Surely we’ve all played some bass riffs on a stretched-out rubber band before, right? [Nicolas Bras] found that the ultimate musical rubber bands are bungee cords, and used seven of them to build a double-bass zither that can be plucked or struck with drumsticks. Be sure to check it out in the build/demo video after the break.
[Nicolas] is what you might call a hardware store hacker. This is not his first instrumental rodeo by far; in fact, he has spent the last 15 years building instruments from stuff like PVC and other commonly-available items.
One thing in this build that’s not so commonly available is the large sound box [Nicolas] built to strap the bungee cords across. He also made custom bridges for the bungees that are topped with triangular wood, which makes them look like little row houses.
In order to actually play the thing, [Nicolas] arranged the row houses in a 2-point bridge system for dual-note strings, which sound good between the bridges and the bungee hooks, but not so much between the bridges themselves. Overall, the zither has a great, mellow sound no matter how he plays it, and we just might have to string one of these up ourselves.
Not a strings person? Then you might be sated by [Nicolas]’ PVC pipes, which play “Popcorn” perfectly.
Continue reading “Bungee-Corded Bass Zither Really Slaps” →
One of the challenges of many walking robot designs is the fact that they draw current just to stay upright. This was exactly the case for one [James Bruton]’s quadruped robots, where the knee motors were getting too hot to touch. Adding springs to take some of the load is not as simple it might seem, so [James] created a bungee assisted cam mechanism to do the job.
For a normal spring-loaded lever, force is proportional to how much the spring is stretched, which will require the actuators to draw more and more current as it lifts the leg higher. For the spring force to remain constant throughout the range of motion, the length of the lever arm must become continuously shorter as the knee is bent. [James] did this by stretching a bungee cord around a cam. The added bulk of the cam does however cause the knees to knock into each other in some scenarios, but [James] plans to adjust the robot’s gait to avoid this. He didn’t get around to actually measuring the current draw reduction, but the motor temperature has dropped significantly, only being slightly warm after a test run.
These tests were done with OpenDog V2, but [James] is already working on the design of V3, which will use 3D printed cycloidal gearboxes. At the moment, that build is still being delayed thanks to the global component shortage. Continue reading “Bungee And Cam Assisted Actuator For OpenDog” →
[Brian] from 24 Hour Engineer has a friend with arthritis who can’t easily play ball with his new puppy — so [Brian] stepped in and built him this awesome tennis ball launcher.
You see, most tennis ball launchers require a solid flick of the wrist, and since just plain old throwing it is out of the question too, [Brian] had to make him something powerful and easy to use. After sketching out some designs he came up with the basic concept that eventually became what is pictured above.
The frame is made of 2″ PVC pipe, which serves two purposes, support, and safety. The bungee cord launching system is actually contained within the pipe, keeping it out of the way, and free from catching on anything during firing. A pair of pulleys mounted at the cord opening ensure the cord doesn’t wear out.
What we really like is the trigger mechanism [Brian] made out of some carefully cut wood, a steel corner brace and a few nuts and bolts. It’s a simple mechanism that provides leverage and an easy way to release the bungee cord. Continue reading “Tennis Ball Launcher Has Puppies Running The 100m Dash” →