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Jonathan's Rover Diary Day 0 1 2 3 4

Day Two

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 Winston
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 ..!

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Jonathan builds his rover
Scientist Diaries

Water or wheels? How did the other members of the Rough Science team cope with the first challenge? Read their diaries to find out: