page details the creation of
yet another of my strange projects.....
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
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)
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
what I could do with a couple of cheap stepper motors (£5
for 2 from eBay including control circuits) building the
basic arm I could think of.
This is much better, the motors have a bit of play in them (and
the joints for that matter)
so there is some free play in the arm, but it is good enough to do
with and at a total cost of £5 plus a bit of wood ans some bolts, it
project in it's self and probably has lots of uses....
I control it with an Arduino Uno (see more info HERE)
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
the right and 150mm above the motors output shaft. This is
the maths came in, you can see more on how I did
arm is very easy to build, it is just two stepper motors
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
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,
is much more complicated than I ever imagined, so there is plenty
be improved on this - but it works.......
So, now I have a working arm I now
need to start thinking about what to
do with it ???
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
some kind of device where it slides a pointer up and down to indicate
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
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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