Youtube video of the pantograph juggler. - - - - Image.
Inspiration comes from Nathan Peterson's juggling machine, and this woodworking machine.
My machine uses a different mechanism than Peterson's machine. I used a pantograph mechanism. The pantograph mechanism was created to duplicate and scale drawings. Any movement at the center of the pantograph is duplicated at the end of the pantograph. The movement is also scaled up by a factor of 2.
In the Pantograph Juggler, The motor is connected to the center of the pantograph mechanism by a ¾ inch cam. For every turn of the motor, the center of the pantograph mechanism makes a 1 ½ inch diameter circle. The end of the pantograph mechanism makes a circle with a 3 inch diameter.
The glass balls are held in aluminum hands at the end of the pantograph mechanism. The throw trajectory is based on hand adjustment. If the hands are tilted down, throws will go toward the sides. If the hands are tilted up, throws will go more upward.
Throw distance is determined by the motor speed and acceleration. The faster the motors go, the farther the balls get thrown. Motor speed does not affect throw direction. The uncoupling of speed and direction greatly simplifies the art of juggling. The code for this project is only 15 lines!
An Arduino UNO controls the motors. The motors are NEMA 17 type bi-polar stepper motors. The motors are driven by L298n chips. The Arduino is powered by a 9V battery and the stepper motors are powered by 8 AA batteries. The AA batteries need to be recharged after ½ hour. The 9V battery should last for more than 40 hours.
A jig saw and a drill are the only power tools required for this project. A table saw, sander, and drill press will make things a lot easier, faster and more precise.
The most difficult part to fabricate is the cam that connects the drive shaft of the motor to the shaft that drives the pantograph arm. Hardwood works well and is easy to work. A relief cut is made near the drive shaft. A bolt and nut tension the wood around the drive shaft.
The pantograph mechanism is constructed from ¼ inch plywood. There are lots of holes on some small pieces. It’s best to cut several extra arm pieces to practice drilling and account for mistakes. 7/8 inch holes are drilled for the bearings. A small amount of hot glue or CA glue holds the bearing in the plywood. I used a 7.5 mm diameter arrow shaft to fit in the bearings. The shaft can be glued into the plywood as well.
Lots of the parts are optional. The leveling feet that I used could easily be replaced by a stack of books. The walls aren’t necessary either, but they will keep you from losing your marbles when attempting to calibrate the throwing hands.
Some materials can be recycled or substituted to reduce cost. The thick sheet of MDF that I used as a base could be recycled from a discarded piece of furniture. The Plexiglas is visually stunning, but the most expensive single component. It could be replaced with plywood.
◦ ½ inch diameter white glass sling shot ammo
◦ ¾ inch plywood for base (24 x 24 inches)
◦ ¼ inch plywood for pantograph mechanism (eight pieces that are 8 x 1.5 inches)
◦ ¼ inch plywood for walls to catch marbles
◦ 12 Skate bearings
◦ 7.5 mm arrow shaft
◦ Aluminum bar - ½ inch x 1/8 inch x 3 ft
◦ Small bolts for hands and cams
◦ ½ inch threaded rod for leveling feet
◦ ¾ inch drywall screws
◦ Plexiglas (two pieces that are 4 inches by 12 inches by ¼ inch thick)
◦ Small bits of hardwood (one piece that is ¾ inches x 2 inches x 1 foot is enough)
◦ Paste Wax on everything that moves
◦ Arduino Uno
◦ 2 x NEMA 17 Stepper Motor
◦ 2 x L298N stepper motor drivers
◦ 9v battery
◦ 8 x AA battery
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