Sensor alignment

IMG_2514 For consistent results, the sensors on a micromouse need to be carefully aligned and then fixed in place. In a perfect world, the emitters would all have the same radiation pattern and would generate the same amount of illumination for a given current. Well, that is never going to happen without hand-picking the devices. That would take a long time so we make do with what we have and work around their limitations. Similarly, the detectors have variations to cope with as well. The first step is to get the emitters lined up and pointing where they should…

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Tyre stretcher

IMG_2510 These new soft tyres are so soft that it is difficult to get them onto the wheels without stretching them way out of shape. No matter how hard I try, they still run unevenly. Some of that is due to the tyre itself but mostly it is just a question of trying to spread the tyre evenly. After several attempts, I gave up and decided to make a small tool to help me with the job…

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New tyres

IMG_2506 That was quick. One of the new sets of tyres just arrived. They are the PN racing 8 degree slicks. I ordered them 3 days ago from Kenon Hobby in the US. These tyres certainly are soft and sticky so I put a pair straight on the test rig and compared them to the tyres I have now. They seem to have about 20% more grip than the current ones. This was encouraging so I mounted them on the micromouse. That is when the first little issue came up…

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Encoder/Motor trouble

This micromouse thing is a bit tricky. I have not been happy with the accuracy of the results I have been getting with Decimus. Occasionally, a move is significantly shorter, or longer than intended. Looking at the code does not help – either the code is fine or I just follow the same thought process leading to the same errors every time I look. There is, however, something odd about the encoders.

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Rise of the Robots

The National Space Centre is having a robot weekend in May this year: See robots from the TV series Robot Wars Compete in the battle arena Take part challenges to test your skills and win prizes Build and test your own robot, including the new LEGO Mindstorm Support your team…

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Tyres and traction

IMG_2504-1 It is true, I am losing my grip. A while ago I posted a link to a Japanese site demonstrating the grip available from a particular micromouse. A common way of doing this is to lock the wheels and place the mouse on a tilting surface. As the slope of the surface is increased, the downforce available to the tyres is progressively reduced until the mouse slips. Part of the downforce is lost due to the angle alone and is proportional to the tangent of the slope.

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dsPIC serial ports

In general the dsPIC is well blessed with peripherals. The dsPIC30F6015 I am using at the moment has two serial ports in addition to a couple of SPI ports and an I2C port. These UARTs seem pretty easy to use as well. Still, like other peripherals on the dsPIC, they still found a way to catch me out. My own fault for not reading the data sheet properly. The trick here is to realise that there are FIFO buffers associated with the ports.

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Decimus performance graphs

Time to do some tuning of the motion control parameters in Decimus. First I wanted to get some idea of how it is behaving with the initial settings. I have added a simple flight recorder function. A 4 kB buffer can hold up to 2000 integers. These are placed in the buffer on every timer tick. Thus I can record one second of two integers. this isn’t much but it is all I have available on the processor. Any future mouse will have to have a bigger data buffer.

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Decimus doing circuits

Decimus After a bit of a break, I have done some more work on Decimus, my DC micromouse. With all the peripherals tested and working, I have been concentrating on the motion controller or profiler. This has turned out to be harder than I expected. The basic idea is simple enough but the implementation turns out to be a bit tricky. Probably in part because I wanted it to be useable with Primus, the beginner’s stepper-driven micromouse.

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Club meeting March 3rd

IMG_2499 Tonight was the monthly Midlands Club meeting. The club meets on the first Monday of each month at the Technology Innovation Centre in Birmingham. We have been running for a couple of years now and anyone interested in micromouse or robotics in general is welcome to come along for a chat. We had a modest turnout tonight, a good chat about (mostly) mouse related matters and a talk about VHDL from Tony Wilcox. There were a few mice to have a look at and compare notes. It was good to see Andrew Lloyd return after travels afar.

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