There's no point in designing a powerful drive and weapon system, if the structural parts which mount these systems fail to withstand punishment from other bots. In the past I have built my robots with a compact internal chassis, which houses all the mechanical and electrical components, and surrounded this with thick armour walls. I wanted to improve this concept for the design of Dullahan, and I considered a variety of options for chassis and armour materials.
A Solid Structure
Ensuring that Dullahan had a rigid inner chassis was very important considering its drive setup makes use of belts and pulleys. As I have found in the past, structural walls made using popular impact resistant plastics, like HDPE, can be prone to bending in large impacts. This is somewhat acceptable when all of the robot's wheels are directly driven, but in the case of Dullahan, this could cause pulleys to become misaligned. Thicker HDPE or even aluminium walls could be used, however I did not want to robot to be too wide, - the use of planetary gearboxes meant it was already a looking like a pretty wide machine!
The resolve this issue, I designed a 4mm thick Hardox 450 inner frame which slotted and bolted together, with weight saving spaces integrated throughout. Although very dense, Hardox is seriously tough stuff; is used for industrial bulldozing equipment due to it's wear resistant properties, and is an incredibly popular material in the UK robot combat scene. I hope that the structural rigidity provided by the interfacing Hardox walls will prevent significant deformation of the chassis.
Finalising the design was a bit worrying though, as once the parts have been waterjet cut there's very little that can be done to remedy errors with ordinary power tools at home. I spent many hours thoroughly scanning over the CAD, and thankfully the effort paid off! Funded by my university and waterjet cut by KCUT, these parts worked a treat and fitted really nicely into the overall design of Dullahan. Countersinking holes was made easy with a tungsten carbide bit, and a generous application of RTD Compound.
Surrounding this rigid inner frame, we developed armour panels to be manufactured from HDPE of varying thicknesses. HDPE is fantastic at absorbing impacts from big spinners, and it is usually my go to choice for armour configurations.
I was able to manufacture all of these components at my home, using my jigsaw, pillar drill and trusty surform plane. However, the spare 20mm sheets I'd saved from previous builds melted and gummed up my jigsaw. It took two hours to cut the sprocket mounts, which look kinda gross and lumpy where the plastic has heated up and reformed. A bit strange, considering that the new 20mm sheet I ordered for the wedges cut no problem at all!
A design first for me was the top shields that cover the wheels, which I feel gave Dullahan a pretty distinctive look, and left some convenient space for our sponsor stickers. These 8mm thick HDPE panels were heated up using a heat gun, bent to the desired angle, and rapidly cooled with water.
Fitting it all together
The chassis has been designed so that the entire machine can be taken apart with an alley key set, an adjustable spanner, and a pair of pliers. This makes transporting the robot significantly easier and aids disassembly in the pits. A few components, such as the rear drive axles, were welded to a steel plate for rigidity, but this steel plate is then bolted to the inner side frames. This means that the robot can essentially be "flat-packed" for simple transportation, and be easily taken apart in areas that need to be repaired.
Overall, this construction makes Dullahan a very durable machine. As is the usual, I think I could have improved the placement of some bolts to simplify disassembly further. Definitely something to consider for a future version, but other than this niggle, I am very happy with the chassis and armour configuration.