Grey Area - a 4WD beetleweight "reaching" vert

[scott (Scott Anderson)]

This is Grey Area, a meta 4WD vert gone wrong.

I’ve been running Attitude Adjuster for many years now, and over the last year or so I’d started to feel like I had mostly optimised the design pretty well as far as it could go and wanted a new challenge.

I first had the idea for Grey Area around Rapture 2023 when I noticed that sometimes with AA I could pin other robots against the arena wall, but not quite reach them with the hammersaw. Instead, it would sort of prop them up and expose their baseplate but be unable to hit it. I wanted to build something like a pop-up wedge from Robot Arena, that would be able to hit some baseplates.

The next puzzle piece was designing a hubmotor for Attitude Adjuster, for Brawl 2024. I wanted the design to be generic enough that I could use it for a little vert, or other vert-on-a-stick shenanigans. Once I had this and tested out its effectiveness at Brawl, I was confident designing something around it.

After Brawl last year, I started seriously thinking about how this would work. I realised I would need some sort of “punching” action to get the motion that I wanted, with the spinner finishing as close to the ground as I could get. I looked at Shrapnel Mine’s flippersaw arrangement, but couldn’t figure out how to get the flip and chop action without it just being a hammersaw. I looked at using linear rails, but they’re heavy and the mechanism to make it work is tricky with a single servo rotation.

I finally settled on a “reverse” 4-bar mechanism like Dead Metal and Head For The Exit. This would allow me to run the mechanism off a servo for simplicity and positional control, save the weight of linear rails, and control the motion so it would finish with the spinner as far down and out as I could get it. As a bonus, with an extension on the rear arm it would also work as a self-righter.

With that I had some fun with various 4-bar linkage simulators and Fusion constraints before getting a rough geometry I was happy with. I made the early decision to kink the front arm of the 4 bar so that I didn’t have to have the front wall of the chassis be too open, as I knew that I wanted this to be a TPU unibody like Attitude Adjuster.

After some playing with the simulator and a 2nd hand servo from BBB’s own Joe Brown, I had a prototype weapon assembly! Stay tuned to see how I designed a robot around it.

[Kraken4me (Alex Revell)]

A weird design, but it could be interesting. Looks safe from overhead attacks, good ground game. Just keep the front facing the right way and I don’t see any glaring issues.

[Strang_H (Henry Strang)]

Dw I think Scott knows what he’s doing

[Joe (Joe Brown)]

@Kraken4me

but it could be interesting

I take it you haven’t watched this year’s Beetle Brawl then

[Jack (Jack Franklin)]

Very cool to get a good look at the four bar.
Its an awesome bot that I really enjoyed watching at Brawl

[Wither (Luca Dingemans)]

answer: it was interesting

a 4 bar vert has always been an idea you go hmmmmmmm by. love the design, love the concept, may rip off

[scott (Scott Anderson)]

It is a weird design, and was interesting!

When I set out to design a robot or a new revision I set myself some constraints and freedoms to help guide the design. I knew I wanted this to have roughly the same platform as Attitude Adjuster, gear-driven 4WD with wheels that stick out the back. I had some large wheels from my beater bar robot, “Limiting Factor” which looked cool, so I wanted to use those on the back. I briefly considered making the punching mechanism an alternative setup of Attitude Adjuster, but the compromises and weight needed were enough that I decided to make it a standalone robot.

Other constraints - I wanted to print it in one piece on my printer, so that set the maximum width. I wanted to reuse the same fork architecture and wedge, if possible. I wanted to make it a TPU chassis with HDPE top and bottom, and try out Repeat Compacts. I had never needed to replace a separate armour mount on Attitude Adjuster, so I decided I’d integrate them in the chassis.

On the freedoms - I decided fairly early that I would need to make this asymmetric to allow the self-designed hubmotor to be close to the middle of the bot, and I liked that it would make it a bit odd to look at.

Here’s an early sketch - I haven’t worked out where to put the servo, and the battery was hanging out in the path of the hubmotor. I was trying to work out whether to make the weapon bulkheads part of the TPU unibody or to make them out of machined HDPE. I eventually decided to make them TPU for simplicity.

Here’s one that shows the ground game. I wanted to make it similar to attitude adjuster, with long forks that ride along the ground but have a keep-away element and a shallow radius closer that acts like a scoop. I designed the keep-away element to be taller to protect the spinner, so it could spin up before it strikes.

Here’s one from a bit further along. I was still experimenting with the idea of directly attaching the rear arm to the servo horn, but I didn’t like how far it stuck out the back.

I eventually decided to go for driving the arm with gears. This let me move the servo closer to the middle of the robot for protection, while expanding the range of motion of the servo. A few iterations later and I was ready to make the first of many hollow PLA prototypes.