at right allows a cam to compress and release the spring of a shock absorber to its maximum extremes. While this spans a small distance, roughly one Lego unit, the force generated (specially if we combine several shock absorbers) is considerable. Enough to power Jumpobot, including its power supply. This simple and compact design is first and foremost is a Lego firing mechanism: add a trigger to control the rotation of the cam and the moving piston of the shock absorber will power the firing itself. The gun needs to be "mounted" (readied) by pulling the piston to its compressed state, much like in a semiautomatic pistol. In fact, I was very very tempted to create a Lego gun, but kangaroos are way cooler than any gun will ever be, so I decided to make a jumping robot first and maybe later come back and revisit the gun. Of the other working Lego guns I know of, only these two have a firing device with shocks. How about a competition for longest range? Capturing the Power Because small shock absorbers have a round connection on each end, a firm attachment from the moving piston to the rest of the rest of the propelling assembly calls for creative solutions, specially if we consider the relatively strong forces at play. The bulky but effective solution in parallel adopted for Jump-O-Bot uses a long Lego Technic liftarm as an extension of the piston. This liftarm also serves a rail guide that slides in between a plate/brick assembly, keeping the shock absober from pivoting out of the way of the actuator cam. Completing the cycle Powering the above set-up with a Lego motor requires an assembly featuring a caster wheel. This assembly will keep the gears rolling during the spring compression phase and free the cam axle from the rest of the train way during the release phase. Allowing the transfer of linear motion at different speed than the compression is key to this particular design, as the torque needed to compress the spring calls for a reduction of the motor speed. Given than the gear train includes a worm gear, which does not backtrack (but provides ample torque), the caster wheel becomes a necessity. Incidentally, it also adds to the "jumpy" character of the bot: as it jumps, a piece pivots sharply back and forth. It certainly reflects on the excitement of the spectators who watch it in action. Needless to say, this gear train does not providen much speed (which the same spectators usually ask for as well!). Anybody up for a spring-based machines speed contest? Learning to land There is not much to be proud about Jump-O-Bot's feet. Like the rest of the robot, they were chosen on a first-come basis and do perform three key fuctions. They maintain the balance of the robot at all times They also tilt the whole structure just so that gravity will make the caster wheel further up fall back into its place in the gear train after jumps. Finally, this tilting also defines the center of gravity of the bot, ensuring once it jumps up in the air, it "falls forward". However, the feet themselves are pretty flumsy - which the rest of the robot is not. A more sturdy design would allow the bot to move in a straight-er line. A smarter design would incorporate real shock absorbers to minimize the rattling of the upper body (I'm thinking RCX here), or even a second set of propellant shock absorbers. For instance, one set would propel the bot up, and then a second set would propel it forward, much like some animal legs work. Jump-O-Bot relies on rapid movements of its mass to drag the structure around, but a feet could also adopt "gun" configuration, with only part of it shooting out of the "sole" to force the structure upwards. Longest leap competition, anyone?
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