Monday, June 2, 2014

TerryTorial: Wheel Feedback, Object detection, Larger size, and now a screen!

Terry the robot now has grown up a little, both semantically and physically. The 12 inch channel that was the link to the rear swivel wheel now has many friends which are up to 15 inches higher than the base beam. This places Terry's main pan/tilt camera at his top a little bit above table height, so he is far more of a presence than he used to be. On the upside, the wheel controller, shaft encoders, and batteries can all live on the lower level and there is more room for the actual core of Terry up top. I'm likely to add one or two more shelves to the middle of Terry for more controllers etc.

There is now also a 16x32 RGB matrix screen up front so Terry can tell you what he is thinking, what speed his wheels are rotating at, and if there is an obstacle that has been detected.

I'm rendering the framebuffer for the screen on the BeagleBone Black using Cairo and Pango (thus & freetype). The image data is extracted from Cairo as 32bit RGBA and packed down into planar data that the arduino expects. That packed framebuffer is then sent over UART to an Arduino 328 which takes care of refreshing the RGB matrix so that fake colour levels are achieved using a software PWM/BAM implementation. Yay for the BBB having 4.5 UARTs. I need to work out how to bring up the TX only UART as that is perfect for the one way communication used to drive the screen.

I should be able to get better colour precision using a Teensy 3.x as the screen driver. The Cortex-M4 just has more cycles to be able to softpwm the screen faster to be able to get a greater perceived colour range.

I customized the font a little in FontForge. Specifically I modified the kerning for "Te" to not waste as much space. The font is based on Cantarell by Dave Crossland. I've only just started on this open font to LED matrix stuff, but with some form of PWM and FreeType rendering the data I hope to be able to get nice antialiased font renders, even at the low resolution of 16x32.

The wheel encoders make a huge difference to the whole experience. Even without full autonomy the encoders allow you to have a repeatable oval or patrol path which can be followed. Also being able to setup the speed to avoid large acceleration or jerky movement so that the higher Terry is still a very stable Terry when on the move.

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