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Step 21st prototype
For the first prototype, I just wanted to see if I could get the stepper gear thing working at all. I cut a spur gear for the stepper, a small stand with a hole in it to press fit the stepper motor and a larger gear that would be the clock mechanism.
After assembly and a quick program, I decided that the clock needed to have two gears (and thus two stepper motors) - one for hours and one for minutes. I also discovered that the numbers needed to always be right side up as the gear traveled around. Thus, the 6 needed to be upside down in the drawing as well as the 3 and nine needed to face outwards.
Another cool thing I discovered during my first prototype is that the Arduino has enough power to step these motors without having a driver circuit. This makes the clock considerably easier to make! Here are a couple of links to tell you about how to hook up the Arduino to the stepper I used...
http://ryanschenk.com/2010/03/driving-a-040-stepper-with-arduino/
http://profmason.com/?p=173
I also began to think about my gears. In my prototype, I used a 10 tooth gear for the gear connected to the stepper and a 100 tooth gear for the ring. 100 really does not translate well into hours or seconds so what else could I use?
My stepper gear has 10 teeth and this actually works well because the stepper I am using has 20 steps per revolution. Thus I can step the stepper 2 times to move exactly 1 tooth.
Therefore, for my minute hand, if I use 60 teeth, then each 2 steps = 1 minute = 1 tooth of movement.
Similarly, my hour hand has 144 teeth because if we divide it by 12, each hour has 12 teeth and therefore each tooth is equal to 5 minutes! Really, the clock does not have to have a minute ring at all. The hour ring can tell you what time it is.
After assembly and a quick program, I decided that the clock needed to have two gears (and thus two stepper motors) - one for hours and one for minutes. I also discovered that the numbers needed to always be right side up as the gear traveled around. Thus, the 6 needed to be upside down in the drawing as well as the 3 and nine needed to face outwards.
Another cool thing I discovered during my first prototype is that the Arduino has enough power to step these motors without having a driver circuit. This makes the clock considerably easier to make! Here are a couple of links to tell you about how to hook up the Arduino to the stepper I used...
http://ryanschenk.com/2010/03/driving-a-040-stepper-with-arduino/
http://profmason.com/?p=173
I also began to think about my gears. In my prototype, I used a 10 tooth gear for the gear connected to the stepper and a 100 tooth gear for the ring. 100 really does not translate well into hours or seconds so what else could I use?
My stepper gear has 10 teeth and this actually works well because the stepper I am using has 20 steps per revolution. Thus I can step the stepper 2 times to move exactly 1 tooth.
Therefore, for my minute hand, if I use 60 teeth, then each 2 steps = 1 minute = 1 tooth of movement.
Similarly, my hour hand has 144 teeth because if we divide it by 12, each hour has 12 teeth and therefore each tooth is equal to 5 minutes! Really, the clock does not have to have a minute ring at all. The hour ring can tell you what time it is.
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