Disperse - a Dumb Meltybrain - Build Log

Bot Builds & Designs
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At my first BBB event, I competed with a Nuts and Bots wedge. This time, I am going to make my own. Inspired by “Death Stick” and based off the design principles of “Nexus”, I am going to make a sit and spin robot.

Upon deciding to make a sit and spin, I remembered that James from Broken Link Robotics had published a design for a 150g meltybrain on GrabCad.

Nexus by James Kirby
Nexus by James Kirby1920×1315 87.9 KB

My Design

My design for Disperse!
My design for Disperse!1920×770 48.4 KB

Certainly not as professional as James’ design but not to bad for V1!

Specific Components

Exterior Chassis / TPU Armour

The orange part is the exterior chassis, which will be printed out of TPU for shock absorption, a standard feature in antweights these days.

Exterior Chassis Top View
Exterior Chassis Top View1310×797 4.93 KB

Top + Bottom Plates

The top and bottom plates which are black, are 3mm thick. This part ensures that the TPU armour is rigid, and holds the whole thing together. As I am 3D printing them, the screw holes will be hard to print. Following Maker’s Muse’s advice, I will have a 0.4mm “sacrificial bridge”. This means that the print can bridge properly, but once the print has finished, I can push through it with a drill or similar. They will be printed out of Overture Super PLA+ a filament I have never used before, but I am excited to test it.

Top and Bottom Plate
Top and Bottom Plate926×694 10.1 KB

Wheel Module

The wheel module will also be printed out of Overture Super PLA+, to ensure no flex. As there is only one wheel, this part needs to be extra-strong to ensure there is no loss of mobility. All walls are at least 5mm thick, and will be printed with 3 perimeters. The tyre is a LEGO 30.4x14 tyre, which fits on to a 3D printed hub that wraps around the DYS BE1806 2300KV motor. It is not uncommon to see this motor driving weapons in antweights and is common in brushless drive for beetleweights too.

Wheel Module Top View
Wheel Module Top View791×652 14.6 KB

Weapon Tooth

For damage, a 20g metal tooth is mounted on the tip of the robot with two M4 screws. It is 3 millimetres thick, so it should be plenty for an antweight fight. It is more likely that a hit to it will break the robot than the tooth. I am still debating whether to make this by hand or get it plasma / laser cut. For PLAnts, I may use a polycarbonate copy of this, which would be easy to swap out on the day.

Weapon Tooth Mount
Weapon Tooth Mount1007×685 22.4 KB

Weapon Tooth Top View
Weapon Tooth Top View507×490 1.35 KB

Electronics

I will be using a 300mah 2S LiPo, a DYS BE1806 brushless motor, a Malenki Nano, and a BBB 20A ESC. I am aware I should just use a standard RX receiver instead of the Malenki, but I already had a Malenki. Rob (creator of Death Stick) uses 25A AM32 BBB Beetleweight ESC for better spin-ups, but once again, I already had a 20A ESC.
In the future, I might branch out to make a proper meltybrain with translational drift and such, but as this is my first bot, I don’t want it to be too complicated.

Other Design Choices

Sandwich Construction

The whole robot is held together in a sandwich construction, with M3 screws. As I am somewhat limited by the 3D printing process, the exterior chassis and the wheel module are divided in two, so that overhands are not an issue. This design choice was entirely from James’ design.

Wheel Armour Shell and Exterior Chassis Cross Section
Wheel Armour Shell and Exterior Chassis Cross Section1189×644 14.2 KB

Centre of Gravity

As this is a one-wheeled sit and spin / meltybrain, Rob (creator of Death Stick) told me that the COG (centre of gravity) should be closer to the wheel than the tip, so that when it is spinning at full speed, the point of contact will be the tooth not the wheel. If all is correct, the COG should be somewhere around the blue circle.

Estimated COG of Robot
Estimated COG of Robot857×667 18.4 KB

Wheel Module Dovetail Join

A predicted force to encounter in fighting is centrifugal forces wanting to pull your robot apart. A design choice I copied from James was the dovetail joint for the wheel module. This should ensure that the M3 screws don’t bear all the load. Also if some fail on one side, the dovetail join should at least stop the wheel module from flying out and pulling all the electronics out with it.

What’s Next for Disperse?

Of course, the hope is to actually build the thing, so that is the next step. At the time of writing, I am in the process of printing a PLA prototype just to make sure everything fits together, before using the harder / longer to print materials such as TPU. I am hoping to eventually complete it by the end of this month (July 2025) but I won’t be signing up for events anytime soon, as that was a mistake I made last time.

The next post will be a fully completed Disperse and maybe a test video (I have a massive metal box to test it in).

Thank you for taking the time to read this, and I am open to any advice or questions.

4 Likes
2

Really cool design, I’m sure it will cause some fun chaos :slight_smile:

3

Thats looking awesome. Hats off to you for such a though out and methodical design - I can’t wait to see it in the arena! Maybe a Death Stick vs Disperse match is in order…

4

Very advanced for a first design, you clearly have experience with CAD and researched thoroughly before starting. The main things to worry about is getting good tip speed and moving in more than a circle, so I hope you’re good at crab walking! But yes will have much weeeeeeeeeeeeeee and silliness

5

Hope to see some meltybrain madness in the box soon

6

Big fan of meltybrains, very happy to see them becoming more popular.

