Decimus 2 sensor geometry

Decimus 2 is now nearly ready to go. I don’t have much hope of having it ready for the Japan contest but it is worth a try. The mouse weighs only 2/3 as much as its predecessor at about 115g with batteries. This weight saving is almost entirely due to the use of the new 1717 size motors. It looks like everything is working so today, I set up the sensors. These have a different alignment to those I have used before.

The forward sensors now point outwards a little. This should give two benefits. First, they will be more sensitive to the presence of walls and posts when running diagonals. Second, there are some possible issues with the shininess of maze walls. By trying to avoid having any sensor pointing at 90 degrees to a wall, the effect of that shininess should be mitigated to a certain extent. Since the forward-facing sensors are quite important for adjusting forward errors and alignment, they need to be reliable. This is a relatively new requirement for my mice as I find new uses for the forward sensors.

The side sensors are nor angled forwards a little for a similar reason. Also, since these have been the primary sensors used for wall edge detection, they now do that a bit further in advance without giving up too much accuracy if the mouse is not well aligned.

The diagonal sensors point slightly more to the rear than before. I hope his will make them a little more reliable for steering as it will place the response further in the shallow part of the curve when there is a rotational error. They can now also be used more reliably for edge detection. The downside is that they will give an edge later than before which may make it harder to do the diagonal turns.

The edge detection is quite critical to the execution of a good turn. If you can get a reliable edge – which must always exist before a turn – then you can use that to initiate the turn.

Aligning the sensors is made much easier by use of my trusty Sony video camera. Althoug not the latest and greatest model it has one major advantage. the Super-nightshot mode allows you to move the IR filter out of the way and view the IR produced by the sensors. Aligning the emitters to appropriate marks on the walls is pretty easy then. After they are aligned, each is held in place with a little epoxy glue. I use the slow setting, standard type as it flows a little to make a nice support for the emitter. you need to be absolutely sure of your setup before applying the epoxy though. Once done, there is not much opportunity for undoing it.