CDG - How (not) to design a first beetleweight

Trouble_2X · 22 November 2024 18:30

CDG, THE ORIGINAL

Hello All,

Some of you may be familiar with my beetleweight CDG and as I haven’t made any changes to it in a while I think it is a good time to go over how it became a working (ish) robot that has survived being beaten up in multiple events at this point.

There are many many good build logs and guides on this Forum and the BBB website as a while but this will start as a great example of what NOT to do.

The Concept:
The idea for CDG originally came from watching NHRL and seeing SMEEEEEE with it’s detachable horizontal spinner (to get the NHRL weight bonus). As shown in this fight. https://www.youtube.com/watch?v=R96ZgEGef-4

The idea was simply what if the spinner was on the front not the back so that the forks and spinner would work at the same time.

I originally made CDG in a video game under the name Coup De Grâce and it looked a lot more like Smeee with an undercutter in the middle than the first version of the beetle did.

The first beetle event I attended was BBB brawl 2022 as part of a pit crew for one of the Lboro Uni bots called Disorder which was built by Max who was the Chair of the society at the time. For Brawl 2023 I decided to build my own beetle. Originally I was going to build a lifter for the event but as a CAD exercise also designed the original version of CDG with all the very little experience I had with bots on a whole and especially spinners. I had used spinners in video games and had built an antweight lifter/flipper at this point but didn’t understand at all how to mount a spinner and it really showed.

I wanted to make it an undercutter but had no idea how to make it both low AND not needlessly complicated to build so instead I made it a flat midcutter.

Regardless at a society social we were discussing the brawl event and what the plans were and when I showed both the lifter and CDG I was encouraged to build CDG. Unsurprisingly it was simply because it was weird looking and cool not the sensible thing to do.

The design and flaws
The CAD was polished up and missing features added but most of it remained the same. it drove using BBB 22mm gearmotors and an Overlander 3530 1100Kv for the spinner. All of this was running off of a 4S 850mah LiPo battery.

Once the CAD was done it was very clear what most of the issues would be before I had even used it. I had ordered the weapon once I had decided on the size needed for components and got this ordered in a waterjet group order (Thanks Sion). My rushing to get this ordered caused 2 issues. 1 was that I had turned the bolt holes on the weapon into construction lines by accident so when I got my weapon it had no bolt holes and I had to spend money to get them machined.

The other was the weapon supports. I had realised that the 3mm hardox I wanted to get them made from would be too heavy. The solution was to make them 2mm. I then promptly learnt that 2mm hardox is almost non-existent. This meant that I had an issue as I couldn’t go for a lighter material as it would need to be thicker and I hadn’t designed the clearance for more than 3mm thickness so the wedges would no longer be on the floor. At 2mm no material I found would be strong enough so there were only 2 options. Either I would have to spend alot more on 3mm Ti supports or buy some 2mm mild steel to use and hope that I didn’t fight a vertical spinner.

I just sent it and chose the latter to save some money. I just accepted that if I fought a vertical I might have had to bend the supports back into shape.

The final MAJOR issues
If anyone has a memory good enough to remember Brawl 2022 then they will remember that CDG was missing a weapon and was instead a hugging wedge. There were 2 causes of this:

I had limited time in the Uni workshop and hadn’t had time to machine the custom weapon axle that i had designed. I could have solved this easily by drilling the holes out and slapping in a shoulder bolt.
The machining of the holes in the weapon took time and postage took time. This meant that while I had left a month for the weapon to be machined and make its way to me when the big day of the event rolled around the weapon was still in transit. The weapon arrived the next Friday.

THE EVENT
When I showed up to BBB Brawl 2023 the bot weighed half the weight limit and was weapon-less so I had very low expectations.
On top of that I was in the first fight and had been rushing around trying to fix a solder on the power light so hadn’t had time to fully prepare (maybe forshadowing )

Fight 1: VS Muhammad Al-Bee AND James and Dan’s robot

This fight was going well. Muhammad Al-Bee had got themselves stuck under the arena wall immediately and CDG was so wide it was easy to stop the spin up of the horizontal and control them.

That was until my wheel fell off. Yep in my rush to the first fight I hadn’t had time to locktite the grub screws on the wheels and it had cost me a fight immediately. Never mind, Onwards and upwards.

Fight 2: Vs Spins and Needles

This fight I was against a team mate in Spins and Needles by Peter (Another Lboro student). The hole in the middle of my bot was almost big enough to enclose the inner ring of the opponent. IIRC I won this fight as when I was hit one of the bearings on Spins and Needles Jammed and caused the weapon ESC to burn out. This meant that the weapon-less bot beat the bot that is surrounded by weapon on the damage/weapon effectiveness category.

