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Alan's Roboclock

updated Nov 13


This page details the creation of yet another of my strange projects.....
This time I had a vary vague idea that I wanted to make a clock using a very simple robotic arm, the idea was to have an old style analogue clock face but instead of the arms moving themselves, the robotic arm moves periodically and pushes the hands round.  
So I first had a try building a robotic arm, this was a very interesting project in it's self as it involved a lot of maths (I have recently been trying to teach myself some maths so this was a good chance to try it out)

Dec 2012: I first tried using servos but whilst this looked promising, it turns out that the angles servos actually move to are very non linear and so I was unable to get any kind of usable accuracy from them.  I then had a try to see what I could do with a couple of cheap stepper motors (5 for 2 from eBay including control circuits) building the most basic arm I could think of.
This is much better, the motors have a bit of play in them (and all the joints for that matter) so there is some free play in the arm, but it is good enough to do something with and at a total cost of 5 plus a bit of wood ans some bolts, it is a good project in it's self and probably has lots of uses....

I control it with an Arduino Uno (see more info HERE)
To position the arm it just requires to be given an x and y coordinate
i.e. tell it to move to 100,150 and the arm will move so that it's tip is 100mm to the right and 150mm above the motors output shaft.  This is where the maths came in, you can see more on how I did this HERE

The arm is very easy to build, it is just two stepper motors mounted so they are facing each other with the output shafts opposite, I then turn both at the same rate to move the shoulder and one on it's own to move the elbow, very simple but works surprisingly well.

The Arduino Sketch for this arm can be seen HERE
In this sketch you enter the coordinates via the serial monitor (e.g. 100,120) and the arm moves to that position. - As I am learning, robotic is much more complicated than I ever imagined, so there is plenty could be improved on this - but it works.......

robot arm 2

Video of arm in action

So, now I have a working arm I now need to start thinking about what to do with it ???
My original plan of an analogue clock face is feasible but a friend had an idea which I am starting to like more; instead of a traditional clock face with hands the robot points to numbers for the minutes, then have some kind of device where it slides a pointer up and down to indicate hours (not figured this out yet) but the bit I really like is his idea of a bell which the arm rings to indicate the hour :-)

Jan 2013:  I have now made a slider for the indication of the hour.  This turned out to be much more difficult than I expected.  The problem was making something easy enough for the very weak arm to move but it needs to stay in place whilst vertical when the arm has moved it.  In the end I used a magnet sliding along a chromed metal bar.
There is a lot more work to do on this, but it is now working to some extent.  The other problem I have is because there is so much free play in the cheap stepper motors accuracy is an issue (I have added some weight to the end of the arm to try and help with this)
See video of the progress so far HERE

May 13: I have not done much recently on this project.  I am stuck at the moment on how to indicate the hours and I am waiting for insparation on how to do this.
I have made a slide which the arm can move up and down but with the limitations on accuracy of the basic arm linkages (and code) I am struggling to make it reliable enough.  I think some other system is required?

I could just use a LED display or something for the hours, but I think the arm moving some kind of indicator would be the main point of this clock (if it has any point ?)

Sep13: I think I have abandoned this project.  I was working on it back in May when I had this sudden realisation that this is just pointless and I have not looked at it since????
I may get back to it some time but I think the real problem was that it was proving very difficult to come up with a way to indicate the hours and I just lost interest and moved on to other things.......

I will leave this page up though as I think the robotic arm is an interesting/easy project in it's self so may be of interest to someone as a first step into robotics?

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