Finally a pleasurable task: assembling rover wheels!
With all parts needed for one wheel hub printed...
... we can proceed with assembling the wheel hubs! Here are parts needed for one wheel hub along with tiny motor and AS5600 sensor on breakout board, along with printed wheel hub with copper rings:
Another setback. A perfect idea on paper but doesn't work in practice. Driving wheels directly from brushless motor seems to be no-go. Brushless motors are known to have really good torque, especially around 80-90% of their defined 'KV' rating. But at really low speeds power is not adequate for driving out a 1kg rover around.
Copper rings around the plastic groove didn't work out - at least soldering a gap between two tabs slotted ends through the gap in the wheel hub. After a few consultations around, Richard suggested using copper wire instead!
The upper side is that 1.5mmm² wire is widely available (and it was so easy walking to shed and getting a few inches) and very easy winding it instead of copper strip. Downside is that barely 3 windings can fit 4.5mm groove and start and they have to be wound at some angle so start and end can fit. Also, they are not flat and on start and end places there was a bulge which affects brushes. At least it is a solution!
When copper rings were in place all that was needed is to make gap between two sides of the ring filled in with solder, sanded smooth down and brushes added.
Of course, it is much easier said than done. And, as you'll soon see, not everything goes as planned (actually this project is riddled with such meandering paths)...
For wheels to turn (steer) 360º we cannot have wires going directly to motors and get twisted. Original idea was to go with a ready-made slip ring like this:
It has 6 independent wires were supposed to handle enough current with acceptable resistance but there was one snag: it would need to go directly at the 'Z' axis over the wheel. That wouldn't be an issue if we didn't plan to have absolute positioning which would use AS5600 (digital potentiometer) which requires tiny, button style magnet to occupy exactly the same place - the top of the wheel (wheel arch really) in the dead centre.
If we are not able to use ready made slip ring there are other options. One is to make our own or to try to pass power in contactlessly. Third option would be to not allow wheel go more than, let's say, 720º; count turns and 'rewind' back when needed. That would, after all, defeat idea of effortlessly steering with 360º freedom.
Moving rover is the most important thing followed only by the ability to steer and control it. Our idea is to use gimbal brushless motors (like these) in the wheel hubs to the drive rover. Brushless motors are quite fast which helps a lot, but also the ones we selected are gimbal motors they are supposed to be able to move very precisely for minute changes in camera movements.
The idea was to start with something like BLheli programmable ESCs but the software inside of them wasn't good enough to drive them slowly. Normally drone ESCs (Electronic Speed Controllers) are made for fine control of speed when props are already rotating quite quickly.
So, the other option was to make a homebrew brushless controller like this: Spining BLDC(Gimbal) motors at super slooooooow speeds with Arduino and L6234. That particular article was the main inspiration - especially as ATmega chips with nRF24L01 were the original idea to sit in side of wheels and drive each wheel. Quite an exciting little side-project...
Great news! We have been accepted for PiWars 2019 and in nothing other than the Advanced category!
It seems that our ability to make unique designs and make a rover ready and on time for two competitions with (some) success in overall score brought us a place. There were over 150 applications and Mike and Tim (the organisers of the PiWars competition) had to pick 30-odd competitors for the first day (Schools and Clubs) and similar amount for the second day (Beginners, Intermediate and Advance category competitors). So, getting there wasn't a small feat!
This time we'll try to attempt something which nobody else did before. And it requires lots of engineering and programming effort. Also, this time we have extra members to help us with it.
Luckily, some of our existing code (and hardware) is at our disposal, so not everything has to be made from scratch.
It is going to be new, different, challenging... It might even deserve a code name this time (hey, team, wake up!)... But for now it is just a next rover, next generation rover or simple M18!
First apologies for such a delayed post. All the stuff we had to put aside for PiWars took priority and
this slowly fall behind. But here we are.
In short summary - we finished 6th, much lower than expected, but still it is good reflection of all our members' hard work. With such luck and errors in judgement we could end up being much further down the list. But, the most important thing - to have good time getting ready for PiWars and enjoyed the event itself hasn't been spoiled - on contrary. I am sure that day was equally great as last years and we'll try not to miss next. And hopefully we won't!
Preparation for the PiWars was really fun. Previous competition's anxiety - will we manage to do anything or not didn't affected us this time. It was more - can we prepare to do ALL challenged to the best of our abilities or not.
Rovers themselves turned to be really great source of fun and idea of having three for the club worked quite well. That magic number allowed us to have always one spare, one with better motors, one with the latest software (before it was replicated to the others), one with bigger wheels, one we like the best, one that always got one wire to the motor unsoldered somehow, one that had connector wires somehow shorter and harder to use than others, one with broken motor, etc...
This year we left the preparation for the challenge as last. And you'll understand in a minute why!