Fight 3: Vs Chain Bastard

One of my favourite fights. It was a very close controlling fight in spite of the lack of mass of CDG causing it traction issues. I had great fun and I don’t think there was anyone I would rather have lost to.

FOOTBALL
While I was working on a new version of CDG there was a football event at Robonerd 2023. I was working on some brushless drive conversions for the new version after being given the idea by Sion and tried them out at this event.

Bot changes:
For the football I flipped the central printed piece upside down to make sure the ball couldn’t get under me and I added some brushless rotalink conversions using 1900Kv Brotherhobby 1507s.

I was teamed up with James and his bot Nitrite. We did pretty well as a team with 7 or 8 goals in the event 4 of which were me and I had a great time.

This was the last time I used this bot for anything other than demonstration purposes so concludes the how NOT to make a beetle part of this build log. There are other issues that occurred with the 2nd version but less so meaning I won’t be going over them unless they lost me a fight.

Trouble_2X · 6 January 2025 15:50

Hello again,

It has been a couple of months since I added to this build log so now time to talk about the 2nd version of CDG.

Design:
After the experiences of the first CDG and having seen what others did to make an undercutter I decided to try and make the 2nd version closer to the original aim.

It used the same spinner as was supposed to be on the original version but used gears to spin it with a tip speed of around 200mph. The spinner was powered by an Emax 2807 1700Kv motor and the drive used the brushless drive shown previously. It also ran off the same 850mah 4S lipo. The brushless power and larger 64mm wheels gave it a much higher 13mph top speed. Polyurethane cast wheels were also used to give more grip.

The weapon motor is quite light for the 270g spinner it is powering so to stop the motor getting too hot the motor mount is made of aluminium so that it is both strong and acts as a heat sink.

As you can probably see the largest improvement was the use of GREEN UHMW (maybe RG1000 idk). The printing was all done by Ranglebox and the UHMW was all machined by the massively helpful Nat of TeamSC. The exception was the top and bottom plates as these were originally supposed to be polycarb like my first beetle but it turned out the Lboro Uni club had ran out of spare polycarb so instead Sion machined them for me last minute from hdpe. Thanks to everyone who helped make parts for me.

The parts were all assembled by myself but everything fit together much better as I designed in assembly aids and assembly drilled holes (drilled once parts were already held in the correct place instead of marking the position and drilling). If you don’t want to use other tools e.g. 3dp guides to assemble then I strongly recommend this method of assembly.

Brawl 2024:

The first event for the robot was BBB brawl 2024.

First fight: Vs Drilliam the Conqueror and Doorstop

Drilliam the conqueror had issues was did not start the fight. The fight started well with a good hit but once again I was the first fight and once again the wheel fell off. I had not time to check parts but this time I had lock-tighted the wheel. The issue is that I used both too little and I hadn’t tightened the grub screw enough so it only had to loosen slightly to fall.

When I put the wheel back on I screwed it on tight enough to round the allen key I used (not great quality) so I then borrowed one (I think from Freeman of Impulse) to make sure it was done up properly and drowned it in locktight. It is now on so tight that the wheel won’t come off without drilling the grub screw out.

In the fight my spinner also stopped as I spun it the wrong way and the nut that holds on the gear on the weapon motor came undone so I had no hope of winning.

Second fight: Vs John Feere

This fight started terribly. CDG kept having intermittent control issues (losing control and restarting the start-up sequence every time). This meant I was being beaten up by the vertical drisk of John Feere. Luckily one of the hits of John Feere managed to fix my intermittent control issue. While this helped I was still stuck in a corner being pummelled.

With a huge stroke of luck for me I managed to get out of the corner and subsequently John Feere lost power. What had happened was that John Feere had hit CDG hard and frequently enough to blow their own 30A fuse.

The damage from this fight largely consisted of the polyurethane starting to come off the wheels. I filled in the gaps in the tread with hot glue (bad traction but at least it was kinda round) and moved on to the next fight.

3rd Fight: Vs Groundbreaker

This fight was great. Finally the bot was working kinda as intended. It started fairly even to begin with with both bots trading blows. CDG then managed to hit one of Groundbreaker’s drive belts and knocked the weapon belt out of its slot. Subsequent hits caused Groundbreaker to lose power won me the fight. IIRC a solder joint went in Groundbreaker causing the KO.

After this fight I changed the hot glue in the wheels to stickyback foam that was given to be my Ellie (thanks a lot) and gave the bot much better driving than previously.

4th fight: Vs Guinness

Another Lboro Uni robot for me to fight. Their lifter wasn’t working so it was my weapon vs their control. The hdpe forks were bent easily but prevented most critical damage to Guinness. What I was able to do was remove the tread from their wheels when I got round to the side.

