Apr 192017

This year has been a bit busy so far, and in February I realised I only had something like three free weekends to get R2 ready for his first outing, Morecambe Comic Con, a deadline I was determined to keep. Between conventions, work trips, and more conventions (including two on back to back weekends), I knew I had a lot of work to do in a short time. Thankfully, with a bit of organisation and a few late nights I finally managed to get him to a showable state. Not quite to the level I wanted, but close enough.

I utilised Github’s issue and project management tools to help organise myself, putting issues in as todo items, as well as logging things that I found were wrong as I went along. This actually helped quite a bit, and I’m going to endeavour to keep using it. I slowly managed to close off some of the items, and R2 was getting more and more complete. I managed to get the electronics and code to a level where it was stable and he wasn’t too fast to react. Had a few dicey moments when direction changes at high speed made him teeter on the edge of doing a faceplant.

And more bits were added, I got his skirt installed finally, after having bought it nearly a year ago. This however involved some fairly major dismantling of R2, which in turn meant I had to finally get the sled finished for him. Overall, I’m quite pleased with the sled, and it allowed me to lay him down gently and take his legs off to get into the base of the frame.

With the skirt all painted and in place, it was time to test the electronics with his new battery. Up to this point I’d been using a couple of SLA batteries, but these were heavy and didn’t fit in properly. Not to mention they were very low capacity. Over the last year I had been collecting old laptop batteries from various sources, and stripping them down to get the 18650 cells out of them. Once I’d tested the cells and selected the decent ones, I made a new battery pack (6s11p) which should provide 24V, with about 22Ah of capacity. A bit of metal folding and riveting, and R2 also had a battery box.

A quick reassembly, and he was back on all three wheels, ready for the final touches. However, time was getting very short indeed by this point. I had one weekend and a few evenings to get the panels on the doors, and to sort out a few other annoying little details. I’d had the idea of using sheet steel for the doors, but had trouble putting the correct curve into the metal to make it sit nicely in the door areas. If I can get this right, then the doors can be attached easily with magnets to the hinge areas, letting me remove them so I can still get the skin off if needs be. Without the right curve tho, this just didn’t work and looked rather poor. Unfortunately, with no time left I simple hot glued them in place, so that at least there was something there. There wasn’t even enough time to paint one of the panels, so was left bare. 

On my last evening to work on him, I made the decision to change the dome drive mechanism. I’d got a new, more powerful motor, but this gave me troubles with the friction drive in that the rubber ring was coming off. I did have a dome gear set, and decided to try that out (once I’d found it. The garage is a bit untidy). Turned out this was a bad idea. The motor gear is only a thin piece of aluminium, and you have to get it exactly in line with the equally thin main gear. With more time (and the correct cad file) I’ll laser cut a much thicker motor gear out of acrylic. This will make it both easier to mesh the two gears, and also a little quieter hopefully.

So, at about 1am I called him finished and went to bed. I was due to set off to a convention the next day in London. To make it even more complicated, there was another convention the weekend after in the same hotel. Rather than drive home, just to drive back again a couple of days later, I opted to stay down in London. I would’ve got another couple of evenings to do more work, but in the end I decided it was the better option.

All I had left to do was get to the convention

Darren Poulson

Long term geek

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