Word of caution on PETG, though - while it’s more flexible than PLA before it breaks, it’s actually less strong overall than PLA, and prone to shattering under big hits, even (especially!) with the CF filler. I hang out in a Meltybrain discord group and most of the PLANT melty builders are using PLA-ST with a lot of success.

7

Take it from me - do not find out the hard way that Petg IS ABSOLUTE CRAP in combat robotics like I did.
Unless you use the cf fill version, It pretty much is only (not the best as well) ok ish to use in gears and mounts etc.

1 Like
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I am going to make it out of PLA-ST probably now, and I have edited the original post so that people reading quickly won’t be confused.

Thank you for the suggestion! I’m glad it won’t be (as) likely to explode during combat.

9

Or a collab for 2v2s…

1 Like
10

Thats such a good idea - will you be taking Disperse to the September ant BBB?

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Probably, I’ll try to go to as many as I can. Might be going to one in Gloucester in August as well.

12

Loved to see this on in action at grocs. Very cool concept, well done! :grinning_face:

13

Apologies for the late update!

Disperse has now competed at two competitions, GROCS and the most recent Bristol Ant Social as of writing. Disperse has won one fight so far, and there is obviously needs to be improvements.

At GROCS, Disperse fought in 3 matches, and a whiteboard against Rotato. The first fight was against “Look What You’ve Done To Our Breakfast”, which went terrible for Disperse. I didn’t use a bi-directional ESC, so once LWYDTOB cornered me, I was just stuck.
The second fight was against Rotato. Joe learnt from his fight against Death Stick and played it smart by reversing into me instead of going weapon on weapon. Eventually bouncing me into the pit.
The third fight was against Burning Tiger, a quick fight, with Disperse getting bounced into the pit almost instantly. (Unfortunately I can’t find the video for this).
I then competed in a grudge match against Rotato, with Joe going weapon on weapon this time. Disperse eventually lost by Rotato getting Disperse in the pit again, but not before Disperse damaged his weapon motor and tore the head off one of Rotato’s motor mount screws.

Disperse MKII

Disperse MKII RENDER
Disperse MKII RENDER1368×770 21 KB

There were clear improvements to make after this event, so I got to work to make a new design - Disperse MKII to compete at the Bristol Ant Social in September 2025. The first thing I new I wanted to do was get some smaller batteries, in MKI, I used a 300mah Liperior battery. This time round, I bought two 200mah LiPo’s from Component Shop. This saved about 6 grams over the other battery.

The next upgrade was to beef up the end with the weapon, witch snapped after every impact. To do this, I completely ditched the steel tooth, which was taking up a lot of the weight budget, and replaced it with some PETG (still not perfect) impact teeth, which bolted on to the main middle TPU part with two M3 Bolts.

image
image1163×794 33.2 KB

Another change was printing the robot in two halves, I completely removed this as it as not needed, and just added extra weight that I had to take out. This helped as weapons from spinners couldn’t get in between the two halves of TPU and fling Disperse to the roof as easy.

I also purchased some longer low-profile button head screws so that I didn’t have to counterbore the plates, which was a common point of failure.

The worst thing I did to Disperse MKII though, was the massive LEGO tyre with a 2205 motor. I used this in the hopes of generating some more RPM, but it turned out it didn’t really achieve it’s purpose (I will elaborate later).

image
image1729×840 145 KB

1v1

The first fight was against Dominic Montanaro. I was surprised when the end just lifted up instead of spinning up. Dominic quickly took advantage of the situation and managed to get me in the pit. I believe the cause of the end lifting up was gyro, in MKI, I used a fairly light wheel with a small diameter. However, as the wheel was so much bigger and heavier this time, the gyro forces when the wheel slipped on the floor just took over. In addition, as I had such a big wheel, it was easy to roll over the short wall into the pit.

The next fight was against James Ferrand’s spinner. With the experience of the first fight, I new to increase the throttle more slowly. It was a good fight with James managing to break one of my teeth, but eventually Disperse managed to completely break James’ weapon mount.

The third 1v1 was against James Luggar. An unfortunate fight for Disperse - I had changed the wheel as it had mild damage, but I had not managed to superglue the tyre to the hub properly, so it either slipped off, or James managed to clip it off. Either way I was forced to tap out to avoid being annihilated by his undercutter.

2v2

Disperse also competed in some 2v2’s, along with Death Stick. In the first fight against Craig and Joe Brown, Craig managed to flip me into the pit straight away, but Rob managed to clutch up and take the win.

The second 2v2 was against Jed Preist + and Ellie Harrington. There isn’t much to say about this fight, apart from how chaotic it was. Eventually Jed and Ellie managed to get us both in the pit.

The last fight was against Aidan Saunders + Josh Miller. Once again, the control bots managed to get both Rob and I into the pit, concluding the day.

The end of Disperse, the start of Valerian

Unfortunately, I can’t see myself continuing with Disperse. I am ditching Disperse and moving onto Valerian - a possibly two wheel drive sit and spin. I will create a new build log on it once I have finished it.

Thank you for reading this, it was quite long and monotonous since I didn’t post for a while, so apologies for being boring.

3 Likes