Now the videos are submitted and we await the results, I thought it would be a good idea to revisit the 3 part blog posts I made back in November 2020 where I talked about the plan for the robot, course and challenges.
The Robot
The robot went pretty much to the original design. She was built from 3mm plywood cut using a scroll saw. The moving eyes worked well. We were trying to look a little more like the Nanny McPhee character, but it was difficult to source the right style of hair and hat, so in the end we went for a more stereotypical 'granny' look with grey hair and a pair of glasses (the glasses came with the wig!). We're very happy with the result.
The sonar sensor and camera are fitted in the nose as planned - these worked well - although we needed to bend the nose down for the "Up The Garden Path" challenge so the camera could see the line properly. It was also a little low for detecting the upper box in the "Feed The Fish Challenge" so we needed to make a sign for the lower box that the camera could detect.
The sonar sensor worked very well - we did have one issue where, after working well for a long time, we then found when we were about to film, the distance sensing wasn't very accurate. After trying to fix it through software changes, in the end we just swapped out the sensor and it was all good. So not sure what happened there.
The robot is controlled by a Raspberry Pi 4 and a Red Robotics Redboard+ motor controller - which, again, was always the plan. We were going to use a 2GB Pi but had issues with bluetooth when trying to connect the headset for voice commands. We swapped the SD card into another 4GB Pi we were using for something else, and it worked perfectly so there must have been something wrong with the bluetooth on the 2GB Pi. So that's why we're using the 4GB version even though we don't really need the extra memory.
We did stick with these 12V motors: https://www.technobotsonline.com/918d100112-1-re-280-1-4mm-metal-geared-motor-100-1.html
If I'm honest they're a little disappointing. Running at 12V they're a similar speed to the 6V Pololu ones we used in Sputnik (running at around 8V), but have less torque. This means that when stopping they have a habit of allowing the robot to run on, rather than stopping dead. Also they didn't run very well at slow speeds. This meant it was harder to turn the robot by slowing down one side, as the faster side tended to just force it to keep going straight.
I think maybe we were a little spoilt by the excellent Pololu motors we had used previously, and I think it's probably worth investing the extra money on better motors. We spent a lot more time trying to get the robot turning slightly left and right for the automated tasks, and I think this would have been saved had we had better motors.
Having said that, they were good value for money and we were able to get running with them straight away (unlike Sputnik where we went through 4 different sets of motors trying to find ones with the torque and speed we wanted).
So all in all, the robot pretty much went to plan, and matches what we said we were going to build in the Pi Wars application.
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