Towards the end I was flipped upside down (CDG drives terribly upside down) but luckily I was able to push Guinness into the pit with seconds to go to secure the 3rd win. This was only possible due to the tread removal from their tyres.

5th Fight: Vs Attitude adjuster

Somehow with that last win I became 1 of the 2 Uni bracket bots to make it into the public bracket. This meant that next I was matched against the amazingly driven Attitude adjuster by Scott. I had no chance in this fight. I was immediately box rushed and Attitude adjuster hit CDG once with hammersaw. This hit just barely went through my 4mm hdpe top armour but a weapon esc wire was pressed against the top plate so was cut immediately. I lost my weapon and was bullied around the arena by the superior drive of attitude adjuster before my exposed link was ejected by a precise shot from the hammer saw that hit the link mount.

It is fair to say that my attitude was successfully adjusted. Very well driven from Scott and congrats on the 3rd place.

Fair to say top 8 was way better than I had expected and CDG got better as the event went on.

Upgrades:

Top armour was increased to 6mm UHMW to protect against hammer saws. New wheels were more durable and semi-wheel guards were added so wheels got hit less. Drive ESCs were changed to Ranglebox 35A Am32 escs. The AM32 software on these made driving much smoother at low speeds and combined with the new wheels made driving much easier.

Mite:
Next I went to the New Mini Beasts in The East (MITE) event.
To keep this short and simple: I lost every fight I did.

Quite simply in the time between events some debris had gotten into the motor and had stopped it working properly. I could get it going by spinning up very slowly so I still got past tech checks but it was almost unusable in fights. I also had no spare weapon motor.

I fought the likes of Chucky, Loughbot (another lboro bot), Sniper and the Barber Surgeon. The fights were good fun but without a weapon I had no chance. The control and traction on the bot isn’t great and both with and without the weapon attached it has enough drive power to wheelie or flip itself over (which happened alot) which made using the drive power that I did have very difficult. I enjoyed the event but the less said about the fights the better.

Upgrades 2:
The motor was replaced to a RCinpower 2806.5 1750KV and battery was changed to a GNB 720mah 4S LiHV for more power and less weight.

BBB champs:
With a new motor I was hoping to be a little more successful at the BBB champs event in November 2024.

First fight: VS Demon Spirit and Babrog

This was a great fight that went the distance. Demon Spirit struggled with drive but I had a great fight with Babrog. I got a few good hits and Eoin did a great job of controlling the fight. Babrog won the JD and deservedly so. It was a close fight until my weapon died (a solder joint came off).

Second Fight: Vs Chris Griffin 2

This was my first time fighting anything with anywhere near the weapon power of Sion’s Chris Griffin 2. Sion is also a good friend so this whole fight was entirely jokes and you will see why.

This fight started well with the giant spinner skimming off my wedge and me getting under. This seemed great as I was winning control… … that was until I tried it again. I got under as expected and this time Chris Griffin was sitting on top of CDG. A hat if you will. Then a few seconds later CDG stopped and was counted out.

It turned out that the link was no longer in CDG anymore. I was really confused with how that had happened when I hadn’t been hit anywhere near the link. There was an unexpected part that turned out to be my downfall. CDG has a zip tie attached the the link for easier removal by the referee. While sitting on top like a hat Chris Griffin had managed to pull the zip tie into the spokes of it’s spinner and pull out the zip tie and link which caused it to win by KO.

Well that isn’t something you see every day.

Once we realised what had happened I found it hilarious if a little unfortunate. Also lead to one of the most silly and confusing double interviews afterwards.

The result with that 2nd loss was that I was out of the tournament. While the results were not very good I could tell from the fights that most of the bot was working much better than the previous events besides the need to fix the link.

For future versions:
Key improvements:
Lower CoG (less wheely-ing for more speed)
More hidden link and zip tie

Desired improvements:
More powerful weapon (larger, upto tip speed limit, more powerful motor)
Billet main chassis (lower maintenance and saves weight)
6mm shaft gearmotors (4mm drive hasn’t failed but is far more likely to)

Kraken4me · 7 January 2025 08:40

I remember seeing the first lying around at GRoCS! That weapon does look a little on the small side, but success at BBB Brawl clearly shows it might not be necessary.

Trouble_2X · 7 January 2025 09:23

Hi Alex, if you mean you have seen my bot flying around at GRoCS then you are sadly mistaken as I have never been.

You are right about the spinner. It is 15cm effective diameter so on the smaller side but not tiny. It looks even smaller because of the width of the bot (iirc 31cm wide so basically 1 ruler). The spinner is that size because of the funky design of the first version. The chassis of the 2nd can fit a spinner up to 21cm effective diameter.