This project has been a long time coming. It has been stop-start since around 2021, over which time I’ve accumulated a lot of parts and spent too much money to back out now.
To many roboteers, heavyweights are the impossible dream of the sport, as it is what we saw growing up on TV on Battlebots or Robot Wars. Despite being so much more expensive, awkward to work on and transport, basically more difficult in everything compared to the smaller weight classes, we do it anyway. All to chase the nostalgia, crowd reaction and the childhood dream.
I bought this partial frame from another roboteer in 2021. It was intended for Series 11 of Robot Wars that never happened. I quickly discovered the difficulty in continuing someone else’s design language that doesn’t match your own, so shelved it and it has lived in a binbag down the side of my Mum’s house ever since.
Fast forward a few years to present day. Based on the data we had acquired from Dojo Sportsman over the last few years, Extreme Robots agreed to a trial of allowing commercial cutting saws in their “non-spinner” category, to boost build variety and sparks for the crowd. It is a big step for a nationwide live scene that has become less about damage and more about keeping machines running across several shows a weekend, resulting in the “meta” builds becoming pretty stagnant in design.
Out comes the project again. Time to put my money where my mouth is.
Oh god why not? It brings me great joy to see a heavyweight build log here. I won’t lie - I’m sad there’s no real heavyweight conest in the UK akin to the ones in the ant and beetleweight classes even if it’s an absolute drain on the wallet! I wish you the best of luck with this build!
The arm is intended as a “Stub” arm, which can have multiple different weapon attachments bolted on to easily without disassembling the whole frame. The saw is the main focus, but I’d like to add a grabber or lifter for Robots Live events in future.
Now, these robots weigh 110kg. Despite being set up for a saw, this arm will still need to either lift opponents or self-right. Accounting for leverage and a ~half meter arm length, that is a lot of force needed at the end of the arm!
For the Ampflow A28-150 motor I have for this project, I need a total reduction of ~140:1 to achieve this with a speed that could still outrun a snail (That’s a lot!).
To start with, I have a 32:1 industrial planetary gearbox. This gives a lot of reduction in a small package. Also means I only need a further reduction of 4.3:1 after that to meet my rough target (Yay, maths!).
There is a problem though. They need attaching. The motor output is 12.5mm in diameter, whereas the input of the gearbox is 19mm. Any shaft sleeve will need to be durable and be near impossible in geometry to make from a strong enough steel myself, so I outsourced a sleeve adapter to be made in China by PCBWay using EDM from tool steel. Let the experts deal with it
Time for some internal shock mounting, which means lots of TPU!
I designed a battery box to contain the… well, batteries and isolate them from shock. I decided on a clamshell design with two interlocking halves and secured together with two M8 bolts. This is a 24V system, so I’m running 2x 6S 6000mah batteries in parallel to combine their capacity.
The battery box took 36 hours total print time! Probably my longest prints to date.
A late addition to the project was custom wheels. This was always intended eventually, but I already had off the shelf Colson wheels that came with the frame so planned on using them. I got bored and scrapped that plan.
Reason for this was the Ampflow drive gearbox output. Despite being 20mm thick steel, it is only supported on one side, meaning any impacts the wheel takes could bend the output shaft and ruin the (very expensive and rare in the UK) gearbox.
So, my logic is the same as the battery box. If I make a softer, more compliant wheel, any impacts the wheel takes will be absorbed, rather than transferred in to the gearbox.
I 3D printed a TPU core, with plenty of holes and features around the circumference to increase the surface area for the tire to key on to. I also left a spline cutout in the centre to inset hardox plates, holding a strong keyway to attach to the gearbox shaft with.
The tire material itself is 60 shore two-part polyurethane mix (Vytaflex 60A), which I mixed and coloured with neon pink mica powder. This cured over 24hrs in to a wheel that will have excellent grip on the arena floor and be truly offensive to any onlooking eyeballs. I love them.
Current CNC is a 4040 Pro Max with a 710W trimmer spindle. Very pleased with it for under a grand, will do HDPE like butter and handles metals quite well too.
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