Pi wars 2019 – it begins!
30th Sep 2018
First the big news: Hitchin’s A and B teams both got in to Pi Wars 2019!
Before the excitement fades, the feeling of worry sets in, how much work have we just committed to? Can we get it done on time this year? Better get cracking!
Mixed progress has been made on Tauradigm this week. We’ve fleshed out the CAD design a little more, estimating what components we need for all the challenges, and checking how they’ll fit:
initial layout
Pi 3b+ in the centre, batteries either side, motor controllers behind them, with a Teensy at the rear (to quickly track the encoders and IMU). The field of view of the distance sensors (mounted on the underside of the main board) are represented by the cones pointing outwards. The grey sketched rectangles represent the IMU (gyro, accelerometer and magnetometer, for figuring out the robots orientation and movement) and a multiplexer, so we can speak to multiple sensors easily.
At this point it was looking fine.
rear encoder
We’d even included a model of the encoders we were planning to use. It was at this point we realised a couple of issues. Firstly, the motors we’d been hoarding (high speed, high power 12mm motors, bought really cheap off ebay in a pack of ten) didn’t have rear motor shafts, so those encoders wouldn’t fit. Secondly, would the encoder magnet interfere with our magnetometer? Come to think of it, would the magnets in the motors interfere? Some quick research suggested they would, many people have had issues with getting magnetometers to work reliably. it looks like we might have to move the IMU as far from the motors as possible. like on the top of a small tower! Ok, if that’s what we need to do…
layout
pi noon setup
Next was a quick mock up of the Pi Noon arrangement, with the camera angled up to see the pin and opponents balloons (an issue we had last year where the balloon disappeared from view just at the critical moment!) and you can see the tower for the IMU. We’ve also added the 5v regulator and the barrel jack for running from a power supply. Looking ok. but space is getting tight and we still need to sort out a solution for the encoders.
ball flinger attachment
Next was a drawing of the firing mechanism for space invaders (target shooting). This design is based closely on Hitchin’s previous ball launcher (for skittles, http://hackhitchin.org.uk/finalstraight/) but this time firing soft juggling balls. There’s been some discussion with the pi wars organisers about whether a speed or energy limit might apply, so this might need to be revised as it requires quite a lot of energy to work properly, even though the speed isn’t that high (probably slower than a nerf dart). We’re also considering vacuum cannons 🙂
Drawing up the launcher highlighted an issue with the camera and IMU mount we had for pi noon above, so that’s going to need a rethink.
For the encoders, it looks like we could go magnetic or optical on the output shaft, or optical mouse sensors looking at the floor. The magentic sensor is probably the most reliable but has a very low resolution and might interfere more with the magnetometer, the optical sensor may be a little big and may be sensitive to dirt, and the mouse sensors are sensitive to distance from the ground (and might need to be too close to be practical).
magnetic encoder on the output shaft
We’re planning a separate post on sensor selection, as it can be challenging and confusing.
That’s it for this week. hopefully we can soon start ordering parts to test.
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