Thursday, 23 January 2020

PiWars 2020: Making the cut

Before I can best plan out how to convert the Thunderbird 2 toy into a successful PiWars competing robot I need to open it up and see what I'm working with. Happily the toy opens up quite nicely, just a case of removing every screw you can see on the underside of the chassis and popping the two halves apart. Most of the internal items also unscrew easily with the notable exception of the tail. Whilst it looks to just be held in place by 2 screws either side, it appears that the manufacturer also glued it into place for extra strength, and by the time I realised this I'd snapped off one of the supports...

Opening up the chassis
The pod themselves open up nicely too, just remove a couple of screws and pop it apart. Remove a few more screws and the launching mechanism for Thunderbird 4 comes out as well.
And opening up a Pod.

In terms of usable space the main two areas of interest are the inside of the cockpit and pod. These can both house a full size Raspberry Pi, barely in the case of the cockpit, and with room to spare in the pod. As my plans are to swap out the pods for different challenges this means the controlling Raspberry Pi must be housed in the cockpit (to comply with the rules of PiWars), leaving the Pod to house the motors and any additional hardware required to complete the challenges.
Tight squeeze on the left, roomy on the right.
With the toy opened up what's the next step? Well, those who read through my PiWars application details in the last posting may have spotted the line at the end stating that the Thunderbird 2 model is too long and needs cutting down to size...
So the length limit is 300mm...
Last year, in PiWars 2019, I made an effort to keep Wall-E looking like the original toy, which turned out to be a challenging task, but at the end I was happy with my decision (Apart from maybe the gear box failures!). With Thunderbird 2 that just isn't going to be an option, so with the cockpit ear marked for holding a Raspberry Pi then its the tail that will have to be chopped off. I had hoped to keep the battery compartment, which is towards the rear, but the vast majority of that also fell outside the 300mm length limit.

Big and cutty
But how to remove it? As I have recently started attending a MakerLab, I've gained access to a variety of big cutting tools  and I decided to give one of those a go. After all a mains powered, table mounted bandsaw thingie should have no trouble cutting through toy grade plastic...
Well technically it had little trouble cutting through Thunderbird 2, however it generated so much heat that the plastic melted back together again afterwards! Requiring a bit of wiggling and hacking at until the tail could be broken away, plus a bunch of post processing to tidy up the cut.
Transitioning from scruffy to nice and smooth.
The tail section has quite a lot of weight to it, so now its been removed Thunderbird 2 gets a little front heavy, and will get even more so when the battery and Raspberry Pi are installed. So the plan is to install counter weights to balance things out. Where I can I hope to reconnect the tail section as an 'attachment' for some of the challenges, and Mike has helpfully confirmed its okay for the attachment section to be on the back. Hopefully a few magnets will be strong enough to hold it in place, whilst also allowing for easy removal. However this isn't strictly necessary and will be in the 'nice to have' list of features.
Thunderbird 2 - Compact edition
With the chassis cut down to size the next step will be installing the brains!

Leo

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