Submitted by Mike Davey
The Nickel-O-Matic robot was designed as an exhibit for the ChiBots booth at iHobby Expo '08 in Chicago. Because there are lots of kids at iHobby Expo, my main design goal was to provide a machine that was entertaining to watch and produced a tangible take home item. With inspiration from Rube Goldberg and the penny arcade machines of the 1900s, Nickel-O-Matic was born. The design is intended to entertain and so provides gratuitous mechanical motion rather than efficient production.
In the simplest terms, Nickel-O-Matic uses inkjet technology to print a custom message on both sides of 1-1/2" diameter blank wooden nickels. The robot uses a BASIC Stamp 2 to control much of the mechanical movement and a Propeller Chip to control the Inkjet system. The two controllers run a total of four hobby servos, three stepper motors, one DC motor, one DC vacuum pump, one inkjet head, and five IR sensors.
The system was built as a number of modules to make design and trouble shooting simpler. The most complex of the modules is the inkjet system. At the center of the inkjet module is a spindle that rotates the wooden nickel under the inkjet head. This spindle is turned with a stepper motor and allows for repeatable placement of the nickel under the inkjet head. The spindle is also moved horizontally under the inkjet head by a second stepper motor coupled to a lead screw and slide mechanism. A Propeller Chip controls all the elements of the inkjet module. The Propeller Chip was chosen for the inkjet system for two reasons. The first is that the inkjet required fast and accurate timing. The Propeller Chip has direct control over the inkjet head through a simple Darlington transistor array. Each of the inkjet's 12 nozzles needs pulsed on for no more than 6 microseconds. The second reason the Propeller Chip was chosen is that the module needed at least 24 IO pins to control the inkjet module. The inkjet head needs 12 pins, the two steppers need 4 pins each, there are three IR sensors, and I needed at least one pin to communicate with the BASIC Stamp 2.
The other five modules are the coin slot, wooden nickel feeder, conveyor, flipper, and crane. These five are all controlled by one BASIC Stamp 2 OEM version. I used the BS2 for these because it is so easy to program in a code, test, alter, test programming style. I did all the BS2 programming and testing for these five modules in a short afternoon.
All of the modules, controllers and electrical components are mounted on a 20" square wooden base. The mechanism is enclosed on all sides with a clear plastic cover. The cover allowed the kids to get within inches of the robot as it was making their wooden nickel. Hidden under the base are the various power supplies for the robot.
While seeing the Nickel-O-Matic in person is the best way to enjoy it and understand how it works, there is also a video at: http://www.youtube.com/watch?v=2F_ifyc5cVc. Here is a step by step explanation of how it works and what happens during the just over one minute that it takes to complete a cycle.
1. The robot is started by inserting a coin into the front coin slot. The coin rolls down a zig-zag ramp, triggers an IR sensor, rings a bell and falls into a coin box. The IR sensor triggers the BS2 to start the system.
2. A hobby servo is signaled to move a small sign that covers the coin opening and also displays a "Please Wait" notice.
3. A hobby servo in the wooden nickel feeder is moved to eject one wooden nickel from the dispensing stack of 50. The nickel moves out of the feeder and onto a conveyor that has been turned on by the BS2.
4. The wooden nickel travels along the conveyor until it is centered at the end in a "V" shaped channel, this triggers an IR sensor located under the conveyor.
5. A stepper motor rotates the crane into position and a hobby servo lowers to pickup the wooden nickel. The vacuum motor is turned on and the wooded nickel is held by vacuum and a rubber sucker to the crane. This is all controlled by the BS2.
6. The crane then lifts, rotates, lowers, and turns off the vacuum placing the wooded nickel on the inkjet spindle.
7. As signal is sent form the BS2 to the Propeller Chip to let it know there is a wooded nickel in position to be printed. The crane then moves out of the way to allow a better view of the printing operation.
8. The Propeller Chip moves the inkjet slide to the home position and starts the printing routine. There are three different "head" designs for the coins, one is text only and the other two combine text and graphics. The printing routine calculates the first row of printing and fires each of the required inkjet nozzles. The spindle is then turned to the position of the next row and the printing routine continues. Once the spindle has rotated once under the inkjet head, the inkjet slide is moved so additional rows of text or graphics can be printed.
9. Once this side of the wooden nickel has been printed, the BS2 is signaled. The BS2 moves the crane to pickup the wooden nickel and places it onto the flipper. The flipper flips the wooden nickel onto the same conveyor that it started out on, but the first printed side is down.
10. The conveyor again runs and the wooden nickel is moved to the end where the crane can lift it and place it back on to the inkjet spindle.
11. The inkjet system is again started and a different design is printed on the "tails" side of the wooden nickel.
12. After the last side is printed, the crane lifts the wooden nickel and drops it into the output chute.
13. The hobby servo that controls the coin slot is then set so that the coin slot is open, and whole system can start again.
During the two days of the 2008 iHobby Expo the Nickel-O-Matic printed over 200 wooden nickels and was enjoyed by young and old alike.
Nickel-O-Matic Source Code (.zip)
Contact Mike Davey