There is always an apparently useless item put in the
trunk as a sort of red herring. This time it seems to
be a base ball. Last night I was thinking how I might
actually make us of this. It seemed to me that we might
be able to make a sort of caster for the rover and so
get over our steering problem.
This seems to work well. I use a piece of metal threading
bent in such a way that the ball always lags behind
the machine and so follows the direction. But because
the main body work on the rover is slanting a little
(with the front two wheels being higher than the back)
on reverse the ball is very close to the ground. This
makes it easy to steer while going forward but a little
erratic on reverse. I think partly because it takes
a little distance for the ball to go from its fully
backward to fully forward following position.
Take the day to carefully wire up the drill motors
to two relays and these are then powered by another
single relay. The idea is that the first two relays
can swap power to the motors (as they are wired up as
change-over relays) while the third turns the power
on and off. I need to make sure these are correctly
wired as I go along otherwise it will get confusing
latter; especially as all the wire (that can take this
sort of current) that we have is the same colour!
Make up the audio oscillator for ‘mission control’.
This is a simple 2 transistor oscillator made up of
NPN transistors taken from the radios they gave us.
By selecting the correct timing resistor via a homemade
keyboard one can make the thing play different notes.
By playing this device near to the tuner one can adjust
it so that key number-1 lights LED1, key-2 lights LED
2 … and so on. Each key then controls one function
of the rover - that’s the theory anyway!
I tried this out but, as sod's law would have it. the
signal from the LEDs is what is called negative logic,
that is when one of the LED goes ON, the signal from
this circuit actually goes from on to off state –
so it is completely the wrong way round to drive the
relays ! I have to make up an inverter circuit for each
of the outputs so that it will behave correctly. This
is no real problem but I have to hunt for the parts
in the radios. This is one of those problems that we
all have on RS that use up valuable time but won’t
even be mentioned on the program … and meanwhile
time is ticking by.
I also tried many different way of powering the rover
and none of them where perfect. For example the 12V
batteries from the drills where a little too high voltage
and made the wheels go to fast which meant it was difficult
to control the thing. Lower voltage batteries from a
cordless power drill gave a much better speed but ran
out of power to fast…
The first test runs looked pretty good today. I wired
up four switches via a cable to test out the way the
rover moved. The machine ran far too fast and was a
bit crazy to control so it lived up to its name of a
Martian took-took! However we showed the principles
and it all looks like it is gong in the right direction,
even if the wheels don’t always!
Robert visits the RS crew for a couple of days. Talked
about the events surrounding Harry’s Nobel Prize
and my little involvement. Nice chap. He got stuck into
helping Mike B with his filtering. With sleeves rolled
up, and his Doctor bedside manner, it was like he was
helping out with a birth ..!